8.3.8 Spread Spectrum Frequency Modulation

The TPS61033 provides a spread spectrum feature which reduces the EMI of the power supply over a wide

frequency range. The device uses a triangle jitter to spread the switching frequency with ±6% of normal

frequency. The frequency of the triangle jitter is typically 10KHz.

8.3.9 Overvoltage Protection

The TPS61033 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 5.75 V typically, the device stops switching. Once

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

8.3.10 Output Short-to-Ground Protection

The TPS61033 starts to limit the output current when the output voltage is below 1.8 V. 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 0.4 V, the output current is limited to approximately 330 mA. Once the short circuit is

released, the TPS61033 goes through the soft start-up again to the regulated output voltage.

8.3.11 Thermal Shutdown

The TPS61033 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.

8.4 Device Functional Modes

TPS61033 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.

8.4.1 PWM Mode

The TPS61033 uses a quasi-constant 2.4-MHz 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 TPS61033 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.

8.4.2 Power-Save Mode

The TPS61033 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 TPS61033 goes

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

voltage, the device continues switching for several cycles because of the delay time of the internal comparator

— then it stops switching. The load is supplied by the output capacitor, and the output voltage declines. When

the FB voltage falls below the PFM reference voltage, after the delay time of the comparator, the device starts

switching again to ramp up the output voltage.

TPS61033

SLVSGI6 – OCTOBER 2022

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