TPSM828213SILR datasheet(9/44 Pages) TI

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To maintain high efficiency at light loads, the device enters Power-Save Mode seamlessly when the load current

decreases. This happens when the load current becomes smaller than half the ripple current of the inductor. The

output current at which this occurs can be approximated with the following equation:

IOUT(PSM-entry)=VIN×tON

−VOUTVINL

(2)

In PSM, the converter operates with a reduced switching frequency and with a minimum quiescent current to

maintain high efficiency. The on-time in PSM is also based on the same tON circuitry. The switching frequency in

PSM is estimated as:

OUT

PSM

OUT

(3)

In PSM, the output voltage rises slightly above the nominal output voltage in PWM mode. This effect is reduced

by increasing the output capacitance.

8.3.2 Low Dropout Operation (100% Duty Cycle)

The device offers a low input-to-output voltage differential by entering 100% duty cycle mode. In this mode, the

high-side MOSFET switch is constantly turned on. This is particularly useful in battery-powered applications to

achieve longest operation time by taking full advantage of the whole battery voltage range. The minimum input

voltage to maintain a minimum output voltage is given by:

VIN (min) = VOUT (min) + IOUT × RDP

(4)

where

• RDP = Resistance from VIN to VOUT, which includes the high-side MOSFET on-resistance and DC resistance

of the inductor

• VOUT (min) = Minimum output voltage the load can accept

8.3.3 Soft Start-up

After enabling the device, there is a 250-µs delay before switching starts. Then, an internal soft start-up circuitry

ramps up the output voltage which reaches nominal output voltage during the start-up time of 1 ms. This avoids

excessive inrush current and creates a smooth output voltage rise slope. It also prevents excessive voltage

drops of primary cells and rechargeable batteries with high internal impedance.

The device is able to start into a pre-biased output capacitor. It starts with the applied bias voltage and ramps the

output voltage to its nominal value.

8.3.4 Switch Current Limit and Hiccup Short Circuit Protection

The switch current limit prevents the device from high inductor current and from drawing excessive current from

the battery or input voltage rail. Excessive current can occur with a shorted or saturated inductor or a heavy load

or shorted output circuit condition. If the inductor current reaches the threshold of ILIMF, the high-side MOSFET

is turned off and the low-side MOSFET remains off while the inductor current flows through its body diode and

quickly ramps down.

When this switch current limit is triggered 32 times, the device stops switching. The device then automatically

starts a new start-up after a typical delay time of 128 µs has passed. This is named HICCUP short-circuit

protection. The device repeats this mode until the high load condition disappears.

8.3.5 Undervoltage Lockout

To avoid mis-operation of the device at low input voltages, undervoltage lockout is implemented that shuts down

the device at voltages lower than VUVLO.

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TPSM82823, TPSM82822, TPSM82821

SLVSEP0E – APRIL 2018 – REVISED MAY 2021

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