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LM2611
SNOS965J – JUNE 2001 – REVISED DECEMBER 2015

LM2611 1.4-MHz Cuk Converter

1 Features 3 Description
•
1 1.4-MHz Switching Frequency The LM2611 is a current mode, PWM inverting
switching regulator. Operating from a 2.7-V to 4-V
• Low RDS(ON) DMOS FET supply, it is capable of producing a regulated
• 1-mVp-p Output Ripple negative output voltage of up to −(36 VIN(MAX)). The
• −5 V at 300 mA From 5-V Input LM2611 utilizes an input and output inductor, which
• Better Regulation Than a Charge Pump enables low voltage ripple and RMS current on both
the input and the output. With a switching frequency
• Uses Tiny Capacitors and Inductors of 1.4 MHz, the inductors and output capacitor can be
• Wide Input Range: 2.7 V to 14 V physically small and low cost. High efficiency is
• Low Shutdown Current: <1 µA achieved through the use of a low RDS(ON) FET.
• 5-Pin SOT-23 Package The LM2611 features a shutdown pin, which can be
activated when the part is not needed to lower the Iq
2 Applications and save battery life. A negative feedback (NFB) pin
provides a simple method of setting the output
• MR Head Bias voltage, using just two resistors. Cycle-by-cycle
• Digital Camera CCD Bias current limiting and internal compensation further
• LCD Bias simplify the use of the LM2611.
• GaAs FET Bias The LM2611 is available as a small 5-pin, SOT-23
• Positive to Negative Conversion package and comes in two grades. Grade A has a
1.2-A current limit and 0.5-Ω RDS(ON), and Grade B
has a 0.9-A current limit and 0.7-Ω RDS(ON).

Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LM2611 SOT-23 (5) 1.60 mm × 2.90 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.

Typical Application Circuit

L1 CCUK L2 VOUT - 5V
15 PH 1 PF 47 PH 300 mA
VIN
5V

5 1 RFB1 CFF
VIN SW 29.4k 330 pF
D
CIN 4 3 COUT
SHDN LM2611A NFB
22 PF 22 PF
GND
2 RFB2
10k

CIN: TAIYO YUDEN X5R JMK325BJ226MM

CCUK: TAIYO YUDEN X5R EMK316BJ105MF
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR32-150
L2: SUMIDA CR32-470

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
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Table of Contents
1 Features .................................................................. 1 7.3 Feature Description................................................... 8
2 Applications ........................................................... 1 7.4 Device Functional Modes........................................ 12
3 Description ............................................................. 1 8 Application and Implementation ........................ 13
4 Revision History..................................................... 2 8.1 Application Information............................................ 13
8.2 Typical Application .................................................. 13
5 Pin Configuration and Functions ......................... 3
6 Specifications......................................................... 3 9 Power Supply Recommendations...................... 19
6.1 Absolute Maximum Ratings ...................................... 3 10 Layout................................................................... 20
6.2 ESD Ratings.............................................................. 3 10.1 Layout Guidelines ................................................. 20
6.3 Recommended Operating Conditions....................... 4 10.2 Layout Example .................................................... 20
6.4 Thermal Information .................................................. 4 11 Device and Documentation Support ................. 21
6.5 Electrical Characteristics........................................... 4 11.1 Community Resources.......................................... 21
6.6 Typical Characteristics .............................................. 6 11.2 Trademarks ........................................................... 21
7 Detailed Description .............................................. 8 11.3 Electrostatic Discharge Caution ............................ 21
7.1 Overview ................................................................... 8 11.4 Glossary ................................................................ 21
7.2 Functional Block Diagram ......................................... 8 12 Mechanical, Packaging, and Orderable
Information ........................................................... 21

4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision I (April 2013) to Revision J Page

• Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section. ................................................................................................. 1

Changes from Revision H (April 2013) to Revision I Page

• Changed layout of National Data Sheet to TI format ........................................................................................................... 19

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5 Pin Configuration and Functions

DBV Package
5-Pin SOT-23
Top View

SW 1 5 VIN

GND 2

NFB 3 4 SHDN

Pin Functions
PIN
TYPE (1) DESCRIPTION
NO. NAME
1 SW A Drain of internal switch. Connect at the node of the input inductor and Cuk capacitor.
2 GND GND Analog and power ground.
3 NFB A Negative feedback. Connect to output via external resistor divider to set output voltage.
4 SHDN I Shutdown control input. VIN = Device on. Ground = Device in shutdown.
Analog and power input. Filter out high frequency noise with a 0.1-µF ceramic capacitor
5 VIN PWR
placed close to the pin.

