TPSM82821 datasheet(8/54 Pages) TI

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OUT

250ns

(1)

In PWM mode, the TPSM8282x operates with pulse width modulation in continuous conduction mode (CCM)

with a tON shown in Equation 1 at medium and heavy load currents. A PWM switching frequency of typically 4

MHz is achieved by this tON circuitry.

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.

The forced PWM version of this device, the TPSM8282xA, does not enter PSM (power save mode) at light load

currents and stays in CCM (continuous conduction mode) regardless of the output current in order to minimize

the output ripple.

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.

TPSM82823, TPSM82822, TPSM82821, TPSM82823A, TPSM82822A, TPSM82821A

SLVSEP0F – AUGUST 2019 – REVISED NOVEMBER 2021

www.ti.com

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TPSM82821 Datasheet(PDF) 8 Page - Texas Instruments

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