■Wide Input Voltage Range ....................1.5V to 12V
■Efficient Voltage Conversion.........................99.9%
■Excellent Power Efficiency ...............................98%
■Low Power Supply..............................80µA @ 5 V
■Low Cost and Easy to Use
— Only Two External Capacitors Required
■Available in Small Outline (SOIC) Package
■Improved ESD Protection ..................... Up to 10kV
■No External Diode Required for High Voltage
Operation
ORDERING INFORMATION
Temperature
Part No.PackageRange
TC7660SCOA8-Pin SOIC0°C to +70°C
TC7660SCPA8-Pin Plastic DIP0°C to +70°C
TC7660SEJA8-Pin CerDIP– 40°C to +85°C
TC7660SEOA8-Pin SOIC– 40°C to +85°C
TC7660SEPA8-Pin Plastic DIP– 40°C to +85°C
TC7660SMJA8-Pin CerDIP– 55°C to +125°C
TC7660EVEvaluation Kit for
Charge Pump Family
GENERAL DESCRIPTION
The TC7660S is a pin-compatible upgrade to the Industry standard TC7660 charge pump voltage converter. It
converts a +1.5V to +12V input to a corresponding -1.5V to
-12V output using only two low-cost capacitors, eliminating
inductors and their associated cost, size and EMI. Added
features include an extended supply range to 12V, and a
IN
frequency boost pin for higher operating frequency, allowing
the use of smaller external capacitors.
The on-board oscillator operates at a nominal frequency
of 10kHz. Frequency is increased to 45kHz when pin 1 is
connected to V+. Operation below 10kHz (for lower supply
current applications) is possible by connecting an external
capacitor from OSC to ground (with pin 1 open).
The TC7660S is available in both 8-pin DIP and 8-pin
small outline (SOIC) packages in commercial and extended
temperature ranges.
C Suffix ..................................................0°C to +70°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 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.
= 0, Test Circuit (Figure 1), unless otherwise
OSC
indicated.
SymbolParameterTest ConditionsMinTypMaxUnit
+
I
+
I
+
V
H
+
V
L
R
OUT
F
OSC
P
EFF
V
OUT EFF
Z
OSC
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
Supply CurrentRL = ∞—80160µA
(Boost pin OPEN or GND)0°C ≤ T
– 40°C ≤ T
≤ +70°C——180
A
≤ +85°C——180
A
– 55°C ≤ TA ≤ +125°C——200
Supply Current0°C ≤ TA ≤ +70°C——300µA
(Boost pin = V
+
)– 40°C ≤ TA ≤ +85°C——350
– 55°C ≤ TA ≤ +125°C——400
Supply Voltage Range, HighMin ≤ TA ≤ Max,3—12V
RL = 10kΩ, LV Open
Supply Voltage Range, LowMin ≤ TA ≤ Max,1.5—3.5V
RL = 10kΩ, LV to GND
Output Source ResistanceI
= 20mA—60100Ω
OUT
I
= 20mA, 0°C ≤ TA ≤ +70°C—70120
OUT
I
= 20mA, – 40°C ≤ TA ≤ +85°C—70120
OUT
I
= 20mA, – 55°C ≤ TA ≤ +125°C—105150
OUT
V+ = 2V, I
0°C ≤ T
= 3mA, LV to GND
OUT
≤ +70°C——250Ω
A
– 55°C ≤ TA ≤ +125°C——400
Oscillator FrequencyPin 7 open; Pin 1 open or GND—10—kHz
Boost Pin = V
+
—45—
Power EfficiencyRL = 5 kΩ; Boost Pin Open9698—%
T
≤ TA ≤ T
MIN
Boost Pin = V
; Boost Pin Open9598—
MAX
+
—88—
Voltage Conversion EfficiencyRL = ∞9999.9—%
Oscillator ImpedanceV+ = 2V—1—MΩ
V+ = 5V—100—kΩ
inputs from sources operating from external supplies be applied prior to "power up" of the TC7660S.
The TC7660S contains all the necessary circuitry to
implement a voltage inverter, with the exception of two
external capacitors, which may be inexpensive 10 µF polarized electrolytic capacitors. Operation is best understood by
considering Figure 2, which shows an idealized voltage
inverter. Capacitor C1 is charged to a voltage V+ for the half
cycle when switches S1 and S3 are closed. (Note: Switches
S2 and S4 are open during this half cycle.) During the second
half cycle of operation, switches S2 and S4 are closed, with
S1 and S3 open, thereby shifting capacitor C1 negatively by
V+ volts. Charge is then transferred from 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 four switches in Figure 2 are MOS power switches;
S1 is a P-channel device, and S2, S3 and S4 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
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 TC7660S 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.
