INVERTING VOL T AGE DOUBLER
EVALUATION
KIT
AVAILABLE
FEATURES
1
TC682
2
GENERAL DESCRIPTION
■ 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
TYPICAL OPERATING CIRCUIT
+2.4V < VIN < +5.5V
V
IN
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.
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
PIN CONFIGURATIONS
3
4
5
GND
TELCOM SEMICONDUCTOR, INC.
V
IN
+
+
C
1
–
+
C
2
–
C
1
–
C
1
TC682
+
C
2
–
2
GND
V
OUT
C
All Caps = 3.3µF
V = – (2 x V )
OUT
C
OUT
+
V
IN
OUT
V
V
C
1
C
2
C
2
OUT
C
C
C
OUT
–
+
–
–
1
+
2
–
2
8-Pin DIP
6
18
27
36
45
18
27
36
45
TC682CPA
TC682EPA
8-Pin SOIC
TC682COA
TC682EOA
NC
+
C
1
V
IN
GND
NC
C
1
V
IN
GND
7
+
8
TC682-2 8/21/96
4-21
V
GND
GND
C
2
+
C
2
–
R
L
C
1
+
C
1
C
2
C
1
–
IN
V
IN
V
OUT
C
All Caps = 3.3µF
OUT
TC682
(+5V)
V
OUT
–
–
6
7
1
2
3
5
4
–
+
+
–
+
TC682
INVERTING VOL T AGE DOUBLER
ABSOLUTE MAXIMUM RATINGS*
VIN.......................................................................... +5.8V
VIN dV/dT ............................................................. 1V/µsec
V
......................................................................– 11.6V
OUT
V
Short-Circuit Duration ............................Continuous
OUT
*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.
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
ELECTRICAL CHARACTERISTICS: Over Operating Temperature Range, V
= +5V, test circuit Figure 1,
IN
unless otherwise indicated.
Symbol Parameter Test Conditions Min Typ Max Unit
V
IN
I
IN
R
OUT
F
OSC
P
EFF
V
OUT EFF
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.
Supply Voltage Range RL = 2kΩ 2.4 — 5.5 V
Supply Current RL = ∞, TA = 25°C — 185 300 µA
RL = ∞ — — 400
V
Source Resistance I
OUT
Source Resistance I
–
= 10mA, TA = 25°C — 140 180 Ω
L
–
= 10mA — — 230
L
–
I
= 5mA, VIN = 2.8V — 170 320
L
Oscillator Frequency — 12 — kHz
Power Efficiency RL = 2kΩ, TA = 25°C9092—%
Voltage Conversion Efficiency V
, RL = ∞ 99 99.9 — %
OUT
PIN DESCRIPTION
Pin No.
8-Pin DIP/SOIC Symbol Description
–
Input. Capacitor C1 negative
1
terminal.
+
Input. Capacitor C2 positive
2
terminal.
–
Input. Capacitor C2 negative
2
terminal
OUT
Output. Negative output voltage
(– 2VIN)
Input. Power supply voltage.
IN
+
Input. Capacitor C1 positive
1
terminal
4-22
1C
2C
3C
4V
5 GND Input. Device ground.
6V
7C
8 N/C No Connection
Figure 1. TC682 Test Circuit
TELCOM SEMICONDUCTOR, INC.
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 T AGE DOUBLER
1
TC682
DETAILED DESCRIPTION
Phase 1
VSS charge storage – before this phase of the clock
cycle, capacitor C1 is already charged to +5V. C
switched to ground and the charge in C
. Since C
+
is at +5V, the voltage potential across capacitor
2
–
is transferred to C
1
C2 is now –10V.
V
= +5V
IN
SW1
+
C
1
–
SW2
–5V
Figure 2. Charge Pump – Phase 1
SW3
+
C
2
–
SW4
–
C
3
+
+
is then
1
V
OUT
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
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.
–
2
• Minimal power is consumed by the drive circuitry
• The impedances of the reservoir and pump capacitors are negligible.
For the TC682, efficiency is as shown below:
Voltage Efficiency = V
V
Power Loss = I
There will be a substantial voltage difference between
–
V
OUT
and 2 V
if the impedances of the pump capacitors
IN
/ (– 2VIN)
OUT
= – 2VIN + V
OUT
V
DROP
(V
OUT
= (I
DROP
OUT
)
) (R
DROP
OUT
)
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.
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).
2
3
4
5
SW1 SW3
6
V
+
C
–
Figure 3. Charge Pump – Phase 2
MAXIMUM OPERATING LIMITS
The TC682 has on-chip zener diodes that clamp V
approximately 5.8V, and V
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.
