LTC3260

Low Noise Dual Supply

Inverting Charge Pump

Features Description
n VIN Range: 4.5V to 32V The LTC®3260 is a low noise dual polarity output power
n Inverting Charge Pump Generates –VIN supply that includes an inverting charge pump with both
n Charge Pump Output Current Up to 100mA positive and negative LDO regulators. The charge pump
n Low Noise Negative LDO Post Regulator operates over a wide 4.5V to 32V input range and can deliver
(ILDO– = 50mA Max) up to 100mA of output current. Each LDO regulator can
n Low Noise Independent Positive LDO Regulator provide up to 50mA of output current. The negative LDO
(ILDO+ = 50mA Max) post regulator is powered from the charge pump output.
n 100µA Quiescent Current in Burst Mode® Operation The LDO output voltages can be adjusted using external
with Both LDO Regulators On resistor dividers.
n 50kHz to 500kHz Programmable Oscillator Frequency
The charge pump employs either low quiescent current
n Stable with Ceramic Capacitors
Burst Mode operation or low noise constant frequency
n Short-Circuit/Thermal Protection
mode. In Burst Mode operation the charge pump VOUT
n Low Profile 3mm × 4mm 14-Pin DFN and Thermally
regulates to –0.94 • VIN, and the LTC3260 draws only
Enhanced 16-Pin MSOP Packages
100µA of quiescent current with both LDO regulators on.
In constant frequency mode the charge pump produces
Applications an output equal to –VIN and operates at a fixed 500kHz
or to a programmed value between 50kHz to 500kHz us-
n Low Noise Bipolar/Inverting Supplies ing an external resistor. The LTC3260 is available in low
n Industrial/Instrumentation Low Noise Bias profile (0.75mm) 3mm x 4mm 14-pin DFN and thermally
Generators enhanced 16-pin MSOP packages.
n Portable Medical Equipment L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
n Portable Instruments and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.

Typical Application
LDO Rejection of VOUT Ripple
±12V Outputs from a Single 15V Input

15V VIN LDO+ 12V VLDO+

10µF 10µF 10mV/DIV
LTC3260 909k AC-COUPLED
EN+ ADJ+ VLDO–
EN– BYP+ 100k 10mV/DIV
10nF AC-COUPLED
MODE GND VOUT
10nF
C+ BYP– 100k 10mV/DIV
1µF AC-COUPLED
C– ADJ –

909k
3260 TA01b
VIN = 15V 1µs/DIV
–15V VOUT LDO– –12V VLDO+ = 12V
10µF RT 10µF VLDO– = –12V
3260 TA01a fOSC = 500kHz
200k ILDO+ = 50mA
ILDO– –50mA

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LTC3260
Absolute Maximum Ratings (Notes 1, 3)

VIN, EN+, EN–, MODE.................................. –0.3V to 36V VOUT, LDO+, LDO – Short-Circuit Duration......... Indefinite
LDO+ ............................................................–16V to 36V Operating Junction Temperature Range
VOUT, LDO – ................................................ –36V to 0.3V (Note 2)................................................... –55°C to 150°C
RT, ADJ+....................................................... –0.3V to 6V Storage Temperature Range.................. –65°C to 150°C
BYP+.......................................................... –0.3V to 2.5V Lead Temperature (Soldering, 10 sec)
ADJ –............................................................. –6V to 0.3V MSE Only........................................................... 300°C
BYP–.......................................................... –2.5V to 0.3V

Pin Configuration
TOP VIEW

TOP VIEW
EN+ 1 14 BYP+
RT 2 13 ADJ+ EN+ 1 16 BYP+
RT 2 15 ADJ+
BYP– 3 12 MODE BYP– 3 14 MODE
ADJ– 4
15
11 EN– ADJ– 4 17 13 EN–
GND LDO– 5 GND 12 LDO+
LDO– 5 10 LDO+ VOUT 6 11 VIN
C– 7 10 C+
VOUT 6 9 VIN
NC 8 9 NC
C– 7 8 C+
MSE PACKAGE
16-LEAD PLASTIC MSOP
DE PACKAGE
TJMAX = 150°C, θJA = 43°C/W
14-LEAD (4mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
TJMAX = 150°C, θJA = 43°C/W
EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB

Order Information
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3260EDE#PBF LTC3260EDE#TRPBF 3260 14-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C
LTC3260IDE#PBF LTC3260IDE#TRPBF 3260 14-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C
LTC3260EMSE#PBF LTC3260EMSE#TRPBF 3260 16-Lead Plastic MSOP –40°C to 125°C
LTC3260IMSE#PBF LTC3260IMSE#TRPBF 3260 16-Lead Plastic MSOP –40°C to 125°C
LTC3260HMSE#PBF LTC3260HMSE#TRPBF 3260 16-Lead Plastic MSOP –40°C to 150°C
LTC3260MPMSE#PBF LTC3260MPMSE#TRPBF 3260 16-Lead Plastic MSOP –55°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping
container.Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

