SI9135 Datasheet, PDF (14/14 Pages) Vishay Siliconix – SMBus Multi-Output Power-Supply Controller

Si9135
Vishay Siliconix
New Product
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-----^R---^E---^F--------------------------
2π × V_OUT × R_CS × BW
ES
R
≤
-^V----^O----^U---^T----^×-----^R-----^C---^S--
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 Ω, C_OUT = 330 µF, ESR approximately
0.1 Ω), 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.
S-60752—Rev. B, 05-Apr-99
14
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