Datasheet

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Setting the Switching Frequency
R
T
+ 0.8
ƪ
ǒ
36 10
3
f
PH
Ǔ* 9
ƫ
(6)
f
SW
− Phase Switching Frequency − kHz
R
T
− Timing Resistance − kΩ
0
0 1000200 400 600 800
50
100
150
200
250
300
350
400
450
500
EN/SYNC Function
TPS40130
SLUS602B – JUNE 2004 – REVISED SEPTEMBER 2005
The clock frequency is programmed by the value of the timing resistor connected from the RT pin to ground.
See Equation 6 .
f
PH
is a single phase frequency, kHz. The RT resistor value is expressed in k Ω . See Figure 4 .
Figure 4. Phase Switching Frequency vs. Timing Resistance
The output ripple frequency is twice that of the single phase frequency. The switching frequency of the controller
can be synchronized to an external clock applied to the EN/SYNC pin. The external clock synchronizes the
rising edge of HDRV and the falling edge of an external clock source. The external clock pulses must be at a
frequency at least 8.2 times higher than the switching frequency set by the RT resistor.
14
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