MAX16126 Datasheet, PDF (14/19 Pages) Maxim Integrated Products – Load-Dump/Reverse-Voltage Protection Circuits

MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Increasing the Operating Voltage Range
The MAX16126/MAX16127 can tolerate -30V to +90V. To
increase the voltage range, connect two back-to-back
zener diodes from IN to GND, and connect a resistor in
series with IN and the power-supply input to limit the cur-
rent drawn by the zener diodes (see Figure 3).
Zener diode D1 clamps positive voltage excursions and
D2 clamps negative voltage excursions. Set the zener
voltages so the worst-case voltages do not exceed the
ratings of the part. Also ensure that the zener diode
power ratings are not exceeded. The combination of
the series resistor and the zener diodes also help snub
pulses on the supply voltage input and can aid in clamp-
ing the low-energy ISO7637-2 pulses.
It is important to compute the peak power dissipation
in the series resistor. Most standard surface-mount
resistors cannot withstand the peak power dissipation
during certain pulse events. Check the resistor data
sheets for pulse power derating curves. If necessary,
connect multiple resistors in parallel or use automotive-
rated resistors.
The shutdown input needs a series resistor to limit the
current if V_IN exceeds the clamped voltage on IN. A good
starting point is 100kI.
Output Reservoir Capacitor
The output capacitor can be used as a reservoir capaci-
tor to allow downstream circuitry to ride out fault transient
conditions. Since the voltage at the output is protected
from input voltage transients, the capacitor voltage rating
can be less than the expected maximum input voltage.
V_BATT
0.1µF
R_S
100kI
D1
D2
100kI
GATE
IN
SHDN
10nF
SRC
MAX16126
MAX16127
GND
100I
DC-DC
CONVERTER
IN
OUT
10µF
GND
OUT
FLAG
Figure 3. Circuit to Increase Operating Voltage Range
���������������������������������������������������������������� Maxim Integrated Products  14