Datasheet

SR 0.39 CT 13.4= ´ +
TPS22965
www.ti.com SLVSBJ0A –AUGUST 2012–REVISED AUGUST 2013
ADJUSTABLE RISE TIME
A capacitor to GND on the CT pins sets the slew rate for each channel. The voltage on the CT pin can be as
high as 12V. Therefore, the minimum voltage rating for the CT cap should be 25V for optimal performance. An
approximate formula for the relationship between CT and slew rate is (the equation below accounts for 10% to
90% measurement on V
OUT
and does NOT apply for CT = 0pF. Use table below to determine rise times for when
CT = 0pF):
(1)
Where,
SR = slew rate (in µs/V)
CT = the capacitance value on the CT pin (in pF)
The units for the constant 13.4 is in µs/V. The units for the constant 0.39 are in µs/(V*pF).
Rise time can be calculated by multiplying the input voltage by the slew rate. The table below contains rise time
values measured on a typical device. Rise times shown below are only valid for the power-up sequence where
V
IN
and V
BIAS
are already in steady state condition, and the ON pin is asserted high.
RISE TIME (µs) 10% - 90%, C
L
= 0.1µF, C
IN
= 1µF, R
L
= 10Ω
TYPICAL VALUES at 25°C, 25V X7R 10% CERAMIC CAP
CTx (pF)
5V 3.3V 1.8V 1.5V 1.2V 1.05V 0.8V
0 127 93 62 55 51 46 42
220 475 314 188 162 141 125 103
470 939 637 359 304 255 218 188
1000 1869 1229 684 567 476 414 344
2200 4020 2614 1469 1211 1024 876 681
4700 8690 5746 3167 2703 2139 1877 1568
10000 18360 12550 6849 5836 4782 4089 3449
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