Document Outline
- Return to Contents
- List of Figures
- 1. TC7660 Test Circuit
- 2. Idealized Charge Pump Inverter
- 3. Simple Negative Converter
- 4. Paralleling Devices Lowers Output Impedance
- 5. Increased Output Voltage by Cascading Devices
- 6. External Clocking
- 7. Lowering Oscillator Frequency
- 8. Positive Voltage Multiplier
- 9. Combined Negative Converter and Positive Multiplier
- 10. Positive Voltage Conversion
- 11. Splitting a Supply in Half
- Features
- Pin Configuration (DIP and SOIC)
- Functional Block Diagram
- General Description
- Ordering Information
- Absolute Maximum Ratings
- Electrical Chracteristics
- Typical Characteristics
- Detailed Description
- Theoretical Power Efficiency Considerations
- Dos and Don'ts
- Simple Negative Voltage Converter
- Paralleling Devices
- Cascading Devices
- Changing the TC7660 Oscillator Frequency
- Positive Voltage Multiplication
- Combined Negative Voltage Conversion
- Efficient Positive Voltage Multiplication/Conversion
- Voltage Splitting
4-51
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
TC7660
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER
FEATURES
s
Converts +5V Logic Supply to
5V System
s
Wide Input Voltage Range .................... 1.5V to 10V
s
Efficient Voltage Conversion ......................... 99.9%
s
Excellent Power Efficiency ............................... 98%
s
Low Power Supply ............................... 80
A @ 5V
IN
s
Low Cost and Easy to Use
-- Only Two External Capacitors Required
s
RS232 Negative Power Supply
s
Available in Small Outline (SO) Package
s
Improved ESD Protection ....................... Up to 3kV
s
No Dx Diode Required for High Voltage Operation
GENERAL DESCRIPTION
The TC7660 is a pin-compatible replacement for the
Industry standard TC7660 charge pump voltage converter.
It converts a +1.5V to +10V input to a corresponding 1.5V
to 10V output using only two low-cost capacitors, eliminat-
ing inductors and their associated cost, size and EMI.
The on-board oscillator operates at a nominal fre-
quency of 10kHz. Operation below 10kHz (for lower supply
current applications) is possible by connecting an external
capacitor from OSC to ground (with pin 1 open).
The TC7660 is available in both 8-pin DIP and 8-pin
SOIC packages in commercial and extended temperature
ranges.
ORDERING INFORMATION
Temperature
Part No.
Package
Range
TC7660COA
8-Pin SOIC
0
C to +70
C
TC7660CPA
8-Pin Plastic DIP
0
C to +70
C
TC7660EOA
8-Pin SOIC
40
C to +85
C
TC7660EPA
8-Pin Plastic DIP
40
C to +85
C
TC7660IJA
8-Pin CerDIP
40
C to +85
C
TC7660MJA
8-Pin CerDIP
55
C to +125
C
TC7660EV
Evaluation Kit for
Charge Pump Family
FUNCTIONAL BLOCK DIAGRAM
1
2
3
4
8
7
6
5
TC7660CPA
TC7660EPA
TC7660IJA
NC
CAP +
GND
CAP
NC
CAP +
GND
CAP
VOUT
LOW
VOLTAGE (LV)
OSC
+
V
VOUT
LOW
VOLTAGE (LV)
OSC
+
V
NC = NO INTERNAL CONNECTION
1
2
3
4
8
7
6
5
TC7660COA
TC7660CPA
TC7660
GND
INTERNAL
VOLTAGE
REGULATOR
RC
OSCILLATOR
VOLTAGE
LEVEL
TRANSLATOR
2
V + CAP +
8
2
7
6
OSC
LV
3
LOGIC
NETWORK
VOUT
5
CAP
4
PIN CONFIGURATION (DIP and SOIC)
TC7660-7 9/30/96
EVALUATION
KIT
AVAILABLE
4-52
TELCOM SEMICONDUCTOR, INC.
TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ...................................................... +10.5V
LV and OSC Inputs
Voltage (Note 1) ........................ 0.3V to (V
+
+ 0.3V)
for V
+
< 5.5V
(V
+
5.5V) to (V
+
+ 0.3V)
for V
+
> 5.5V
Current Into LV (Note 1) ..................... 20
A for V
+
> 3.5V
Output Short Duration (V
SUPPLY
5.5V) ......... Continuous
Power Dissipation (T
A
70
C) (Note 2)
CerDIP ............................................................800mW
Plastic DIP ...................................................... 730mW
SOIC ...............................................................470mW
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
Storage Temperature Range ................ 65
C to +150
C
Lead Temperature (Soldering, 10 sec) ................. +300
C
*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 operation sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods
may affect device reliability.
ELECTRICAL CHARACTERISTICS:
Specifications Measured Over Operating Temperature Range With,
V
+
= 5V, C
OSC
= 0, Test Circuit (Figure 1), unless otherwise indicated.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
I+
Supply Current
R
L
=
--
80
180
A
V
+
H
Supply Voltage Range, High
Min
T
A
Max,
3
--
10
V
R
L
= 10 k
, LV Open
V
+
L
Supply Voltage Range, Low
Min
T
A
Max,
1.5
--
3.5
V
R
L
= 10 k
, LV to GND
R
OUT
Output Source Resistance
I
OUT
= 20mA, T
A
= 25
C
--
70
100
I
OUT
= 20mA, 0
C
T
A
+70
C
--
--
120
(C Device)
I
OUT
= 20mA, 40
C
T
A
+85
C
--
--
130
(I Device)
I
OUT
= 20mA, 55
C
T
A
+125
C
--
104
150
(M Device)
V
+
= 2V, I
OUT
= 3 mA, LV to GND
--
150
300
0
C
T
A
+70
C
V
+
= 2V, I
OUT
= 3 mA, LV to GND
--
160
600
55
C
T
A
+125
C (Note 3)
F
OSC
Oscillator Frequency
Pin 7 open
--
10
--
kHz
P
EFF
Power Efficiency
R
L
= 5 k
95
98
--
%
V
OUT
E
FF
Voltage Conversion Efficiency
R
L
=
97
99.9
--
%
Z
OSC
Oscillator Impedance
V
+
= 2V
--
1
--
M
V
+
= 5V
--
100
--
k
NOTES: 1. Connecting any input terminal to voltages greater than V+ or less than GND may cause destructive latch-up. It is recommended that no
inputs from sources operating from external supplies be applied prior to "power up" of the TC7660.
2. Derate linearly above 50
C by 5.5 mW/
C.
3. TC7660M only.
4. The TC7660 can be operated without the Dx diode over full temperature and voltage range.
4-53
TELCOM SEMICONDUCTOR, INC.
7
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TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 1)
500
450
400
200
150
100
50
0
55
25
0
+25
+50
+75 +100 +125
TEMPERATURE (
C)
Output Source Resistance vs. Temperature
OUTPUT SOURCE RESISTANCE (
)
V + = +2V
V + = +5V
25
0
+25
+75 +100 +125
12
10
8
6
4
2
+50
Operating Voltage vs. Temperature
55
SUPPLY VOLTAGE (V)
TEMPERATURE (
C)
0
7
8
10k
1k
100
OUTPUT SOURCE RESISTANCE (
)
TA = +25
C
Output Source Resistance vs. Supply Voltage
6
5
4
3
2
1
0
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (Hz)
100
POWER CONVERSION EFFICIENCY (%)
98
96
92
90
88
86
84
82
80
94
100
1k
10k
Power Conversion Eff. vs. Osc. Freq.
TEMPERATURE (
C)
OSCILLATOR FREQUENCY (kHz)
Unloaded Osc. Freq. vs. Temperature
20
55
18
16
14
12
10
8
6
25
0
+25 +50
+75 +100 +125
V+ = +5V
OSCILLATOR CAPACITANCE (pF)
10k
OSCILLATOR FREQUENCY (Hz)
1
Freq. of Osc. vs. Ext. Osc. Capacitance
1k
100
10
10
100
1000
10k
IOUT = 1 mA
TA = +25
C
V+ = +5V
TA = +25
C
V+ = +5V
IOUT = 1 mA
IOUT = 15 mA
10
SUPPLY VOLTAGE RANGE
4-54
TELCOM SEMICONDUCTOR, INC.
TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TYPICAL CHARACTERISTICS (Cont.)
