lm25066apsqx National Semiconductor Corporation, lm25066apsqx Datasheet - Page 26

• Manufacturer Part Number: lm25066apsqx
• Description: Lm25066a System Power Management And Protection Ic With Pmbus
• Manufacturer: National Semiconductor Corporation

www.national.com
SYSTEM CONSIDERATIONS
A) Continued proper operation of the LM25066A hot swap
circuit requires capacitance be present on the supply side of
the connector into which the hot swap circuit is plugged in, as
depicted in
SOURCE” section is necessary to absorb the transient gen-
erated whenever the hot swap circuit shuts off the load cur-
rent. If the capacitance is not present, inductance in the
supply lines will generate a voltage transient at shut-off which
can exceed the absolute maximum rating of the LM25066A,
resulting in its destruction.
PC BOARD GUIDELINES
The following guidelines should be followed when designing
the PC board for the LM25066A:
- Place the LM25066A close to the board’s input connector to
minimize trace inductance from the connector to the MOS-
FET.
- Place a small capacitor, C
VIN and GND pins of the LM25066A to help minimize tran-
sients which may occur on the input supply line. Transients of
several volts can easily occur when the load current is shut
off.
- Place a 1 µF capacitor as close as possible to VREF pin.
- Place a 1 µF capacitor as close as possible to VDD pin.
- The sense resistor (R
LM25066A. In particular, the trace to the VIN pin should be
Figure
16. The capacitor in the “LIVE POWER
S
) should be placed close to the
IN
, (1nF) directly adjacent to the
FIGURE 15. Adding Delay to the Power Good Output Pin
FIGURE 16. Output Diode Required for Inductive Loads
26
B) If the load powered by the LM25066A hot swap circuit has
inductive characteristics, a Schottky diode is required across
the LM25066A’s output, along with some load capacitance.
The capacitance and the diode are necessary to limit the
negative excursion at the OUT pin when the load current is
shut off. If the OUT pin transitions more than 0.3V negative
the LM25066A will internally reset, erasing the volatile setting
for retries and warning thresholds. See
made as low resistance as practical to ensure maximum cur-
rent and power measurement accuracy. Connect R
Kelvin techniques shown in
- The high current path from the board’s input to the load (via
Q
other to minimize loop inductance.
- The ground connections for the various components around
the LM25066A should be connected directly to each other,
and to the LM25066A’s GND pin, and then connected to the
system ground at one point. Do not connect the various com-
ponent grounds to each other through the high current ground
line.
- Provide adequate heat sinking for the series pass device
(Q
1
1
), and the return path, should be parallel and close to each
) to help reduce stresses during turn-on and turn-off.
Figure
7.
Figure
30146054
16.
30146052
S
using the