4component selection – Texas Instruments TPS40090EVM-002 User Manual
Page 7
SLUU195 − June 2004
7
TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.5-V at 100 A
+
+
+
1.5V/100A
+
+
+
+
+
Figure 3. TPS40090EVM−002 Schematic Part 3 − Power Stage
4
Component Selection
4.1
Frequency of Operation
The clock oscillator frequency for the TPS40090 is programmed with a single resistor from RT
(pin 16) to signal ground. Equation (1) from the datasheet allows selection of the R
T
resistor in
k
Ω
for a given switching frequency in kHz.
R
T
+
R12
+
K
PH
ǒ
39.2
10
3
f
*
1.024
PH
*
7
Ǔ
(k
W
)
where
•
K
PH
is the coefficient that depends on the number of active phases
•
f
PH
is the single phase frequency, in kHz
•
for 2-phase and 3-phase configurations K
PH
=1.333
•
for 4-phase K
PH
=1.0 is a single phase frequency, kHz.
The R
T
resistor value is returned by the last expression in k
Ω
. For 420 kHz, R
T
is calculated as
65.8 k
Ω
and a resistor with a 64.9-k
Ω
standard value is used.
(1)