(1) A = Analog, I = Input, GND = Ground, PWR = Power

6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN MAX UNIT
Input voltage, VIN 14.5 V
SW voltage –0.4 36 V
NFB voltage –6 0.4 V
SHDN voltage –0.4 14.5 V
Maximum junction temperature 125 °C
(2)
Power dissipation Internally limited
Lead temperature 300 °C
Storage temperature, Tstg −65 150 °C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal
resistance, θJA, and the ambient temperature, TA. See the Electrical Characteristics table for the thermal resistance of various layouts.
The maximum allowable power dissipation at any ambient temperature is calculated using: PD (MAX) = (TJ(MAX) − TA)/θJA. Exceeding
the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown.

6.2 ESD Ratings

VALUE UNIT
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2) ±2000
V(ESD) Electrostatic discharge V
Machine Model (MM) (3) ±200

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) The human body model is a 100-pF capacitor discharged through a 1.5-kΩ resistor into each pin.
(3) The machine model is a 200-pF capacitor discharged directly into each pin.

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6.3 Recommended Operating Conditions

MIN NOM MAX UNIT
Supply voltage 2.7 14 V
Operating junction temperature, TJ −40 125 °C

6.4 Thermal Information

LM2611
THERMAL METRIC (1) DBV (SOT-23) UNIT
5 PINS
RθJA Junction-to-ambient thermal resistance 163.5 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 115.2 °C/W
RθJB Junction-to-board thermal resistance 27.4 °C/W
ψJT Junction-to-top characterization parameter 12.9 °C/W
ψJB Junction-to-board characterization parameter 26.9 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance n/a °C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.

6.5 Electrical Characteristics

Specifications in standard type face are for TJ = 25°C, unless otherwise specified. VIN = 5 V and IL = 0 A, unless otherwise
specified.
(1) (2) (1)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VIN Input voltage TJ = −40°C to +85°C 2.7 14 V
Grade A 1.2
Grade A; TJ = −40°C to +85°C 1 2
ISW Switch current limit A
Grade B 0.9
Grade B; TJ = −40°C to +85°C 0.7
Grade A 0.5 0.65
RDSON Switch ON resistance Ω
Grade B 0.7 0.9
Device enabled; TJ = −40°C to +85°C 1.5
SHDNTH Shutdown threshold V
Device disabled; TJ = −40°C to +85°C 0.5
VSHDN = 0 V 0
ISHDN Shutdown pin bias current VSHDN = 5 V 0 µA
VSHDN = 5 V; TJ = −40°C to +85°C 1
VIN = 3 V −1.23
NFB Negative feedback reference V
VIN = 3 V; TJ = −40°C to +85°C −1.205 −1.255
VNFB =−1.23 V −4.7
INFB NFB pin bias current µA
VNFB =−1.23 V; TJ = −40°C to +85°C −2.7 −6.7
VSHDN = 5 V, Switching 1.8
VSHDN = 5 V, Switching; mA
3.5
TJ = −40°C to +85°C
VSHDN = 5 V, Not Switching 270
Iq Quiescent current
VSHDN = 5 V, Not Switching; µA
500
TJ = −40°C to +85°C
VSHDN = 0 V 0.024
µA
VSHDN = 0 V; TJ = −40°C to +85°C 1
%VOUT/
Reference line regulation 2.7 V ≤ VIN ≤ 14 V 0.02 %/V
ΔVIN

(1) All limits are specified at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits
are 100% tested through statistical analysis. All limits at temperature extremes via correlation using standard Statistical Quality Control
(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
(2) Typical numbers are at 25°C and represent the expected value of the parameter.
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Electrical Characteristics (continued)

Specifications in standard type face are for TJ = 25°C, unless otherwise specified. VIN = 5 V and IL = 0 A, unless otherwise
specified.
(1) (2) (1)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
TJ = 25°C 1.4
fS Switching frequency MHz
TJ = −40°C to +85°C 1 1.8
TJ = 25°C 88%
DMAX Maximum duty cycle
TJ = −40°C to +85°C 82%
IL Switch leakage VSW = 5 V, Not Switching 1 µA

