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Soft Start
95%
EN
5%
V
OUT
t
Start
t
RAMP
100% Duty Cycle Low Dropout Operation
V (min)=
I
V (max)+I (max)x(r (max)+R )
O O DS(on) L
(3)
Undervoltage Lockout
Mode Selection
TPS65050, TPS65051, TPS65052
TPS65054, TPS65056
SLVS710A – JANUARY 2007 – REVISED AUGUST 2007
The two converters have an internal soft start circuit that limits the inrush current during start-up. During soft
start, the output voltage ramp up is controlled as shown in Figure 20 .
Figure 20. Soft Start
The converters offer a low input to output voltage difference while still maintaining operation with the use of the
100% duty cycle mode. In this mode, the P-channel switch is constantly turned on. This is useful in
battery-powered applications to achieve longest operation time by taking full advantage of the whole battery
voltage range. (i.e. The minimum input voltage to maintain regulation depends on the load current and output
voltage) and can be calculated as:
with:
• I
O
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
O
(max) = nominal output voltage plus maximum output voltage tolerance
The undervoltage lockout circuit prevents the device from malfunctioning at low input voltages and from
excessive discharge of the battery and disables all internal circuitry. The undervoltage lockout threshold, sensed
at the V
CC
pin is typically 1.8 V, max 2 V.
The MODE pin allows mode selection between forced PWM Mode and power Safe Mode for both converters.
Connecting this pin to GND enables the automatic PWM and power save mode operation. The converters
operates in fixed frequency PWM mode at moderate to heavy loads and in the PFM mode during light loads,
maintaining high efficiency over a wide load current range.
Copyright © 2007, Texas Instruments Incorporated Submit Documentation Feedback 21
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