2
0
Output Voltage vs. Load Current
OUTPUT VOLTAGE (V)
1
0
1
2
1
2
3
4
5
6
7
8
LOAD CURRENT (mA)
SLOPE 150
TA = +25
C
V+ = +2V
LOAD CURRENT (mA)
POWER CONVERSION EFFICIENCY (%)
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
SUPPLY CURRENT (mA) (Note)
10
20
30
40
50
60
TA = +25
C
V+ = +5V
Supply Current and Power Conversion Efficiency vs. Load Current
POWER CONVERSION EFFICIENCY (%)
0
LOAD CURRENT (mA)
10
20
30
40
50
60
70
80
90
100
1.5
3.0
4.5
6.0
7.5
9.0
0
2
4
6
8
10
12
14
16
18
20
SUPPLY CURRENT (mA) (Note)
TA = +25
C
V+ = 2V
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
0
0
Output Voltage vs. Output Current
1
2
3
4
5
6
7
8
9
10
10
20 30 40 50
60 70 80
90 100
TA = +25
C
LV OPEN
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
Output Voltage vs. Load Current
1
0
5
4
3
2
0
1
2
3
4
5
10
20
30
40
50
60
70
80
TA = +25
C
V+ = +5V
SLOPE 55
4-55
TELCOM SEMICONDUCTOR, INC.
7
6
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TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
Figure 1. TC7660 Test Circuit
Detailed Description
The TC7660 contains all the necessary circuitry to
implement a voltage inverter, with the exception of two
external capacitors, which may be inexpensive 10
F polar-
ized electrolytic capacitors. Operation is best understood by
considering Figure 2, which shows an idealized voltage
inverter. Capacitor C
1
is charged to a voltage, V
+
, for the half
cycle when switches S
1
and S
3
are closed. (Note: Switches
S
2
and S
4
are open during this half cycle.) During the second
half cycle of operation, switches S
2
and S
4
are closed, with
S
1
and S
3
open, thereby shifting capacitor C
1
negatively by
V
+
volts. Charge is then transferred from C
1
to C
2
, such that
the voltage on C
2
is exactly V
+
, assuming ideal switches and
no load on C
2
.
V+
GND
S3
S1
S2
S4
C2
VOUT
= VIN
Figure 2. Idealized Charge Pump Inverter
The four switches in Figure 2 are MOS power switches;
S
1
is a P-channel device, and S
2
, S
3
and S
4
are N-channel
devices. The main difficulty with this approach is that in
integrating the switches, the substrates of S
3
and S
4
must
always remain reverse-biased with respect to their sources,
but not so much as to degrade their ON resistances. In
addition, at circuit start-up, and under output short circuit
conditions (V
OUT
= V
+
), the output voltage must be sensed
and the substrate bias adjusted accordingly. Failure to
accomplish this will result in high power losses and probable
device latch-up.
This problem is eliminated in the TC7660 by a logic
network which senses the output voltage (V
OUT
) together
with the level translators, and switches the substrates of S
3
and S
4
to the correct level to maintain necessary reverse
bias.
The voltage regulator portion of the TC7660 is an
integral part of the anti-latch-up circuitry. Its inherent voltage
drop can, however, degrade operation at low voltages. To
improve low-voltage operation, the LV pin should be
connected to GND, disabling the regulator. For supply
voltages greater than 3.5V, the LV terminal must be left
open to ensure latch-up-proof operation and prevent device
damage.
Theoretical Power Efficiency
Considerations
In theory, a capacitive charge pump can approach
100% efficiency if certain conditions are met:
(1) The drive circuitry consumes minimal power.
(2) The output switches have extremely low ON
resistance and virtually no offset.
(3) The impedances of the pump and reservoir
capacitors are negligible at the pump frequency.
1
2
3
4
8
7
6
5
TC7660
+
V+
(+5V)
VO
C1
10
F
COSC
*
+
C2
10
F
IL
RL
NOTES:
For large values of COSC (>1000pF), the values
of C1 and C2 should be increased to 100
F.
IS
*
4-56
TELCOM SEMICONDUCTOR, INC.
TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
The TC7660 approaches these conditions for negative
voltage multiplication if large values of C
1
and C
2
are used.