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6.6 Typical Characteristics

0.55 1

0.5 0.8

RDS(ON) (:)
RDS(ON) (:)

0.45 0.6

0.4 0.4

0.35 0.2

0.3 0
2 4 6 8 10 12 14 -50 0 50 100 150
VIN (V) TEMPERATURE (oC)
VIN = 5 V

Figure 1. RDS(ON) vs VIN Figure 2. RDS(ON) vs Ambient Temperature

1.45 1.4

1.4
SWITCH CURRENT LIMIT (A)

SWITCH CURRENT LIMIT (A) 1.39

1.35
1.38
1.3
1.37
1.25

1.36
1.2

1.15 1.35
2 4 6 8 10 12 -50 0 50 100 150
VIN (V) TEMPERATURE (oC)
VIN = 5 V

Figure 3. Switch Current Limit vs VIN Figure 4. Switch Current Limit vs Ambient Temperature
1.48 1.50

1.46 1.48
OSCILLATOR FREQUENCY (MHz)
OSCILLATOR FREQUENCY (MHz)

1.44 1.46
1.44
1.42
1.42
1.40
1.40
1.38
1.38
1.36
1.36
1.34 1.34
1.32 1.32
1.30 1.30
0 2 4 6 8 10 12 14 -60 -40 -20 0 20 40 60 80 100120 140 160
VIN (V) TEMPERATURE (oC)
VIN = 5 V

Figure 5. Oscillator Frequency vs VIN Figure 6. Oscillator Frequency vs Ambient Temperature

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Typical Characteristics (continued)

-1.215 -1.218

-1.22 -1.220

-1.225 -1.222

VNFB (V)
-1.23 -1.224
VNFB (V)

-1.235 -1.226

-1.24 -1.228

-1.245 -1.230

-1.25 -1.232
0 5 10 15 -55 -30 -5 20 45 70 95 120
VIN (V) TEMPERATURE (oC)
TA = 25°C VOUT = −5 V VIN = 5 V
Figure 7. VNFB vs VIN Figure 8. VNFB vs Ambient Temperature
4.45 4.4

4.4 4.3
INFB (PA)

4.35 4.2
INFB (PA)

4.3 4.1

4.25 4.0

4.2 3.9
0 5 10 15 -50 -25 0 25 50 75 100 125 150
VIN (V) TEMPERATURE (oC)
TA = 25°C VOUT = −5 V VIN = 3.5 V VOUT = −5 V

Figure 9. INFB vs VIN Figure 10. INFB vs Ambient Temperature

260 0.9

255 0.85
SHUTDOWN VOLTAGE (V)

250 0.8

245 0.75
On Threshold
IQ(PA)

240 0.7

235 0.65
Off Threshold
230 0.6

225 0.55

0.5
220
-50 0 50 100 150 -50 0 50 100 150
TEMPERATURE (oC) TEMPERATURE (oC)
VIN = 5 V

Figure 11. Iq vs Ambient Temperature (No Load) Figure 12. VSHUTDOWN vs Ambient Temperature

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7 Detailed Description

7.1 Overview
The LM2611 consists of a current mode controller with an integrated primary switch and integrated current
sensing circuitry. The feedback is connected to the internal error amplifier and a type II/III internal compensation
scheme is used. A ramp generator provides some slope compensation to the system. SHDN pin is a logic input
designed to shut down the converter.

