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POWER-UP INTO A NON-PREBIASED OUTPUT — AUTO-TRACK™ FUNCTION

UDG−06074

2 k

Ω

0.1 W

1 %

330

µF

560

µF

2

8

1

7

3

9

10

PTH12060W

4

6

+

GND

L

O

A

D

Q1

BSS138

1=Turn−Off

+

Margin

Down

Margin

Up

Inhibit

Track

GND

GND

VoAdj

5

PTH12050W/L

SLTS214H – MAY 2003 – REVISED OCTOBER 2007

The Auto-Track function is unique to the PTH/PTV family, and is available with all POLA products. Auto-Track

was designed to simplify the amount of circuitry required to make the output voltage from each module power up

and power down in sequence. The sequencing of two or more supply voltages during power up is a common

requirement for complex mixed-signal applications that use dual-voltage VLSI ICs such as the TMS320™ DSP

family, microprocessors, and ASICs.

Basic Power-Up Using Auto-Track™

For applications requiring output voltage on/off control, each series of the PTH family incorporates the track

control pin. The Auto-Track feature should be used instead of the inhibit feature wherever there is a requirement

for the output voltage from the regulator to be turned on/off.

Figure 11 shows the typical application for basic start-up. Note the discrete transistor (Q1). The track input has

its own internal pull-up to a potential of 5 V to 13.2 V The input is not compatible with TTL logic devices. An

open-collector (or open-drain) discrete transistor or supply voltage supervisor (TPS3808 or TPS7712) is

recommended for control.

Figure 11. Basic Start-up Control Circuit

Turning on Q1 applies a low voltage to the track control pin and disables the output of the module. If Q1 is then

turned off, the output ramps immediately to the regulated output voltage. A regulated output voltage is produced

within 35 ms. With the initial application of the input source voltage, the track pin must be held low (Q1 turned

ON) for at least 40 ms. Figure 12 shows the typical rise in both the output voltage and input current, following the

turn off of Q1. The turn off of Q1 corresponds to the rise in the waveform, Q1 Vds. The waveforms were

measured with a 10-A constant current load.

Copyright © 2003–2007, Texas Instruments Incorporated

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