Si85xx
Preliminary Rev. 0.4 21
3.4. Single-Phase Buck Converter Example
In this example, the Si850x is configured to operate in a single-phase synchronous buck converter (Figure 18).
This converter has a PWM frequency of 1 MHz and a maximum duty cycle of 80%.
This is an example of a half-wave application that can be addressed with Single-Ended output mode. The PWM
period is calculated to be 1/10
–6
= 1.0 µs, and the worst-case value, t
R
, is 0.2 x 1.0 x 10
–6
= 200 ns at 80%
maximum duty cycle (R
TRST
=20k).
In this example, the current measurement is made when the buck switch is on; so, PH2 is chosen as the reset
signal by connecting PH2 to R1 and grounding R2. The PH2 signal can be obtained at the input of the driver
external to the PWM controller or the output of the controller's internal driver (through a resistor divider if the driver
output swings beyond the device VDD range).
Figure 18. Si850x Single-Phase Buck Converter
VDD
VOUT
2 Vpp
IIN
IOUT
L1
C3
Q1
Q2
PH1
PH2
R1
OUT
VDD1
GND1
VIN
Si850x
VDD2
R2
PWM
RESET
PH2
Si850x State
I > 0I = 0
Current
MEASURE
GND2
TRST
R
TRST
100 ns
GND3
C1
0.1 µF
C2
1 µF
