Datasheet
= + +
I O O DS(on) (L)
xV min V I max (r max R )
I
SKIP
V
I
25
»
W
V (nominal)
O
0.8%
1.6%
–1.6%
t
TPS62110, TPS62111
TPS62112, TPS62113
www.ti.com
SLVS585C –JULY 2005–REVISED OCTOBER 2012
Figure 18. Power-Save Mode Output-Voltage Thresholds
The typical PFM (SKIP) current threshold for the TPS6211x 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 TPS6211x 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 TPS6211x.
The soft start is implemented as a digital circuit increasing the switch current in steps of 300 mA, 600 mA, and
1200 mA for 250 µsec each. Then, the switch current limit is set to 2.4 A typical. 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.
The TPS6211x can start into a pre-biased output. During monotonic pre-biased start up, the N-Channel MOSFET
is not allowed to turn on until the internal ramp of the device sets an output voltage above the pre-bias voltage.
100% DUTY-CYCLE, LOW-DROPOUT OPERATION
The TPS6211x 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
r
DS(on)
max = maximum P-channel switch r
DS(on)
R
(L)
= dc resistance of the inductor
V
O
= lowest output voltage that the load can accept.
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