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 LTC3260
Electrical Characteristics The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = EN+ = EN– = 12V, MODE = 0V, RT = 200kΩ.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Charge Pump
VIN Input Voltage Range l 4.5 32 V
VUVLO VIN Undervoltage Lockout Threshold VIN Rising l 3.8 4 V
VIN Falling l 3.4 3.6 V
IVIN VIN Quiescent Current Shutdown, EN+ = EN– = 0V 2 5 µA
EN– = 0V, ILDO+ = 0mA 30 50 µA
MODE = VIN, EN+ = 0V, IVOUT = ILDO– = 0mA 80 160 µA
MODE = VIN, IVOUT = ILDO+ = ILDO– = 0mA 100 200 µA
MODE = 0V, IVOUT = 0mA 3.5 5.5 mA
VRT RT Regulation Voltage 1.200 V
VOUT VOUT Regulation Voltage MODE = 12V –0.94 • VIN V
MODE = 0V –VIN V
fOSC Oscillator Frequency RT = GND 450 500 550 kHz
ROUT Charge Pump Output Impedance MODE = 0V, RT = GND 32 Ω
ISHORT_CKT Max IVOUT Short-Circuit Current VOUT = GND l 100 160 250 mA
VMODE(H) MODE Threshold Rising l 1.1 2.0 V
VMODE(L) MODE Threshold Falling l 0.4 1.0 V
IMODE MODE Pin Internal Pull-Down Current VIN = MODE = 32V 0.7 µA
50mA Positive Regulator
LDO+ Output Voltage Range l 1.2 32 V
VADJ+ ADJ+ Reference Voltage l 1.176 1.200 1.224 V
IADJ+ ADJ+ Input Current VADJ+ = 1.2V –50 50 nA
ILDO+(SC) LDO+ Short-Circuit Current l 50 100 mA
Line Regulation 0.04 mV/V
Load Regulation 0.03 mV/mA
VDROPOUT + LDO+ Dropout Voltage ILDO + = 50mA 400 800 mV
Output Voltage Noise CBYP+ = 10nF 100 µVRMS
VEN+(H) EN+ Threshold Rising l 1.1 2.0 V
VEN+(L) EN+ Threshold Falling l 0.4 1.0 V
IEN+ EN+ Pin Internal Pull-Down Current VIN = EN+ = 32V 0.7 µA
50mA Negative Regulator
LDO– Output Voltage Range l –32 –1.2 V
VADJ– ADJ– Reference Voltage l –1.224 –1.200 –1.176 V
IADJ– ADJ– Input Current VADJ – = –1.2V –50 50 nA
ILDO–(SC) LDO– Short-Circuit Current l 50 100 mA
Line Regulation 0.002 mV/V
Load Regulation 0.02 mV/mA
VDROPOUT– LDO– Dropout Voltage ILDO– = 50mA 200 500 mV
Output Voltage Noise CBYP– = 10nF 100 µVRMS
VEN(H) EN– Threshold Rising l 1.1 2.0 V
VEN(L) EN– Threshold Falling l 0.4 1.0 V
IEN– EN– Pin Internal Pull-Down Current VIN = EN– = 32V 1.4 µA

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LTC3260
Electrical Characteristics
Note 1: Stresses beyond those listed under Absolute Maximum Ratings these specifications is determined by specific operating conditions in
may cause permanent damage to the device. Exposure to any Absolute conjunction with board layout, the rated package thermal impedance and
Maximum Rating condition for extended periods may affect device other environmental factors.
reliability and lifetime. The junction temperature (TJ, in °C) is calculated from the ambient
Note 2: The LTC3260 is tested under pulsed load conditions such that temperature (TA, in °C) and power dissipation (PD, in Watts) according to
TJ ≈ TA. The LTC3260E is guaranteed to meet specifications from the formula:
0°C to 85°C junction temperature. Specifications over the –40°C to TJ = TA + (PD • θJA),
125°C operating junction temperature range are assured by design, where θJA = 43°C/W is the package thermal impedance.
characterization and correlation with statistical process controls. The
Note 3: This IC includes overtemperature protection that is intended
LTC3260I is guaranteed over the –40°C to 125°C operating junction
to protect the device during momentary overload conditions. Junction
temperature range, the LTC3260H is guaranteed over the –40°C to 150°C
temperatures will exceed 150°C when overtemperature protection is
operating junction temperature range and the LTC3260MP is tested and
active. Continuous operation above the specified maximum operating
guaranteed over the full –55°C to 150°C operating junction temperature
junction temperature may result in device degradation or failure.
range. Note that the maximum ambient temperature consistent with

Typical Performance Characteristics

(TA = 25°C, CFLY = 1µF, CIN = COUT = CLDO+ = CLDO– = 10µF unless otherwise noted)
Oscillator Frequency
vs Supply Voltage Oscillator Frequency vs RT Shutdown Current vs Temperature
600 600 30

RT = GND
500 500 25
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)

400 400 SHUTDOWN CURRENT (µA) 20

300 300 15

RT = 200kΩ
200 200 10 VIN = 32V

100 100 5 VIN = 12V

VIN = 5V
0 0 0
0 5 10 15 20 25 30 35 1 10 100 1000 10000 –50 –25 0 25 50 75 100 125 150
SUPPLY VOLTAGE (V) RT (kΩ) TEMPERATURE (°C)
3260 G02
3260 G01 3260 G03

Quiescent Current vs Supply Quiescent Current vs Temperature

Quiescent Current vs Temperature Voltage (Constant Frequency Mode) (Constant Frequency Mode)
160 16 10
VIN = 12V VIN = 12V
9
140 14
Burst Mode OPERATION 8 fOSC = 500kHz
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (µA)

QUIESCENT CURRENT (mA)

