SI9136_11 Datasheet, PDF (14/16 Pages) Vishay Siliconix – Multi-Output Power-Supply Controller

Si9136
Vishay Siliconix
DESCRIPTION OF OPERATION (CONT’D)
Grounding:
There are two separate grounds on the Si9136, 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 Si9136 have their grounds tied (internally)
together. These two grounds are then tied together
(externally) at a single point, to ensure Si9136 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 Si9136.
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 Si9136 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:
V_REF
C_LOAD ≥ _{2π x VOUTx RCS 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 Si9136 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
Technology 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?70818.
www.vishay.com
Document Number: 70818
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