TPS62260_08 Datasheet, PDF (16/31 Pages) Texas Instruments – 2.25 MHz 600 mA Step Down Converter in 2x2SON/TSOT-23 Package

TPS62260, TPS62261
TPS62262, TPS62263
SLVS763B – JUNE 2007 – REVISED FEBRUARY 2008
Output voltage
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Voltage Positioning
Vout +1%
PFM Comparator
threshold
Light load
PFM Mode
Vout (PWM)
moderate to heavy load
PWM Mode
Figure 34. 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 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:
V_INmin = V_Omax + I_Omax × (R_DS(on)max + R_L)
With:
I_Omax = maximum output current plus inductor ripple current
R_DS(on)max = maximum P-channel switch RDSon.
R_L = DC resistance of the inductor
V_Omax = 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 1.85V with falling V_IN.
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.
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