120 WITH BOTH LDOs ON 12

7
100 10 6
80 8 fOSC = 500kHz 5

Burst Mode OPERATION 4 fOSC = 200kHz

60 6
WITH NEGATIVE LDO ON fOSC = 200kHz
3
40 4
2
fOSC = 50kHz fOSC = 50kHz
20 POSITIVE LDO ON 2 1
0 0 0
–50 –25 0 25 50 75 100 125 150 0 5 10 15 20 25 30 35 –50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C) SUPPLY VOLTAGE (V) TEMPERATURE (°C)
3260 G04 3260 G05 3260 G06

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 LTC3260
Typical Performance Characteristics
(TA = 25°C, CFLY = 1µF, CIN = COUT = CLDO+ = CLDO– = 10µF unless otherwise noted)
Voltage Loss (VIN – |VOUT|)
Effective Open-Loop Resistance VOUT Short-Circuit Current vs Output Current (Constant
vs Temperature vs Supply Voltage Frequency Mode)
60 250 3.0
fOSC = 500kHz VIN = 12V
EFFECTIVE OPEN-LOOP RESISTANCE (Ω)

VOUT SHORT-CIRCUIT CURRENT (mA)

50 2.5
200 RT = GND fOSC = 200kHz

VOLTAGE LOSS (V)

40 2.0
150 fOSC = 50kHz
30 1.5
100
20 RT = 200kΩ 1.0

VIN = 32V 50
10 0.5
VIN = 25V
VIN = 12V fOSC = 500kHz
0 0 0
–50 –25 0 25 50 75 100 125 150 0 5 10 15 20 25 30 35 0.1 1 10 100
TEMPERATURE (°C) SUPPLY VOLTAGE (V) OUTPUT CURRENT (mA)
3620 G07 3260 G08 3260 G09

Effective Open-Loop Resistance LDO+ Dropout Voltage

vs Supply Voltage ADJ+ Pin Voltage vs Temperature vs Temperature
90 1.224 800
VIN = 12V
EFFECTIVE OPEN-LOOP RESISTANCE (Ω)

80 700 ILDO+ = 50mA

LDO+ DROPOUT VOLTAGE (mV)

fOSC = 200kHz
70
1.212 600
ADJ+ PIN VOLTAGE (V)

60
500
50
fOSC = 500kHz 1.200 400
40
300
30

20 1.188 200

10 100

0 1.176 0
0 5 10 15 20 25 30 35 –50 –25 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150
SUPPLY VOLTAGE (V) TEMPERATURE (°C) TEMPERATURE (°C)
3260 G10 3260 G11 3260 G12

LDO+ Supply Rejection LDO+ GND Pin Current vs ILOAD LDO+ Load Regulation
60 0.14 1.2006
VIN = 12V VIN = 12V
UNITY GAIN
0.12 1.2004
50
LDO+ SUPPLY REJECTION (dB)

GND PIN CURRENT (mA)

0.10
40 1.2002
0.08
VLDO+ (V)

30 1.2000
0.06
20 1.1998
VIN = 6.5V 0.04
VLDO+ = 5V
10 ILDO+ = 50mA 0.02 1.1996
VRIPPLE = 50mVRMS
CLDO+ = 10µF
0 0 1.1994
0.1 1 10 100 1000 0 1 10 100 0.1 1 10 100
FREQUENCY (kHz) ILOAD (mA) ILDO+ (mA)
3260 G13 3260 G14 3260 G15

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 LTC3260
Typical Performance
+
Characteristics
–
(TA = 25°C, CFLY = 1µF, CIN = COUT = CLDO = CLDO = 10µF unless otherwise noted)
LDO– Dropout Voltage
ADJ– Pin Voltage vs Temperature vs Temperature LDO– Power Supply Rejection
–1.176 400 60
VOUT = –12V
–
350 ILDO = 50mA
50

LDO– DROPOUT VOLTAGE (mV)

LDO– SUPPLY REJECTION (dB)

–1.188 300
ADJ– PIN VOLTAGE (V)

40
250

–1.200 200 30

150
20
VOUT = –6.5V
–1.212 100 VLDO– = –5V
10 ILDO– = –50mA
50 VRIPPLE = 50mVRMS
CLDO– = 10µF
–1.224 0 0
–50 –25 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150 0.1 1 10 100 1000
TEMPERATURE (°C) TEMPERATURE (°C) FREQUENCY (kHz)
3260 G16 3260 G17 3260 G18

LDO– Load Regulation LDO Rejection of VOUT Ripple LDO+ Load Transient
–1.1994
VOUT = –12V
UNITY GAIN VLDO+
VLDO+
–1.1996
10mV/DIV 10mV/DIV
AC-COUPLED AC-COUPLED
–1.1998 VLDO–
10mV/DIV
VLDO– (V)

AC-COUPLED
–1.2000
VOUT
10mV/DIV 20mA
–1.2002 AC-COUPLED ILDO+
2mA

–1.2004 VIN = 15V 1µs/DIV 3260 G20

VIN = 12V 40µs/DIV 3260 G21

VLDO+ = 12V VLDO+ = 5V

VLDO– = –12V
–1.2006
0.1 1 10 100 fOSC = 500kHz
ILDO+ = 50mA
ILDO– (mA)
ILDO– –50mA
3260 G19

VOUT Transient (Burst Mode VOUT Transient

LDO – Load Transient Operation, MODE = H) (MODE = Low to High)

