EVALUATION
KIT
AVAILABLE
1
TC7662A
CHARGE PUMP DC-TO-DC CONVERTER
FEATURES
s
s
s
s
s
s
s
Wide Operating Range ............................. 3V to 18V
Increased Output Current .............................. 40mA
Pin Compatible with ICL7662/SI7661/TC7660/
LTC1044
No External Diodes Required
Low Output Impedance @ I
L
= 20mA ....... 40
Ω
Typ.
No Low-Voltage Terminal Required
CMOS Construction
GENERAL DESCRIPTION
The TC7662A is a pin-compatible upgrade to the In-
dustry 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 addi-
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
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
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 com-
mercial and extended temperature ranges.
PIN CONFIGURATION
NC 1
C
+
2
GND 3
C
–
4
8 V
DD
7 OSC
2
3
ORDERING INFORMATION
Part No.
TC7662ACPA
TC7662AEPA
TC7662AIJA
TC7662AMJA
TC7660EV
Package
Temperature
Range
4
8-Pin Plastic DIP
0°C to +70°C
8-Pin Plastic DIP
– 40°C to +85°C
8-Pin CerDIP
– 25°C to +85°C
8-Pin CerDIP
– 55°C to +125°C
Evaluation Kit for
Charge Pump Family
TC7662A
6 NC
5 V
OUT
5
NC = NO INTERNAL CONNECTION
FUNCTIONAL BLOCK DIAGRAM
8
I
COSC
7
LEVEL
SHIFT
P SW1
2
CAP
+
VDD
6
+
CP
EXT
GND
3
+
–
Q
F/F
C
Q
COMPARATOR
WITH HYSTERESIS
VREF
LEVEL
SHIFT
N SW4
+
LEVEL
SHIFT
TC7662A
OUT
N SW2
4
–
CR
EXT
7
RL
CAP
LEVEL
SHIFT
N SW3
5
VOUT
TC7662A-5 9/11/96
8
4-77
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP
DC-TO-DC CONVERTER
TC7662A
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage V
DD
to GND .................................... +18V
Input Voltage (Any Pin) ........... (V
DD
+ 0.3) to (V
SS
– 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 (T
A
≤
70°C)
Plastic DIP ......................................................730mW
CerDIP............................................................800mW
Package Thermal Resistance
CPA, EPA
θ
JA
.............................................. 140°C/W
IJA, MJA
θ
JA
.................................................. 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 perma-
nent 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.
ELECTRICAL CHARACTERISTICS:
V
DD
= 15V, T
A
= +25°C (See Test Circuit), unless otherwise specified.
Symbol
V
DD
I
S
Parameter
Supply Voltage
Supply Current
V
DD
= +15V
Test Conditions
R
L
=
∞
0°C
≤
T
A
≤
+70°C
– 55°C
≤
T
A
≤
+125°C
0°C
≤
T
A
≤
+70°C
– 55°C
≤
T
A
≤
+125°C
I
L
= 20mA, V
DD
= +15V
I
L
= 40mA, V
DD
= +15V
I
L
= 3mA, V
DD
= +5V
V
DD
= +15V
R
L
= 2 kΩ
V
DD
= +15V
R
L
=
∞
Over Operating Temperature Range
Min
3
—
—
—
—
—
—
—
—
—
—
93
99
96
Typ
—
510
560
650
190
210
210
40
50
100
12
97
99.9
—
Max
18
700
—
—
—
—
—
50
60
125
—
—
—
—
Unit
V
µA
V
DD
= +5V
R
O
Output Source
Resistance
Oscillator Frequency
Power Efficiency
Voltage Efficiency
Ω
C
OSC
P
EFF
V
EFF
kHz
%
%
4-78
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP
DC-TO-DC CONVERTER
TC7662A
TEST CIRCUIT
EPR
1
NC
+ 10 µF
CP
1
2
3
4
TC7662A
8
7
6
5
NC
C OSC
IS
IL
RL
V
(+5V)
ESL
ESR
C
+
2
VOUT
(–5V)
CR
+
10 µF
Figure 1.
Capacitor Equivalent Circuit
APPLICATIONS INFORMATION
Theory of Operation
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
capacitor.
