EVALUATION
KIT
AVAILABLE
1
TCM680
+5V TO ±10V VOLTAGE CONVERTER
2
FEATURES
GENERAL DESCRIPTION
■
■
■
■
■
The TCM680 is a dual charge pump voltage converter
that develops output voltages of +2VIN and – 2VIN from a
single input voltage of +2.0V to +5.5V. Common applications include ±10V from a single +5V logic supply, and ±6V
from a +3V lithium battery.
The TCM680 is packaged in a space-saving 8-pin
SOIC package and requires only four inexpensive external
capacitors. The charge pumps are clocked by an on-board
8kHz oscillator. Low output source impedances (typically
150Ω) provides maximum output currents of 10mA for each
output. Typical power conversion efficiency is 85%.
High efficiency, small installed size and low cost make
the TCM680 suitable for a wide variety of applications that
need both positive and negative power supplies derived
from a single input voltage.
99% Voltage Conversion Efficiency
85% Power Conversion Efficiency
Wide Voltage Range ......................... +2.0V to +5.5V
Only 4 External Capacitors Required
Space Saving 8-Pin SOIC Design
APPLICATIONS
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±10V From +5V Logic Supply
±6V From a 3V Lithium Cell
Handheld Instruments
Portable Cellular Phones
LCD Display Bias Generator
Panel Meters
Operational Amplifier Power Supplies
PIN CONFIGURATIONS (DIP AND SOIC)
–
C1
+
C2
2
–
C2
3
–
VOUT
4
TCM680CPA
TCM680EPA
+
7
C1
6
VIN
5
GND
C1–
1
8
+
C2
C–
2
7
+
VOUT
+
C1
6
VIN
5
GND
2
V–
OUT
3
TCM680COA
TCM680EOA
4
4
ORDERING INFORMATION
+
VOUT
8
1
3
Part No.
Package
Temperature
TCM680COA
TCM680CPA
TCM680EOA
TCM680EPA
TC7660EV
8-Pin SOIC
0°C to +70°C
8-Pin Plastic DIP
0°C to +70°C
8-Pin SOIC
– 40°C to +85°C
8-Pin Plastic DIP
– 40°C to +85°C
Charge Pump Family
Evaluation Kit
5
6
TYPICAL OPERATING CIRCUIT
2.0V<VIN < +5.5V
+5V
+
C1
4.7µF
+
C2
4.7µF
+
C1
VIN
4.7µF
+
+
7
C4
+
VOUT = ( 2 x VIN)
VOUT
C1–
+
C2 TCM680
–
VOUT
C2–
GND
– = (– 2 x V )
VOUT
IN
4.7µF
+
C3
GND
8
GND
TC660-2 9/4/96
TELCOM SEMICONDUCTOR, INC.
4-13
+5V TO ±10V VOLTAGE CONVERTER
TCM680
ABSOLUTE MAXIMUM RATINGS*
VIN ..................................................................................................... +6.0V
+
VOUT .............................................................................................. +12.0V
–
V OUT
............................................................................................. – 12.0V
–
V OUT
Short-Circuit Duration ............................ Continuous
+
VOUT Current ............................................................ 75mA
VIN dV/dT .............................................................. 1V/µsec
Power Dissipation (TA ≤ 70°C)
Plastic DIP ...................................................... 730mW
Small Outline .................................................. 470mW
Storage Temperature ............................ – 65°C to +150°C
Lead Temperature (Soldering, 10 sec) ................. +300°C
*Stresses above those listed in "Absolute Maximum Ratings" may cause
permanent damage to the device. These are stress ratings only and
functional operation of the device at these or other conditions above those
indicated in the operation section of the specification is not implied.
Exposure to the Absolute Maximum Ratings conditions for extended
periods of time may affect device reliability.
