PTH05050WAS datasheet(12/22 Pages) TI

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Output On/Off Inhibit

Vo (2V/Div)

Iin (2A/Div)

Q1Vds (5V/Div)

10 ms/div

PTH05020W

V IN

CIN

1,000

µF

COUT

330

µF

1 =Inhibit

GND

V OUT

Vo Sense

BSS138

RSET

GND

Auto-Track™ Function

PTH05050W

SLTS213D – MAY 2003 – REVISED JUNE 2007

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

Inhibit control pin. The inhibit feature can be used wherever there is a requirement for the output voltage from

the regulator to be turned off. The power modules function normally when the Inhibit pin is left open-circuit,

providing a regulated output whenever a valid source voltage is connected to VI with respect to GND.

Figure 8 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit control

has its own internal pull-up to Vin potential. The input is not compatible with TTL logic devices. An open-collector

(or open-drain) discrete transistor is recommended for control.

Figure 8.

Figure 9.

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

turned off, the module will execute a soft-start power-up. A regulated output voltage is produced within 20 msec.

Figure 9 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 5-A load.

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.

How Auto-Track™ Works

Auto-Track works by forcing the module output voltage to follow a voltage presented at the Track control pin(1).

This control range is limited to between 0 V and the module set-point voltage. Once the track-pin voltage is

raised above the set-point voltage, the module output remains at its set-point(2). As an example, if the Track pin

of a 2.5-V regulator is at 1 V, the regulated output is 1 V. If the voltage at the Track pin rises to 3 V, the

regulated output does not go higher than 2.5 V.

Under Auto-Track control, the regulated output from the module follows the voltage at its Track pin on a

volt-for-volt basis. By connecting the Track pin of a number of these modules together, the output voltages follow

a common signal during power up and power down. The control signal can be an externally generated master

ramp waveform, or the output voltage from another power supply circuit(3). For convenience, the Track input

incorporates an internal RC-charge circuit. This operates off the module input voltage to produce a suitable

rising waveform at power up.

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