VLDO– VOUT VOUT

10mV/DIV 500mV/DIV 500mV/DIV
AC-COUPLED AC-COUPLED AC-COUPLED

–5mA
IOUT– MODE
– –2mA –50mA
ILDO
–20mA

3260 G23 3260 G24

VIN = 12V 40µs/DIV 3260 G22
VIN = 12V 2ms/DIV VIN = 12V 2ms/DIV
VLDO– = –5V fOSC = 500kHz fOSC = 500kHz
REFER TO FIGURE 3 IOUT = –5mA

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 LTC3260
Pin Functions (DFN/MSOP)

EN+ (Pin 1/ Pin 1): Logic Input. A logic “high” on the EN+ LDO+ (Pin 10/ Pin 12): Positive Low Dropout (LDO+)
pin enables the positive low dropout (LDO+) regulator. Output. This pin requires a low ESR capacitor with at least
RT (Pin 2/Pin 2): Input Connection for Programming the 2µF capacitance to ground for stability.
Switching Frequency. The RT pin servos to a fixed 1.2V EN– (Pin 11/ Pin 13): Logic Input. A logic “high” on the
when the EN– pin is driven to a logic “high”. A resistor from EN– pin enables the inverting charge pump as well as the
RT to GND sets the charge pump switching frequency. If negative LDO regulator.
the RT pin is tied to GND, the switching frequency defaults MODE (Pin 12/ Pin 14): Logic Input. The MODE pin deter-
to a fixed 500kHz. mines the charge pump operating mode. A logic “high”
BYP– (Pin 3/ Pin 3): LDO– Reference Bypass Pin. Connect on the MODE pin forces the charge pump to operate in
a capacitor from BYP– to GND to reduce LDO– output Burst Mode operation regulating VOUT to approximately
noise. Leave floating if unused. –0.94 • VIN with hysteretic control. A logic “low” on the
MODE pin forces the charge pump to operate as an open-
ADJ– (Pin 4/ Pin 4): Feedback Input for the Negative Low
Dropout Regulator. This pin servos to a fixed voltage of loop inverter with a constant switching frequency. The
–1.2V when the control loop is complete. switching frequency in both modes is determined by an
external resistor from the RT pin to GND. In Burst Mode
LDO– (Pin 5/ Pin 5): Negative Low Dropout (LDO–) Linear operation, this represents the frequency of the burst cycles
Regulator Output. This pin requires a low ESR (equivalent before the part enters the low quiescent current sleep state.
series resistance) capacitor with at least 2µF capacitance
to ground for stability. ADJ+ (Pin 13/ Pin 15): Feedback Input for the Positive
Low Dropout (LDO+) Regulator. This pin servos to a fixed
VOUT (Pin 6/ Pin 6): Charge Pump Output Voltage. In voltage of 1.2V when the control loop is complete.
constant frequency mode (MODE = low) this pin is driven
BYP+ (Pin 14/Pin 16): LDO+ Reference Bypass Pin. Con-
to –VIN. In Burst Mode operation, (MODE = high) this pin
nect a capacitor from BYP+ to GND to reduce LDO+ output
voltage is regulated to –0.94 • VIN using an internal burst
noise. Leave floating if unused.
comparator with hysteretic control.
GND (Exposed Pad Pin 15/ Exposed Pad Pin 17): Ground.
C– (Pin 7/ Pin 7): Flying Capacitor Negative Connection.
The exposed package pad is ground and must be soldered
C+ (Pin 8/ Pin 10): Flying Capacitor Positive Connection. to the PC board ground plane for proper functionality and
NC (Pins 8, 9 MSOP Only): No Connect. These pins are not for rated thermal performance.
connected to the LTC3260 die. These pins should be left
floating, connected to ground or shorted to adjacent pins.
VIN (Pin 9/ Pin 11): Input Voltage for Both Charge Pump
and Positive Low Dropout (LDO+) Regulator. VIN should
be bypassed with a low impedance ceramic capacitor.

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LTC3260
Block Diagram
Note: Pin numbers are as per DFN package. Refer to the Pin Functions section for corresponding MSOP pin numbers.

1
EN+
INVERTING
CHARGE PUMP
VIN LDO+
9 10

S1
S3
C+
8

S2
C–
7 +
–
S4 ADJ+
13
VOUT
6 1.2V BYP+
14
REF

50kHz
RT TO BYP–
2 –1.2V
500kHz REF 3
OSC
ADJ–
4
– +
EN– CHARGE
11
PUMP
AND
MODE INPUT
12
LOGIC

LDO–
5

GND
15

Operation (Refer to the Block Diagram)

The LTC3260 is a high voltage low noise dual output Charge Pump Constant Frequency Operation
regulator. It includes an inverting charge pump and two The LTC3260 provides low noise constant frequency op-
LDO regulators to generate bipolar low noise supply rails eration when a logic low is applied to the MODE pin. The
from a single positive input. It supports a wide input power charge pump and oscillator circuit are enabled using the
supply range from 4.5V to 32V. EN– pin. At the beginning of a clock cycle, switches S1 and
S2 are closed. The external flying capacitor across the C+
Shutdown Mode
and C– pins is charged to the VIN supply. In the second
In shutdown mode, all circuitry except the internal bias is phase of the clock cycle, switches S1 and S2 are opened,
turned off. The LTC3260 is in shutdown when a logic low while switches S3 and S4 are closed. In this configuration
is applied to both the enable inputs (EN+ and EN–). The the C+ side of the flying capacitor is grounded and charge
LTC3260 only draws 2µA (typical) from the VIN supply is delivered through the C– pin to VOUT. In steady state
in shutdown. the VOUT pin regulates at –VIN less any voltage drop due
to the load current on VOUT or LDO.

