PVIN

EN

VOUT

FB

GND

L1

OFF

ON

C1

C2

MODE

PFM

PWM

PG

R1

R2

RDummy

TPSM81033

SW

AVIN

Output

Voltage

time

PG

time

tglitch

Output voltage

discharge from RDummy

EN

Figure 6-1. Implement Output Discharge by PG function

6.3.8 Overvoltage Protection

The TPSM81033 has an output overvoltage protection (OVP) to protect the device if the external feedback

resistor divider is wrongly populated. When the output voltage is above 5.75V typically, the device stops

switching. Once the output voltage falls 0.1V below the OVP threshold, the device resumes operating again.

6.3.9 Output Short-to-Ground Protection

The TPSM81033 starts to limit the output current when the output voltage is below 1.8V. The lower the output

voltage reaches, the smaller the output current is. When the VOUT pin is short to ground, and the output voltage

becomes less than 0.4V, the output current is limited to approximately 330mA. Once the short circuit is released,

the TPSM81033 goes through the soft start-up again to the regulated output voltage.

6.3.10 Thermal Shutdown

The TPSM81033 goes into thermal shutdown once the junction temperature exceeds 170°C. When the

junction temperature drops below the thermal shutdown recovery temperature, typically 155°C, the device starts

operating again.

6.4 Device Functional Modes

TPSM81033 has two optional modes in light load by configuring the MODE pin: auto PFM mode and forced

PWM to balance the efficiency and noise immunity in light load.

6.4.1 PWM Mode

The TPSM81033 uses a quasi-constant 2.4MHz frequency pulse width modulation (PWM) at moderate to heavy

load current. Based on the input voltage to output voltage ratio, a circuit predicts the required on-time. At the

beginning of the switching cycle, the NMOS switching FET. The input voltage is applied across the inductor and

the inductor current ramps up. In this phase, the output capacitor is discharged by the load current. When the

on-time expires, the main switch NMOS FET is turned off, and the rectifier PMOS FET is turned on. The inductor

transfers its stored energy to replenish the output capacitor and supply the load. The inductor current declines

because the output voltage is higher than the input voltage. When the inductor current hits the valley current

threshold determined by the output of the error amplifier, the next switching cycle starts again.

The TPSM81033 has a built-in compensation circuit that can accommodate a wide range of input voltage, output

voltage, inductor value, and output capacitor value for stable operation.

6.4.2 Power-Save Mode

The TPSM81033 integrates a power-save mode with PFM to improve efficiency at light load. When the load

current decreases, the inductor valley current set by the output of the error amplifier no longer regulates the

output voltage. When the inductor valley current hits the low limit, the output voltage exceeds the setting voltage

as the load current decreases further. When the FB voltage hits the PFM reference voltage, the TPSM81033

goes into the power-save mode. In the power-save mode, when the FB voltage rises and hits the PFM reference

TPSM81033

SLVSHL0D – JUNE 2024 – REVISED DECEMBER 2024

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