SI9135_11 Datasheet, PDF (14/16 Pages) Vishay Siliconix – SMBus Multi-Output Power-Supply Controller

Si9135
Vishay Siliconix
DESCRIPTION OF OPERATION (CONT’D)
SMBus Commands
individually or as a group commanded on or off using a code
word on the SMBus, as detailed in the SMBus Truth Table.
The command sequence is:
1. Receive a start bit, which is a falling edge on the SDA line
while the SCL line is high.
2. Receive a one-byte address, which for Si9135 is
01100000.
3. Send an acknowledge bit.
4. Receive a one-byte command.
5. Send an acknowledge bit.
6. Receive a stop bit, which is a rising edge on the SDA line
while the SCL line is high.
This is a total of 20 bits, which at the maximum clock
frequency of 100 kHz translates into 200 µsec before any
change in the status of Si9135 ban be accomplished.
If Si9135 receives a command to turn on (respectively, off) a
converter that is already on (respectively, off) it shall not
falsely command the converter off (respectively, on).
Si9135 must be able to receive a stop command at any time
during a command sequence. If Si9135 receives a stop
command during a command sequence, it must not change
the state of any converter, and must be ready to receive the
next command sequence.
Grounding
There are two separate grounds on the Si9135, analog
signal ground (GND) and power ground (PGND). The
purpose of two separate grounds is to prevent the high
currents on the power devices (both external and internal)
from interfering with the analog signals. The internal
components of Si9135 have their grounds tied (internally)
together. These two grounds are then tied together
(externally) at a single point, to ensure Si9135 noise
immunity.
This separation of grounds should be maintained in the
external circuitry, with the power ground of all power devices
being returned directly to the input capacitors, and the small
signal ground being returned to the GND pin of Si9135.
ON/OFF Function
Logic-low shuts off the appropriate section by disabling the
gate drive stage. High-side and low-side gate drivers are
turned off when ON/OFF pins are logic-low. Logic-high
enables the DH and DL pins.
Stability
Buck Converters:
In order to simplify designs, the Si9135 requires no specified
external components except load capacitors for stability
control. Meanwhile, it achieves excellent regulation and
efficiency. The converters are current mode control, with a
bandwidth substantially higher than the LC tank dominant
pole frequency of the output filter. To ensure stability, the
minimum capacitance and maximum ESR values are:
C_LOAD
V_REF
2π x V_OUT x R_CS x BW
ESR
V_OUT x Rcs
V_REF
Where V_REF = 3.3 V, V_OUT is the output voltage (5 V or
3.3 V), Rcs is the current sensing resistor in ohms and BW =
50 khz.
With the components specified in the application circuit
(L = 10 µH, RCS = 0.02 , C_OUT = 330 µF, ESR
approximately 0.1 , the converter should have a bandwidth
at approximately 50 kHz, with minimum phase margin of 65°,
and dc gain above 50 dB.
Other Outputs
The Si9135 also provides a 3.3 V reference which can be
external loaded up to 1 mA, as well as, a 5 V LDO output
which can be loaded 30 mA, or even more depending on the
system application. When the 5 V buck converter is turned
on, the 5 V LDO output is shorted with the 5 V buck converter
output, so its loading capability is substantially increased.
For stability, the 3.3 V reference output requires a 1 µF
capacitor, and 5 V LDO output requires a 4.7 µF capacitor.
Vishay Siliconix maintains worldwide manufacturing capability. Products may be manufactured at one of several qualified locations. Reliability data for Silicon Tech-
nology and Package Reliability represent a composite of all qualified locations. For related documents such as package/tape drawings, part marking, and reliability
data, see www.vishay.com/ppg?70817.
www.vishay.com
Document Number: 70817
14
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