+
C
1
SW4SW2
2
–
–10V
–
to – 11.6V. Never exceed the
OUT
OUT
–
C
3
+
7
to
IN
Figure 4. Inverting Voltage Doubler
4-23
8
TC682
INVERTING VOL T AGE DOUBLER
Capacitor Selection
The output resistance of the TC682 is determined, in
part, by the ESR of the capacitors used. An expression for
R
is derived as shown below:
OUT
R
= 2(R
OUT
+2(
+1/(f
+ESR
Assuming all switch resistances are approximately
equal...
R
= 16R
OUT
+1/(f
R
is typically 140Ω at +25°C with VIN = +5V and
OUT
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 R
However, be careful about ESR. This term can quickly
become dominant with large electrolytic capacitors. Table 1
shows R
OUT
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
V
RIPPLE
For a 10µF (0.5Ω ESR) capacitor for C3, f
and I
= 10mA the peak-to-peak ripple voltage at the
OUT
output will be less then 60mV. In most applications (I
= 10mA) a 10-20µF capacitor and 1-5µF pump capacitors
will suffice. Table 2 shows V
(assume 1Ω ESR).
SW1
R
SW1
PUMP
SW
PUMP
+ R
+ R
C3
+ 4ESR
ESR
SW2 +
ESR
SW2 +
x C1) +1/(f
+ 4ESR
C1
x C1) +1/(f
+ R
C1
C1
PUMP
PUMP
SW3
+ R
x C2)
x C2)
+ R
SW3
C2
SW4
+ R
SW4
+ ESR
+ ESRC2)
+ ESRC2)
C3
OUT
for various values of C1 and C2 (assume 0.5Ω
is given below:
)
OUT
= 10kHz
PUMP
OUT
for different values of C3
= {1/[2(f
P-P VRIPPLE
x C3)] + 2(ESRC3)} (I
PUMP
RIPPLE
Table 2. V
C3 (µF) V
Peak- to-Peak vs. C3 (I
RIPPLE
RIPPLE
0.50 1020
1.00 520
3.30 172
5.00 120
10.00 70
22.00 43
100.00 25
OUT
(mV)
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 V
lated 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 I
–
= 10mA, the charge pump will droop 1.5V.
L
–
, which is regu-
OUT
= 10mA)
Table 1. R
C1, C2 (µF) R
4-24
vs. C1, C2
OUT
OUT
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
(Ω)
TELCOM SEMICONDUCTOR, INC.
INVERTING VOL T AGE DOUBLER
V
IN
1
TC682
2
GND
10µF
+
3V
–
10µF
10µF
+
–
+
–
10µF
C
C
C
C
+
1
–
1
+
2
–
2
V
IN
TC682
GND
+
10µF
–
–
V
OUT
10µF
+
–
V
IN
+
C
1
–
C
1
TC682
+
C
2
–
C
2
GND
–
V
OUT
–
–
22µF
C
OUT
+
NEGATIVE
SUPPLY
3
4
Figure 5. Paralleling TC682 for Lower Output Source Resistance
5
V
+
1
–
1
+
–
2
IN
TC682
GND
+
V
SS
–
V
OUT
–
22µF
+
–
C
OUT
V
IN
NEGATIVE LDO
REGULATOR
V
OUT
1µF
–
GROUND
6
–5 SUPPLY
+
–
+
C
C
C
2
–
C
Figure 6. Negative Supply Derived from 3V Battery
TELCOM SEMICONDUCTOR, INC.
TC54VC2702Exx
V
IN
V
V
SS
OUT
7
LOW BATTERY
8
4-25
TC682
INVERTING VOL T AGE DOUBLER
TYPICAL CHARACTERISTICS (F
Output Resistance vs. V
240
220
200
180
160
140
OUTPUT RESISTANCE (Ω)
120
12 3
Supply Current vs. V
300
NO LOAD
250
200
150
VIN (V)
4
IN
= 12kHz)
OSC
IN
C1– C3 = 3.3µF
5 0 510156
(V)
OUT
V
–10.0
–10.5
120
–7.5
–8.0
–8.5
–9.0
–9.5
200
180
160
140
V
vs. Load Current
OUT
V
= 5V
IN
LOAD CURRENT (mA)
Output Source Resistance vs. Temperature
V
= 5V
IN
I
= 10mA
OUT
100
SUPPLY CURRENT (µA)
50
12 3
4
VIN (V)
200
V
150
100
50
OUTPUT RIPPLE (mV PK-PK)
0
0
56
Output Ripple vs. Output Current
= 5V
IN
C3 =10µF
C3 =100µF
5
OUTPUT CURRENT (mA)
10
100
OUTPUT SOURCE RESISTANCE (Ω)
80
–50 0 50 100
TEMPERATURE (°C)
15
20
4-26
TELCOM SEMICONDUCTOR, INC.
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