EVALUATION
KIT
AVAILABLE
TC7662B
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER
FEATURES
s
s
s
s
s
Wide Operating Voltage Range: 1.5V to 15V
Boost Pin (Pin 1) for Higher Switching Frequency
High Power Efficiency is 96%
Easy to Use – Requires Only 2 External Non-Critical
Passive Components
Improved Direct Replacement for Industry Stan-
dard ICL7660 and Other Second Source Devices
GENERAL DESCRIPTION
The TC7662B is a pin-compatible upgrade to the Indus-
try standard TC7660 charge pump voltage converter. It
converts a +1.5V to +15V input to a corresponding – 1.5 to
– 15V output using only two low-cost capacitors, eliminating
inductors and their associated cost, size and EMI.
The on-board oscillator operates at a nominal fre-
quency of 10kHz. Frequency is increased to 35kHz when
pin 1 is connected to V
+
, allowing the use of smaller external
capacitors. Operation below 10kHz (for lower supply current
applications) is also possible by connecting an external
capacitor from OSC to ground (with pin 1 open).
The TC7662B is available in both 8-pin DIP and 8-pin
small outline (SO) packages in commercial and extended
temperature ranges.
APPLICATIONS
s
s
s
s
s
Simple Conversion of +5V to
±
5V Supplies
Voltage Multiplication V
OUT
=
±
nV
IN
Negative Supplies for Data Acquisition Systems
and Instrumentation
RS232 Power Supplies
Supply Splitter, V
OUT
=
±
V
S
/2
ORDERING INFORMATION
Part No.
Package
8-Pin SOIC
8-Pin Plastic DIP
8-Pin SOIC
8-Pin Plastic DIP
Temperature
Range
0°C to +70°C
0°C to +70°C
– 40°C to +85°C
– 40°C to +85°C
PIN CONFIGURATION
(DIP AND SOIC)
BOOST 1
CAP + 2
8 V+
7 OSC
BOOST 1
CAP + 2
GND 3
CAP – 4
8 V+
7 OSC
TC7662BCOA 6 LOW
VOLTAGE (LV)
TC7662BEOA
5 VOUT
TC7662BCOA
TC7662BCPA
TC7662BEOA
TC7662BEPA
GND 3 TC7662BCPA 6 LOW
VOLTAGE (LV)
TC7662BEPA
– 4
5 VOUT
CAP
TC7660EV
Evaluation Kit for
Charge Pump Family
FUNCTIONAL BLOCK DIAGRAM
V + CAP +
8
BOOST
1
2
OSC
7
RC
OSCILLATOR
÷
2
VOLTAGE–
LEVEL
TRANSLATOR
4
CAP –
LV
6
5
INTERNAL
VOLTAGE
REGULATOR
LOGIC
NETWORK
VOUT
TC7662B
3
GND
© 2001 Microchip Technology Inc.
DS21469A
TC7662B-8 9/11/96
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC7662B
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ...................................................... +16.5V
LV, Boost and OSC Inputs Voltage (Note 1)
V+<5.5V ..................................... – 0.3V to (V
+
+ 0.3V)
>5.5V .................................. (V
+
– 5.5V) to (V
+
+ 0.3V)
Current Into LV (Note 1)
V
+
>3.5V ............................................................ 20µA
Output Short Duration
(V
SUPPLY
≤
5.5V) ....................................... Continuous
Power Dissipation (T
A
≤
70
°
C)
(Note 2)
Plastic DIP ...................................................... 730mW
SO ..................................................................470mW
Operating Temperature Range
C Suffix .................................................. 0°C to +70°C
E Suffix ............................................. – 40°C to +85°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:
V
+
= 5V, T
A
= +25°C, OSC = Free running, Test Circuit Figure 2, Unless
Otherwise Specified.