ELECTRICAL CHARACTERISTICS: VIN = +5V, TA = +25°C, test circuit Figure 1, unless otherwise indicated.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
Supply Voltage Range
Supply Current
MIN. ≤ TA ≤ MAX., RL = 2kΩ
VIN = 3V, RL = ∞
VIN = 5V, RL = ∞
VIN = 5V, 0°C ≤ TA ≤ +70°C, RL = ∞
VIN = 5V, – 40°C ≤ TA ≤ +85°C, RL = ∞
IL– = 10mA, IL+ = 0mA, VIN = 5V
IL–= 5mA, IL+ = 0mA, VIN = 2.8V
–
IL = 10mA, IL+ = 0mA, VIN = 5V:
0°C ≤ TA ≤ +70°C
– 40°C ≤ TA ≤ +85°C
IL+ = 10mA, IL– = 0mA, VIN = 5V
IL+ = 5mA, IL– = 0mA, VIN = 2.8V
IL+ = 10mA, IL– = 0mA, VIN = 5V:
0°C ≤ TA ≤ +70°C
– 40°C ≤ TA ≤ +85°C
2.0
—
—
—
—
—
—
1.5 to 5.5
0.5
1
—
—
140
180
5.5
1
2
2.5
3
180
250
V
mA
—
—
—
—
—
—
140
180
220
250
180
250
—
—
—
—
97
97
—
—
21
85
99
99
220
250
—
—
—
—
Negative Charge Pump Output
Source Resistance
Positive Charge Pump Output
Source Resistance
FOSC
PEFF
VOUT EFF
Oscillator Frequency
Power Efficiency
Voltage Conversion Efficiency
RL = 2kΩ
+
VOUT, RL = ∞
–
V OUT, RL = ∞
Ω
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
8-Pin
DIP/SOIC Symbol
1
2
3
4
5
6
7
8
C1–
+
C2
C2–
–
V OUT
GND
VIN
C1+
+
VOUT
Description
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.
Output. Positive output voltage (+2VIN)
VIN
C1
C2
4.7µF
1
–
C1
+
8
VOUT
2
+
C2
+
C1 7
4.7µF
+
VOUT
C4
10µF
6
3 C – TCM680 V
IN
2
4
–
V OUT
GND
+
RL
5
GND
C3
10µF
RL–
–
VOUT
Figure 1. Test Circuit
4-14
TELCOM SEMICONDUCTOR, INC.
+5V TO ±10V VOLTAGE CONVERTER
1
TCM680
DETAILED DESCRIPTION
VIN = +5V
–
Phase 1
VSS charge storage – The positive side of capacitors C1
and C2 are connected to +5V at the start of this phase. C1+ is
then switched to ground and the charge in C1– is transferred
to C2–. Since C2+ is connected to +5V, the voltage potential
across capacitor C2 is now 10V.
SW1
+
–
VDD
SW3
VSS
+
C1
C2
–
SW2
2
C4
+
–
C3
+
SW4
–5V
3
VIN = +5V
–
+
SW1
+
–
Figure 4. Charge Pump – Phase 3
C4
VDD
SW3
VSS
+
C1
C2
–
SW2
–
+
SW4
C3
–5V
Phase 4
VDD transfer – The fourth phase of the clock connects
the negative terminal of C2 to ground, and transfers the
generated 10V across C2 to C4, the VDD storage capacitor.
Again, simultaneously with this, the positive side of capacitor C1 is switched to +5V and the negative side is connected
to ground, and the cycle begins again.
Figure 2. Charge Pump – Phase 1
4
+5V
–
Phase 2
VSS transfer – Phase two of the clock connects the
negative terminal of C2 to the VSS storage 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.
SW1
+
–
SW3
+
C1
SW2
+
–
C4
VDD
5
VSS
C2
–
+
SW4
C3
–10V
+5V
Figure 5. Charge Pump – Phase 4
–
SW1
+
–
C1
SW2
SW3
+
–
C2
+
–
+
SW4
6
C4
VDD
MAXIMUM OPERATING LIMITS
VSS
The TCM680 has on-chip zener diodes that clamp VIN
+
–
to 5.8V, V OUT to 11.6V, 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
TCM680 will operate over the entire operating temperature
range with an input voltage of 2V to 5.5V.
