Microchip Technology TC7662AMJA, TC7662AEPA, TC7662ACPA Datasheet

EVALUATION

KIT

AVAILABLE

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 @ IL = 20mA .......40Ω Typ.

■ No Low-Voltage Terminal Required

■ CMOS Construction

ORDERING INFORMATION

Temperature

Part No. Package Range

TC7662ACPA 8-Pin Plastic DIP 0°C to +70°C
TC7662AEPA 8-Pin Plastic DIP – 40°C to +85°C
TC7662AIJA 8-Pin CerDIP – 25°C to +85°C
TC7662AMJA 8-Pin CerDIP – 55°C to +125°C

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 low-cost 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 10kHz (for lower supply current applications) is also
possible by connecting an external capacitor 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.

PIN CONFIGURATION

PDIP/CerDIP

NC

C

GND

C

+

–

1
2
3

TC7662A

4

8

V

DD

OSC

7
6

NC

5

V

OUT

FUNCTIONAL BLOCK DIAGRAM

C

OSC

© 2001 Microchip Technology Inc. DS21468

NC = NO INTERNAL CONNECTION

8

V

P SW1

N SW4

N SW2

N SW3

DD

TC7662A

2

+

CAP

+

C

P

EXT

GND
3

+

OUT

C

R

EXT

4

–

CAP

5
V

OUT

R

L

TC7662A-5 9/11/96

I

7

LEVEL

SHIFT

LEVEL

SHIFT

LEVEL

SHIFT

LEVEL

SHIFT

+
–

COMPARATOR
WITH HYSTERESIS

V

REF

Q

F/F

C

Q

TC7662A

CHARGE PUMP DC-TO-DC CONVERTER

ABSOLUTE MAXIMUM RATINGS*

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

Input Voltage (Any Pin) ........... (VDD + 0.3) to (VSS – 0.3)

Current Into Any Pin.................................................10mA

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

Power Dissipation (TA ≤ 70°C)

Plastic DIP......................................................730mW

CerDIP ...........................................................800mW

SOIC...........................................................................

ELECTRICAL CHARACTERISTICS: V

= 15V, TA = +25°C (See Test Circuit), unless otherwise specified.

DD

Package Thermal Resistance

CPA, EPA θJA.............................................. 140°C/W

IJA, MJA θJA.................................................. 90°C/W

Storage Temperature Range ................– 65°C to +150°C

Lead Temperature (Soldering, 10 sec) .................+300°C

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

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

* 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 operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.

Symbol Parameter Test Conditions Min Typ Max Unit

V
I

R

C
P

V

DD

S

O

OSC
EFF

EFF

Supply Voltage 3 — 18 V
Supply Current RL = ∞

= +15V — 510 700 µA

V

DD

0°C ≤ T
– 55°C ≤ T
V
0°C ≤ T

≤ +70°C — 560 —

A

≤ +125°C — 650 —

A

= +5V — 190 —

DD

≤ +70°C — 210 —

A

– 55°C ≤ TA ≤ +125°C — 210 —

Output Source IL = 20mA, VDD = +15V — 40 50 Ω
Resistance I

= 40mA, VDD = +15V — 50 60

L

IL = 3mA, VDD = +5V — 100 125
Oscillator Frequency — 12 — kHz
Power Efficiency VDD = +15V 93 97 — %

RL = 2 kΩ
Voltage Efficiency VDD = +15V 99 99.9 — %

= ∞

R

L

Over Operating Temperature Range 96 — —

TC7662A-5 9/11/96

2

© 2001 Microchip Technology Inc. DS21468

CHARGE PUMP DC-TO-DC CONVERTER

TTL

Q

Q

100 k

TO PIN 7
TC7662A

TC7662A

TEST CIRCUIT

I

S

NC

C

1
2

+

10 µF

P

3
4

TC7662A

8
7

6

NC

5

C

OSC

C

R

+

I

L

R

L

10 µF

+

V
(+5V)

V

OUT

(–5V)

APPLICATIONS INFORMATION
Theory of Operation

The TC7662A is a capacitive charge pump (some­times called a switched-capacitor circuit), where four
MOSFET switches control the charge and discharge of a
capacitor.

The functional diagram (page 1) shows how the switch­ing action works. SW1 and SW2 are turned on simulta­neously, charging C1 to the supply voltage, VDD. This
assumes that the 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

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 turned ON. The charge in C1 is then
transferred to C
VERTED. 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 Oscillator Frequency vs. C
page 5.)

C1) <C1/(0.5 f

DS(ON)

, BUT WITH THE POLARITY IN-

OUT

OSC

).

EXT

EPR

ESL

Figure 1. Capacitor Equivalent Circuit

ESR

C

Note one of its characteristics is ESR (equivalent series
resistance). This parasitic resistance winds up in series with
the load. Thus, both voltage and power conversion effi­ciency are compromised if a low ESR capacitor is not used.

For example, in the "Test Circuit", changing CP and C
capacitors from typical ESR to low ESR types, the effective
converter output impedance changed from 45Ω to 40Ω, an
improvement of 12%.

This applies to all types of capacitors, including film
types (polyester, polycarbonate etc.).

Some applications information suggests that the ca­pacitor is not critical and attributes the limiting factor to the
capacitor's reactance value. Let's examine this:

XC =

1

2πf C

and ZC = ,

X

DS

C

where DS (duty cycle) = 50%.

Thus, ZC ≈ 1.33Ω at f = 12kHz, where C = 10µF.

For the TC7662A, f = 12,000Hz, and a typical value of
C would be 10µF. This is a reactive impedance of ≈1.33Ω.
If the ESR is as great as 5Ω, the reactive value is not as
critical as it would first appear, since the ESR would dominate.
The 5Ω value is typical of a general-purpose electrolytic
capacitor.

Synchronizing

The TC7662A may be synchronized by connecting pin
7 of the TC7662A through a 100k resistor in series with a
diode to a negative-going pulse source. The negative pulse
voltage can be +5V with a 5 microsecond duration going
negative to 0V.

,

R

Capacitors

In early charge pump converters, capacitors were not
considered critical due to the high R
switches. In order to understand this, let’s look at a model of
a typical electrolytic capacitor (Figure 1).

© 2001 Microchip Technology Inc. DS21468

of the MOSFET

DS(ON)

Figure 2. Synchronization

3

TC7662A-5 9/11/96