PFMModeatLightLoad

PFMRipple

PWMModeatHeavyLoad

NominalDCOutputVoltage

(

)

IN

OUT

OUT

DS(on)

L

V min = V

max + I

max

R

max + R

´

TPS62690

TPS62691

TPS62697

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SLVS965B

– MARCH 2011 – REVISED JANUARY 2012

Figure 35. Operation in PFM Mode and Transfer to PWM Mode

MODE SELECTION

The MODE pin allows to select the operating mode of the device. Connecting this pin to GND enables the

automatic PWM and power-save mode operation. The converter operates in regulated frequency PWM mode at

moderate to heavy loads and in the PFM mode during light loads, which maintains high efficiency over a wide

load current range.

Pulling the MODE pin high forces the converter to operate in the PWM mode even at light load currents. The

advantage is that the converter modulates its switching frequency according to a spread spectrum PWM

modulation technique allowing simple filtering of the switching harmonics in noise-sensitive applications. In this

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

For additional flexibility, it is possible to switch from power-save mode to PWM mode during operation. This

allows efficient power management by adjusting the operation of the converter to the specific system

requirements.

LOW DROPOUT, 100% DUTY CYCLE OPERATION

The device starts to enter 100% duty cycle mode once input and output voltage come close together. In order to

maintain the output voltage, the P-channel MOSFET is turned on 100% for one or more cycles.

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:

(1)

With:

Copyright

© 2011–2012, Texas Instruments Incorporated

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