Symbol
I
+
Parameter
Supply Current (Note 3)
(Boost pin OPEN OR GND)
Test Conditions
R
L
=
∞,
+25°C
0°C
≤
T
A
≤
+70°C
– 40°C
≤
T
A
≤
+85°C
– 55°C
≤T
A
≤
+125°C
0°C
≤
T
A
≤
+70°C
– 40°C
≤
T
A
≤
+85°C
– 55°C
≤
T
A
≤
+125°C
R
L
= 10 kΩ, LV Open, T
MIN
≤
T
A
≤
T
MAX
R
L
= 10 kΩ, LV to GND, T
MIN
≤
T
A
≤
T
MAX
I
OUT
= 20mA, 0°C
≤
T
A
≤
+70°C
I
OUT
= 20mA, – 40°C
≤
T
A
≤
+85°C
I
OUT
= 20mA, – 55°C
≤
T
A
≤
+125°C
I
OUT
= 3mA, V
+
= 2V, LV to GND ,
0°C
≤
T
A
≤
+70°C
I
OUT
= 3mA, V
+
= 2V, LV to GND ,
– 40°C
≤
T
A
≤
+85°C
I
OUT
= 3mA, V
+
= 2V, LV to GND ,
– 55°C
≤
T
A
≤
+125°C
C
OSC
= 0,Pin 1 Open or GND
Pin 1 = V
+
R
L
= 5kΩ
T
MIN
≤
T
A
≤
T
MAX
R
L
=
∞
V
+
= 2V
V
+
= 5V
Min
—
—
—
—
—
Typ
80
—
—
—
—
Max
160
180
180
200
300
350
400
15
3.5
100
120
150
250
300
400
—
—
—
—
—
Unit
µA
µA
µA
µA
µA
I
+
Supply Current
(Boost pin = V+)
Supply Voltage Range, High
(Note 4)
Supply Voltage Range, Low
Output Source Resistance
V
+
H
V
L
R
OUT
+
3.0
1.5
—
—
—
—
—
—
5
96
95
99
—
—
—
—
65
—
—
—
—
—
10
35
96
97
99.9
1
100
V
V
Ω
Ω
Ω
Ω
Ω
Ω
kHz
%
%
MΩ
kΩ
f
OSC
P
Eff
V
OUT
Eff
Z
OSC
NOTES:
Oscillator Frequency
Power Efficiency
Voltage Conversion Efficiency
Oscillator Impedance
1. Connecting any 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 TC7662B.
2. Derate linearly above 50°C by 5.5 mW/°C.
3. In the test circuit, there is no external capacitor applied to pin 7. However, when the device is plugged into a test socket, there is usually a very
small but finite stray capacitance present, of the order of 5pF.
4. The TC7662B can operate without an external diode over the full temperature and voltage range. This device will function in existing designs which
incorporate an external diode with no degradation in overall circuit performance.
TC7662B-8 9/11/96
2
© 2001 Microchip Technology Inc.
DS21469A
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC7662B
DETAILED DESCRIPTION
The TC7662B contains all the necessary circuitry to
complete a negative voltage converter, with the exception of
two external capacitors which may be inexpensive 1µF
polarized electrolytic types. The mode of operation of the
device may be best understood by considering Figure 2,
which shows an idealized negative voltage converter. Ca-
pacitor 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
. The TC7662B approaches this ideal situation
more closely than existing non-mechanical circuits.
In the TC7662B, the four switches of 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 ap-
proach 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 would result in high power losses
and probable device latchup.
The problem is eliminated in the TC7662B 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 TC7662B is an
integral part of the anti-latchup circuitry; however, its inher-
ent voltage drop can degrade operation at low voltages.
Therefore, to improve low voltage operation, the “LV” pin
should be connected to GND, disabling the regulator. For
supply voltages greater than 3.5 volts, the LV terminal must
be left open to insure latchup proof operation and prevent
device damage.
V+
1
2
C1 +
10
µF
3 TC7662B
4
8
7
6
5
RL
VO
C2
10
µF
IL
IS
V+
(+5V)
THEORETICAL POWER EFFICIENCY
CONSIDERATIONS
In theory, a voltage converter can approach 100%
efficiency if certain conditions are met:
A. The drive circuitry consumes minimal power.
B. The output switches have extremely low ON resistance
and virtually no offset.