7.2 Functional Block Diagram

VI
N
5 1 SW

R5 R6 THERMAL
PWM COMPARATOR SHUTDOWN
+
gm - FF
R DRIVER
- R Q
RC
RAMP
Q1 Q2
x10
GENERATOR ¦ + R s

CURRENT LIMIT
R3 CC
COMPARATOR
30k
1.4MHz
+
R4
140k OSCILLATOR 0.05
VO 3 NFB -

R1 CFF
EXTERNAL (OPTIONAL) SHDN
4 SHUTDOWN 2 GND

R2
EXTERNAL

7.3 Feature Description

7.3.1 Cuk Converter
+ L1 - + CCUK - - L2 + + L1 - + CCUK - - L2 +

+ +

VIN
COUT VOUT COUT VOUT
VIN

- -
a b

Figure 13. Operating Cycles of a Cuk Converter

The LM2611 is a current mode, fixed frequency PWM switching regulator with a −1.23-V reference that makes it
ideal for use in a Cuk converter. The Cuk converter inverts the input and can step up or step down the absolute
value. Using inductors on both the input and output, the Cuk converter produces very little input and output
current ripple. This is a significant advantage over other inverting topologies such as the buck-boost and flyback.
The operating states of the Cuk converter are shown in Figure 13. During the first cycle, the transistor switch is
closed and the diode is open. L1 is charged by the source and L2 is charged by CCUK, while the output current is
provided by L2. In the second cycle, L1 charges CCUK and L2 discharges through the load. By applying the volt-
second balance to either of the inductors, use Equation 1 to determine the relationship of VOUT to the duty cycle
(D).

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Feature Description (continued)

D
VOUT = - VIN
1-D (1)
The following sections review the steady-state design of the LM2611 Cuk converter.

7.3.2 Output and Input Inductor

Figure 14 and Figure 15 show the steady-state voltage and current waveforms for L1 and L2, respectively.
Referring to Figure 13 (a), when the switch is closed, VIN is applied across L1. In the next cycle, the switch opens
and the diode becomes forward biased, and VOUT is applied across L1 (the voltage across CCUK is VIN − VOUT.)
vL1(V)

VIN

VOUT

iL1(A)

'IL1
IL1

Figure 14. Voltage and Current Waveforms in Inductor L1 of a Cuk Converter

The voltage and current waveforms of inductor L2 are shown in Figure 15. During the first cycle of operation,
when the switch is closed, VIN is applied across L2. When the switch opens, VOUT is applied across L2.
L1A CCUK L1B VOUT-5V
22PH 2.2PF 22PH 375mA

VIN
12V

VDD 5 1 RFB1 CFF

5V 29.4k 1000pF
VIN SW
D
4 3 COUT
LM2611A NFB 22PF
CIN SHDN
22PF GND
RFB2
2
10k

CIN: VISHAY/SPRAGUE 595D226X0020C2T

CCUK: TAIYO YUDEN X5R LMK212BJ105MG
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-220 or MURATA LZH3C220 (UNCOUPLED)

Figure 15. Schematic of the Cuk Converter Using LM2611

Equation 2 to Equation 5 define the values given in Figure 14 and Figure 15:
IL2 = IOUT (2)

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Feature Description (continued)

VIN ´ D ´ TS
DiL2 =
2 ´ L2 (3)
D D
IL1 = IL2 = IOUT
1-D 1-D (4)
V ´ D ´ TS
DiL1 = IN
2 ´ L1 (5)
Use these equations to choose correct core sizes for the inductors. The design of the LM2611's internal
compensation assumes L1 and L2 are equal to 10 to 22 µH, thus TI recommends staying within this range.

7.3.3 Switch Current Limit

The LM2611 incorporates a separate current limit comparator, making current limit independent of any other
variables. The current limit comparator measures the switch current versus a reference that represents current
limit. If at any time the switch current surpasses the current limit, the switch opens until the next switching period.
To determine the maximum load for a given set of conditions, both the input and output inductor currents must be
considered. The switch current is equal to iL1 + iL2, and is drawn in Figure 16. In summary, Equation 6 shows:
iSW(PEAK) = iL1 + iL2 = IL1 + IL2 + DiL1 + DiL2
æ D ö VIN ´ D ´ TS æ 1 1 ö
= IOUT ´ ç 1 + ÷ + ´ ç + ÷
è 1-D ø 2 è L1 L 2 ø (6)
ISW(PEAK) must be less than the current limit (1.2 A typical), but will also be limited by the thermal resistivity of the
LM2611 device's 5-pin, SOT-23 package (θJA = 265°C/W).
iSW(A)

ICL

'iL1 +'iL2
IL1+ IL2

ISW

t
iSW

The peak value is equal to the sum of the average currents through L1 and L2 and the average-to-peak current
ripples through L1 and L2.

Figure 16. Switch Current Waveform in a Cuk Converter.

