ncp3122 ON Semiconductor, ncp3122 Datasheet - Page 13

• Manufacturer Part Number: ncp3122
• Description: Dual 2.0 A, Step-down Dc/dc Switching Regulator
• Manufacturer: ON Semiconductor

Power Good
that indicates when the output voltage has reached 90%
(min) of the nominal output voltage. This output can be
pulled up to the appropriate level with an external resistor.
pin, which is a function of V
“Typical Operating Characteristics” section. The PG pin is
held low during a soft-start. Once a soft-start is completed,
the PG goes high if there are no faults and no delays
associated with it.
Current Limit
occurs. The NCP3122 contains pulse-by-pulse current
limiting to protect the power switch and external
components. The current through each channel is
continuously monitored. The current limit is set to allow
Thermal Shutdown
the device from overheating when the die temperature
exceeds 160°C (typically). If the chip temperature exceeds
the overtemperature shutdown trip point, the fault signal is
activated. This will disable the step down converter
operation, and the chip temperature will start to decrease.
The power good is an open drain and active high output
The power good comparator senses the voltage at the FB
The power good output transistor behavior is shown in the
The NCP3122 protects a power system if overcurrent
The NCP3122 has a thermal shutdown feature to protect
out
.
Figure 30. Hiccup Overload Protection
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NCP3122
13
peak switch current in excess of 2.6 A (minimum). Current
limiting is implemented by monitoring the high-side
P-channel switch current during conduction with a current
limit comparator. When the peak of the switching current
reaches the current limit, the power switch turns off.
Hiccup Overload Protection (OLM – Over Load Mode)
from damage during overload conditions. Within normal
operation, the external soft-start capacitor is pulled up by a
current source that delivers 8.75 mA to the SS pin capacitor.
The soft-start capacitor continues to charge until it reaches
the saturation voltage of the current source, typically V
4 V. When the overload condition is detected, the soft-start
capacitor is discharged to 0.1 V and is again charged to 1 V.
This is periodically repeated until the overload condition is
detected. The transconductance error amplifier output is tied
to ground when the soft-start capacitor is discharged.
When the chip temperature drops 15°C below the
overtemperature shutdown trip point, the fault signal is
deactivated and the step down converter operation starts
again with soft-start. The thermal event sends the device
immediately into the OFF state. The currrent consumption
is equal 5 mA (typical) if the thermal condition is reached.
Hiccup mode is a method of protecting the power supply
ss
=