4-21
TELCOM SEMICONDUCTOR, INC.
7
6
5
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3
1
2
8
INVERTING VOLTAGE DOUBLER
FEATURES
■99.9% Voltage Conversion Efficiency
■92% Power Conversion Efficiency
■Wide Input Voltage Range ...............+2.4V to +5.5V
■Only 3 External Capacitors Required
■185µA Supply Current
■Space-Saving 8-Pin SOIC and 8-Pin Plastic DIP
Packages
APPLICATIONS
■– 10V from +5V Logic Supply
■– 6V from a Single 3V Lithium Cell
■Portable Handheld Instruments
■Cellular Phones
■LCD Display Bias Generator
■Panel Meters
■Operational Amplifier Power Supplies
GENERAL DESCRIPTION
The TC682 is a CMOS charge pump converter that
provides an inverted doubled output from a single positive
supply. An on-board 12kHz (typical) oscillator provides the
clock and only 3 external capacitors are required for full
circuit implementation.
Low output source impedance (typically 140Ω), pro-
vides output current up to 10mA. The TC682 features low
quiescent current and high efficiency, making it the ideal
choice for a wide variety of applications that require a
negative voltage derived from a single positive supply (for
example: generation of – 6V from a 3V lithium cell or – 10V
generated from a +5V logic supply).
The minimum external parts count and small physical
size of the TC682 make it useful in many medium-current,
dual voltage analog power supplies.
TC682
PIN CONFIGURATIONS
ORDERING INFORMATION
Part No. Package Temp. Range
T
C682COA 8-Pin SOIC 0°C to +70°C
TC682CPA 8-Pin Plastic DIP 0°C to +70°C
T
C682EOA 8-Pin SOIC – 40°C to +85°C
TC682EPA 8-Pin Plastic DIP – 40°C to +85°C
TC7660EV Evaluation Kit for
Charge Pump Family
GND
+
–
+
–
+
GND
C2+
C2–
C1+
C1
C2
C1–
VIN
VIN
VOUT VOUT
IN
V = – (2 x V )
OUT
All Caps = 3.3
µ
F
COUT
TC682
+2.4V < VIN < +5.5V
TC682-2 8/21/96
TYPICAL OPERATING CIRCUIT
18
27
36
45
TC682CPA
TC682EPA
GND
VOUT
C2–
C1–
C2+C1+
NC
NC
VIN
18
27
36
45
TC682COA
TC682EOA
GND
VOUT
C2–
C1–
C2+C1+
VIN
8-Pin DIP
8-Pin SOIC
EVALUATION
KIT
AVAILABLE
4-22 TELCOM SEMICONDUCTOR, INC.
ABSOLUTE MAXIMUM RATINGS*
VIN .......................................................................... +5.8V
VIN dV/dT .............................................................1V/µsec
VOUT ......................................................................– 11.6V
VOUT Short-Circuit Duration ............................Continuous
Power Dissipation (TA ≤ 70°C)
Plastic DIP
...........................................................
730mW
SOIC...............................................................470mW
Storage Temperature Range ................– 65°C to +150°C
Lead Temperature (Soldering, 10 sec) .................+300°C
PIN DESCRIPTION
Pin No.
8-Pin DIP/SOIC Symbol Description
1C
1
–
Input. Capacitor C1 negative
terminal.
2C
2
+
Input. Capacitor C2 positive
terminal.
3C
2
–
Input. Capacitor C2 negative
terminal
4V
OUT Output. Negative output voltage
(– 2VIN)
5 GND Input. Device ground.
6V
IN Input. Power supply voltage.
7C
1
+
Input. Capacitor C1 positive
terminal
8 N/C No Connection
Figure 1. TC682 Test Circuit
V
GND
GND
C2+
C2–
RL
C1+
C1
C2
C1–
IN
VIN
VOUT
C
All Caps = 3.3
µ
F
OUT
TC682
(+5V)
VOUT
–
–
6
7
1
2
3
5
4
–
+
+
–
+
*This is a stress rating 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: Over Operating Temperature Range, VIN = +5V, test circuit Figure 1,
unless otherwise indicated.
