EVALUATION
KIT
AVAILABLE
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER
TC7662B
FEATURES
■ 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
APPLICATIONS
■ Simple Conversion of +5V to ±5V Supplies
■ Voltage Multiplication V
■ Negative Supplies for Data Acquisition Systems
and Instrumentation
■ RS232 Power Supplies
■ Supply Splitter, V
OUT
PIN CONFIGURATION (DIP AND SOIC)
BOOST
CAP
GND
CAP
1
+
2
3
–
4
TC7662BCPA
TC7662BEPA
+
8
V
7
OSC
LOW
6
VOLTAGE (LV)
V
5
OUT
OUT
= ±VS/2
BOOST
CAP
GND
CAP
= ±nV
1
+
2
TC7662BCOA
3
TC7662BEOA
–
4
IN
+
8
V
7
OSC
LOW
6
VOLTAGE (LV)
V
5
OUT
GENERAL DESCRIPTION
The TC7662B is a pin-compatible upgrade to the Industry 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 frequency 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.
ORDERING INFORMATION
Temperature
Part No. Package Range
TC7662BCOA 8-Pin SOIC 0°C to +70°C
TC7662BCPA 8-Pin Plastic DIP 0°C to +70°C
TC7662BEOA 8-Pin SOIC – 40°C to +85°C
TC7662BEPA 8-Pin Plastic DIP – 40°C to +85°C
TC7660EV Evaluation Kit for
Charge Pump Family
FUNCTIONAL BLOCK DIAGRAM
LV
1
7
OSCILLATOR
6
TC7662B
BOOST
OSC
© 2001 Microchip Technology Inc. DS21469A
RC
÷ 2
INTERNAL
VOLTAGE
REGULATOR
VOLTAGE–
LEVEL
TRANSLATOR
V+CAP
82
3
GND
+
LOGIC
NETWORK
4
5
CAP
V
OUT
–
TC7662B-8 9/11/96
TC7662B
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
ABSOLUTE MAXIMUM RATINGS*
Operating Temperature Range
C Suffix ..................................................0°C to +70°C
Supply Voltage ...................................................... +16.5V
LV, Boost and OSC Inputs Voltage (Note 1)
V+<5.5V.....................................– 0.3V to (V+ + 0.3V)
E Suffix .............................................– 40°C to +85°C
Storage Temperature Range ................– 65°C to +150°C
Lead Temperature (Soldering, 10 sec) .................+300°C
>5.5V .................................. (V+ – 5.5V) to (V+ + 0.3V)
Current Into LV (Note 1)
V+ >3.5V ............................................................ 20µA
Output Short Duration
(V
≤ 5.5V).......................................Continuous
SUPPLY
Power Dissipation (TA ≤ 70°C) (Note 2)
Plastic DIP ......................................................730mW
SO ..................................................................470mW
ELECTRICAL CHARACTERISTICS: V
+
= 5V, TA = +25°C, OSC = Free running, Test Circuit Figure 2, Unless
* 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 permanent 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.
Otherwise Specified.
Symbol Parameter Test Conditions Min Typ Max Unit
+
I
+
I
+
V
H
+
V
L
R
OUT
f
OSC
P
Eff
V
Eff Voltage Conversion Efficiency RL = ∞ 99 99.9 — %
OUT
Z
OSC
Supply Current (Note 3) RL = ∞, +25°C — 80 160 µA
(Boost pin OPEN OR GND) 0°C ≤ TA ≤ +70°C — — 180 µA
– 40°C ≤ TA ≤ +85°C — — 180 µA
– 55°C ≤TA ≤ +125°C — — 200 µA
Supply Current 0°C ≤ TA ≤ +70°C — — 300 µA
(Boost pin = V+) – 40°C ≤ T
≤ +85°C 350
A
– 55°C ≤ TA ≤ +125°C 400
Supply Voltage Range, High RL = 10 kΩ, LV Open, T
≤ TA ≤ T
MIN
MAX
3.0 — 15 V
(Note 4)
Supply Voltage Range, Low RL = 10 kΩ, LV to GND, T
Output Source Resistance I
= 20mA, 0°C ≤ TA ≤ +70°C — 65 100 Ω
OUT
I
= 20mA, – 40°C ≤ TA ≤ +85°C — — 120 Ω
OUT
I
= 20mA, – 55°C ≤ TA ≤ +125°C — — 150 Ω
OUT
I
= 3mA, V+ = 2V, LV to GND , — — 250 Ω
OUT
0°C ≤ T
I
OUT
– 40°C ≤ T
I
OUT
≤ +70°C
A
= 3mA, V+ = 2V, LV to GND , — — 300 Ω
≤ +85°C
A
= 3mA, V+ = 2V, LV to GND , — — 400 Ω
≤ TA ≤ T
MIN
MAX
1.5 — 3.5 V
– 55°C ≤ TA ≤ +125°C
Oscillator Frequency C
= 0,Pin 1 Open or GND 5 10 — kHz
OSC
Pin 1 = V
+
35
Power Efficiency RL = 5kΩ 96 96 — %
T
≤ TA ≤ T
MIN
MAX
95 97
Oscillator Impedance V+ = 2V — 1 — MΩ
V+ = 5V — 100 — kΩ
NOTES:
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. Capacitor C1 is charged to a voltage V+ for the half cycle when
switches S1 and S3 are closed. (Note: Switches S2 and S
are open during this half cycle.) During the second half cycle
of operation, switches S2 and S4 are closed, with S1 and S
open, thereby shifting capacitor C1 negatively by V+ volts.
