CHARGE PUMP DC-TO-DC CONVERTER
EVALUATION
KIT
AVAILABLE
1
TC7662A
FEATURES
■ Wide Operating Range .............................3V to 18V
■ Increased Output Current .............................. 40mA
■ Pin Compatible with ICL7662/SI7661/TC7660/
LTC1044
■ No External Diodes Required
■ Low Output Impedance @ IL = 20mA....... 40Ω Typ.
■ No Low-Voltage Terminal Required
■ CMOS Construction
ORDERING INFORMATION
Temperature
Part No. Package Range
TC7662ACPA 8-Pin Plastic DIP 0°C to +70°C
TC7662AEPA 8-Pin Plastic DIP – 40°C to +85°C
TC7662AIJA 8-Pin CerDIP – 25°C to +85°C
TC7662AMJA 8-Pin CerDIP – 55°C to +125°C
TC7660EV Evaluation Kit for
Charge Pump Family
GENERAL DESCRIPTION
The TC7662A is a pin-compatible upgrade to the Industry standard TC7660 charge pump voltage converter. It
converts a +3V to +18V input to a corresponding – 3V to
-18V output using only two low-cost capacitors, eliminating
inductors and their associated cost, size and EMI. In addition 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
operates at a nominal frequency of 12kHz. Operation below 10kHz (for lower supply current applications) is also
possible by connecting an external capacitor from OSC to
ground.
The TC7662A directly is recommended for designs
requiring greater output current and/or lower input/output
voltage drop. It is available in 8-pin DIP packages in commercial and extended temperature ranges.
PIN CONFIGURATION
NC
C
GND
C
+
–
1
2
3
TC7662A
4
8
V
DD
OSC
7
6
NC
5
V
OUT
2
3
4
5
FUNCTIONAL BLOCK DIAGRAM
C
OSC
TELCOM SEMICONDUCTOR, INC.
NC = NO INTERNAL CONNECTION
8
V
P SW1
N SW4
N SW2
N SW3
DD
6
2
+
CAP
+
C
P
EXT
GND
3
+
C
OUT
4
CAP
R
EXT
–
5
V
OUT
R
L
TC7662A-5 9/11/96
7
8
4-77
I
7
LEVEL
SHIFT
LEVEL
SHIFT
LEVEL
SHIFT
LEVEL
SHIFT
+
–
COMPARATOR
WITH HYSTERESIS
V
REF
F/F
C
Q
Q
TC7662A
TC7662A
CHARGE PUMP
DC-TO-DC CONVERTER
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage VDD to GND .................................... +18V
Input Voltage (Any Pin) ........... (VDD + 0.3) to (VSS – 0.3)
Current Into Any Pin.................................................10mA
Operating Temperature Range
C Suffix..................................................0°C to +70°C
I Suffix .............................................. – 25°C to +85°C
E Suffix.............................................– 40°C to +85°C
M Suffix .......................................... – 55°C to +125°C
Power Dissipation (TA ≤ 70°C)
Plastic DIP......................................................730mW
CerDIP............................................................800mW
ELECTRICAL CHARACTERISTICS: V
= 15V, TA = +25°C (See Test Circuit), unless otherwise specified.
DD
Package Thermal Resistance
CPA, EPA θJA.............................................. 140°C/W
IJA, MJA θJA.................................................. 90°C/W
Storage Temperature Range ................– 65°C to +150°C
Lead Temperature (Soldering, 10 sec) .................+300°C
ESD Protection..................................................... ±2000V
Output Short Circuit................. Continuous (at 5.5V Input)
*Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional
operation of the device at these or any other conditions above those
indicated in the operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.
Symbol Parameter Test Conditions Min Typ Max Unit
V
I
R
C
P
V
DD
S
O
OSC
EFF
EFF
Supply Voltage 3 — 18 V
Supply Current RL = ∞
= +15V — 510 700 µA
V
DD
= +5V — 190 —
V
DD
Output Source IL = 20mA, VDD = +15V — 40 50 Ω
Resistance I
Oscillator Frequency — 12 — kHz
Power Efficiency VDD = +15V 93 97 — %
Voltage Efficiency VDD = +15V 99 99.9 — %
0°C ≤ T
– 55°C ≤ T
0°C ≤ T
– 55°C ≤ TA ≤ +125°C — 210 —
L
IL = 3mA, VDD = +5V — 100 125
RL = 2 kΩ
R
Over Operating Temperature Range 96 — —
≤ +70°C — 560 —
A
≤ +125°C — 650 —
A
≤ +70°C — 210 —
A
= 40mA, VDD = +15V — 50 60
= ∞
L
4-78
TELCOM SEMICONDUCTOR, INC.
TTL
Q
Q
100 k
TO PIN 7
TC7662A
EPR
ESL
ESR
C
CHARGE PUMP
DC-TO-DC CONVERTER
TEST CIRCUIT
1
TC7662A
I
S
NC
C
1
2
+
10 µF
P
3
4
TC7662A
8
7
6
NC
5
C
OSC
C
R
+
I
L
R
L
10 µF
+
V
(+5V)
V
OUT
(–5V)
APPLICATIONS INFORMATION
Theory of Operation
The TC7662A is a capacitive charge pump (sometimes called a switched-capacitor circuit), where four
MOSFET switches control the charge and discharge of a
capacitor.
