MICROCHIP TC7662A Technical data

M

Charge Pump DC-to-DC Converter

TC7662A

Features

• Wide Operating Range

- 3V to 18V

• Increased Output Current (40mA)

• Pin Compatible with ICL7662/SI7661/TC7660/
LTC1044

• No External Diodes Required

• Low Output Impedance @ I

-40Ω Typ.

• No Low-Voltage Terminal Required

• CMOS Construction

• Available in 8-Pin PDIP and 8-Pin CERDIP

Packages

= 20mA

L

Applications

• Laptop Computers

• Disk Drives

• Process Instrumentation

• µP-based Controllers

Device Selection Table

Part

Number

TC7662ACPA 8-Pin PDIP 0°C to +70°C
TC7662AEPA 8-Pin PDIP -40°C to +85°C

TC7662AIJA 8-Pin CERDIP -25°C to +85°C

TC7662AMJA 8-Pin CERDIP -55°C to +125°C

Package

Operating

Temp.

Range

Package Type

8-Pin PDIP

8-Pin CERDIP

NC

C

1

+

2

8

V

DD

7

OSC

TC7662A

GND

C

3

–

4

6

NC

V

5

OUT

General Description

The TC7662A is a pin-compatible upgrade to the
industry standard TC7660 charge pump voltage
converter. It converts a +3V to +18V input to a
corresponding -3V to -18V output using only two low­cost capacitors, eliminating inductors and their
associated cost, size and EMI. In addition to a wider
power supply input range (3V to 18V versus 1.5V to
10V for the TC7660), the TC7662A can source output
currents as high as 40mA. The on-board oscillator
operates at a nominal frequency of 12kHz. Operation
below 12kHz (for lower supply current applications) is
also possible by connecting an ex tern al ca pacitor from
OSC to ground.

The TC7662A directly is recommended for designs
requiring greater output current and/or lower input/
output voltage drop. It is available in 8-pin PDIP and
CERDIP packages in commercial and extended
temperature ranges.

 2002 Microchip Technology Inc. DS21468B-page 1

TC7662A

Functional Block Diagram

+

–

DS21468B-page 2  2002 Microchip Technology Inc.

TC7662A

1.0 ELECTRICAL
CHARACTERISTICS

Absolute Maximum Ratings*

Supply Voltage VDD to GND.................................+18V

Input Voltage (Any Pin).........(V

+ 0.3) to (V

DD

SS

– 0.3)

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.

Current into Any Pin............................................10mA

Output Short Circuit ........... Continuous (at 5.5V Input)

ESD Protection ................................................±2000V

Package Power Dissipation (T

≤ 70°C)

A

8-Pin CERDIP..........................................800mW

8-Pin PDIP...............................................730mW

Package Thermal Resistance
CPA, EPA θ
IJA, MJA θ

.........................................140°C/W

JA

............................................90°C/W

JA

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

TC7662A ELECTRICAL SPECIFICATIONS

Electrical Characteristics: VDD = 15V, TA = +25°C, Test circuit (Figure 3- 1) unless otherw ise noted.

Symbol Parameter Min Typ Max Units Test Conditions

V
I

R

F
P

V

DD

S

O

OSC
EFF

EFF

Supply Voltage 3 — 18 V
Supply Current —

—
—
—
—
—
—

Output Source Resistance —

—
—

Oscillator Frequency — 12 — kHz
Power Efficiency 93

—

Voltage Efficiency 99

—

96

—

510
560
650
190
210
210

40
50

100

97

—

99.9

—
—

—

700

—
—
—
—
—

50
60

125

—
—

—
—
—

µAR

Ω I

%VDD = +15V

%VDD = +15V

= ∞

L

VDD = +15V
0

°C ≤ T

≤ +70°C

A

≤ T

= +5V

≤ T

= 2kΩ

= ∞

≤ +125°C

A

≤ +70°C

A

≤ +125°C

A

-55°C
V

DD

0

°C ≤ T

-55°C
= 20mA, VDD = +15V

L

I

= 40mA, VDD = +15V

L

= 3mA, VDD = +5V

I

L

R

L

R

L

Over operating temperature range.

