variation is typically between the nominal switching frequency and up to 288 kHz above the nominal switching

frequency. When the device is externally synchronized, the TPSM8281x follows the external clock and the

internal spread spectrum block is turned off. SSC is also disabled during soft start.

7.3.6 Undervoltage Lockout (UVLO)

If the input voltage drops, the undervoltage lockout prevents mis-operation of the device by switching off both the

MOSFETs. The device is fully operational for voltages above the rising UVLO threshold and turns off if the input

voltage goes below the falling threshold.

7.3.7 Power-Good Output (PG)

The device has a power-good output with window comparator. The PG pin goes high impedance after the FB

pin voltage is above 95% and less than 107% of the nominal voltage, and is driven low after the voltage falls

below 90% or rises higher than 110% of the nominal voltage (typical). Table 7-2 shows the typical PG pin logic.

The PG pin is an open-drain output and is specified to sink up to 2 mA. The power good output requires a pullup

resistor connected to any voltage rail less than VIN. The PG signal can be used for sequencing of multiple rails

by connecting to the EN pin of other converters. If not used, the PG pin can be left floating or connected to GND.

Table 7-2. Power-Good Pin Logic

DEVICE STATE

PG LOGIC STATUS

HIGH IMPEDANCE

LOW

Enabled (EN = High)

0.95 × VFB_NOM ≤ VFB ≤ 1.07 × VFB_NOM

√

VFB < 0.9 × VFB_NOM or VFB > 1.1 ×

VFB_NOM

√

Shutdown (EN = Low)

√

UVLO

2 V ≤ VIN < VUVLO

√

Thermal Shutdown

TJ > TJSD

√

Power Supply Removal

VIN < 2 V

undefined

The PG pin has a 40-μs deglitch time on the falling edge. See Figure 7-1.

VO

VTH,PG

VTH,PG

PG

UVP

VTH,PG

VTH,PG

OVP

tPG,DLY

tPG,DLY

tPG,DLY

tPG,DLY

Figure 7-1. Power-Good Transient and Delay Behavior

7.3.8 Thermal Shutdown

The junction temperature (TJ) of the device is monitored by an internal temperature sensor. If TJ exceeds 180°C

(typical), the device goes into thermal shutdown. Both the high-side and low-side power FETs are turned off and

PG goes low. When TJ decreases below the hysteresis amount of typically 15°C, the converter resumes normal

operation, beginning with soft start. During PFM the thermal shutdown is not active.

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TPSM82816

SLUSEY7A – DECEMBER 2022 – REVISED JUNE 2024

Copyright © 2024 Texas Instruments Incorporated

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