nx2113 Microsemi Corporation, nx2113 Datasheet - Page 16

• Manufacturer Part Number: nx2113
• Description: 300khz & 600khz Synchronous Pwm Controller With Programmable Bus Uvlo
• Manufacturer: Microsemi Corporation

Under Voltage Lock Out comparator is disabled. After
half of start up time, the Feedback UVLO comparator is
enabled. The FB UVLO threshold is set to be half of
voltage at the positive input of error amplifier. With this
set up, if the output is short before soft start, the
Feedback UVLO comparator can catch it and turn off
the driver. The short circuit operation waveform during
normal operation and during the soft start are shown as
follows.
dition.
short.
Rev. 2.0
11/18/05
operates. Before half of the start up time, the Feedback
Figure 16 - Feedback UVLO with start up at
Figure 15 - Operation waveforms during short con-
CH2-output voltage
CH4-load current
CH3-FB voltage
CH1-SW voltage
CH4-load current
10A/DIV
0.5V/DIV
10V/DIV
10A/DIV
1V/DIV
cuit protection. However, since feedback does not have
accurate information of current, this protection only pro-
vides certain level of over current protection. MOSFET
should design such that it can survive with high pulse
current for a short period of time.
and the resistor value of voltage divider on enable pin
should be big enough to keep enable pin high during
short. Otherwise, once output shorts, the input bus volt-
age drops, the chip is disabled before Feedback UVLO
takes effect, and the system goes into hiccup status.
This phenomena is easy to be found during system
startup, if related resistor and capacitor value is not big
enough.
Layout Considerations
frequency switching converters. Layout will affect noise
pickup and can cause a good design to perform with
less than expected results.
connection in the top layer with wide, copper filled ar-
eas. The inductor, output capacitor and the MOSFET
should be close to each other as possible. This helps to
reduce the EMI radiated by the power traces due to the
high switching currents through them. Place input ca-
pacitor directly to the drain of the high-side MOSFET, to
The Feedback UVLO can provide certain short cir-
Figure 17 -Hiccup with start up at short.
The layout is very important when designing high
Start to place the power components, make all the
The value of the capacitor on enable pin to ground
NX2113/2113A
CH2-Output voltage
CH4-load current
10A/DIV
1V/DIV
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