Energy is lost only in the transfer of charge between
capacitors if a change in voltage occurs. The energy lost
is defined by:
E = 1/2 C
1
(V
1
2
V
2
2
)
V
1
and V
2
are the voltages on C
1
during the pump and
transfer cycles. If the impedances of C
1
and C
2
are relatively
high at the pump frequency (refer to Figure 2), compared to
the value of R
L
, there will be a substantial difference in
voltages V
1
and V
2
. Therefore, it is not only desirable to
make C
2
as large as possible to eliminate output voltage
ripple, but also to employ a correspondingly large value for
C
1
in order to achieve maximum efficiency of operation.
Dos and Don'ts
Do not exceed maximum supply voltages.
Do not connect LV terminal to GND for supply voltages
greater than 3.5V.
Do not short circuit the output to V
+
supply for voltages
above 5.5V for extended periods; however, transient
conditions including start-up are okay.
When using polarized capacitors in the inverting mode,
the + terminal of C
1
must be connected to pin 2 of the
TC7660 and the + terminal of C
2
must be connected to
GND Pin 3.
Simple Negative Voltage Converter
Figure 3 shows typical connections to provide a nega-
tive supply where a positive supply is available. A similar
scheme may be employed for supply voltages anywhere in
the operating range of +1.5V to +10V, keeping in mind that
pin 6 (LV) is tied to the supply negative (GND) only for supply
voltages below 3.5V.
Figure 3. Simple Negative Converter
Paralleling Devices
Any number of TC7660 voltage converters may be
paralleled to reduce output resistance (Figure 4). The reser-
voir capacitor, C
2
, serves all devices, while each device
requires its own pump capacitor, C
1
. The resultant output
resistance would be approximately:
R
OUT
(of TC7660)
n (number of devices)
R
OUT
=
2
2
f
C
1
The output characteristics of the circuit in Figure 3 are
those of a nearly ideal voltage source in series with 70
.
Thus, for a load current of 10mA and a supply voltage of
+5V, the output voltage would be 4.3V.
The dynamic output impedance of the TC7660 is due,
primarily, to capacitive reactance of the charge transfer
capacitor (C
1
). Since this capacitor is connected to the
output for only 1/2 of the cycle, the equation is:
X
C
= = 3.18
,
where f = 10kHz and C
1
= 10
F.
1
2
3
4
8
7
6
5
TC7660
10
F
+
V
+
10
F
+
VOUT
*
1. VOUT = n V
+
for 1.5V
V
+
10V
NOTES:
*
C1
C2
4-57
TELCOM SEMICONDUCTOR, INC.
7
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TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
Figure 5. Increased Output Voltage by Cascading Devices
Figure 4. Paralleling Devices Lowers Output Impedance
device latch-up, a 1k
resistor must be used in series with
the clock output. In a situation where the designer has
generated the external clock frequency using TTL logic, the
addition of a 10k
pull-up resistor to V
+
supply is required.
Note that the pump frequency with external clocking, as with
internal clocking, will be 1/2 of the clock frequency. Output
transitions occur on the positive-going edge of the clock.
It is also possible to increase the conversion efficiency
of the TC7660 at low load levels by lowering the oscillator
frequency. This reduces the switching losses, and is achieved
by connecting an additional capacitor, C
OSC
, as shown in
Figure 7. Lowering the oscillator frequency will cause an
undesirable increase in the impedance of the pump (C
1
) and
the reservoir (C
2
) capacitors. To overcome this, increase the
values of C
1
and C
2
by the same factor that the frequency
has been reduced. For example, the addition of a 100pF
capacitor between pin 7 (OSC) and pin 8 (V
+
) will lower the
oscillator frequency to 1kHz from its nominal frequency of
10kHz (a multiple of 10), and necessitate a corresponding
increase in the values of C
1
and C
2
(from 10
F to 100
F).
Cascading Devices
The TC7660 may be cascaded as shown (Figure 6) to
produce larger negative multiplication of the initial supply
voltage. However, due to the finite efficiency of each device,
the practical limit is 10 devices for light loads. The output
voltage is defined by:
V
OUT
= n (V
IN
)
where n is an integer representing the number of devices
cascaded. The resulting output resistance would be ap-
proximately the weighted sum of the individual TC7660
R
OUT
values.
Changing the TC7660 Oscillator Frequency
It may be desirable in some applications (due to noise or
other considerations) to increase the oscillator frequency.