C. The impedances of the pump and reservoir capacitors
are negligible at the pump frequency.
The TC7662B approaches these conditions for nega-
tive voltage conversion 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
12
– V
22
)
where 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 desirable not only 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
1. Do not exceed maximum supply voltages.
2. Do not connect the LV terminal to GND for supply
voltages greater than 3.5 volts.
3. Do not short circuit the output to V
+
supply for voltages
above 5.5 volts for extended periods; however,
transient conditions including start-up are okay.
S1
VIN
C1
S2
S3
S4
C2
VOUT = – VIN
NOTE:
For large values of C
OSC
(>1000 pF), the values
of C
1
and C
2
should be increased to 100 µF.
+
Figure 1. TC7662B Test Circuit
© 2001 Microchip Technology Inc.
DS21469A
Figure 2. Idealized Negative Voltage Capacitor
3
TC7662B-8 9/11/96
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC7662B
4. When using polarized capacitors in the inverting mode,
the + terminal of C
1
must be connected to pin 2 of the
TC7662B and the – terminal of C
2
must be connected
to GND.
5. If the voltage supply driving the TC7662B has a large
source impedance (25-30 ohms), then a 2.2µF capaci-
tor from pin 8 to ground may be required to limit the
rate of rise of the input voltage to less than 2V/µsec.
voltage and temperature (See the Output Source Resis-
tance graphs), typically 23Ω at +25°C and 5V. Careful
selection of C
1
and C
2
will reduce the remaining terms,
minimizing the output impedance. High value capacitors will
reduce the 1/(f
PUMP
x C
1
) component, and low ESR capaci-
tors will lower the ESR term. Increasing the oscillator fre-
quency will reduce the 1/(f
PUMP
x C
1
) term, but may have the
side effect of a net increase in output impedance when C
1
>
10µF and there is not enough time to fully charge the
capacitors every cycle. In a typical application when f
OSC
=
10kHz and C = C
1
= C
2
= 10µF:
R
O
≅
2 x 23 +
(5 x
10
3
1
x 10 x 10
-6
)
TYPICAL APPLICATIONS
Simple Negative Voltage Converter
The majority of applications will undoubtedly utilize the
TC7662B for generation of negative supply voltages. Figure
3 shows typical connections to provide a negative supply
where a positive supply of +1.5V to +15V is available. Keep
in mind that pin 6 (LV) is tied to the supply negative (GND)
for supply voltages below 3.5 volts.
V+
1
10
µF
+
–
2
3
4
TC7662B
8
7
6
5
–
10
µF
+
VOUT = –V+
RO
–
V+
+
VOUT
+ 4 x ESR
C1
+ ESR
C2
R
O
≅
(46 + 20 + 5 x ESR
C
)
Ω
Since the ESRs of the capacitors are reflected in the
output impedance multiplied by a factor of 5, a high value
could potentially swamp out a low 1/(f
PUMP
x C
1
) term,
rendering an increase in switching frequency or filter capaci-
tance ineffective. Typical electrolytic capacitors may have
ESRs as high as 10Ω.
Output Ripple
ESR also affects the ripple voltage seen at the output.
The total ripple is determined by 2 voltages, A and B, as
shown in Figure 4. Segment A is the voltage drop across the
ESR of C
2
at the instant it goes from being charged by C
1
(current flowing into C
2
) to being discharged through the
load (current flowing out of C
2
). The magnitude of this
current change is 2 x I
OUT
, hence the total drop is 2 x I
OUT
x
ESR
C2
volts. Segment B is the voltage change across C
2
during time t
2
, the half of the cycle when C
2
supplies current
to the load. The drop at B is I
OUT
x t
2
/C
2
volts. The peak-to-
peak ripple voltage is the sum of these voltage drops:
V
RIPPLE
≅
a.
b.
