MAX6397 MAXIM [Maxim Integrated Products], MAX6397 Datasheet - Page 9

• Manufacturer Part Number: MAX6397
• Description: Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 2a. MAX6397/MAX6398 GATE Waveform During Over-
voltage Switch Mode
Figure 2b. MAX6397/MAX6398 GATE Waveform During Over-
voltage Limit Mode
GATE cycles on-off-on-off-on in a sawtooth waveform
until OUT remains below the overvoltage fault threshold
and GATE remains constantly on (V
voltage limiter’s sawtooth GATE output operates the
MOSFET in a switched-linear mode while the input volt-
age remains above the overvoltage fault threshold. The
sawtooth frequency depends on the load capacitance,
load current, and MOSFET turn-on time (GATE charge
current and GATE capacitance).
GATE goes high when the following startup conditions
are met: V
high, an overvoltage fault is not present and the device
is not in thermal shutdown.
IN
is above the UVLO threshold, SHDN is
_______________________________________________________________________________________
10ms/div
4ms/div
Overvoltage Protection Switch/Limiter
IN
+ 10V). The over-
V
10V/div
V
10V/div
V
10V/div
V
10V/div
V
10V/div
V
10V/div
IN
GATE
OUT
IN
GATE
OUT
Controllers Operate Up to 72V
When operating in overvoltage mode, the MAX6397/
MAX6398 feedback path (Figure 3) consists of IN,
SET’s internal comparator, the internal gate charge
pump, and the external n-channel MOSFET resulting in
a switch-on/off function. When the programmed over-
voltage threshold is tripped, the internal fast compara-
tor turns off the external MOSFET, pulling GATE to OUT
within t
the load. When IN decreases below the adjusted over-
voltage threshold, the MAX6397/MAX6398 slowly
enhance GATE above OUT, reconnecting the load to
the power source.
When operating in overvoltage limiter mode, the
MAX6397/MAX6398 feedback path (Figure 4) consists
of OUT, SET’s internal comparator, the internal gate
charge pump and the external n-channel MOSFET,
which results in the external MOSFET operating as a
voltage regulator.
During normal operation, GATE is enhanced 10V above
OUT. The external MOSFET source voltage is monitored
through a resistor-divider between OUT and SET. When
OUT rises above the adjusted overvoltage threshold, an
internal comparator sinks the charge-pump current, dis-
charging the external GATE, regulating OUT at the set
overvoltage threshold. OUT remains active during the
overvoltage transients and the MOSFET continues to con-
duct during the overvoltage event, operating in switched-
linear mode.
Figure 3. Overvoltage Switch Protection Configuration
OV
and disconnecting the power source from
V
BATT
R1
R2
IN
SET
Overvoltage Monitoring
MAX6397
MAX6398
GATE
GND
Overvoltage Limiter
OUT
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