MP161 – INTEGRATED POWER SOLUTION FOR HOME/INDUSTRIAL AUTOMATION
Feedback Capacitor
L1
FR1
L
The feedback capacitor provides a sample-and-
hold function. For both fixed and adjustable
output setups, VCC is used as the feedback
C1
C2
capacitor.
A
1µF
VCC
capacitor
is
recommended, typically, but the optimized VCC
capacitor may vary in different applications. A
large VCC capacitor is preferred since it results
in small no-load consumption and good light-
load regulation, and also helps increase the
hiccup duration during protections. However,
stability may be affected when the feedback
capacitor is too large.
N
Figure 6: Half-Wave Rectifier
Table 2: Recommended Capacitance
Surge
Voltage
500V
1000V
2000V
C1
C2
1μF
1μF
2.2μF
2.2μF
3.3μF
3.3μF
Dummy Load
Input and Output Capacitors of LDO
A dummy load is required to maintain the
switching regulator output voltage under no-
load condition. The switching regulator delivers
a certain amount of power under no-load
Place an input ceramic capacitor (1 - 10µF)
between VIN and GND. A larger value in this
range improves the line transient response.
condition due to
a
minimum switching
Place an output ceramic capacitor (1 - 10µF)
between VO and GND. A larger value in this
range improves load transient response.
frequency determined by the feedback R-C
discharge rate. This power is dissipated by the
dummy load so that output voltage does not run
away.
Relay
The coil of relay is connected between VIN and
VOUTx.
A large dummy load current leads to better
regulation but larger no-load consumption. The
current is a compromise between small no-load
consumption and good no-load regulation.
Typically, a resistor is used as a dummy load.
In Figure 7, the dummy load resistor is not used
because there is already ~250µA of
consumption current on VIN, which can act as a
dummy load.
PCB Layout Guidelines
Efficient PCB layout is critical for stable
operation, good EMI, and good thermal
performance. For best results, follow the
guidelines below.
1) Minimize the loop area formed by the input
capacitor,
700V
switching
regulator,
Surge Performance
freewheeling diode, inductor, and output
capacitor.
The input capacitor can also be used for surge
suppression. There is no need to use other
2) Place the power inductor far away from the
input filter while keeping the loop area to a
minimum.
surge
suppression
components
if
an
appropriate input capacitor value is chosen.
Figure 6 shows the typical half-wave rectifier
used in low-power offline applications. Table 2
shows the capacitance required under normal
conditions for different surge levels. FR1 is a
20Ω/2W fused resistor, and L1 is 1mH for this
recommendation.
3) Place a bypass capacitor around 47pF
between FB and SOURCE as close to the
IC as possible.
4) Connect a large copper area to GND for
better LDO thermal performance.
MP161 Rev. 1.0
8/4/2017
www.MonolithicPower.com
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