EVALUATION

1
KIT
AVAILABLE
TC7662A

CHARGE PUMP DC-TO-DC CONVERTER

FEATURES GENERAL DESCRIPTION
2
■ Wide Operating Range ............................. 3V to 18V The TC7662A is a pin-compatible upgrade to the In-
■ Increased Output Current .............................. 40mA dustry standard TC7660 charge pump voltage converter. It
■ Pin Compatible with ICL7662/SI7661/TC7660/ converts a +3V to +18V input to a corresponding – 3V to
LTC1044 -18V output using only two low-cost capacitors, eliminating
■ No External Diodes Required inductors and their associated cost, size and EMI. In addi-
Low Output Impedance @ IL = 20mA ....... 40Ω Typ.
■
■
■
No Low-Voltage Terminal Required
CMOS Construction
tion to a wider power supply input range (3V to 18V versus
1.5V to 10V for the TC7660), the TC7662A can source
output currents as high as 40mA. The on-board oscillator
3
operates at a nominal frequency of 12kHz. Operation be-
low 10kHz (for lower supply current applications) is also
possible by connecting an external capacitor from OSC to
ORDERING INFORMATION ground.
The TC7662A directly is recommended for designs

Part No. Package

Temperature
Range
requiring greater output current and/or lower input/output
voltage drop. It is available in 8-pin DIP packages in com-
mercial and extended temperature ranges.
4
TC7662ACPA 8-Pin Plastic DIP 0°C to +70°C
TC7662AEPA 8-Pin Plastic DIP – 40°C to +85°C
PIN CONFIGURATION
TC7662AIJA 8-Pin CerDIP – 25°C to +85°C
TC7662AMJA 8-Pin CerDIP – 55°C to +125°C
NC 1 8 VDD
TC7660EV Evaluation Kit for
+ 2 7 OSC
Charge Pump Family C
GND 3
C– 4
TC7662A 6 NC
5 VOUT
5
NC = NO INTERNAL CONNECTION

FUNCTIONAL BLOCK DIAGRAM

8 VDD
I

COSC 7

LEVEL
SHIFT
P SW1
6
Q
2
+ F/F CAP+
C
– Q
LEVEL N SW4 +
SHIFT CP
COMPARATOR
WITH HYSTERESIS EXT
GND

VREF 3

OUT
+
CR
7
LEVEL N SW2
SHIFT EXT
TC7662A
4
CAP – RL

LEVEL N SW3
SHIFT

8
5
VOUT

TC7662A-5 9/11/96

TELCOM SEMICONDUCTOR, INC. 4-77

 CHARGE PUMP
DC-TO-DC CONVERTER

TC7662A

ABSOLUTE MAXIMUM RATINGS* Package Thermal Resistance

CPA, EPA θJA .............................................. 140°C/W
Supply Voltage V DD to GND .................................... +18V IJA, MJA θJA .................................................. 90°C/W
Input Voltage (Any Pin) ........... (V DD + 0.3) to (V SS – 0.3) Storage Temperature Range ................ – 65°C to +150°C
Current Into Any Pin ................................................. 10mA Lead Temperature (Soldering, 10 sec) ................. +300°C
Operating Temperature Range ESD Protection ..................................................... ±2000V
C Suffix .................................................. 0°C to +70°C Output Short Circuit ................. Continuous (at 5.5V Input)
I Suffix .............................................. – 25°C to +85°C
E Suffix ............................................. – 40°C to +85°C *Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
M Suffix .......................................... – 55°C to +125°C
above those listed under Absolute Maximum Ratings may cause perma-
Power Dissipation (TA ≤ 70°C) nent damage to the device. These are stress ratings only and functional
Plastic DIP ......................................................730mW operation of the device at these or any other conditions above those
CerDIP............................................................800mW indicated in the operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.

ELECTRICAL CHARACTERISTICS: VDD = 15V, TA = +25°C (See Test Circuit), unless otherwise specified.
Symbol Parameter Test Conditions Min Typ Max Unit
V DD Supply Voltage 3 — 18 V
IS Supply Current RL = ∞
V DD = +15V — 510 700 µA
0°C ≤ TA ≤ +70°C — 560 —
– 55°C ≤ TA ≤ +125°C — 650 —
V DD = +5V — 190 —
0°C ≤ TA ≤ +70°C — 210 —
– 55°C ≤ TA ≤ +125°C — 210 —
RO Output Source IL = 20mA, V DD = +15V — 40 50 Ω
Resistance IL = 40mA, V DD = +15V — 50 60
IL = 3mA, V DD = +5V — 100 125
COSC Oscillator Frequency — 12 — kHz
PEFF Power Efficiency V DD = +15V 93 97 — %
RL = 2 kΩ
VEFF Voltage Efficiency VDD = +15V 99 99.9 — %
RL = ∞
Over Operating Temperature Range 96 — —

4-78 TELCOM SEMICONDUCTOR, INC.

