Datasheet

MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
14Maxim Integrated
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
Increasing the
Input Voltage Operating Range
With proper external component selection, the MAX16126/
MAX16127’s input voltage operating range can be
extended beyond 30V. Normally the input voltage can
swing up to 90V in protection mode, but normal opera-
tion is listed in the electrical characteristics table to 30V.
Higher voltage operation is permissible so long as the
resulting GATE bias voltage does not exceed 45V with
respect to GND.
To enable operating voltages above 30V, a 6.8V
Zener diode clamp can be added GATE-to-SRC to the
external switches to limit the maximum GATE voltage.
The circuit in Figure 4 shows the recommended arrange-
ment. When V
IN
= 35V, V
GATE
= 35V + 6.8V or 41.8V.
When V
IN
> 35V, the MAX16126/MAX16127 detects
the input over voltage condition by sensing the voltage
at the OVSET pin and turns off the charge pump. The
resistive voltage divider on OVSET must be selected
to disable the circuit before the gate voltage reaches
45V. The MAX16126TCA/MAX16127TCA automatically
reenable GATE drive when the input voltage drops 5%
below the overvoltage threshold. For the MAX16126TCD,
the latch-mode option, GATE drive is enabled by either
power cycling the IN voltage below UVLO threshold or by
toggling SHDN. See the Ordering Information section for
other available options.
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.
Figure 3. Circuit to Increase Input Voltage Protection Range
GND
GATE
V
BATT
SRC OUT
IN OUT
DC-DC
CONVERTER
SHDN
IN
GND
D1
D2
*SYSTEM GROUND
*
**
MAX16126
MAX16127
100kI
FLAG
100I
10µF
10nF
100I
R
S