Output voltage

Light load

PFM Mode

V

(PWM)

OUT

V

+ 1%

PFM Comparator

threshold

OUT

Voltage Positioning

Moderate to heavy load

PWM Mode

TLV62065

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SLVSAC4B – NOVEMBER 2010 – REVISED DECEMBER 2015

Device Functional Modes (continued)

During the power-save mode, the output voltage is monitored with a PFM comparator. As the output voltage falls

below the PFM comparator threshold of VOUTnominal +1%, the device starts a PFM current pulse. For this the high-

side MOSFET switch will turn on and the inductor current ramps up. After the ON-time expires the switch will be

turned off and the low-side MOSFET switch will be turned on until the inductor current becomes zero.

The converter effectively delivers a current to the output capacitor and the load. If the load is below the delivered

current the output voltage will rise. If the output voltage is equal or higher than the PFM comparator threshold,

the device stops switching and enters a sleep mode with typical 18-µA current consumption.

In case the output voltage is still below the PFM comparator threshold, further PFM current pulses will be

generated until the PFM comparator threshold is reached. The converter starts switching again once the output

voltage drops below the PFM comparator threshold due to the load current.

The PFM mode is exited and PWM mode entered in case the output current can no longer be supported in PFM

mode.

Figure 7. Power-Save Mode Operation With Automatic Mode Transition

7.4.2.1 100% Duty Cycle Low Dropout Operation

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

In order 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 by Equation 1:

VINmin = VOmax + IOmax × (RDS(on)max + RL)

where

•

IOmax = maximum output current

•

RDS(on)max = maximum P-channel switch RDS(on)

•

RL = DC resistance of the inductor

•

VOmax = nominal output voltage plus maximum output voltage tolerance

(1)

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