C3
–10V
Figure 3. Charge Pump – Phase 2
7
Phase 3
VDD charge storage – The third phase of the clock is
identical to the first phase – the charge transferred in C1
produces –5V in the negative terminal of C1, which is applied
to the negative side of capacitor C2. Since C2+ is at +5V, the
voltage potential across C2 is 10V.
TELCOM SEMICONDUCTOR, INC.
8
4-15
+5V TO ±10V VOLTAGE CONVERTER
TCM680
EFFICIENCY CONSIDERATIONS
Capacitor Selection
Theoretically a charge pump can approach 100% efficiency under the following conditions:
• The charge Pump switches have virtually no offset
and extremely low on resistance
• Minimal power is consumed by the drive circuitry
• The impedances of the reservoir and pump capacitors are negligible
For the TCM680, efficiency is as shown below:
The TCM680 requires only 4 external capacitors for
operation. These can be inexpensive polarized aluminum
electrolytic types. For the circuit in Figure 6 the output
characteristics are largely determined by the external
capacitors. An expression for ROUT can be derived as shown
below:
Efficiency V+ = VDD /(2VIN)
VDD = 2VIN – V+DROP
V+DROP = (I+OUT)(R+OUT)
R–OUT = 4(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2)
+4(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4+ ESRC2)
+1/(fPUMP x C1) + 1/(fPUMP x C2) + ESRC3
Efficiency V– = VSS /(– 2VIN)
VSS = 2VIN – V–DROP
V–DROP = (I–OUT)(R–OUT)
Assuming all switch resistances are approximately
equal...
Power Loss = (V+DROP)(I+OUT) + (V–DROP)(I–OUT)
There will be a substantial voltage difference between
(V+OUT – VIN) and VIN for the positive pump and between
V+OUT and V O
– UT if the impedances of the pump capacitors C1
and C2 are high with respect to the output loads.
Larger values of reservoir capacitors C3 and C4 will
reduce output ripple. Larger values of both pump and
reservoir capacitors improve the efficiency. See "Capacitor
Selection" in Applications Section.
APPLICATIONS
Positive and negative Converter
The most common application of the TCM680 is as a
dual charge pump voltage converter which provides positive
and negative outputs of two times a positive input voltage.
The simple circuit of Figure 6 performs this same function
using the TCM680 and external capacitors, C1, C2, C3 and C4.
C1
22µF
C1–
+
8
VOUT
2 C+
2
+ 7
C1
1
C2
+
VOUT
C4
22µF
22µF
6
3 C – TCM680 V
IN
2
4
–
V OUT
GND
R+OUT = 4(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2)
+4(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2)
+1/(fPUMP x C1) + 1/(fPUMP x C2) + ESRC4
VIN
5
GND
R+OUT = 32RSW + 8ESRC1 + 8ESRC2 + ESRC4
+1/(fPUMP x C1) + 1/(fPUMP x C2)
R–OUT = 32RSW + 8ESRC1 + 8ESRC2 + ESRC3
+1/(fPUMP x C1) + 1/(fPUMP x C2)
ROUT is typically 140Ω at +25°C with VIN = +5V and C1
and C2 as 4.7µF low ESR capacitors. The fixed term
(32RSW) is about 130Ω. 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 and C4 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 and C4. Typically
the larger the value of C3 and C4 the less the ripple for a
given load current. The formula for VRIPPLE(p-p) is given
below:
V+RIPPLE(p-p) = {1/[2(fPUMP /3) x C4] + 2(ESRC4)}(I+OUT)
V–RIPPLE(p-p) = {1/[2(fPUMP /3) x C3] + 2(ESRC3)}(I–OUT)
For a 10µF (0.5Ω ESR) capacitor for C3, C4,
fPUMP = 21kHz and IOUT = 10mA the peak-to-peak ripple
voltage at the output will be less than 100mV. In most
applications (IOUT < = 10mA) 10-20µF output capacitors and
1-5µF pump capacitors will suffice. Table 2 shows VRIPPLE
for different values of C3 and C4 (assume 1Ω ESR).
C3
22µF
–
VOUT
Figure 6. Positive and Negative Converter
4-16
TELCOM SEMICONDUCTOR, INC.