7.3.4 Input Capacitor

The input current waveform to a Cuk converter is continuous and triangular, as shown in Figure 14. The input
inductor insures that the input capacitor sees fairly low ripple currents. However, as the input inductor gets
smaller, the input ripple goes up. The RMS current in the input capacitor is shown in Equation 7.
1 VIN
ICIN(RMS) =
2 3 æ V ö
fsL1 ç i + 1÷
ç Vo ÷
è ø (7)
The input capacitor should be capable of handling the RMS current. Although the input capacitor is not so critical
in a Cuk converter, a 10-µF or higher value good quality capacitor prevents any impedance interactions with the
input supply. TI recommends connecting a 0.1-µF or 1-µF ceramic bypass capacitor on the VIN pin (pin 5) of the
IC. This capacitor must be connected very close to pin 5 (within 0.2 inches).

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Feature Description (continued)

7.3.5 Output Capacitor
Like the input current, the output current is also continuous, triangular, and has low ripple (see IL2 in Figure 15).
The output capacitor must be rated to handle its RMS current:
DiL2 1 VIN
ICOUT(RMS) = =
3 2 3 æ V ö
fsL 2 ç i + 1÷
ç Vo ÷
è ø (8)
For example, ICOUT(RMS) can range from 30 mA to 180 mA with 10 µH ≤ L1,2 ≤ 22 µH, −10 V ≤ VOUT ≤ −3.3 V, and
2.7 V ≤ VIN ≤ 30 V (VIN may be 30 V if using separate power and analog supplies, see Split Supply Operation in
the Typical Application section). The worst case conditions are with L1,2, VOUT(MAX), and VIN(MAX). Many capacitor
technologies will provide this level of RMS current, but ceramic capacitors are ideally suited for the LM2611.
Ceramic capacitors provide a good combination of capacitance and equivalent series resistance (ESR) to keep
the zero formed by the capacitance and ESR at high frequencies. Use Equation 9 to calculate the ESR zero.
1
fESR = (Hz)
2pCOUTESR (9)
A general rule of thumb is to keep fESR > 80 kHz for LM2611 Cuk designs. Low ESR tantalum capacitors will
usually be rated for at least 180 mA in a voltage rating of 10 V or above. However the ESR in a tantalum
capacitor (even in a low ESR tantalum capacitor) is much higher than in a ceramic capacitor and could place fESR
low enough to cause the LM2611 to become unstable.

7.3.6 Improving Transient Response and Compensation

The compensator in the LM2611 is internal. However, a zero-pole pair can be added to the open-loop frequency
response by inserting a feed-forward capacitor, CFF, in parallel to the top feedback resistor (RFB1). Phase margin
and bandwidth can be improved with the added zero-pole pair. This in turn improves the transient response to a
step load change (see Figure 17 and Figure 18). The position of the zero-pole pair is a function of the feedback
resistors and the capacitor value:
1
wZ = (rad / s)
CFFRFB1 (10)
1 æ RFB1 ö
wp = ç1 + ÷ (rad / s)
CFFRFB1 è RFB2 ø (11)
The optimal position for this zero-pole pair will vary with circuit parameters such as D, IOUT, COUT, L1, L2, and
CCUK. For most cases, the value for the zero frequency is between 5 kHz to 20 kHz. Notice how the pole
position, ωp, is dependant on the feedback resistors RFB1 and RFB2, and therefore also dependant on the output
voltage. As the output voltage becomes closer to −1.26 V, the pole moves towards the zero, tending to cancel it
out. If the absolute magnitude of the output voltage is less than 3.3 V, adding the zero-pole pair will not have
much effect on the response.

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Feature Description (continued)

Figure 17. 130-mA to 400-mA Transient Response Figure 18. 130-mA to 400-mA Transient Response
of the Circuit in Figure 24 With CFF= 1 nF of the Circuit in Figure 24 With CFF Disconnected

7.4 Device Functional Modes

7.4.1 Hysteretic Mode
As the output current decreases, the energy stored in the Cuk capacitor eventually exceeds the energy required
by the load. The excess energy is absorbed by the output capacitor, causing the output voltage to increase out of
regulation. The LM2611 detects when this happens and enters a pulse-skipping, or hysteretic mode. In pulse-
skipping mode, the output voltage increases as illustrated in Figure 20 as opposed to the regular PWM operation
shown in Figure 19. Figure 19 shows the LM2611 in PWM Mode with very-low ripple. Figure 20 shows the
LM2611 in pulse-skipping mode at low loads. In this mode, the output ripple increases slightly.

