lm26480sqx-bf National Semiconductor Corporation, lm26480sqx-bf Datasheet - Page 20

• Manufacturer Part Number: lm26480sqx-bf
• Description: Lm26480 Externally Programmable Dual High-current Step-down Dc/dc And Dual Linear Regulators
• Manufacturer: National Semiconductor Corporation

www.national.com
Design implementation of the flexible power-on reset. An in-
ternal power-on reset of the IC is used with EN1 and EN2 to
produce a reset signal (LOW) to the delay timer nPOR. EN1
and RDY1 or EN2 and RDY2 are used to generate the set
signal (HIGH) to the delay timer. S=R=1 never occurs. The
mask timers are triggered off EN1 and EN2 which are gated
with RDY1, and RDY2 to generate outputs to the final AND
gate to generate the nPOR.
UNDER VOLTAGE LOCK OUT
The LM26480 features an “under voltage lock out circuit”. The
function of this circuit is to continuously monitor the raw input
Design Implementation of the Flexible Power-On Reset
20
supply voltage (VINLDO12) and automatically disables the
four voltage regulators whenever this supply voltage is less
than 2.8 VDC.
The circuit incorporates a bandgap based circuit that estab-
lishes the reference used to determine the 2.8 VDC trip point
for a V
used to gate the enable signals to the four regulators of the
LM26480. When VINLDO12 is greater than 2.8 VDC the four
enables control the four regulators, when VINLDO12 is less
than 2.8 VDC the four regulators are disabled by the V
tector being in the “Not OK” state. The circuit has built in
hysteresis to prevent chattering occurring.
IN
OK – Not OK detector. This V
IN
OK signal is then
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IN
de-