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 LTC3260
Operation (Refer to the Block Diagram)
The charge transfer frequency can be adjusted between mizes the charge pump ROL, quickly charges the output
50kHz and 500kHz using an external resistor on the RT up to the burst threshold and optimizes the duration of
pin. At slower frequencies the effective open-loop output the low current sleep state.
resistance (ROL) of the charge pump is larger and it is able
to provide smaller average output current. Figure 1 can Charge Pump Soft-Start
be used to determine a suitable value of RT to achieve a The LTC3260 has built in soft-start circuitry to prevent
required oscillator frequency. If the RT pin is grounded, excessive current flow during start-up. The soft-start is
the part operates at a constant frequency of 500kHz. achieved by internal circuitry that slowly ramps the amount
of current available at the output storage capacitor. The
600
soft-start circuitry is reset in the event of a commanded
500 shutdown or thermal shutdown.
OSCILLATOR FREQUENCY (kHz)

400 Charge Pump Short-Circuit/Thermal Protection

300 The LTC3260 has built-in short-circuit current limit as
well as overtemperature protection. During a short-circuit
200
condition, the part automatically limits its output current
100
to approximately 160mA. If the junction temperature
exceeds approximately 175°C the thermal shutdown
0
1 10 100 1000 10000 circuitry disables current delivery to the output. Once
RT (kΩ) the junction temperature drops back to approximately
3260 F01
165°C current delivery to the output is resumed. When
Figure 1. Oscillator Frequency vs RT thermal protection is active the junction temperature is
Charge Pump Burst Mode Operation beyond the specified operating range. Thermal protection
is intended for momentary overload conditions outside
The LTC3260 provides low power Burst Mode operation normal operation. Continuous operation above the speci-
when a logic high is applied to the MODE pin. In Burst fied maximum operating junction temperature may impair
Mode operation, the charge pump charges the VOUT pin to device reliability.
–0.94 • VIN (typical). The part then shuts down the internal
oscillator to reduce switching losses and goes into a low Positive Low Dropout Linear Regulator (LDO+)
current state. This state is referred to as the sleep state in
The positive low dropout regulator (LDO+) supports a load
which the IC consumes only about 100µA with both LDOs
of up to 50mA. The LDO+ takes power from the VIN pin
enabled. When the output voltage droops enough to over-
and drives the LDO+ output pin to a voltage programmed
come the burst comparator hysteresis, the part wakes up
by the resistor divider connected between the LDO+, ADJ+
and commences charge pump cycles until output voltage
and GND pins. For stability, the LDO+ output must be by-
exceeds –0.94 • VIN (typical). This mode provides lower
passed to ground with a low ESR ceramic capacitor that
operating current at the cost of higher output ripple and
maintains a capacitance of at least 2µF across operating
is ideal for light load operation.
temperature and voltage.
The frequency of charging cycles is set by the external
The LDO+ is enabled or disabled via the EN+ logic input pin.
resistor on the RT pin. The charge pump has a lower
When the LDO+ is enabled, a soft-start circuit ramps its
ROL at higher frequencies. For Burst Mode operation it is
regulation point from zero to the final value over a period
recommended that the RT pin be tied to GND. This mini-
of 75µs, reducing the inrush current on VIN.

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LTC3260
Operation (Refer to the Block Diagram)
Figure 2 shows the LDO+ regulator application circuit. negative by the charge pump circuitry. Soft-start circuitry
The LDO+ output voltage VLDO+ can be programmed by in the charge pump also provides soft-start functionality
choosing suitable values of R1 and R2 such that: for the LDO– and prevents excessive inrush currents.
 R1  Figure 3 shows the LDO– regulator application circuit.
VLDO+ = 1.2V •  + 1 The LDO– output voltage VLDO– can be programmed by
 R2 
choosing suitable values of R1 and R2 such that:
An optional capacitor of 10nF can be connected from the
BYP+ pin to ground. This capacitor bypasses the internal  R1 
VLDO – = –1.2V •  + 1
1.2V reference of the LTC3260 and improves the noise  R2 
performance of the LDO+. If this function is not used the
BYP+ pin should be left floating. When the inverting charge pump is in Burst Mode opera-
tion (MODE = high), the typical hysteresis on the VOUT
LTC3260 VIN pin is 2% of VIN voltage. The LDO– voltage should be set
0 high enough above VOUT in order to prevent LDO– from
EN+
entering dropout during normal operation.
LDO+ LDO
1
COUT
OUTPUT An optional capacitor of 10nF can be connected from the
R1
ADJ+ BYP– pin to ground. This capacitor bypasses the internal
BYP+ R2 –1.2V reference of the LTC3260 and improves the noise
1.2V CBYP+ performance of the LDO–. If this function is not used the
REF GND
3260 F02
BYP – pin should be left floating.
In order to improve transient response, an optional
Figure 2: Positive LDO Application Circuit
capacitor, CADJ–, may be used as shown in Figure 3. A
recommended value for CADJ– is 10pF. Experimentation
Negative Low Dropout Linear Regulator (LDO–) with capacitor values between 2pF and 22pF may yield
The negative low dropout regulator (LDO–) supports a improved transient response.
load of up to 50mA. The LDO– takes power from the VOUT
pin (output of the inverting charge pump) and drives the LTC3260
LDO– output pin to a voltage programmed by the resis- –1.2V GND
CBYP–
tor divider connected between the LDO–, ADJ– and GND
REF BYP–
R2
pins. For stability, the LDO– output must be bypassed to ADJ–

