APL3546A Datasheet, PDF (10/17 Pages) Anpec Electronics Coropration – Power -Distribution Switches with Soft Start

APL3546A
Application Information
Power Sequencing
Layout Consideration
VIN
EN
threshold
EN
At start-up, it is necessary to ensure that the V and EN are
IN
sequenced correctly.
Input Capacitor
A
1µF
ceramic
bypass
capacitor
from
V
IN
to
GND,
located
near the APL3546A, is strongly recommended to suppress
the ringing during short-circuit fault event. Without the by-
pass capacitor, the output short may cause sufficient ring-
ing on the input (from supply lead inductance) to damage
internal control circuitry.
The PCB layout should be carefully performed to maxi-
mize thermal dissipation and to minimize voltage drop,
droop and EMI. The following guidelines must be
considered:
1. Please place the input capacitors near the VIN pin as
close as possible.
2. Output decoupling capacitors for load must be placed
near the load as close as possible for decoupling high
frequency ripples.
3. Locate APL3546A and output capacitors near the load
to reduce parasitic resistance and inductance for excel-
lent load transient performance.
4. The negative pins of the input and output capacitors
and the GND pin must be connected to the ground plane
of the load.
5. Keep V and V traces as wide and short as possible.
IN
OUT
Output Capacitor
A low-ESR 10µF MLCC, aluminum electrolytic or tanta-
lum between VOUT and GND is strongly recommended
to reduce the voltage droop during hot-attachment of
downstream peripheral. Higher-value output capacitor is
better when the output load is heavy. Additionally, bypass-
ing the output with a 0.1µF ceramic capacitor improves
the immunity of the device to short-circuit transients.
Current Limit Setting
The current limit can be set by connecting resistor from
the current limit adjustable pin ISET to ground. The re-
quired value of resistor R_ISET for current limit is calcuated
as follows:
RISET = 510000 / ILIM
Soft-Start Capacitor
The APL3546A has a built-in adjustable soft-start control
for user to set an optimum soft-start time for the
application. The soft-start time can be calculated by the
equation, described in the paragraph of Soft-Start in Func-
tional Description section. The soft-start time will become
internally controlled as if there is no C_SS, t_SS=2ms when
V_IN=12V. Please note that there minimum value of soft
start capacitor in different VIN input voltage. Please make
sure the C_SS is in the recommended value.
Copyright © ANPEC Electronics Corp.
10
Rev. A.3 - Jul., 2013
www.anpec.com.tw