Datasheet
Outputvoltage
Vout (PWM)
Vout +1%
PFMComparator
threshold
VoltagePositioning
Lightload
PFMMode
moderatetoheavyload
PWMMode
TPS62560, TPS62561
TPS62562
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SLVS815C –JANUARY 2008–REVISED DECEMBER 2009
Figure 28. Power Save Mode Operation With Automatic Mode Transition
100% Duty-Cycle Low-Dropout Operation
The device starts to enter 100% duty-cycle mode once 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 V
IN
, 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:
V
IN
min = V
OUT
max + I
OUT
max × (R
DS(on)
max + R
L
)
with:
I
OUT
max = maximum output current plus inductor ripple current
R
DS(on)
max = maximum P-channel switch R
DS(on)
R
L
= dc resistance of the inductor
V
OUT
max = nominal output voltage plus maximum output voltage tolerance
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
threshold is typically 1.85 V with falling V
IN
.
MODE SELECTION
The MODE terminal allows mode selection between forced-PWM mode and power-save mode.
Connecting this terminal to GND enables the power-save mode with automatic transition between PWM and
PFM modes. Pulling the MODE terminal 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 state of the MODE terminal can be changed during operation to allow efficient power management by
adjusting the operation mode of the converter to the specific system requirements.
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