1
EVALUATION
KIT
AVAILABLE
TC682
INVERTING VOLTAGE DOUBLER
2
FEATURES
GENERAL DESCRIPTION
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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), provides 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.
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
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– 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
TYPICAL OPERATING CIRCUIT
VIN
3
4
ORDERING INFORMATION
Part No.
Package
Temp. Range
TC682COA
TC682CPA
TC682EOA
TC682EPA
TC7660EV
8-Pin SOIC
8-Pin Plastic DIP
8-Pin SOIC
8-Pin Plastic DIP
Evaluation Kit for
Charge Pump Family
0°C to +70°C
0°C to +70°C
– 40°C to +85°C
– 40°C to +85°C
5
+2.4V < VIN < +5.5V
PIN CONFIGURATIONS
+
C1
–
+
C2
–
C1+
C1–
C2+
C2–
TC682
VOUT
GND
6
8-Pin DIP
VIN
VOUT = – (2 x VIN )
VOUT
+
GND
All Caps = 3.3µF
C1–
1
8
NC
C2+
2
7
C1+
C2–
3
6
VIN
VOUT
4
5
GND
COUT
TC682CPA
TC682EPA
7
8-Pin SOIC
C1– 1
8
NC
C2+ 2
7
C1+
6
VIN
5
GND
C2– 3
VOUT
4
TC682COA
TC682EOA
8
TC682-2 8/21/96
TELCOM SEMICONDUCTOR, INC.
4-21
INVERTING VOLTAGE DOUBLER
TC682
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
*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
IIN
Supply Voltage Range
Supply Current
VOUT Source Resistance
Source Resistance
FOSC
PEFF
VOUT EFF
Oscillator Frequency
Power Efficiency
Voltage Conversion Efficiency
2.4
—
—
—
—
—
—
90
99
—
185
—
140
—
170
12
92
99.9
5.5
300
400
180
230
320
—
—
—
V
µA
ROUT
RL = 2kΩ
RL = ∞, TA = 25°C
RL = ∞
IL– = 10mA, TA = 25°C
IL– = 10mA
IL– = 5mA, VIN = 2.8V
RL = 2kΩ, TA = 25°C
VOUT, RL = ∞
Ω
kHz
%
%
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.
PIN DESCRIPTION
Pin No.
8-Pin DIP/SOIC Symbol Description
1
C1–
2
C2+
3
C2–
4
5
6
7
8
VOUT
GND
VIN
C1+
N/C
Input. Capacitor C1 negative
terminal.
Input. Capacitor C2 positive
terminal.
Input. Capacitor C2 negative
terminal
Output. Negative output voltage
(– 2VIN)
Input. Device ground.
Input. Power supply voltage.
Input. Capacitor C1 positive
terminal
No Connection
VIN
(+5V)
6
+
C1
–
7
C1+
1
C1–
2
C2+
3
C2–
VIN
TC682
+
C2
–
V OUT
GND
5
4
–
VOUT
–
C
+ OUT
RL
GND
All Caps = 3.3µF
Figure 1. TC682 Test Circuit
4-22
TELCOM SEMICONDUCTOR, INC.
INVERTING VOLTAGE DOUBLER
1
TC682
DETAILED DESCRIPTION
EFFICIENCY CONSIDERATIONS
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.
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 capacitors are negligible.
3
For the TC682, efficiency is as shown below:
VIN = +5V
SW1
+
–
SW3
C1
C2
–
SW2
–
+
SW4
Power Loss
Figure 2. Charge Pump – Phase 1
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.
+5V
+
–
C1
SW2
= IOUT (VDROP)
C3
–5V
SW1
Voltage Efficiency = VOUT / (– 2VIN)
VOUT = – 2VIN + VDROP
VDROP = (IOUT) (ROUT)
VOUT
+
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 Selection" in Applications section.
–
4
5
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).
6
SW3
+
2
VOUT
C2
–
+
SW4
C3
C1
22µF
1
–10V
22µF
3 C –
2
4
MAXIMUM OPERATING LIMITS
The TC682 has on-chip zener diodes that clamp VIN to
–
approximately 5.8V, and VOUT
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.
TELCOM SEMICONDUCTOR, INC.
C1+ 7
2 C +
2
C2
Figure 3. Charge Pump – Phase 2
–
C1
TC682
–
V OUT
VIN
GND
6
VIN
7
5
GND
C3
22µF
–
VOUT
8
Figure 4. Inverting Voltage Doubler
4-23
INVERTING VOLTAGE DOUBLER
TC682
Capacitor Selection
Table 2. VRIPPLE Peak- to-Peak vs. C3 (IOUT = 10mA)
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).
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 resistance 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 VOUT
, which is regulated to – 5V by the negative LDO. The input to the TC682
can vary from 3V to 5.5V without affecting regulation appreciably. 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.
Table 1. ROUT vs. C1, C2
4-24
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
TELCOM SEMICONDUCTOR, INC.
INVERTING VOLTAGE DOUBLER
1
TC682
2
VIN
C1+
+
VIN
+
10µF
C1+
VIN
10µF
–
–
C1–
C1–
+
+
10µF
–
V–
10µF
–
C2–
3
TC682
TC682
C2+
OUT
GND
C+
2
C2–
–
VOUT
NEGATIVE
SUPPLY
GND
–
+
– 22µF
COUT
GND
4
Figure 5. Paralleling TC682 for Lower Output Source Resistance
5
+
C1+
VIN
10µF
–
+
3V
–
+
10µF
–
C1–
C2+
TC682
VSS
–
–
VOUT
C2
GROUND
+
VOUT
VIN
GND
–
22µF
+ C
–
–
6
1µF
–5 SUPPLY
NEGATIVE LDO
REGULATOR
OUT
7
TC54VC2702Exx
VOUT
VIN
LOW BATTERY
VSS
8
Figure 6. Negative Supply Derived from 3V Battery
TELCOM SEMICONDUCTOR, INC.
4-25
INVERTING VOLTAGE DOUBLER
TC682
TYPICAL CHARACTERISTICS (FOSC = 12kHz)
VOUT vs. Load Current
Output Resistance vs. VIN
240
–7.5
VIN = 5V
220
–8.0
200
–8.5
VOUT (V)
OUTPUT RESISTANCE (Ω)
C1– C3 = 3.3µF
180
–9.0
160
–9.5
140
–10.0
120
–10.5
1
2
3
5
4
6
0
5
VIN (V)
Supply Current vs. VIN
NO LOAD
250
200
150
100
2
3
5
4
200
VIN = 5V
IOUT = 10mA
180
160
140
120
100
80
–50
50
1
15
Output Source Resistance vs. Temperature
OUTPUT SOURCE RESISTANCE (Ω)
SUPPLY CURRENT (µA)
300
10
LOAD CURRENT (mA)
6
0
VIN (V)
50
100
TEMPERATURE (°C)
Output Ripple vs. Output Current
OUTPUT RIPPLE (mV PK-PK)
200
VIN = 5V
150
C3 =10µF
100
C3 =100µF
50
0
0
5
10
15
20
OUTPUT CURRENT (mA)
4-26
TELCOM SEMICONDUCTOR, INC.