njw4800 New Japan Radio Co.,Ltd, njw4800 Datasheet - Page 12

• Manufacturer Part Number: njw4800
• Description: 30v/4a Half Bridge Driver
• Manufacturer: New Japan Radio Co.,Ltd

NJW4800
PWM is high (above 2.2V), the high-side switch is turned on. When the signal at PWM is low (less than 0.9V), the
low-side switch is turned on.
high-side SW gate is driven with V
300µsec(typ.). (ex. Fig2)
prevent short circuit (high-side and low-side) where both the
high-side and low-side switches are off. (ex. Fig3)
regulator. The NJW4800 operates at frequencies up to
1.2MHz.
compensates the leak current of the High-side SW.
over-current protection circuit operates at 5.5A (typ.) and stops the SW operation. The FLT signal is output from FLT
terminal at the same time. The over-current protection operation is released at the PWM input signal falling edge. (ex.
Fig4)
current limit. Because that time big electric power consumption occurs instantaneously in NJW4800, you should design
sufficient heat dissipation.
diode by inductive kickback.
Therefore, an external diode should be considered usage against reverse-current regeneration according to the kind of
the application.
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FUNCTIONAL EXPLANATION
High-side, Low-side Switch
The SW output drives the load. It is controlled by the logic input signal from PWM terminal at PWM. When the signal at
The NJW4800 uses built-in Nch MOSFETs (R
There is a dead time region (20nsec (typ.): design value) to
The NJW4800 is suitable for high-frequency switching
The OUT terminal is pulled down inside with 100kΩ,
Over Current Protection Function
The internal over-current protection circuit monitors the flow currents of both the high-side and low-side switches. The
If OUT terminal is shorted directly to GND, a large surge current is flowing for fast current change and may exceed
When a load condition is inductive property, a reverse direction current flows to the high-side and low-side SW body
The built-in over-current protection circuit has not aimed at protection against the inductive kickback.
PWM Input
High Side SW
Low Side SW
Current Limit
Fault Output
(FLT pin Pull-Up)
Fig4. Timing Chart of High-side/Low-side Switch at Over Current Protection Operating
High
Low
ON
OFF
ON
OFF
ON
OFF
High
Low
+
+5V that generated by bootstrap. The high-side SW turn on time is limited to
ON
=0.25Ω typ.) for both the high-side and low-side switches. The
The Overcurrent Protection is
released with the falling edge
Hi-Z
Hi-Z
High Side
SW
Low Side
SW
Fig3. SW Function and Dead Time Relation
Dead Time 20ns typ.
ON
OFF
ON
OFF
Hi-Z
Hi-Z
Ver.2010-09-29