Datasheet

V (nominal)
O
0.8%
1.6%
-1.6%
t
W
»
2 5
I
V
S K I P
I
( )
)(
max
)(
maxmaxmin
L
R
onDS
r
O
I
O
V
I
V +×+=
TPS62110-HT
www.ti.com SLVSAO9B –DECEMBER 2010– REVISED FEBRUARY 2011
DETAILED DESCRIPTION (continued)
Figure 10. Power Save Mode Output Voltage Thresholds
The typical PFM (SKIP) current threshold for the TPS62110 is given by:
(1)
Equation 1 is valid for input voltages up to 7 V. For higher voltages, the skip current threshold is not increased
further. The converter enters the fixed frequency PWM mode as soon as the output voltage falls below V
O
–
1.6% (nominal).
SOFT START
The TPS62110 has an internal soft-start circuit that limits the inrush current during start-up. This prevents
possible voltage drops of the input voltage when a battery or a high-impedance power source is connected to the
input of the TPS62110.
The soft start is implemented as a digital circuit increasing the switch current in steps of 300 mA, 600 mA,
1200 mA. The typical switch current limit is 2.4 A. Therefore, the start-up time depends on the output capacitor
and load current. Typical start-up time with a 22-μF output capacitor and 800-mA load current is 1 ms.
100% DUTY CYCLE LOW DROPOUT OPERATION
The TPS62110 offers the lowest possible 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
particularly useful in battery-powered applications to achieve the longest operation time, 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 is calculated as:
(2)
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
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