ground with a low ESR ceramic capacitor that maintains a LDO–

CADJ– R1
LDO
capacitance of at least 2µF across operating temperature EN–
1
OUTPUT
COUT
and voltage. 3260 F03
0
The LDO– is enabled or disabled via the EN– logic input VOUT
pin. Initially, when the EN– logic input is low, the charge
pump circuitry is disabled and the VOUT pin is at GND. Figure 3: Negative LDO Application Circuit
When EN– is switched high, the VOUT pin will be driven

3260fa

10
 LTC3260
Applications Information
Effective Open-Loop Output Resistance minimum turn-on time. The peak-to-peak output ripple at
The effective open-loop output resistance (ROL) of a charge the VOUT pin is approximately given by the expression:
pump is a very important parameter which determines the IOUT  1 
strength of the charge pump. The value of this parameter VRIPPLE(P-P) ≈  – tON 
COUT  fOSC 
depends on many factors such as the oscillator frequency
(fOSC), value of the flying capacitor (CFLY), the nonoverlap where COUT is the value of the output capacitor, fOSC is the
time, the internal switch resistances (RS) and the ESR of oscillator frequency and tON is the on-time of the oscillator
the external capacitors. (1µs typical).
Typical ROL values as a function of temperature are shown Just as the value of COUT controls the amount of output
in Figure 4 ripple, the value of CIN controls the amount of ripple present
60 at the input (VIN) pin. The amount of bypass capacitance
fOSC = 500kHz
required at the input depends on the source impedance
EFFECTIVE OPEN-LOOP RESISTANCE (Ω)

50
driving VIN. For best results it is recommended that VIN
40 be bypassed with at least 2µF of low ESR capacitance. A
high ESR capacitor such as tantalum or aluminum will
30 have higher input noise than a low ESR ceramic capacitor.
20
Therefore, a ceramic capacitor is recommended as the
main bypass capacitance with a tantalum or aluminum
10 VIN = 32V
VIN = 25V
capacitor used in parallel if desired.
VIN = 12V
0
–50 –25 0 25 50 75 100 125 150 Flying Capacitor Selection
TEMPERATURE (°C)
3620 F04
The flying capacitor controls the strength of the charge
Figure 4. Typical ROL vs Temperature
pump. A 1µF or greater ceramic capacitor is suggested
for the flying capacitor for applications requiring the full
Input/Output Capacitor Selection rated output current of the charge pump.

The style and value of capacitors used with the LTC3260 For very light load applications, the flying capacitor may
determine several important parameters such as regulator be reduced to save space or cost. For example, a 0.2µF
control loop stability, output ripple, charge pump strength capacitor might be sufficient for load currents up to 20mA.
and minimum turn-on time. To reduce noise and ripple, A smaller flying capacitor leads to a larger effective open-
it is recommended that low ESR ceramic capacitors be loop resistance (ROL) and thus limits the maximum load
used for the charge pump and LDO outputs. All capacitors current that can be delivered by the charge pump.
should retain at least 2µF of capacitance over operating
Ceramic Capacitors
temperature and bias voltage. Tantalum and aluminum
capacitors can be used in parallel with a ceramic capacitor Ceramic capacitors of different materials lose their capaci-
to increase the total capacitance but should not be used tance with higher temperature and voltage at different rates.
alone because of their high ESR. In constant frequency For example, a capacitor made of X5R or X7R material
mode, the value of COUT directly controls the amount of will retain most of its capacitance from –40°C to 85°C
output ripple for a given load current. Increasing the size of whereas a Z5U or Y5V style capacitor will lose considerable
COUT will reduce the output ripple at the expense of higher capacitance over that range. Z5U and Y5V capacitors may

3260fa

11
LTC3260
Applications Information
also have a poor voltage coefficient causing them to lose The flying capacitor nodes C+ and C– switch large cur-
60% or more of their capacitance when the rated voltage rents at a high frequency. These nodes should not be
is applied. Therefore when comparing different capacitors, routed close to sensitive pins such as the LDO feedback
it is often more appropriate to compare the amount of pins (ADJ+ and ADJ–) and internal reference bypass pins
achievable capacitance for a given case size rather than (BYP+ and BYP–).
discussing the specified capacitance value. The capacitor
manufacture’s data sheet should be consulted to ensure Thermal Management
the desired capacitance at all temperatures and voltages. At high input voltages and maximum output current, there
Table 1 is a list of ceramic capacitor manufacturers and can be substantial power dissipation in the LTC3260. If
their websites. the junction temperature increases above approximately
Table 1 175°C, the thermal shutdown circuitry will automatically
AVX www.avxcorp.com
deactivate the output. To reduce the maximum junction
Kemet www.kemet.com
temperature, a good thermal connection to the PC board
Murata www.murata.com
ground plane is recommended. Connecting the exposed pad
of the package to a ground plane under the device on two
Taiyo Yuden www.t-yuden.com
layers of the PC board can reduce the thermal resistance
Vishay www.vishay.com
of the package and PC board considerably.
TDK www.component.tdk.com

