TPS6734I

FIXED 12-V 120-mA BOOST-CONVERTER SUPPLY

SLVS127A – AUGUST 1995 – REVISED JANUARY 1999

5

POST OFFICE BOX 655303

soft start

Soft start causes the output voltage to increase to the regulation point at a controlled rate of rise. 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. Even if SS has

no capacitor installed, some distributed capacitance will always be present. A soft-start cycle is initiated when

either the enable signal (EN) is switched high, or an overcurrent fault condition triggers the discharge of the

soft-start capacitor.

overcurrent comparator

The overcurrent comparator monitors the current in the power switch. The comparator trips and initiates a

soft-start cycle if the power-switch current exceeds 1.5-A peak. On each clock cycle, the power switch turns on

and attempts to deliver current until the overcurrent limits are exceeded.

enable (EN)

A logic low on EN puts the TPS6734 in shutdown mode. In shutdown, the output power switch, voltage

reference, and other functions are shut off, the supply current is reduced to 3

µA maximum, and the soft-start

capacitor is discharged through a 1-M

Ω resistance. The output voltage falls to a diode drop below the input

voltage because of the current path from input to output through the inductor and diode.

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

– 0.3 V to 15 V

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

SS, COMP, EN (see Note 1)

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

Peak switch current

1.5 A

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

Reference current

2.5 mA

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

Continuous power dissipation

See Dissipation Rating Table

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

–40

°C to 85°C

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

–65

°C to 150°C

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

Lead temperature 1,6 mm (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.