NJW4800
ꢁBoot Strap
In order to drive the gate of the high side SW, the voltage that is higher than power supply voltage is necessary.
The bootstrap condenser generates the power supply voltage of V++5V to BS terminal and it supplies the power to the
gate of the high side SW. As Shown as Fig5 in detail.
Power Line
Power Line
V+
V+
Regulator Voltage
Regulator Voltage
VDD
OFF
VDD
V+=5V is generated to
the BS terminal.
BS
Regulator
5V
Regulator
5V
ON
CBS
CBS
CBS is
High Side
Gate Driver
High Side
Gate Driver
charged to 5V
OUT becomes V+
voltage
OUT
OUT
ON
OFF
Low Side
Low Side
Gate Driver
Gate Driver
High-side SW: OFF
Low-side SW: ON
High-side SW: ON
Low-side SW: OFF
Fig5. High-side SW driven by Boot Strap
You should connect bootstrap condenser larger than CBS=0.1µF between BS Terminal and OUT Terminal.
The internal counter decides the bootstrap condenser Charge and Discharge time.
A capacitor discharge time (tHPWM) for High-side SW Maximum ON Time is 300ms (typ).
A capacitor charge time (tHPWM / 128) for Low-side SW Minimum ON Time is 2.34µs (typ).
ꢁBuilt-in Regulator
The REG Terminal outputs Reference Voltage (5V).
It can be used as generating of the voltage for the bootstrap or a power supply voltage for other device(s). You should
connect capacitor (CREG) larger than 1µF for stable regulator output.
This regulator current capability (IOREG) is 30mA (min) at (VREG1×0.95). This regulator over current protection is a
drooping characteristic type. It has drooping characteristic at over current protection function.
ꢁThermal Shut Down Function
When NJW4800 chip temperature exceeds the 170°C, internal thermal shutdown circuit operates and SW function is
stopped. The Fault signal is output simultaneously from the FLT terminal. In order to return SW operation, you should
make chip surface temperature (Junction Temperature: Tj) below the 150°C*.
This function is a circuit to prevent IC at the high temperature from malfunctioning and is not something that urges
positive use. You should make sure to operate inside the junction temperature range rated. (* Design value)
Ver.2010-09-29
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NJRC [ NEW JAPAN RADIO ]
