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DESCRIPTION (CONT.)

DEVICE RATINGS

ABSOLUTE MAXIMUM RATINGS

RECOMMENDED OPERATING CONDITIONS

TPS40042

SLUS777 – NOVEMBER 2007

One of three short circuit threshold levels may be selected by the addition of an external resistor from the COMP

pin to circuit ground (no resistor is the default setting). During power on, and before the internal soft start

commands the output voltage to rise, the TPS40042 enters a calibration cycle, measures the current out of the

COMP pin, and selects an internal SCP threshold voltage. At the end of the 1.5-ms calibration time, the output

voltage is allowed to enter soft-start. During operation, the selected SCP threshold voltage is compared to the

upper MOSFET’s voltage drop during its ON time to determine whether there is an overload condition. If the

voltage across the MOSFET exceeds the threshold voltage, the TPS40042 counts seven continuous pulses

before shutting completely OFF for seven soft start charge/discharge cycles, after which, the TPS40042 attempts

to restart the output.

During startup, both the high-side MOSFET switch and the synchronous rectifier are held in the OFF state until

the internal soft start commands an output voltage higher than the voltage currently at the output. This may

happen when the output is pre-biased at some voltage greater than zero and less than the desired regulation

voltage. When the internal soft start first commands the output to rise, the pulse width of the synchronous

rectifier is slowly increased from zero to the full 1-D conduction time by a number of discrete steps. In this way,

inductor current is not allowed to reverse quickly, and ensures a monotonic startup of the output whether the

output starts from zero or from a pre-bias level. If power is applied to the device while the EN (enable low) pin is

allowed to float high, the TPS40042 remains OFF. Only when the EN pin is pulled down towards ground is the

controller allowed to start.

ORDERING INFORMATION

OPERATING FREQUENCY

PACKAGE

TAPE AND REEL QTY.

PART NUMBER

600 kHz

Plastic 10-pin SON (DRC)

250

TPS40042DRCT

600 kHz

Plastic 10-pin SON (DRC)

3000

TPS40042DRCR

Over operating free-air temperature range (unless otherwise noted, all voltages are with respect to GND.)

PARAMETER

VALUE

UNIT

VDD

6.5

SW

-3 to 10.5

SW

transient (< 50 ns)

-5

BOOT

SW+6.5

V

HDRV

SW to SW+6.5

EN, FB, LDRV

-0.3 to 6.5

,REFIN

COMP

-0.3 to 3

Operating junction temperature

-40 to 150

°C

Storage junction temperature

-55 to 150

over operating free-air temperature range (unless otherwise noted)

PARAMETER

MIN

TYP

MAX

UNIT

Input voltage to VDD pin

3.0

5.5

V

Voltage applied to REFIN pin during regulation

0.5

1.5

V

Junction temperature

-40

125

°C

2

Copyright © 2007, Texas Instruments Incorporated

Product Folder Link(s): TPS40042