Layout Considerations Derating Power at High Temperatures

Due to high switching frequency and high transient currents To prevent an overtemperature condition in high power
produced by LTC3260, careful board layout is necessary applications, Figure 6 should be used to determine the
for optimum performance. A true ground plane and short maximum combination of ambient temperature and power
connections to all the external capacitors will improve dissipation.
performance and ensure proper regulation under all condi- The power dissipated in the LTC3260 should always fall
tions. Figure 5 shows an example layout for the LTC3260. under the line shown for a given ambient temperature. The
power dissipated in the LTC3260 has three components.
Power dissipated in the positive LDO:
GND
PLDO+ = (VIN – VLDO+) • ILDO+

CFLY
Power dissipated in the negative LDO:
VIN VOUT PLDO– = (|VOUT| – |VLDO–|) • ILDO– and
Power dissipated in the inverting charge pump:
CBYP–
LDO+ LDO–
PCP = (VIN – |VOUT|) • (IOUT + ILDO–)
CBYP+ RT where IOUT denotes any additional current that might be
pulled directly from the VOUT pin. The LDO– current is
also supplied by the charge pump through VOUT and is
GND
therefore included in the charge pump power dissipation.
3260 F05
The total power dissipation of the LTC3260 is given by:
Figure 5. Recommended Layout
PD = PLDO+ + PLDO– + PCP

3260fa

12
 LTC3260
Applications Information
6
θJA = 43°C/W
The derating curve in Figure 6 assumes a maximum ther-
mal resistance, θJA, of 43°C/W for the package. This can
MAXIMUM POWER DISSIPATION (W)

5
be achieved with a four layer PCB that includes 2oz Cu
4 traces and six vias from the exposed pad of the LTC3260
to the ground plane.
3
TJ = 150°C It is recommended that the LTC3260 be operated in the
2
region corresponding to TJ ≤ 150°C for continuous op-
1
RECOMMENDED eration as shown in Figure 6. Operation beyond 150°C
OPERATION
should be avoided as it may degrade part performance
0 and lifetime. At high temperatures, typically around 175°C,
–50 –25 0 25 50 75 100 125 150 175
AMBIENT TEMPERATURE (°C) the part is placed in thermal shutdown and all outputs are
3260 F06 disabled. When the part cools back down to a low enough
Figure 6. Maximum Power Dissipation vs Ambient Temperature temperature, typically around 165°C, the outputs are re-
enabled and the part resumes normal operation.

Typical Applications
Low Power ±24V Power Supply from a Single-Ended 28V Input Supply

9 10
28V VIN LDO+ 24V
C1 C4
LTC3260 4.7µF R1
4.7µF
1 13 1.91M
EN+ ADJ+
11 14 R2
EN– BYP+
100k
12 15
MODE GND
8 3 R3
C2 C+ BYP– 100k
7 4
1µF C– ADJ–
R4
6 5 1.91M
VOUT LDO– –24V
C3 C7 3260 TA02
4.7µF RT 4.7µF
2

High Voltage Input to Bipolar Output with Highly Efficient Dividing/Inverting Charge Pump

11 12
13.5V TO 32V VIN LDO+ 5V
C1 1 R1 C4
4.7µF EN+ 4.7µF
13 15 316k
50V EN– ADJ+
10 + 16 R2
C2 C BYP+
1µF D1 C5 100k
50V MBR0540 0.01µF
LTC3260
D2 C6
3 0.01µF R3
MBR0540
D3 BYP– 100k
– 4
MBR0540 C3 ADJ
1µF R4
50V 7 5 316k
C– LDO– –5V
NOTE: THE LTC3260 WILL ALWAYS RUN 6 C7
VOUT 4.7µF
IN CONTINUOUS FREQUENCY REGARDLESS C8
OF THE MODE PIN SETTING BECAUSE VOUT 4.7µF 3260 TA04

IS ALWAYS LESS THAN –1/2VIN MODE GND RT 25V

 V –V –I •ROL 
14 17 2 VOUT ~ –  IN F OUT – VF 
 2 

3260fa

13
LTC3260
Typical Applications
28V Dual Tracking Bipolar Supply with Outputs from ±5V to ±25V

11 12
28V VIN LDO+ OUT
C1 1 R1 C3
4.7µF EN+ 4.7µF
13 15 732k
50V EN– ADJ+ 35V
10 + 16 R2
C BYP+
C2 C4 73.2k
1µF 0.01µF R3
50V LTC3260
4 500k
7
C– ADJ–
– 3
BYP
C5
R4
0.01µF
732k
14 5
MODE LDO– –OUT
2 6 C6
RT VOUT C7 4.7µF
GND 4.7µF 35V
17 50V
3260 TA05

3260fa

14
 LTC3260
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

DE Package
14-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1708 Rev B)
R = 0.115 0.40 ±0.10
4.00 ±0.10
TYP
(2 SIDES)
8 14
R = 0.05
0.70 ±0.05
TYP

3.60 ±0.05 3.30 ±0.05 3.30 ±0.10

3.00 ±0.10
PACKAGE
2.20 ±0.05 1.70 ±0.05 (2 SIDES) 1.70 ±0.10 PIN 1 NOTCH
OUTLINE
PIN 1 R = 0.20 OR
TOP MARK 0.35 × 45°
(SEE NOTE 6) CHAMFER
(DE14) DFN 0806 REV B