+
V
+
C
1
10µF
= V+), the output voltage must be sensed
OUT
OUT
1
2
TC7660S
3
4
8
7
*
6
5
C
OSC
) together
I
S
+
V
(+5V)
I
L
R
L
TC7660S
Figure 2. Idealized Charge Pump Inverter
The voltage regulator portion of the TC7660S 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
3
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.
The TC7660S approaches these conditions for negative voltage multiplication if large values of C1 and C2 are
used. Energy is lost only in the transfer of chargebetween capacitors if a change in voltage occurs. The
energy lost is defined by:
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
E = 1/2 C1 (V
1
– V
2
)
2
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.
3
TC7660S-14 9/16/96
TC7660S
SUPER CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
Dos and Don'ts
• Do not exceed maximum supply voltages.
• Do not connect the 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 C1 must be connected to pin 2 of the
TC7660S and the + terminal of C2 must be connected
to GND.
Simple Negative Voltage Converter
Figure 3 shows typical connections to provide a negative 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 +12V, keeping in mind that
pin 6 (LV) is tied to the supply negative (GND) only for supply
voltages below 3.5V.
+
V
The output characteristics of the circuit in Figure 3 are
those of a nearly ideal voltage source in series with 70Ω.
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 TC7660S is due,
primarily, to capacitive reactance of the charge transfer
capacitor (C1). Since this capacitor is connected to the
output for only 1/2 of the cycle, the equation is:
2
XC = = 3.18Ω,
2πf C
1
where f = 10kHz and C1 = 10µF.
Paralleling Devices
Any number of TC7660S voltage converters may be
paralleled to reduce output resistance (Figure 4). The reservoir capacitor, C2, serves all devices, while each device
requires its own pump capacitor, C1. The resultant output
resistance would be approximately:
Figure 5. Increased Output Voltage by Cascading Devices
10µF
Cascading Devices
The TC7660S may be cascaded as shown (Figure 5) 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
= – n (VIN)
OUT
where n is an integer representing the number of devices
cascaded. The resulting output resistance would be approximately the weighted sum of the individual TC7660S
R
values.
OUT
Changing the TC7660S Oscillator Frequency
It may be desirable in some applications (due to noise or
other considerations) to increase the oscillator frequency.
Pin 1, frequency boost pin may be connected to V+ to
increase oscillator frequency to 45kHz from a nominal of
10kHz for an input supply voltage of 5.0 volts. The oscillator
may also be synchronized to an external clock as shown in
Figure 6. In order to prevent possible device latch-up, a 1kΩ
resistor must be used in series with the clock output. In a
+
V
CMO
GATE
V
OUT
10µF
+
10µF
+
V
1
2
+
3
TC7660S
4
8
1 kΩ
7
6
5
1
2
+
10µF
+
3
4
TC7660S
"n"
8
7
6
5
+
V
10µF
situation where the designer has generated the external
clock frequency using TTL logic, the addition of a 10kΩ pullup 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 TC7660S at low load levels by lowering the oscillator
frequency. This reduces the switching losses, and is achieved
by connecting an additional capacitor, C
, as shown in
OSC
Figure 7. Lowering the oscillator frequency will cause an
undesirable increase in the impedance of the pump (C1) and
the reservoir (C2) capacitors. To overcome this, increase the
values of C1 and C2 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 C1 and C2 (from 10µF to 100µF).
Positive Voltage Multiplication
The TC7660S may be employed to achieve positive
voltage multiplication using the circuit shown in Figure 8. In
this application, the pump inverter switches of the TC7660S
are used to charge C1 to a voltage level of V+–VF (where V
is the supply voltage and VF is the forward voltage drop of
diode D1). On the transfer cycle, the voltage on C1 plus the
supply voltage (V+) is applied through diode D2 to capacitor
C2. The voltage thus created on C2 becomes (2V+) – (2VF),
or twice the supply voltage minus the combined forward
voltage drops of diodes D1 and D2.
The source impedance of the output (V
on the output current, but for V+ = 5V and an output current
of 10mA, it will be approximately 60Ω.