Figure 3. Simple Negative Converter and its Output Equivalent
The output characteristics of the circuit in Figure 3 can
be approximated by an ideal voltage source in series with a
resistance as shown in Figure 3b. The voltage source has a
value of–(V+). The output impedance (R
O
) is a function of
the ON resistance of the internal MOS switches (shown in
Figure 2), the switching frequency, the value of C
1
and C
2
,
and the ESR (equivalent series resistance) of C
1
and C
2
. A
good first order approximation for R
O
is:
R
O
≅
2(R
SW1
+ R
SW3
+ ESR
C1
) + 2(R
SW2
+ R
SW4
+
ESR
C1
) +
f
OSC
2
1
f
PUMP
x C
1
(
2 x f
PUMP
x C
2
+ ESR
C2
x I
OUT
1
)
t
2
t
1
+ ESR
C2
0
B
(f
PUMP
=
, R
SWX
= MOSFET switch resistance)
V
Combining the four R
SWX
terms as R
SW
, we see that:
R
O
≅
2 x R
SW
+
1
f
PUMP
x C
1
+ 4 x ESR
C1
+ ESR
C2
Ω
A
– (V+)
R
SW
, the total switch resistance, is a function of supply
TC7662B-8 9/11/96
Figure 4. Output Ripple
4
© 2001 Microchip Technology Inc.
DS21469A
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC7662B
Paralleling Devices
Any number of TC7662B voltage converters may be
paralleled to reduce output resistance (Figure 5). 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
=
R
OUT
(of TC7662B)
n (number of devices)
Changing the TC7662B Oscillator Frequency
It may be desirable in some applications (due to noise or
other considerations) to increase the oscillator frequency.
This is achieved by one of several methods described
below:
By connecting the BOOSTPin (Pin 1) to V
+
, the oscillator
charge and discharge current is increased and, hence the
oscillator frequency is increased by approximately 3-1/2
times. The result is a decrease in the output impedance and
ripple. This is of major importance for surface mount appli-
cations where capacitor size and cost are critical. Smaller
capacitors, e.g., 0.1µF, can be used in conjunction with the
Boost Pin in order to achieve similar output currents com-
pared to the device free running with C
1
= C
2
= 1µF or 10µF.
(Refer to graph of Output Source Resistance as a Function
of Oscillator Frequency).
Increasing the oscillator frequency can also be achieved
by overdriving the oscillator from an external clock as shown
in Figure 7. In order to prevent device latchup, a 1kΩ resistor
must be used in series with the clock output. In a situation
where the designer has generated the external clock fre-
quency using TTL logic, the addition of a 10kΩ pullup
resistor to V
+
supply is required. Note that the pump fre-
quency 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.
V+
1
2
+
10µF
3
4
8
1 kΩ
7
CMOS
GATE
V+
V
1
2
C1
3
4
8
7
+
1
2
C1
3
4
8
7
RL
TC7662B
"1"
6
5
TC7662B
"n"
6
5
+
C2
Figure 5. Paralleling Devices
Cascading Devices
The TC7662B may be cascaded as shown 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 TC7662B
R
OUT
values.
TC7662B
6
5
+
10µF
VOUT
Figure 7. External Clocking
V+
1
2
10µF
+
3
4
TC7662B
"1"
8
7
6
5
10µF
+
1
2
3
4
TC7662B
"n"
8
7
6
5
+
*VOUT = –nV+
10µF
VOUT
10µF
Figure 6. Cascading Devices for Increased Output Voltage
© 2001 Microchip Technology Inc.
DS21469A
It is also possible to increase the conversion efficiency
of the TC7662B at low load levels by lowering the oscillator
frequency. This reduces the switching losses, and is shown
in Figure 8. However, lowering the oscillator frequency will
cause an undesirable increase in the impedance of the
pump (C
1
) and reservoir (C
2
) capacitors; this is overcome by
increasing 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 V
+
will lower
the oscillator frequency to 1kHz from its nominal frequency
of 10kHz (multiple of 10), and thereby necessitate a corre-
sponding increase in the value of C
1
and C
2
(from 10µF to
100µF).
5
TC7662B-8 9/11/96
