hip6501a Intersil Corporation, hip6501a Datasheet - Page 10

• Manufacturer Part Number: hip6501a
• Description: Triple Linear Power Controller With Acpi Control Interface
• Manufacturer: Intersil Corporation

Application Guidelines
Soft-Start Interval
The 5VSB output of a typical ATX supply is capable of
725mA. During power-up in a sleep state, it needs to provide
sufficient current to charge up all the output capacitors and
simultaneously provide some amount of current to the output
loads. Drawing excessive amounts of current from the 5VSB
output of the ATX can lead to voltage collapse and induce a
pattern of consecutive restarts with unknown effects on the
system’s behavior or health.
The built-in soft-start circuitry allows tight control of the slew-
up speed of the output voltages controlled by the HIP6501A,
thus enabling power-ups free of supply drop-off events.
Since the outputs are ramped up in a linear fashion, the
current dedicated to charging the output capacitors can be
calculated with the following formula:
I
C
V
Σ
capacitance and the voltage of an output.
Due to the various system timing events, it is recommended
that the soft-start interval not be set to exceed 30ms.
Additionally, the recommended soft-start capacitor range
spans from 5nF up to 0.22µF (0.1µF recommended).
Shutdown
In case of a FAULT condition that might endanger the
computer system, or at any other time, the HIP6501A can be
shut down by pulling the SS pin below the specified
shutdown level (typically 0.8V) with an open drain or open
collector device capable of sinking a minimum of 2mA.
Pulling the SS pin low effectively shuts down all the pass
elements. Upon release of the SS pin, the HIP6501A
SS
I COUT
FIGURE 11. 2.5/3.3V
SS
BG
(C
- soft-start current (typically 10µA)
OUT
- soft-start capacitor
- bandgap voltage (typically 1.26V)
10kΩ
R
1kΩ
SEL
=
xV
R
------------------------------- -
C SS
OUT
SEL
FAULT/MSEL
CIRCUITRY DETAILS
V
I SS
2.5V
3.3V
×
MEM
) - sum of the products between the
V BG
MEM
×
Σ
(
OUTPUT VOLTAGE SELECTION
C OUT V OUT
10
40µA
×
MEM VOLTAGE
SELECT COMP
-
+
)
0.2V
, where
+
-
HIP6501A
undergoes a new soft-start cycle and resumes normal
operation in accordance to the ATX supply and control pins
status.
Layout Considerations
The typical application employing a HIP6501A is a fairly
straight-forward implementation. Similar to any other linear
regulators, attention has to be paid to a few potentially
sensitive small signal components, such as those connected
to high-impedance nodes or those supplying critical by-pass
currents.
The power components (pass transistors) and the controller
IC should be placed first. The controller should be placed in
a central position on the motherboard, closer to the memory
load if possible. Ensure the VSEN2 connection is properly
sized to carry 200mA without significant resistive losses. The
pass transistors should be placed on pads capable of
heatsinking, matching the device’s power dissipation. Where
applicable, multiple via connections to a large internal plane
can significantly lower localized device temperature rise.
Placement of the decoupling and bulk capacitors should
follow a placement reflecting their purpose. As such, the
high-frequency decoupling capacitors (C
placed as close as possible to the load they are decoupling;
the ones decoupling the controller (C
the controller pins, the ones decoupling the load close to the
load connector or the load itself (if embedded). The bulk
KEY
+12V
+5V
V
Q3
SB
C
OUT1
VIA CONNECTION TO GROUND PLANE
IN
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT/POWER PLANE LAYER
FIGURE 12. PRINTED CIRCUIT BOARD ISLANDS
HF1
Q2
C
C
BULK1
SS
C
12V
12V
SS
3V3DLSB
3V3DL
HIP6501A
GND
5VDLSB
5VSB
VSEN2
DRV2
5VDL
C
DLA
5VSB
12V
C
BULK3
HF
, C
Q1
) should be
5VSB
C
C
IN
V
BULK2
December 30, 2004
OUT2
+3.3V
V
) close to
Q5
C
OUT3
+5V
HF3
C
IN
IN
HF2
FN4749.6
Q4