Figure 19. PWM Mode Figure 20. Pulse-Skipping Mode

7.4.1.1 Thermal Shutdown

If the junction temperature of the LM2611 exceeds 163°C, the device enters thermal shutdown. In thermal
shutdown, the part deactivates the driver and the switch turns off. The switch remains off until the junction
temperature drops to 155°C, at which point the part begins switching again. It will typically take 10 ms for the
junction temperature to drop from 163°C to 155°C with the switch off.

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8 Application and Implementation

NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM2611 is a Cuk controller with an integrated switch. The following section provides an approach to sizing
the components for the target application and shows some typical examples of applications to help the designer.

8.2 Typical Application

8.2.1 Cuk Converter With Integrated Switch
L1A CCUK L1B VOUT-5V
22PH 2.2PF 22PH 375mA

VIN
12V

VDD 5 1 RFB1 CFF

5V 29.4k 1000pF
VIN SW
D
4 3 COUT
LM2611A NFB 22PF
CIN SHDN
22PF GND
RFB2
2
10k

CIN: VISHAY/SPRAGUE 595D226X0020C2T

CCUK: TAIYO YUDEN X5R LMK212BJ105MG
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-220 or MURATA LZH3C220 (UNCOUPLED)

Figure 21. Typical Cuk Converter Implementation Using LM26211

8.2.1.1 Design Requirements

The first variables needed are the output voltage and the input voltage range (min to max). The input voltage
range ensures that the IC is suitable for the application and that the absolute maximum voltage are respected.
The expected maximum output current is also needed to verify that the IC can deliver the required current.

8.2.1.2 Detailed Design Procedure

The first components to choose are the power inductors. Typically a smaller inductance yields a smaller solution
footprint and lower cost but the higher ripple makes a smaller inductance not compatible with every application.
Due to the internal compensation, TI recommends a 10-µH to 22-µH inductor. Try to choose the inductors so that
the peak-to-peak ripple is lower than 0.3 A of the average current by using Equation 3 and Equation 5.
Using the maximum output current and the input voltage range, calculate the worst case peak current in the
switch using Equation 6. If the peak current is above the peak current limit for this part, consider increasing the
inductance and re-calculate. If the inductance is above 22 µH for each inductor, the designer will have to pay
special attention to stability over the extended range of operation (it's always a good practice to do so even if the
inductance is within the recommended range).
Using the desired output voltage, calculate the value of the feedback resistors. The reference voltage is 1.23 V.
Resistors of 50 kΩ or less must be used due to the leakage at the NFB pin.

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Typical Application (continued)

It is a good idea to add a placeholder for a small capacitor across the top feedback resistor to act as a feed-
forward component to optimize transient response. Optimization of the feed-forward capacitor depends a lot on
the specific parameters including the parasitic components associated with the capacitors. Experimentation is
key to ensure ideal sizing of the capacitor (either using load transient response or a loop response analyzer).
See Improving Transient Response and Compensation for details regarding the CFF capacitor.

8.2.1.3 Application Curves

700 700
MAXIMUM OUTPUT CURRENT (mA)

MAXIMUM OUTPUT CURRENT (mA)

600 600

500 500

400 400

300 300

200 200

100 100

0 0
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
OUTPUT VOLTAGE (-V) OUTPUT VOLTAGE (-V)
Figure 22. Maximum Output Current vs Output Voltage at Figure 23. Maximum Output Current vs Output Voltage at
VIN = 12 V (L1 = L2 = 22 µH) VIN = 5 V (L1 = L2 = 22 µH)

8.2.2 5-V to –5-V Inverting Converter

L1 CCUK L2 VOUT - 5V
15 PH 1 PF 47 PH 300 mA
VIN
5V

5 1 RFB1 CFF
VIN SW 29.4k 330 pF
D
CIN 4 3 COUT
SHDN LM2611A NFB
22 PF 22 PF
GND
2 RFB2
10k

CIN: TAIYO YUDEN X5R JMK325BJ226MM

CCUK: TAIYO YUDEN X5R EMK316BJ105MF
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR32-150
L2: SUMIDA CR32-470

Figure 24. 5-V to –5-V Inverting Converter Schematic

8.2.2.1 Design Requirements

This design converts 5 V (VIN) to –5 V (VOUT). Adjust RFB2 to set a different output voltage.