 2002 Microchip Technology Inc. DS21468B-page 3

TC7662A

2.0 PIN DESCRIPTIONS

The descriptions of the pins are listed in Table 2-1.

TABLE 2-1: PIN FUNCTION TABLE

Pin No.

(8-Pin PDIP,

CERDIP)

1 NC No connection.
2C
3 GND Ground terminal.
4C
5V
6 NC No connection.
7 OSC Oscillator control input. Bypass with an external capacitor to slow the oscillator.
8V

Symbol Description

+

Charge pump capacitor positive terminal.

-

Charge pump capacitor negative terminal.

OUT

DD

Output voltage.

Power supply positive voltage input.

DS21468B-page 4  2002 Microchip Technology Inc.

TC7662A

3.0 DETAILED DESCRIPTION

The TC7662A is a c apac itive ch arge pump (sometime s
called a switched-capacitor circuit), where four
MOSFET switches con trol th e cha rge and disc harge of
a capacitor.

The functional block diag ram sho ws how the switc hin g
action works. SW1 and SW2 are turned on simulta­neously, charging C
assumes that th e ON resistance of the MOSFETs in
series with the capacitor produce a charging time
(3 time constants) less than the ON time provided by
the oscillator frequency, as shown:

3 (R

DS(ON) CP

In the next cycle, SW1 and SW2 are turned OFF and,
after a very short interval with all switches OFF
(preventing large currents from occurring due to cross
conduction), SW3 and SW4 are turn ed ON. The charge

is then transferred to CR, but with the polarity

in C

P

inverted. In this way, a negative voltage is derived.
An oscillator supplies pulses to a flip-flop that is fed to

a set of level shifters. These level shifters then drive
each set of switches at one-half the oscillator
frequency.

The oscillator has a pin that controls the frequency
of oscillation. Pin 7 can have a capacitor added that
is connected to ground. This will lower the frequency
of the oscillator by adding capacitance to the
internal timing capacitor of the TC7662A. (See Typical
Characteristics – Oscillator Frequency vs. C

FIGURE 3-1: TC7662A TEST CIRCUIT

NC

+

10µF

C

P

to the su pply vol tage, VDD. This

P

) <CP/(0.5 f

1

2

TC7662A

3

4

OSC

8

7

6

5

NC

).

C

OSC

.)

OSC

I

S

V

DD

(+5V)

I

L

R

L

V

OUT

(-5V)

C

10µF

R

+

3.1 Theoretical Power Efficiency
Considerations

In theory, a voltage converter can approach 100%
efficiency if cert a in co ndi tio ns are me t:

1. The drive circuitry consumes minimal power.

2. The output switches ha ve extremely low ON

resistance and virtually no offset.

3. The impedances of the pump and reservoir

capacitors are negligible at the pump frequency.

The TC7662A approaches these conditions for
negative voltage conversion if large values of C

are used.

C

R

and

P

Note: Energy is lost only in the transfer of charge

between capacitors if a change in voltage
occurs.

The energy lost is defined by:

2

E = 1/2 C

(V

P

2

– V

1

)

2

V1 and V2 are the volta ges o n CP during the pump and
transfer cycles. If the impedances of C

and CR are

P

relatively high a t the pump fre quency (ref er to Figure 3-

1), compared to the value of R

substantial di fference in voltage s V
it is desirable not only to make C

, there will be a

L

and V2. Therefore,

1

as large as possible

R

to eliminate output voltage ripple, but also to employ a
correspondingly large value for CP in order to achieve
maximum efficiency of operation.

3.2 Dos and Don’ts

• Do not exceed maximum supply voltages.

• Do not short circuit the output to V+ supply for

voltages above 5.5V for extended periods;
however , tran sie nt con di tion s inc lu din g st art-up
are okay.

• When using polarized capacitors in the inverting

mode, the + terminal of C
pin 2 of the TC7662A and the + terminal of C
must be connected to GND (pin 3).

• If the voltage supply driving the TC7662A 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 o f rise of the inpu t volt age
to less than 2V/µsec.

must be connected to

P

R

 2002 Microchip Technology Inc. DS21468B-page 5