+5V TO ±10V VOLTAGE CONVERTER
1
TCM680
Paralleling Devices
Table 1. ROUT vs. C1 ,C2
C1, C2 (µF)
ROUT (Ω)
0.1
1089
0.47
339
1
232
3.3
165
4.7
157
10
146
22
141
100
137
Paralleling multiple TCM680s reduces the output resistance of both the positive and negative converters. The
effective output resistance is the output resistance of a
single device divided by the number of devices. As illustrated in Figure 7, each requires separate pump capacitors
C1 and C2, but all can share a single set of reservoir
capacitors.
±5V Regulated Supplies From A Single
3V Battery
C3, C4 (µF)
VRIPPLE (mV)
0.47
1540
1
734
3.3
236
4.7
172
10
91
22
52
100
27
3
Figure 8 shows a complete ±5V power supply using one
3V battery. The TCM680 provides +6V at V+OUT, which is
regulated to +5V by the TC55, and –5V by the negative LDO.
The input to the TCM680 can vary from 3V to 6V without
affecting regulation appreciably. With higher input voltage,
more current can be drawn from the outputs of the TCM680.
With 5V at VIN, 10mA can be drawn from both regulated
outputs simultaneously. Assuming 150Ω source resistance
for both converters, with (I+L + IL) = 20mA, the positive charge
pump will droop 3V, providing +7V for the negative charge
pump.
Table 2. VRIPPLE (p-p) vs. C3, C4 (IOUT = 10mA)
2
4
5
VIN
+
+
C1
VIN
+
+
C1
10µF
10µF
–
–
–
C1
–
C1
TCM680
TCM680
+
+
10µF
6
VIN
–
+
C2
–
VOUT
–
C2
+
–
C–
2
GND
–
VOUT
C2
NEGATIVE
SUPPLY
10µF
GND
–
+
–
COUT
7
22µF
GND
8
Figure 7. Paralleling TCM680 for Lower Output Source Resistance
TELCOM SEMICONDUCTOR, INC.
4-17
+5V TO ±10V VOLTAGE CONVERTER
TCM680
+
+
C1
VIN
+
3V
+
COUT
+
22µF
TC55RP5002Exx
+
VOUT
VIN
VOUT
+6V
10µF
–
–
+5 SUPPLY
+
VSS
C1–
1µF
–
GROUND
+ TCM680
–
+
C2
10µF
–
–
VOUT
C2–
GND
–
1µF
VSS
–6V
+
VOUT
VIN
–5 SUPPLY
–
22µF
+ C–
OUT
NEGATIVE LDO
TC54VC2702Exx
VOUT
VIN
LOW BATTERY
VSS
Figure 8. Split Supply Derived from 3V Battery
4-18
TELCOM SEMICONDUCTOR, INC.
+5V TO ±10V VOLTAGE CONVERTER
1
TCM680
TYPICAL CHARACTERISTICS
V+OUT or V–OUT
Output Resistance vs. VIN
10.0
C1 – C4 = 10µF
2
VIN = 5V
250
9.0
VOUT (V)
OUTPUT RESISTANCE (Ω)
300
+ or V – vs. Load Current
VOUT
OUT
200
3
8.0
150
ROUT
100
1
2
4
3
VIN (V)
5
7.0
6
0
5
15
10
LOAD CURRENT (mA)
+
–
Output Voltage vs. Output Current From VOUT to VOUT
Supply Current vs. VIN
1.4
4
10.0
VOUT (V)
1.0
0.8
NO LOAD
0.6
9.0
5
8.0
0.4
0.2
1
2
4
3
5
7.0
6
0
VIN (V)
6
8
4
2
+
–
OUTPUT CURRENT (mA) From VOUT TO VOUT
10
6
Output Source Resistance vs. Temperature
180
OUTPUT SOURCE RESISTANCE (Ω)
SUPPLY CURRENT (mA)
VIN = 5V
1.2
VIN = 5V
IOUT = 10mA
160
7
ROUT
140
120
100
-50
TELCOM SEMICONDUCTOR, INC.
0
50
TEMPERATURE (°C)
8
100
4-19