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Typical Application (continued)

8.2.2.2 Application Curves

90 700

MAXIMUM OUTPUT CURRENT (mA)

85
600
80
75 500
EFFICIENCY (%)

70
400
65
60 300
55
200
50
45 100
40
0.05 0
0.15 0.25 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
LOAD CURRENT (A) OUTPUT VOLTAGE (-V)
Figure 25. Efficiency vs Load Current Figure 26. Maximum Output Current vs Output Voltage, 5
V to –5 V

8.2.3 9-V to –5-V Inverting Converter

L1 CCUK L2
10 PH 10 PH VOUT - 5V
VIN 1 PF
9V

1 RFB1 CFF
5
29.4k 330 pF
VIN SW
CIN D
4 3 COUT
22 PF SHDN LM2611A NFB
22 PF
GND
RFB2
2 10k

CIN: TAIYO YUDEN X5R JMK325BJ226MM

CCUK: TAIYO YUDEN X5R EMK316BJ105MF
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR32-100
L2: SUMIDA CR32-100

Figure 27. 9-V to –5-V Inverting Converter Schematic

8.2.3.1 Design Requirements

This design converts 9 V (VIN) to –5 V (VOUT). Adjust RFB2 to set a different output voltage.

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Typical Application (continued)

8.2.3.2 Application Curve
700

MAXIMUM OUTPUT CURRENT (mA)

60060
0
50
500
0
40
400 0
30
300 0
20
200 0
10
100 0
0
0 4 6 8 10 12 14 16 18 20
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

OUTPUT VOLTAGE (-V)

Figure 28. Maximum Output Current vs Output Voltage, 9 V to – 5 V

8.2.4 12-V to –5-V Inverting Converter

L1 CCUK L2
22 PH 2.2 PF 22 PH VOUT - 5V
VIN
12V

5 1 RFB1 CFF
VIN SW 29.4k 1000 pF
CIN D
4 3 COUT
22 PF SHDN LM2611A NFB
22 PF
GND
2 RFB2
10k

CIN: TAIYO YUDEN X5R JMK325BJ226MM

CCUK: TAIYO YUDEN X5R EMK316BJ225ML
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR32-220
L2: SUMIDA CR32-220

The maximum output current vs output voltage (adjust RFB2 to set a different output voltage) when the input voltage is
12 V.

Figure 29. 12-V to –5-V Inverting Converter Schematic

8.2.4.1 Design Requirements

This design converts 12 V (VIN) to –5 V (VOUT). Adjust RFB2 to set a different output voltage.

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Typical Application (continued)

8.2.4.2 Application Curve
700

MAXIMUM OUTPUT CURRENT (mA)

600

500

400

300

200

100

0
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
OUTPUT VOLTAGE (-V)

Figure 30. Maximum Output Current vs Output Voltage, 12 V to –5 V

8.2.5 LM2611 Operating With Separate Power and Biasing Supplies

L1A CCUK L1B VOUT-5V
22PH 2.2PF 22PH 375mA

VIN
12V

VDD 5 1 RFB1 CFF

5V 29.4k 1000pF
VIN SW
D
CBYP 4 3 COUT
LM2611A NFB 22PF
CIN 0.1PF SHDN
22PF GND
RFB2
2
10k

CIN: VISHAY/SPRAGUE 595D226X0020C2T

CCUK: TAIYO YUDEN X5R EMK316BJ225ML
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR32-220

Figure 31. LM2611 Operating With Separate Power and Biasing Supplies Schematic

8.2.5.1 Design Requirements

Follow the design requirements in Cuk Converter With Integrated Switch.

8.2.5.2 Detailed Design Procedure

8.2.5.2.1 Split Supply Operation

The LM2611 may be operated with separate power and bias supplies. In the circuit shown in Figure 31, VIN is the
power supply that the regulated voltage is derived from, and VDD is a low current supply used to bias the
LM2611. Equation 12 and Equation 13 show the conditions for the supplies are:
2.7 V ≤ VDD ≤ 14 V (12)
0 V ≤ VIN ≤ (36 - IVOUTI) V (13)

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Typical Application (continued)

As the input voltage increases, the maximum output current capacbility increases. Using a separate, higher
voltage supply for power conversion enables the LM2611 to provide higher output currents than it would with a
single supply that is limited in voltage by VIN(MAX).

