SI9135_11 Datasheet, PDF (12/16 Pages) Vishay Siliconix – SMBus Multi-Output Power-Supply Controller

Si9135
Vishay Siliconix
5V
V_IN
Linear
Regulator
V_L
4V
3.3 V
Reference
2.4 V
4.5 V
SMBUS
Interface
Controller
300 kHz/
200 kHz
Oscillator
Figure 5. Complete Si9135 Block Diagram
5V
Buck
Controller
3.3 V
Buck
Controller
12 V
Flyback
Controller
FB₅
CS₅
BST₅
DH5
LX₅
DL5
FB₃
CS₃
BST₃
DH3
LX₃
DL3
FYBFY
ICSP
ICSN
BSTFY
DHFY
LXFY
DLFY
DESCRIPTION OF OPERATION
Start-up Sequence
Si9135 is normally controlled by its SMBus interface after V_IN
is applied. Initially, if there is no incoming SMBus control
command, it comes up in its default power on sequence, first
the LDO 5 V will come up within its tolerance, and then the
precision 3.3 V reference will come up. Immediately
afterwards, the oscillator will begin and 3.3 V BUCK
converter will turn on and then 5 V BUCK converter and at
last 12 V FLYBACK converter. If Si9135 receives any SMBus
controlling command after LDO 5 V is established, the
designated converters will be allowed to turn on or off
independently depending on the command received. In the
event of all three converters are turned off, the oscillator will
be turned off, the total system would only draw 35 µA supply
current.
Each converter can soft-start separately. The integrated
internal soft-start circuitry for each converter gradually
increases the inductor maximum peak current during soft-
start period (approximately 4 msec), preventing excessive
currents being drawn from the input during startup. The soft-
start is controlled by initial default start up sequence or
incoming SMBus command.
Si9135 converters a 5.5 V to 30 V input voltage to five
outputs, two BUCK (step-down) high current, PWM, switch-
mode supplies, one at 3.3 V and one at 5 V, one FLYBACK
12 V PWM switch-mode supply, one precision 3.3 V
reference and one 5 V Low Drop Out linear regulator output.
Switch-mode supply output current capabilities depend on
external components (can exceed 10 A). With typical
application shown on the application diagram, the two BUCK
converters deliver 4 A and the FLYBACK converters deliver
0.25 A. The recommended load current for precision 3.3 V
reference output is less than 1 mA, the recommended load
current for 5 V LDO output current is less than 30 mA. In
order to maximize the power efficiency, when the 5 V BUCK
converter supply is above 4.5 V, the BUCK converter’s
output is internal connected to LDO output.
www.vishay.com
Document Number: 70817
12
S11-0975-Rev. D, 16-May-11
This document is subject to change without notice.
THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000