7 1
0.25 ±0.05 0.200 REF 0.75 ±0.05 0.25 ±0.05
0.50 BSC 0.50 BSC
3.00 REF 3.00 REF
0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
NOTE:
1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
PACKAGE OUTLINE MO-229 MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
2. DRAWING NOT TO SCALE 5. EXPOSED PAD SHALL BE SOLDER PLATED
3. ALL DIMENSIONS ARE IN MILLIMETERS 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE

3260fa

15
LTC3260
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev E)

BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102 2.845 ±0.102
(.112 ±.004) 0.889 ±0.127 (.112 ±.004)
(.035 ±.005)
1 8 0.35
REF

5.23 1.651 ±0.102

1.651 ±0.102 3.20 – 3.45
(.206) 0.12 REF
(.065 ±.004) (.126 – .136) (.065 ±.004)
MIN
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
16 9 FOR REFERENCE ONLY
0.305 ±0.038 0.50 NO MEASUREMENT PURPOSE
(.0120 ±.0015) (.0197) 4.039 ±0.102
TYP BSC (.159 ±.004)
(NOTE 3) 0.280 ±0.076
RECOMMENDED SOLDER PAD LAYOUT
16151413121110 9 (.011 ±.003)
REF
DETAIL “A”
0.254
(.010) 3.00 ±0.102
0° – 6° TYP 4.90 ±0.152
(.118 ±.004)
(.193 ±.006)
GAUGE PLANE (NOTE 4)

0.53 ±0.152
(.021 ±.006)
1234567 8
DETAIL “A” 1.10 0.86
0.18 (.043) (.034)
(.007) MAX REF

SEATING
PLANE 0.17 – 0.27 0.1016 ±0.0508
(.007 – .011) (.004 ±.002)
TYP 0.50
NOTE: (.0197)
MSOP (MSE16) 0911 REV E

1. DIMENSIONS IN MILLIMETER/(INCH) BSC

2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.

3260fa

16
 LTC3260
Revision History
REV DATE DESCRIPTION PAGE NUMBER
A 09/12 Changed Operating Junction Temperature. 2
Add H- and MP-grade options. Throughout
Add Junction to heading of Electrical Characteristics table. 3
Add H- and MP-grade into Note 2. 4
Modified Shutdown Current vs Temperature curve for operation to 150°C. 4
Modified Quiescent Current vs Temperature curve for operation to 150°C. 4
Corrected Figure 5 Pinout RT and CBYP. 12
Removed Thermal Shutdown curve from Figure 6. 13
Clarified 150°C Operation in Derating Power section. 12, 13
Updated Related Parts list. 18

3260fa

17
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3260
Typical Application
Low Noise ±12V Power Supply from a Single-Ended 15V Input Supply (Frequency = 200kHz)

9 10
15V VIN LDO+ 12V
C1 C4
10µF LTC3260 10µF R1
1 13 909k
EN+ ADJ+
11 14 R2
EN– BYP+ C5 100k
12 15 10nF
MODE GND
C6
8 3 10nF R3
C2 C+ BYP– 100k
7 4
1µF C– ADJ–
R4
6 5 909k
– –12V
VOUT LDO
C3 C7 3260 TA03
RT 10µF
10µF
2
R5
200k

Related Parts
PART NUMBER DESCRIPTION COMMENTS
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Shutdown SO8 Package
LTC1514/LTC1515 Step-Up/Step-Down Switched-Capacitor DC/DC Converters VIN: 2V to 10V, VOUT: 3.3V to 5V, IQ = 60µA, SO8 Package
LT®1611 150mA Output, 1.4MHz Micropower Inverting Switching Regulator VIN: 0.9V to 10V, VOUT = ±34V, ThinSOT™ Package
LT1614 250mA Output, 600kHz Micropower Inverting Switching Regulator VIN: 0.9V to 6V, VOUT = ±30V, IQ = 1mA, MS8, SO8
Packages
LTC1911 250mA, 1.5MHz Inductorless Step-Down DC/DC Converter VIN: 2.7V to 5.5V, VOUT = 1.5V/1.8V, IQ = 180µA,
MS8 Package
LTC3250/LTC3250-1.2/ Inductorless Step-Down DC/DC Converters VIN: 3.1V to 5.5V, VOUT = 1.2V, 1.5V, IQ = 35µA,
LTC3250-1.5 ThinSOT Package
LTC3251 500mA Spread Spectrum Inductorless Step-Down DC/DC VIN: 2.7V to 5.5V, VOUT: 0.9V to 1.6V, 1.2V, 1.5V, IQ = 9µA,
Converter MS10E Package
LTC3252 Dual 250mA, Spread Spectrum Inductorless Step-Down DC/DC VIN: 2.7V to 5.5V, VOUT: 0.9V to 1.6V, IQ = 50µA,
Converter DFN12 Package
LT1054/LT1054L Switched-Capacitor Voltage Converters with Regulator VIN: 3.5V to 15V/7V, IOUT = 100mA/125mA, N8, S08,
SO16 Packages
LTC3261 High Voltage, Low Quiescent Current Inverting Charge Pump VIN: 4.5V to 32V, VOUT = –VIN, IOUT = 100mA, MSOP-12
Package

3260fa

18 Linear Technology Corporation

LT 0912 REV A • PRINTED IN USA

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com  LINEAR TECHNOLOGY CORPORATION 2012