Outputvoltage

Vout (PWM)

Vout +1%

PFMComparator

threshold

VoltagePositioning

Lightload

PFMMode

moderatetoheavyload

PWMMode

TPS62590

SLVS897B

– JANUARY 2009 – REVISED APRIL 2011

www.ti.com

Figure 19. Power Save Mode Operation

100% Duty Cycle Low Dropout Operation

The device starts to enter 100% duty cycle Mode once the input voltage comes close the nominal output voltage.

To maintain the output voltage, the High-Side MOSFET switch is turned on 100% for one or more cycles.

With further decreasing VIN the High-Side MOSFET switch is turned on completely. In this case, the converter

offers a low input-to-output voltage difference. 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 regulation depends on the load current and output voltage, and can be

calculated as:

With:

Undervoltage Lockout

The undervoltage lockout circuit prevents the device from malfunctioning at low input voltages and from

excessive discharge of the battery and disables the output stage of the converter. The undervoltage lockout

MODE SELECTION

The MODE pin allows mode selection between forced PWM mode and Power Save Mode.

Connecting this pin to GND enables the Power Save Mode with automatic transition between PWM and PFM

mode. Pulling the MODE pin high forces the converter to operate in fixed frequency PWM mode even at light

load currents. This allows simple filtering of the switching frequency for noise sensitive applications. In this mode,

the efficiency is lower compared to the power save mode during light loads.

The condition of the MODE pin can be changed during operation and allows efficient power management by

adjusting the operation mode of the converter to the specific system requirements.

12

Copyright

© 2009–2011, Texas Instruments Incorporated