lm25066apsqx National Semiconductor Corporation, lm25066apsqx Datasheet - Page 19

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

Application Section
DESIGN-IN PROCEDURE
(Refer to
is the step-by-step procedure for hardware design of the
LM25066A. This procedure refers to section numbers that
provide detailed information on the following design steps.
The recommended design-in procedure is as follows:
MOSFET Selection: Determine MOSFET value based on
breakdown voltage, current and power ratings.
Current Limit, R
(I
mum load current, allowing for tolerances in the current sense
resistor value and the LM25066A Current Limit threshold volt-
age. Use equation 1 to determine the value for R
Power Limit Threshold: Determine the maximum allowable
power dissipation for the series pass MOSFET (Q
device’s SOA information. Use equation 2 to determine the
value for R
Turn-on Time and TIMER Capacitor, C
ue for the timing capacitor at the TIMER pin (C
tion 3. The fault timeout period (t
the circuit’s turn-on-time. The turn-on time can be estimated
using the equations in the TURN-ON TIME section of this data
sheet, but should be verified experimentally. Review the re-
sulting insertion time, and the restart timing if retry is enabled.
UVLO, OVLO: Choose option A, B, C, or D from the UVLO,
OVLO section of the Application Information to set the UVLO
and OVLO thresholds and hysteresis. Use the procedure for
the appropriate option to determine the resistor values at the
UVLO/EN and OVLO pins.
LIM
). This threshold must be higher than the normal maxi-
Figure 6
PWR
.
for Typical Application Circuit) Shown here
S
: Determine the current limit threshold
FAULT
) MUST be longer than
T
: Determine the val-
FIGURE 6. Typical Application Circuit
T
) using equa-
1
S
), using the
.
19
Power Good: Choose the appropriate output voltage and
calculate the required resistor divider from the output voltage
to the FB pin. Choose either VDD or OUT to connect properly
sized pull-up resistor for the Power Good output (PGD).
Refer to Programming Guide section: After all hardware
design is complete, refer to the programming guide for a step
by step procedure regarding software.
MOSFET SELECTION
It is recommended that the external MOSFET (Q
be based on the following criteria:
- The BV
tem voltage (V
occur at V
inserted or removed.
- The maximum continuous current rating should be based on
the current limit threshold (e.g., 25 mV/R
load current, since the circuit can operate near the current
limit threshold continuously.
- The Pulsed Drain Current spec (I
the current threshold for the circuit breaker function (45 mV/
R
- The SOA (Safe Operating Area) chart of the device, and the
thermal properties, should be used to determine the maxi-
mum power dissipation threshold set by the R
The programmed maximum power dissipation should have a
reasonable margin from the maximum power defined by the
MOSFET’s SOA curve if the device is set to infinitely retry the
MOSFET will be repeatedly stressed during fault restart cy-
cles. The MOSFET manufacturer should be consulted for
guidelines.
S
when CL = CB = GND).
DSS
SYS
rating should be greater than the maximum sys-
when the circuit card, or adjacent cards, are
SYS
), plus ringing and transients which can
DM
) must be greater than
S
), not the maximum
PWR
30146001
www.national.com
1
) selection
resistor.