The functional diagram (page 1) shows how the switching action works. SW1 and SW2 are turned on simultaneously, charging C1 to the supply voltage, VDD. This
assumes that the ON resistance of the MOSFETs in series
with the capacitor produce a charging time (3 time constants) less than the ON time provided by the oscillator
frequency, as shown:
3 (R
In the next cycle, SW1 and SW2 are turned OFF and,
after a very short interval with all switches OFF (preventing
large currents from occurring due to cross conduction),
SW3 and SW4 are turned ON. The charge in C1 is then
transferred to C
VERTED. In this way, a negative voltage is derived.
An oscillator supplies pulses to a flip-flop that is fed to a
set of level shifters. These level shifters then drive each set
of switches at one-half the oscillator frequency.
The oscillator has a pin that controls the frequency of
oscillation. Pin 7 can have a capacitor added that is connected to ground. This will lower the frequency of the
oscillator by adding capacitance to the internal timing capacitor of the TC7662A. (See Oscillator Frequency vs. C
page 5.)
C1) <C1/(0.5 f
DS(ON)
, BUT WITH THE POLARITY IN-
OUT
OSC
).
EXT
Figure 1. Capacitor Equivalent Circuit
Note one of its characteristics is ESR (equivalent series
resistance). This parasitic resistance winds up in series with
the load. Thus, both voltage and power conversion efficiency are compromised if a low ESR capacitor is not used.
For example, in the "Test Circuit", changing CP and C
capacitors from typical ESR to low ESR types, the effective
converter output impedance changed from 45Ω to 40Ω, an
improvement of 12%.
This applies to all types of capacitors, including film
types (polyester, polycarbonate etc.).
Some applications information suggests that the capacitor is not critical and attributes the limiting factor to the
capacitor's reactance value. Let's examine this:
XC =
where DS (duty cycle) = 50%.
Thus, ZC ≈ 1.33Ω at f = 12kHz, where C = 10 µF.
For the TC7662A, f = 12,000Hz, and a typical value of
C would be 10 µF. This is a reactive impedance of ≈1.33Ω.
If the ESR is as great as 5Ω, the reactive value is not as
critical as it would first appear, since the ESR would dominate.
The 5Ω value is typical of a general-purpose electrolytic
capacitor.
1
2πf C
and ZC = ,
X
DS
C
Synchronizing
The TC7662A may be synchronized by connecting pin
7 of the TC7662A through a 100k resistor in series with a
diode to a negative-going pulse source. The negative pulse
voltage can be +5V with a 5 microsecond duration going
negative to 0V.
,
2
3
R
4
5
6
7
Capacitors
In early charge pump converters, capacitors were not
considered critical due to the high R
switches. In order to understand this, let’s look at a model of
a typical electrolytic capacitor (Figure 1).
TELCOM SEMICONDUCTOR, INC.
of the MOSFET
DS(ON)
Figure 2. Synchronization
8
4-79
TC7662A
TYPICAL APPLICATIONS
Combined Negative Converter and Positive Multiplier
+
V
8
7
6
V = –V
OUT
5
C
10 µF
+
R2
V
D1
V
+
D2
+
C
10 µF
C
P2
10 µF
1
2
+
3
TC7662A
4
C 1
P
+
Lowering Output Resistance by Paralleling Devices
+
V
CHARGE PUMP
DC-TO-DC CONVERTER
V = 2V –2V
OUT D
R1
+
C
10 µF
P1
1
2
+
3
TC7662A TC7662A
4
8
7
C
+
P2
6
10 µF
5
1
2
3
4
8
7
6
5
C
10 µF
V
R
OUT
+
Positive Voltage Multiplier
+
1
2
3
4
C
10 µF
TC7662A
+
P
V
8
7
V
D1
6
5
Split V In Half
1
2
3
4
+
TC7662A
100 µF
C
P
10 µF
8
7
6
5
C
R
V
D2
+
V
+
V = 2V –2 V
OUT D
++
C
R
10 µF
V =
OUT
+
+
V
2
4-80
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP
DC-TO-DC CONVERTER
TYPICAL CHARACTERISTICS
1
TC7662A
Supply Current vs. Temperature
700
600
500
400
300
200
SUPPLY CURRENT (µA)
100
0
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
+
V = 15V
+
V = 5V
Frequency vs. Temperature
20
18
16
14
12
Oscillator Frequency vs. C
10k
1k
100
FREQUENCY (Hz)
10
1 10 100 1000 10,000
CAPACITANCE (pF)
Output Resistance vs. Temperature
160
140
Ω
120
100
80
+
V = 5V, I = 3 mA
L
EXT
TA = +25
2
°C
3
4
5
10
FREQUENCY (kHz)
8
6
–60 –40 –20 0 20 40 60 80 100 120 140
TEMPERATURE (
Power Conversion Efficiency vs. I
110
100
90
EFFICIENCY
80
70
60
50
40
30
20
10
POWER CONVERSION EFFICIENCY (%)
16 32 48 64 80
8244056720
LOAD CURRENT (mA)
°C)
LOAD
SUPPLY
CURRENT
TA = +25°C
TELCOM SEMICONDUCTOR, INC.
60
OUTPUT RESISTANCE ( )
40
20
–60 –40 –20 0 20 40 60 80 100 120 140
165
150
135
120
105
90
75
60
45
30
15
0
110
100
90
Ω
80
70
60
50
40
30
SUPPLY CURRENT (mA)
OUTPUT RESISTANCE ( )
20
10
+
V = 15V, I = 20 mA
TEMPERATURE (°C)
L
Output Resistance vs. Input Voltage
TA = +25°C
20 mA
4 8 12 16 20
2 6 10 14 180
INPUT VOLTAGE (V)
6
7
8
4-81
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