Charge is then transferred from C1 to C2 such that the
voltage on C2 is exactly V+, assuming ideal switches and no
load on C2. 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; S1 is a P-channel device and S2, S3 and S
are N-channel devices. The main difficulty with this approach is that in integrating the switches, the substrates of
S3 and S4 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
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
with the level translators, and switches the substrates of S
and S4 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 inherent 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
+
C
10 µF
1
TC7662B
3
4
= V+), the output voltage must
OUT
) together
OUT
I
I
R
S
L
L
V
(+5V)
8
7
6
5
+
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.
4
C. The impedances of the pump and reservoir capacitors
are negligible at the pump frequency.
3
The TC7662B approaches these conditions for nega-
tive voltage conversion if large values of C1 and C2 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:
2
4
E = 1/2 C1 (V
1
– V
2
)
2
where V1 and V2 are the voltages on C1 during the pump and
transfer cycles. If the impedances of C1 and C2 are relatively
high at the pump frequency (refer to Figure 2) compared to
the value of RL, there will be a substantial difference in
voltages V1 and V2. Therefore, it is desirable not only to
make C2 as large as possible to eliminate output voltage
ripple, but also to employ a correspondingly large value for
C1 in order to achieve maximum efficiency of operation.
Dos and Don’ts
3
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.
S
V
IN
1
S
3
S
2
C
1
C
S
4
2
V
OUT
= – V
IN
NOTE: For large values of C
of C
and C2 should be increased to 100 µF.
1
Figure 1. TC7662B Test Circuit
(>1000 pF), the values
OSC
V
O
C
2
10 µF
+
Figure 2. Idealized Negative Voltage Capacitor
3
TC7662B-8 9/11/96© 2001 Microchip Technology Inc. DS21469A
TC7662B
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
4. When using polarized capacitors in the inverting mode,
the + terminal of C1 must be connected to pin 2 of the
TC7662B and the – terminal of C2 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 capacitor from pin 8 to ground may be required to limit the
rate of rise of the input voltage to less than 2V/µsec.
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
Figure 3. Simple Negative Converter and its Output Equivalent
2
+
–
TC7662B
3
4
a. b.
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 (RO) is a function of
the ON resistance of the internal MOS switches (shown in
Figure 2), the switching frequency, the value of C1 and C2,
and the ESR (equivalent series resistance) of C1 and C2. A
good first order approximation for RO is:
8
7
6
5
10 µF
R
O
V
V
= –V+
–
+
OUT
–
V+
+
OUT
voltage and temperature (See the Output Source Resistance graphs), typically 23Ω at +25°C and 5V. Careful
selection of C1 and C2 will reduce the remaining terms,
minimizing the output impedance. High value capacitors will
reduce the 1/(f
x C1) component, and low ESR capaci-
PUMP
tors will lower the ESR term. Increasing the oscillator frequency will reduce the 1/(f
x C1) term, but may have the
PUMP
side effect of a net increase in output impedance when C1 >
10µF and there is not enough time to fully charge the
capacitors every cycle. In a typical application when f
OSC
=
10kHz and C = C1 = C2 = 10µF:
RO ≅ 2 x 23 + + 4 x ESRC1 + ESR
(5 x 103 x 10 x 10-6)
1
C2
RO ≅ (46 + 20 + 5 x ESRC) 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
x C1) term,
PUMP
rendering an increase in switching frequency or filter capacitance 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 C2 at the instant it goes from being charged by C
(current flowing into C2) to being discharged through the
load (current flowing out of C2). The magnitude of this
current change is 2 x I
ESRC2 volts. Segment B is the voltage change across C
during time t2, the half of the cycle when C2 supplies current
to the load. The drop at B is I
peak ripple voltage is the sum of these voltage drops:
V
≅ ( + ESR
RIPPLE
2 x f
, hence the total drop is 2 x I
OUT
x t2/C2 volts. The peak-to-
OUT
1
x I
PUMP
x C
2
C2
OUT
OUT
)
1
x
2
RO ≅ 2(R
(f
= , R
PUMP
Combining the four R
RO ≅ 2 x RSW + + 4 x ESRC1 + ESRC2Ω
+ R
SW1
ESRC1) + + ESR
f
OSC
2
+ ESRC1) + 2(R
SW3
SW2
1
f
x C
PUMP
SWX
terms as RSW, we see that:
SWX
1
= MOSFET switch resistance)
1
f
x C
PUMP
1
+ R
C2
RSW, the total switch resistance, is a function of supply
TC7662B-8 9/11/96
SW4
+
t
2
0
V
– (V+)
4
B
A
Figure 4. Output Ripple
t
1
© 2001 Microchip Technology Inc. DS21469A
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