CS5157 View Datasheet(PDF) - ON Semiconductor
Part Name
Description
MFG CO.
'CS5157' PDF : 16 Pages View PDF
CS5157
A heatsink may be added to TO−220 components to
reduce their thermal impedance. A number of PC board
layout techniques such as thermal vias and additional copper
foil area can be used to improve the power handling
capability of surface mount components.
EMI Management
As a consequence of large currents being turned on and off
at high frequency, switching regulators generate noise as a
consequence of their normal operation. When designing for
compliance with EMI/EMC regulations, additional
components may be added to reduce noise emissions. These
components are not required for regulator operation and
experimental results may allow them to be eliminated. The
input filter inductor may not be required because bulk filter
and bypass capacitors, as well as other loads located on the
board will tend to reduce regulator di/dt effects on the circuit
board and input power supply. Placement of the power
component to minimize routing distance will also help to
reduce emissions.
2.0 μH
33 Ω
1000 pF
Layout Guidelines
1. Place 12 V filter capacitor next to the IC and connect
capacitor ground to pin 11 (PGND).
2. Connect pin 11 (PGND) with a separate trace to the
ground terminals of the 5.0 V input capacitors.
3. Place fast feedback filter capacitor next to pin 8 (VFFB)
and connect it’s ground terminal with a separate, wide
trace directly to pin 14 (LGND).
4. Connect the ground terminals of the Compensation
capacitor directly to the ground of the fast feedback
filter capacitor to prevent common mode noise from
effecting the PWM comparator.
5. Place the output filter capacitor(s) as close to the load
as possible and connect the ground terminal to pin 14
(LGND).
6. Connect the VFB pin directly to the load with a separate
trace (remote sense).
7. Place 5.0 V input capacitors close to the switching
MOSFET and synchronous MOSFET.
Route gate drive signals VGATE(H) (pin 10) and VGATE(L)
(pin 12 when used) with traces that are a minimum of 0.025
inches wide.
1.0 μF
VCOMP
VCC
0.1 μF
15
To the negative terminal
of the input capacitors
11
Figure 20. Filter Components
2.0 μH
+
1200 pF × 3.0/16 V
Figure 21. Input Filter
8
100 pF
5
VFFB
SOFT START
OFF TIME
To the negative terminal of the output capacitors
Figure 22. Layout Guidelines
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13
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