Datasheet

PFMModeatLightLoad

PFMRipple

PWMModeatHeavyLoad

NominalDCOutputVoltage

TPS62660, TPS62665

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SLVS871C –FEBRUARY 2010– REVISED JULY 2011

Figure 41. 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 operates with a fixed frequency that 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.

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

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

requirements.

ENABLE

The device starts operation when EN is set high and starts up with the soft start as previously described. For

proper operation, the EN pin must be terminated and must not be left floating.

Pulling the EN pin low forces the device into shutdown, with a shutdown quiescent current of typically 0.1μA. In

this mode, the P and N-channel MOSFETs are turned off, the internal resistor feedback divider is disconnected,

and the entire internal-control circuitry is switched off.

SOFT START

The TPS62660/62 has an internal soft-start circuit that limits the inrush current during start-up. This limits input

voltage drops when a battery or a high-impedance power source is connected to the input of the converter.

The soft-start system progressively increases the on-time from a minimum pulse-width of 35ns as a function of

the output voltage. This mode of operation continues for c.a. 100μs after enable. Should the output voltage not

have reached its target value by this time, such as in the case of heavy load, the soft-start transitions to a second

mode of operation.

The converter then operates in a current limit mode, specifically the P-MOS current limit is set to half the nominal

limit, and the N-channel MOSFET remains on until the inductor current has reset. After a further 100 μs, the

device ramps up to the full current limit operation if the output voltage has risen above 0.5V (approximately).

Therefore, the start-up time mainly depends on the output capacitor and load current.

The TPS62661 device starts-up immediately into a nominal current limit mode thereby ramping-up the output

voltage with maximum speed (<60μs typ.). The start-up time mainly depends on the output capacitor and load

current.