This is achieved by overdriving the oscillator from an exter-
nal clock, as shown in Figure 6. In order to prevent possible
1
2
3
4
8
7
6
5
TC7660
V
+
1
2
3
4
8
7
6
5
TC7660
C1
RL
C2
C1
"n"
"1"
+
1
2
3
4
8
7
6
5
V
+
1
2
3
4
8
7
6
5
10
F
10
F
"n"
"1"
10
F
VOUT
1. VOUT = n V
+
for 1.5V V 10V
+
NOTES:
*
*
+
+
+
TC7660
TC7660
4-58
TELCOM SEMICONDUCTOR, INC.
TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
Figure 6. External Clocking
Figure 7. Lowering Oscillator Frequency
Positive Voltage Multiplication
The TC7660 may be employed to achieve positive
voltage multiplication using the circuit shown in Figure 8. In
this application, the pump inverter switches of the TC7660
are used to charge C
1
to a voltage level of V
+
V
F
(where V
+
is the supply voltage and V
F
is the forward voltage drop of
diode D
1
). On the transfer cycle, the voltage on C
1
plus the
supply voltage (V
+
) is applied through diode D
2
to capacitor
C
2
. The voltage thus created on C
2
becomes (2 V
+
) (2 V
F
),
or twice the supply voltage minus the combined forward
voltage drops of diodes D
1
and D
2
.
The source impedance of the output (V
OUT
) will depend
on the output current, but for V
+
= 5V and an output current
of 10 mA, it will be approximately 60
.
Figure 8. Positive Voltage Multiplier
Combined Negative Voltage Conversion
and Positive Supply Multiplication
Figure 9 combines the functions shown in Figures 3 and
8 to provide negative voltage conversion and positive volt-
age multiplication simultaneously. This approach would be,
for example, suitable for generating +9V and 5V from an
existing +5V supply. In this instance, capacitors C
1
and C
3
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C
2
and C
4
are pump and reservoir, respectively, for the multi-
plied positive voltage. There is a penalty in this configuration
which combines both functions, however, in that the source
impedances of the generated supplies will be somewhat
higher due to the finite impedance of the common charge
pump driver at pin 2 of the device.
Figure 9. Combined Negative Converter and Positive Multiplier
Efficient Positive Voltage
Multiplication/Conversion
Since the switches that allow the charge pumping op-
eration are bidirectional, the charge transfer can be per-
formed backwards as easily as forwards. Figure 10 shows
a TC7660 transforming 5V to +5V (or +5V to +10V, etc.).
The only problem here is that the internal clock and switch-
drive section will not operate until some positive voltage has
been generated. An initial inefficient pump, as shown in
Figure 9, could be used to start this circuit up, after which it
will bypass the other (D
1
and D
2
in Figure 9 would never turn
on), or else the diode and resistor shown dotted in Figure 10
can be used to "force" the internal regulator on.
1
2
3
4
8
7
6
5
TC7660
+
V +
+
CMOS
GATE
10F
VOUT
10F
1 k
V +
1
2
3
4
8
7
6
5
+
V
+
VOUT
C1
COSC
+
C2
TC7660
1
2
3
4
8
7
6
5
+
V +
VOUT =
(2 V +) (2 VF)
C1
D1
+
+
C3
C4
VOUT =
(V+ VF)
C2
TC7660
D2
+
1
2
3
4
8
7
6
5
V+
VOUT =
(2 V+) (2 VF)
+
C2
D1
D2
+
C1
TC7660
4-59
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
TC7660
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
1
2
3
4
8
7
6
5
+
VOUT = V
10F
+
1 M
V INPUT
C1
10F
TC7660
+
R
L1
R
L2
V
OUT
=
V
+
V
2
50 F
100 k
50 F
V
+
V
50 F
+
1 M
1
2
8
7
TC7660
3
4
6
5
+
Voltage Splitting
The same bidirectional characteristics used in Figure 10
can also be used to split a higher supply in half, as shown in
Figure 11. The combined load will be evenly shared be-
tween the two sides. Once again, a high value resistor to the
LV pin ensures start-up. Because the switches share the
load in parallel, the output impedance is much lower than in
the standard circuits, and higher currents can be drawn from
the device. By using this circuit, and then the circuit of Figure
5, +15V can be converted (via +7.5V and 7.5V) to a nominal
15V, though with rather high series resistance (~250
).
Figure 10. Positive Voltage Conversion
Figure 11. Splitting a Supply in Half
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