SI8250 Datasheet, PDF (19/30 Pages) Silicon Laboratories – DIGITAL POWER CONTROLLER

Si8250/1/2
5. Example Applications
Isolated DC/DC Converter: A 35 W, 400 kHz Si8250-based half bridge converter is shown in Figure 6. This circuit
is the same as that of the target (evaluation) board shipped in the Si8250DK development kit.
VIN+
0.010
1uH
2.2uF
P3
DRIVER
P4
DRIVER
6:1
0.01uF
IRLR8113
200
180nH
6 x 100uF
Ceramic
.0.001
VOUT
120uF
33K
4.7
DRIVER
1K
33K
2.2uF
3V3P
VDD
DC BAL
AIN
VIN
AIN
4.7 4.7
FDS3572
DRIVER
200
IRLR8113
180nH
IOUT Vsense
~+
10K
~-
3.9K
7.5
0.01uF
FDS3572
P2
P1
IPK
P3
PH4
P4
PH3
PH2
PH1
VIN-
1.2nF _1K
IIN
AIN
TX
GND
C8051F300
Microcontroller
Isolator
RX
3V3P
3V3P
VDDA VDDB
VDD
GNDA GNDB
GND
Si8250
Digital Controller
Figure 6. Isolated Half-Bridge DC/DC Converter
The Si8250/1/2 is located on the secondary-side of the power supply for optimum transient response. DPWM
outputs PH3 and PH4 control gates of the synchronous rectifiers via a dual driver I.C. DPWM outputs PH1 and
PH2 control the gates of the primary-side switching transistors with isolation provided by a Silicon Laboratories
isolator. A current transformer circuit provides peak current sensing. Primary side analog parameters (input voltage
and current and the filter node voltage) are digitized by a Silicon Laboratories C8051F300 microcontroller and
passed to the Si8250/1/2 using the on-board UART through additional channels of the isolator I.C. to the
Si8250/1/2. The Si8250/1/2 is uses the application software included with the Si8250DK development kit after
being configured for the half-bridge application using the tools supplied in the kit.
When power is applied, the CPU executes an internal reset followed by initialization of all parameters. The
Si8250/1/2 remains in a low-power state, monitoring digitized VIN data from the primary-side MCU until VIN is
within specified limits. At this time, the controller is fully enabled and executes soft-start by monitoring Vout while
sequentially incrementing the loop voltage reference (REFDAC) until the supply output voltage is within specified
range, at which time steady-state operation begins.
During steady-state operation, the MCU operates in interrupt mode where hardware events divert program
execution to specific routines in priority order.
Preliminary Rev. 0.8
19