8.2.6 Shutdown and Soft-Start

RSS VSHDN CSS
100k 0.1uF

L1A CCUK L1B

VIN 22uH 1uF 22uH VOUT

5 1 RFB1 CFF
CIN VIN SW 29.4k 1000pF
22uF D
4 3
SHDN LM2611A NFB COUT
22uF
GND RFB2
2 10k

Figure 32. LM2611 Soft-Start Circuit

8.2.6.1 Design Requirements

Follow the design requirements in Cuk Converter With Integrated Switch.

8.2.6.2 Detailed Design Procedure

8.2.6.2.1 Shutdown and Soft-Start

A soft-start circuit is used in switching power supplies to limit the input inrush current upon start-up. Without a
soft-start circuit, the inrush current can be several times the steady-state load current, and thus apply
unnecessary stress to the input source. The LM2611 does not have soft-start circuitry, but implementing the
circuit in Figure 32 lowers the peak inrush current. The SHDN pin is coupled to the output through CSS. The
LM2611 is toggled between shutdown and run states while the output slowly decreases to its steady-state value.
The energy required to reach steady state is spread over a longer time and the input current spikes decrease
(see Figure 33 and Figure 34).

8.2.6.3 Application Curves

Figure 33. Start-Up Waveforms With a Soft-Start Circuit Figure 34. Start-Up Waveforms Without a Soft-Start Circuit

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Typical Application (continued)

8.2.7 High Duty Cycle and Load Current
L1 CCUK L2 VOUT
2.7V d VIN d 14V 22uH 1uF 22uH -5V

5 1 RFB1 CFF1
VIN SW 29.4k 1000pF
D
CIN 4 3 COUT
SHDN LM2611A NFB
10uF 22uF
GND
RFB2
2
1k

RFB3 CFF2
9k 1uF

CIN: TAIYO YUDEN X5R JMK325BJ106MN

CCUK: TAIYO YUDEN X5R TMK316BJ105ML
COUT: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1, L2: SUMIDA CDRH6D28-220

Figure 35. LM2611 High Current Schematic

8.2.7.1 Design Requirements

Follow the design requirements in Cuk Converter With Integrated Switch.

8.2.7.2 Detailed Design Procedure

8.2.7.2.1 High Duty Cycle and Load Current Operation

The circuit in Figure 35 is used for high duty cycles (D > 0.5) and high load currents. The duty cycle begins to
increase beyond 50% as the input voltage drops below the absolute magnitude of the output voltage. RFB3 and
CFF2 are added to the feedback network to introduce a low frequency lag compensation (pole-zero pair)
necessary to stabilize the circuit under the combination of high duty cycle and high load currents.

9 Power Supply Recommendations

The power supply must never exceed the absolute maximum rating of the device given in Absolute Maximum
Ratings. If the regulator is connected to the input supply through long wires or PCB traces, special care is
required to achieve good performance. The parasitic inductance and resistance of the input cables can have an
adverse effect on the operation of the regulator. The parasitic inductance, in combination with the low ESR
ceramic input capacitors, can form an under-damped resonant circuit. This circuit may cause overvoltage
transients at the VIN pin, each time the input supply is cycled on and off.

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10 Layout

10.1 Layout Guidelines

• Connection between L1 and SW pin should be kept as short as possible to minimize inductance
• Connection between CCUK and SW should also be kept short
• The feedback resistor should be placed close to the NFB pin to minimize the path of the higher impedance
feedback node
• The feedback trace leading from Vout to the output to the feedback resistors should not pass under the
switch node between L1 and CCUK and the switch node between CCUK, L2 and D
• The feedback trace leading from Vout to the output to the feedback resistors should not pass under the
inductors L1 and L2
• A bypass capacitor CBYP of 0.1 µF should be placed close to VIN and GND pin

10.2 Layout Example

Figure 36. Example Layout Top

Figure 37. Example Layout Bottom

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11 Device and Documentation Support

11.1 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.

11.2 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.3 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.

11.4 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

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 IMPORTANT NOTICE

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