TPS6735

FIXED NEGATIVE 5V 200mA INVERTING DC/DC CONVERTER

SLVS141A − JULY 1996 − REVISED JANUARY 1997

5

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251−1443

SS clamp

The SS clamp circuit limits the signal level on error-amplifier output during start-up. The voltage on SS is

amplified and used to override the error-amplifier output until it rises above that output, at which point the error

amplifier takes over. This prevents the input to the PWM comparator from exceeding its common-mode range

(i.e., error amplifier output too high to be reached by the current ramp) by limiting the maximum voltage on the

error-amplifier output during start-up.

Soft start causes the output voltage to increase to the regulation point at the controlled rate. The voltage on the

charging soft-start capacitor gradually raises the clamp on the error amplifier output voltage, limiting surge

currents at power up by increasing the current limit threshold on a cycle-by-cycle basis. A soft-start cycle is

initiated when either the enable (EN) signal is switched high or an overcurrent fault condition triggers the

discharge of the soft-start capacitor.

undervoltage lockout (UVLO)

The supply voltage is fed through a voltage divider to the input of the UVLO and compared to a reference. The

undervoltage-lockout logic prevents the MOSFET from turning on while the supply voltage is below the

undervoltage-lockout voltage threshold, and once the supply voltage on VCC is above the threshold, an SS cycle

is initiated.

DISSIPATION RATING TABLE

PACKAGE

TA ≤ 25°C

POWER RATING

DERATING FACTOR

ABOVE TA = 25°C

TA = 70°C

POWER RATING

TA = 85°C

POWER RATING

D

725 mW

5.8 mW/

°C

464 mW

377 mW

P

1175 mW

9.4 mW/

°C

752 mW

611 mW

absolute maximum ratings over operating free-air temperature range (unless otherwise noted)†

Pin voltages:

VCC (see Note 1)

−0.3 V to 7 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OUT to VCC

12.5 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FB (see Note 1)

25 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS, COMP, EN voltage range (see Note 1)

−0.3 V to VCC +0.3 V

. . . . . . . . . . . . . . . . . . . .

Peak switch current

2 A

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reference current

2.5 mA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Continuous total power dissipation

See Dissipation Rating Table

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operating free-air temperature range, TA

−40

°C to 85°C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Storage temperature range, Tstg

−65

°C to 150°C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Lead temperature 1,6mm (1/16 inch) from case for 10 s

260

°C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

† Stresses beyond 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 beyond those indicated under “recommended operating conditions” is not

implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

NOTE 1: All voltage values are with respect to network terminal ground.

recommended operating conditions

MIN

NOM

MAX

UNIT

Supply voltage

4

6.2

V

Decoupling capacitor

1

µF

Input capacitor

47

µF

Reference capacitor

10

µF

Output capacitor

100

µF

Compensation capacitor

82

pF

Inductor

10

µH