Symbol Parameter Test Conditions Min Typ Max Unit
VIN Supply Voltage Range RL = 2kΩ2.4 — 5.5 V
IIN Supply Current RL = ∞, TA = 25°C — 185 300 µA
RL = ∞— — 400
ROUT VOUT Source Resistance IL
– = 10mA, TA = 25°C — 140 180 Ω
Source Resistance IL
– = 10mA — — 230
IL
– = 5mA, VIN = 2.8V — 170 320
FOSC Oscillator Frequency — 12 — kHz
PEFF Power Efficiency RL = 2kΩ, TA = 25°C9092—%
V
OUT EFF Voltage Conversion Efficiency VOUT, RL = ∞99 99.9 — %
TelCom Semiconductor reserves the right to make changes in the circuitry or specifications detailed in this manual at any time without notice. Minimums
and maximums are guaranteed. All other specifications are intended as guidelines only. TelCom Semiconductor assumes no responsibility for the use
of any circuits described herein and makes no representations that they are free from patent infringement.
INVERTING VOL TAGE DOUBLER
TC682
4-23
TELCOM SEMICONDUCTOR, INC.
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Phase 2
VSS transfer – phase two of the clock connects the
negative terminal of C2 to the negative side of reservoir
capacitor C3 and the positive terminal of C2 to ground,
transferring the generated – 10V to C3. Simultaneously, the
positive side of capacitor C1 is switched to +5V and the
negative side is connected to ground. C2 is then switched to
VCC and GND and Phase 1 begins again.
Figure 3. Charge Pump – Phase 2
DETAILED DESCRIPTION
Phase 1
VSS charge storage – before this phase of the clock
cycle, capacitor C1 is already charged to +5V. C1
+ is then
switched to ground and the charge in C1
– is transferred to C2
–
. Since C2
+ is at +5V, the voltage potential across capacitor
C2 is now –10V.
Figure 2. Charge Pump – Phase 1
MAXIMUM OPERATING LIMITS
The TC682 has on-chip zener diodes that clamp VIN to
approximately 5.8V, and V–
OUT to – 11.6V. Never exceed the
maximum supply voltage or excessive current will be shunted
by these diodes, potentially damaging the chip. The TC682
will operate over the entire operating temperature range with
an input voltage of 2V to 5.5V.
EFFICIENCY CONSIDERATIONS
Theoretically a charge pump voltage multiplier can
approach 100% efficiency under the following conditions:
• The charge pump switches have virtually no offset
and are extremely low on resistance.
• Minimal power is consumed by the drive circuitry
• The impedances of the reservoir and pump capaci-
tors are negligible.
For the TC682, efficiency is as shown below:
Voltage Efficiency = VOUT / (– 2VIN)
VOUT = – 2VIN + VDROP
VDROP = (IOUT) (ROUT)
Power Loss = IOUT (VDROP)
There will be a substantial voltage difference between
V–
OUT and 2 VIN if the impedances of the pump capacitors
C1 and C2 are high with respect to their respective output
loads.
Larger values of reservoir capacitor C3 will reduce
output ripple. Larger values of both pump and reservoir
capacitors improve the efficiency. See "Capacitor Selec-
tion" in Applications section.
APPLICATIONS
Negative Doubling Converter
The most common application of the TC682 is as a
charge pump voltage converter which provides a negative
output of two times a positive input voltage (Figure 4).
Figure 4. Inverting Voltage Doubler
V
IN
= +5V
V
OUT
–5V
SW4
SW1
SW2
SW3
C
2
C
3
C
1
+
–
+
+
––
+5V
V
OUT
–10V
SW4SW2
SW1 SW3
C
2
C
3
C
1
+
–
+
+
––
C
1
+
C
1
C
2
C
3
C
2
+
V
IN
V
IN
V
OUT
GND GND
TC682
22µF
22µF
22µF
7
6
54
3
2
1
V
OUT
C
2
–
C
1
–
–
–
INVERTING VOL TAGE DOUBLER
TC682
4-24 TELCOM SEMICONDUCTOR, INC.
TC682
INVERTING VOL TAGE DOUBLER
Capacitor Selection
The output resistance of the TC682 is determined, in
part, by the ESR of the capacitors used. An expression for
ROUT is derived as shown below:
ROUT = 2(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2)
+2(
RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2)
+1/(fPUMP x C1) +1/(fPUMP x C2)
+ESRC3
Assuming all switch resistances are approximately
equal...
ROUT = 16RSW + 4ESRC1 + 4ESRC2 + ESRC3
+1/(fPUMP x C1) +1/(fPUMP x C2)
ROUT is typically 140Ω at +25°C with VIN = +5V and
3.3µF low ESR capacitors. The fixed term (16RSW) is about
80-90Ω. It can be seen easily that increasing or decreasing
values of C1 and C2 will affect efficiency by changing ROUT.