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 voltage multiplication simultaneously. This approach would be,
for example, suitable for generating +9V and – 5V from an
existing +5V supply. In this instance, capacitors C1 and C
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C
and C4 are pump and reservoir, respectively, for the multiplied 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.
Efficient Positive Voltage
Multiplication/Conversion
Since the switches that allow the charge pumping operation are bidirectional, the charge transfer can be performed backwards as easily as forwards. Figure 10 shows
a TC7660S transforming – 5V to +5V (or +5V to +10V, etc.).
The only problem here is that the internal clock and switchdrive 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 (D1 and D2 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.
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 between
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 (~250Ω).
+
V
3
2
+
Figure 9. Combined Negative Converter and Positive Multiplier
1
2
TC7660S
3
4
C
1
8
7
6
5
+
C
2
+
D
1
V
(2 V+) – (2 VF)
D
2
+
Negative Voltage Generation for
Display ADCs
The TC7106 is designed to work from a 9V battery. With
a fixed power supply system, the TC7106 will perform
conversions with input signal referenced to power supply
ground.
V
OUT
OUT
C
=
C
= –V
3
4
+
1
2
3
4
TC7660S-14 9/16/96
+
V
8
D
7
TC7660S
Figure 8. Positive Voltage Multiplier
6
5
1
D
2
+
C
1
V
OUT
(2 V+) – (2 VF)
+
C
2
Negative Supply Generation for
4¹⁄₂ Digit Data Acquisition System
The TC7135 is a 4¹⁄₂ digit ADC operating from ±5V
=
supplies. The TC7660S provides an inexpensive –5V source.
(See AN16 and AN17 for TC7135 interface details and
software routines.)
Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by
updates. It is your re sponsib ility to en sure t hat you r appl ication m eets with y our sp ecificat ions. No represen tation or warra nty is given and no liability is
assumed by Microc hip Technology Incorporated with respec t to the accur acy or use of such infor mation, or infrin gemen t of patents or o th er i nte ll ect ua l
property rights arising from such use or otherwise. Use of Microchipís products as critical components in life support systems is not authorized except with
express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellectual property rights. The Micro chip logo and name are registered trad emarks of Microchip Technology Inc. in the U.S.A. and oth er countries. All rights
reserved. All other trademarks mentioned herein are the property of their respective companies.
New York
150 Motor Parkway, Suite 202
Hauppauge, NY 11788
Tel: 631-273-5305 Fax: 631-273-5335
San Jose
Microchip Technology Inc.
2107 North First Street, Suite 590
San Jose, CA 95131
Tel: 408-436-7950 Fax: 408-436-7955
Microchip Technology Beijing Office
Unit 915
New China Hong Kong Manhattan Bldg.
No. 6 Chaoyangmen Beidajie
Beijing, 100027, No. China
Tel: 86-10-85282100 Fax: 86-10-85282104
China - Shanghai
Microchip Technology Shanghai Office
Room 701, Bldg. B
Far East International Plaza
No. 317 Xian Xia Road
Shanghai, 200051
Tel: 86-21-6275-5700 Fax: 86-21-6275-5060
Hong Kong
Microchip Asia Pacific
RM 2101, Tower 2, Metroplaza
223 Hing Fong Road
Kwai Fong, N.T., Hong Kong
Tel: 852-2401-1200 Fax: 852-2401-3431
India
Microchip Technology Inc.
India Liaison Office
Divyasree Chambers
1 Floor, Wing A (A3/A4)
No. 11, OíShaugnessey Road
Bangalore, 560 025, India
Tel: 91-80-2290061 Fax: 91-80-2290062
Japan
Microchip Technology Intl. Inc.
Benex S-1 6F
3-18-20, Shinyokohama
Kohoku-Ku, Yokohama-shi
Kanagawa, 222-0033, Japan
Tel: 81-45-471- 6166 Fax: 81-45-471-6122
Korea
Microchip Technology Korea
168-1, Youngbo Bldg. 3 Floor
Samsung-Dong, Kangnam-Ku
Seoul, Korea
Tel: 82-2-554-7200 Fax: 82-2-558-5934
ASIA/PACIFIC
(continued)
Singapore
Microchip Technology Singapore Pte Ltd.
200 Middle Road
#07-02 Prime Centre
Singapore, 188980
Tel: 65-334-8870 Fax: 65-334-8850
Arizona Microchip Technology SARL
Parc díActivite du Moulin de Massy
43 Rue du Saule Trapu
Batiment A - ler Etage
91300 Massy, France
Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79