The functional diagram (page 1) shows how the switch-
ing action works. SW1 and SW2 are turned on simulta-
neously, charging C1 to the supply voltage, V
DD
. This
assumes that the ON resistance of the MOSFETs in series
with the capacitor produce a charging time (3 time con-
stants) less than the ON time provided by the oscillator
frequency, as shown:
3 (R
DS(ON)
C1) <C1/(0.5 f
OSC
).
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
OUT
, BUT WITH THE POLARITY IN-
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 con-
nected to ground. This will lower the frequency of the
oscillator by adding capacitance to the internal timing ca-
pacitor of the TC7662A. (See Oscillator Frequency vs. C
EXT
,
page 5.)
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 effi-
ciency are compromised if a low ESR capacitor is not used.
For example, in the "Test Circuit", changing C
P
and C
R
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 ca-
pacitor is not critical and attributes the limiting factor to the
capacitor's reactance value. Let's examine this:
X
C
=
X
1
and Z
C
=
C
,
DS
2πf C
3
4
where DS (duty cycle) = 50%.
Thus, Z
C
≈
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.
5
6
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.
7
Q
TTL
100 k
Q
TO PIN 7
TC7662A
Capacitors
In early charge pump converters, capacitors were not
considered critical due to the high R
DS(ON)
of the MOSFET
switches. In order to understand this, let’s look at a model of
a typical electrolytic capacitor (Figure 1).
TELCOM SEMICONDUCTOR, INC.
Figure 2.
Synchronization
4-79
8
CHARGE PUMP
DC-TO-DC CONVERTER
TC7662A
TYPICAL APPLICATIONS
Combined Negative Converter and Positive Multiplier
V+
1
2
CP2
10
µF
+
3
4
CP1
+
TC7662A
8
7
6
5
+
VOUT
VD1
= –V+
VD2
+
C R2
10
µF
VOUT = 2V+ –2VD
C R1
10
µF
Lowering Output Resistance by Paralleling Devices
V+
1
2
CP1 +
10
µF
3
4
TC7662A
8
7
6
5
CP2 +
10
µF
1
2
3
4
TC7662A
8
7
6
5
CR
10
µF
+
VOUT
Positive Voltage Multiplier
V+
1
2
3
4
TC7662A
8
7
6
5
+
VD1
VD2
CP
10
µF
+
VOUT = 2V+–2 VD
CR
10
µF
Split V+ In Half
V+
1
2
CP +
10
µF
3
4
TC7662A
8
7
6
5
V+
VOUT =
2
CR +
100
µF
4-80
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP
DC-TO-DC CONVERTER
TC7662A
TYPICAL CHARACTERISTICS
Supply Current vs. Temperature
700
TA = +25°C
1
Oscillator Frequency vs. C
EXT
10k
2
SUPPLY CURRENT (µA)
600
500
400
300
200
100
0
–60 –40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120 140
V + = 5V
+
V = 15V
FREQUENCY (Hz)
1k
3
1
10
100
1000
CAPACITANCE (pF)
10,000
100
10
Frequency vs. Temperature
20
160
Output Resistance vs. Temperature
4
16
14
12
10
8
6
–60 –40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120 140
OUTPUT RESISTANCE (
Ω
)
18
140
120
100
80
60
40
20
–60 –40 –20
V+ = 15V, IL = 20 mA
V + = 5V, IL = 3 mA
FREQUENCY (kHz)
5
100 120 140
0
20 40 60 80
TEMPERATURE (°C)
6
Power Conversion Efficiency vs. I
LOAD
POWER CONVERSION EFFICIENCY (%)
110
100
90
80
70
60
50
40
30
20
10
0
8
16
48
24 32 40
56
LOAD CURRENT (mA)
TA = +25°C
64
72
80
SUPPLY
CURRENT
EFFICIENCY
165
150
110
100
Output Resistance vs. Input Voltage
TA = +25°C
OUTPUT RESISTANCE (
Ω
)
SUPPLY CURRENT (mA)
135
120
105
90
75
60
45
30
15
0
90
80
70
60
50
40
30
20
10
0
2
4
8
12 14
6
10
INPUT VOLTAGE (V)
16
18
20
4-81
7
20 mA
8
TELCOM SEMICONDUCTOR, INC.
京公网安备 11010802033920号
EEWORLD