CHARGE PUMP
DC-TO-DC CONVERTER 1
TC7662A

TEST CIRCUIT

1 8
IS
V
+
EPR
2
NC
IL (+5V)
2 7
+ 10 µF ESL ESR C
3 TC7662A 6 C OSC RL
CP NC
4 5 VOUT
(–5V) Figure 1. Capacitor Equivalent Circuit

CR
+
10 µF Note one of its characteristics is ESR (equivalent series
resistance). This parasitic resistance winds up in series with
3
the load. Thus, both voltage and power conversion effi-
ciency are compromised if a low ESR capacitor is not used.
APPLICATIONS INFORMATION For example, in the "Test Circuit", changing CP and CR
capacitors from typical ESR to low ESR types, the effective
Theory of Operation converter output impedance changed from 45Ω to 40Ω, an
improvement of 12%.
The TC7662A is a capacitive charge pump (some-
times called a switched-capacitor circuit), where four
MOSFET switches control the charge and discharge of a
This applies to all types of capacitors, including film
types (polyester, polycarbonate etc.).
4
capacitor. Some applications information suggests that the ca-
The functional diagram (page 1) shows how the switch- pacitor is not critical and attributes the limiting factor to the
ing action works. SW1 and SW2 are turned on simulta- capacitor's reactance value. Let's examine this:
neously, charging C1 to the supply voltage, VDD. This
1 X
assumes that the ON resistance of the MOSFETs in series XC = and ZC = C ,
with the capacitor produce a charging time (3 time con- 2πf C DS
stants) less than the ON time provided by the oscillator
frequency, as shown: where DS (duty cycle) = 50%.
5
Thus, ZC ≈ 1.33Ω at f = 12kHz, where C = 10 µF.
3 (RDS(ON) C1) <C1/(0.5 fOSC). For the TC7662A, f = 12,000Hz, and a typical value of
C would be 10 µF. This is a reactive impedance of ≈1.33Ω.
In the next cycle, SW1 and SW2 are turned OFF and, If the ESR is as great as 5Ω, the reactive value is not as
after a very short interval with all switches OFF (preventing critical as it would first appear, since the ESR would dominate.
large currents from occurring due to cross conduction), The 5Ω value is typical of a general-purpose electrolytic
SW3 and SW4 are turned ON. The charge in C1 is then
transferred to COUT, BUT WITH THE POLARITY IN-
capacitor.
6
VERTED. In this way, a negative voltage is derived. Synchronizing
An oscillator supplies pulses to a flip-flop that is fed to a The TC7662A may be synchronized by connecting pin
set of level shifters. These level shifters then drive each set 7 of the TC7662A through a 100k resistor in series with a
of switches at one-half the oscillator frequency. diode to a negative-going pulse source. The negative pulse
The oscillator has a pin that controls the frequency of voltage can be +5V with a 5 microsecond duration going
oscillation. Pin 7 can have a capacitor added that is con- negative to 0V.
nected to ground. This will lower the frequency of the
oscillator by adding capacitance to the internal timing ca- 7
pacitor of the TC7662A. (See Oscillator Frequency vs. CEXT,
page 5.) Q

TTL
Capacitors 100 k
Q TO PIN 7
In early charge pump converters, capacitors were not TC7662A
considered critical due to the high RDS(ON) of the MOSFET
switches. In order to understand this, let’s look at a model of
a typical electrolytic capacitor (Figure 1). Figure 2. Synchronization
8
TELCOM SEMICONDUCTOR, INC. 4-79
 CHARGE PUMP
DC-TO-DC CONVERTER

TC7662A

TYPICAL APPLICATIONS

Combined Negative Converter and Positive Multiplier

V+
1 8
2 7 VD1
CP2 + VD2
10 µF
3 TC7662A 6 VOUT = 2V+ –2VD
V = –V+
4 5 OUT + C R1
C R2 10 µF
CP1 + 10 µF
+

Lowering Output Resistance by Paralleling Devices

V+

1 8 1 8
2 7 2 7
CP1 + CP2 +
3 TC7662A 6 3 TC7662A 6
10 µF 10 µF
4 5 4 5
VOUT
CR
10 µF +

Positive Voltage Multiplier

V+
1 8
2 7 VD1
3 6 VD2
TC7662A VOUT = 2V+–2 VD
4 5 + CP + CR
10 µF 10 µF

Split V+ In Half
V+
1 8
2 7
CP +
3 6
10 µF TC7662A
4 5

V+
VOUT =
2
CR +
100 µF

4-80 TELCOM SEMICONDUCTOR, INC.

CHARGE PUMP
DC-TO-DC CONVERTER 1
TC7662A

TYPICAL CHARACTERISTICS

700
Supply Current vs. Temperature Oscillator Frequency vs. CEXT 2
TA = +25°C
600 10k
SUPPLY CURRENT (µA)

FREQUENCY (Hz)
500

400 + 1k
V = 15V

300 3
200 100
V + = 5V
100

0 10
–60 –40 –20 0 20 40 60 80 100 120 140 1 10 100 1000 10,000
TEMPERATURE (°C) CAPACITANCE (pF)

Frequency vs. Temperature Output Resistance vs. Temperature

4
20 160

18 140
OUTPUT RESISTANCE ( Ω)
FREQUENCY (kHz)

16 120
V + = 5V, IL = 3 mA
14

12
100

80
5
10 60
V+ = 15V, IL = 20 mA
8 40

6 20
–60 –40 –20 0 20 40 60 80 100 120 140 –60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE (°C) TEMPERATURE (°C)
6
Power Conversion Efficiency vs. I LOAD Output Resistance vs. Input Voltage
110 165 110
POWER CONVERSION EFFICIENCY (%)

100 150 100 TA = +25°C

OUTPUT RESISTANCE (Ω)

90 135 90
SUPPLY CURRENT (mA)

EFFICIENCY

7
80 120 80
70 105 70
60 90 60
20 mA
50 75 50
SUPPLY
40 CURRENT 60 40
30 45 30
20 30 20
10 TA = +25°C 15 10

0 8 16 24 32 40 48
LOAD CURRENT (mA)
56 64 72 80
0
0 2 4 6 8 10 12 14
INPUT VOLTAGE (V)
16 18 20 8
TELCOM SEMICONDUCTOR, INC. 4-81