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Overtemperature Protection (OTP)

Auto-Track™ Function

How Auto-Track™ Works

Typical Application

PTH05T210W

SLTS263D – NOVEMBER 2005 – REVISED OCTOBER 2006

A thermal shutdown mechanism protects the module’s internal circuitry against excessively high temperatures. A

rise in the internal temperature may be the result of a drop in airflow, or a high ambient temperature. If the

internal temperature exceeds the OTP threshold, the module’s Inhibit control is internally pulled low. This turns

the output off. The output voltage drops as the external output capacitors are discharged by the load circuit. The

recovery is automatic, and begins with a soft-start power up. It occurs when the sensed temperature decreases

by about 10

°C below the trip point.

The overtemperature protection is a last resort mechanism to prevent thermal stress to the regulator.

Operation at or close to the thermal shutdown temperature is not recommended and reduces the long-term

reliability of the module. Always operate the regulator within the specified safe operating area (SOA) limits

for the worst-case conditions of ambient temperature and airflow.

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.

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

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.

When 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

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

rising waveform at power up.

The basic implementation of Auto-Track allows for simultaneous voltage sequencing of a number of Auto-Track

compliant modules. Connecting the Track inputs of two or more modules forces their track input to follow the

same collective RC-ramp waveform, and allows their power-up sequence to be coordinated from a common

Track control signal. This can be an open-collector (or open-drain) device, such as a power-up reset voltage

supervisor IC. See U3 in Figure 18.

To coordinate a power-up sequence, the Track control must first be pulled to ground potential. This should be

done at or before input power is applied to the modules. The ground signal should be maintained for at least

20 ms after input power has been applied. This brief period gives the modules time to complete their internal

that includes a built-in time delay, is an ideal component for automatically controlling the Track inputs at power

up.

Figure 18 shows how a TPS3808 supply voltage supervisor IC (U3) can be used to coordinate the sequenced

power up of 5-V PTH modules. The output of the TPS3808 supervisor becomes active above an input voltage of

0.8 V, enabling it to assert a ground signal to the common track control well before the input voltage has

reached the module's undervoltage lockout threshold. The ground signal is maintained until approximately 27 ms

after the input voltage has risen above U3's voltage threshold, which is 4.65 V. The 27-ms time period is

controlled by the capacitor C3. The value of 4700 pF provides sufficient time delay for the modules to complete

their internal soft-start initialization. The output voltage of each module remains at zero until the track control

voltage is allowed to rise. When U3 removes the ground signal, the track control voltage automatically rises.

This causes the output voltage of each module to rise simultaneously with the other modules, until each reaches

its respective set-point voltage.

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