However, be careful about ESR. This term can quickly
become dominant with large electrolytic capacitors. Table 1
shows ROUT for various values of C1 and C2 (assume 0.5Ω
ESR). C1 must be rated at 6VDC or greater while C2 and C3
must be rated at 12VDC or greater.
Output voltage ripple is affected by C3. Typically the
larger the value of C3 the less the ripple for a given load
current. The formula for P-P VRIPPLE is given below:
VRIPPLE = {1/[2(fPUMP x C3)] + 2(ESRC3)} (IOUT)
For a 10µF (0.5Ω ESR) capacitor for C3, fPUMP = 10kHz
and IOUT = 10mA the peak-to-peak ripple voltage at the
output will be less then 60mV. In most applications (IOUT <
= 10mA) a 10-20µF capacitor and 1-5µF pump capacitors
will suffice. Table 2 shows VRIPPLE for different values of C3
(assume 1Ω ESR).
Table 1. ROUT vs. C1, C2
C1, C2 (µF) ROUT (Ω)
0.05 4085
0.10 2084
0.47 510
1.00 285
3.30 145
5.00 125
10.00 105
22.00 94
100.00 87
Table 2. VRIPPLE Peak- to-Peak vs. C3 (IOUT = 10mA)
C3 (µF) VRIPPLE (mV)
0.50 1020
1.00 520
3.30 172
5.00 120
10.00 70
22.00 43
100.00 25
Paralleling Devices
Paralleling multiple TC682s reduces the output resis-
tance of the converter. The effective output resistance is the
output resistance of a single device divided by the number
of devices. As illustrated in Figure 5, each requires separate
pump capacitors C1 and C2, but all can share a single
reservoir capacitor.
–5V Regulated Supply From A Single
3V Battery
Figure 6 shows a – 5V power supply using one 3V
battery. The TC682 provides – 6V at V –
OUT, which is regu-
lated to – 5V by the negative LDO. The input to the TC682
can vary from 3V to 5.5V without affecting regulation appre-
ciably. A TC54 device is connected to the battery to detect
undervoltage. This unit is set to detect at 2.7V. With higher
input voltage, more current can be drawn from the outputs
of the TC682. With 5V at VIN, 10mA can be drawn from the
regulated output. Assuming 150Ω source resistance for the
converter, with IL
–= 10mA, the charge pump will droop 1.5V.
4-25
TELCOM SEMICONDUCTOR, INC.
7
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TC682
INVERTING VOL TAGE DOUBLER
C
1
–
C
2
+
V
OUT
V
OUT
10µF
10µF
10µF
10µF
22µF
C
OUT
V
IN
V
IN
V
IN
GND
GND
NEGATIVE
SUPPLY
TC682
C
2
–
C
1
C
1
C
1
+
C–
TC682
GND
+
–
+
–
+
–
+
–
+
–
–
–
–
2
C+
2
–
+
Figure 5. Paralleling TC682 for Lower Output Source Resistance
Figure 6. Negative Supply Derived from 3V Battery
C
1
C
1
V
IN
V
SS
V
IN
V
OUT
V
SS
V
IN
V
OUT
GND
TC682
3V C
2
C
2
GROUND
–5 SUPPLY
LOW BATTERY
NEGATIVE LDO
REGULATOR
TC54VC2702Exx
V
OUT
C
OUT
–
1µF
+
–+
–
+
–
+
–
+
–
+
+
–
–
10µF
22µF
10µF
–
4-26 TELCOM SEMICONDUCTOR, INC.
TYPICAL CHARACTERISTICS (FOSC = 12kHz)
VIN (V) LOAD CURRENT (mA)
240
220
200
180
140
160
120
12 345 0 510156
OUTPUT RESISTANCE (Ω)
Output Resistance vs. V
IN
–7.5
–8.0
–8.5
–9.0
–9.5
–10.0
–10.5
VOUT (V)
VOUT vs. Load Current
V
IN
(V)
300
250
200
150
50
100
12 3456
SUPPLY CURRENT (µA)
Supply Current vs. V
IN
VIN = 5V
C1– C3 = 3.3µF
TEMPERATURE (°C)
–50 0 50 100
200
180
160
140
120
100
80
OUTPUT SOURCE RESISTANCE (Ω)
Output Source Resistance vs. Temperature
V
IN
= 5V
IOUT = 10mA
NO LOAD
V
IN
= 5V
OUTPUT CURRENT (mA)
200
150
100
50
00515
10 20
OUTPUT RIPPLE (mV PK-PK)
Output Ripple vs. Output Current
C3 =100µF
C3 =10µF
TC682
INVERTING VOL TAGE DOUBLER
