SC2738 Semtech Corporation, SC2738 Datasheet - Page 7

• Manufacturer Part Number: SC2738
• Description: Ultra Low Output Voltage Dual Linear FET Controller
• Manufacturer: Semtech Corporation

supplied to the MOSFET drain should be greater than
the output under-voltage threshold when that
output is enabled. This assumes that the drop through
the pass MOSFET is negligible. If not, then this drop needs
to be taken into account also since:
V
If the supply to the SC2738 IN pin comes up before the
supply to the MOSFET drain, then that output should be
enabled as the supply to the MOSFET drain is applied
- the Power Good signal for this rail would be ideal. If the
power supply to the MOSFET drain comes up before the
power supply to the SC2738 IN pin, then the output can
either be enabled with the supply to the IN pin or after-
wards. Please see the example below.
Example: SC2738 powered from 5V, output 1 powered
from 1.8V set for 1.5V out, output 2 not shown for
POWER MANAGEMENT
Applications Infomation (Cont.)
OUT
2004 Semtech Corp.
= V
DRAIN
- (I
OUT
x R
DS(ON)
).
SC2738 Supply Comes Up Before MOSFET Drain Supply
MOSFET Drain Supply Comes Up Before SC2738 Supply
Figure 1: Power Supply Sequencing
7
simplicity. Worst case under-voltage threshold is 60%
(over temperature) of 1.5V, or 0.9V. The typical enable
threshold is ~1V. See Figure 1 below.
Component Selection
Output Capacitors: low ESR capacitors such as Sanyo
POSCAPs or Panasonic SP-caps are recommended for
bulk capacitance, with ceramic bypass capacitors for
decoupling high frequency transients.
Input Capacitors: placement of low ESR capacitors such
as Sanyo POSCAPs or Panasonic SP-caps at the input to
the MOSFET (V
during fast load changes, thus improving overall transient
response. If V
the upstream voltage regulator, additional capacitance
may not be required. In this case a 0.1µF ceramic
capacitor will suffice. The input supply to the SC2738
should be bypassed with a 0.1µF ceramic capacitor.
DRAIN
DRAIN
) will help to hold up the power supply
is located at the bulk capacitors for
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SC2738