MICROCHIP TC7662A Technical data

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

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

OSC

TC7662A

GND

–

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

– 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)

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

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

Package Thermal Resistance CPA, EPA θ IJA, MJA θ

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

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

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

F P

OSC EFF

EFF

Supply Voltage 3 — 18 V Supply Current —

— — — — — —

Output Source Resistance —

— —

Oscillator Frequency — 12 — kHz Power Efficiency 93

—

Voltage Efficiency 99

—

510 560 650 190 210 210

40 50

100

—

99.9

— —

—

700

— — — — —

50 60

125

— —

— — —

µAR

Ω I

%VDD = +15V

= ∞

VDD = +15V 0

°C ≤ T

≤ +70°C

≤ T

= +5V

≤ T

= 2kΩ

= ∞

≤ +125°C

≤ +70°C

≤ +125°C

-55°C V

°C ≤ T

-55°C = 20mA, VDD = +15V

= 40mA, VDD = +15V

= 3mA, VDD = +5V

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

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

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

10µF

to the su pply vol tage, VDD. This

) <CP/(0.5 f

TC7662A

OSC

(+5V)

OUT

(-5V)

10µF

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.

and

Note: 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

– V

)

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

and CR are

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

and V2. Therefore,

as large as possible

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

 2002 Microchip Technology Inc. DS21468B-page 5

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