Datasheet

MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
12Maxim Integrated
Setting Overvoltage and Undervoltage
Thresholds (MAX16127)
The MAX16127 operates in limiter mode and uses sepa-
rate resistive dividers to set the undervoltage and over-
voltage thresholds. The top of the overvoltage divider
connects to OUT and the top of the undervoltage divider
connects to TERM (see Figure 2).
Use the following formula to calculate R4:
TOTAL_OV
TH
OV
R
R4 V
V
= ×
where R
TOTAL_OV
= R3 + R4, V
TH
is the 1.225V OVSET
rising threshold and V
OV
is the desired overvoltage
threshold. The falling threshold of V
TH
is 5% below the
rising threshold.
Similarly, to calculate the values of R1 and R2:
TOTAL_UV
TH TH-HYS
UV
R
R2 (V - V )
V
= ×
where R
TOTAL_UV
= R1 + R2, V
TH
is the 1.225V UVSET
rising threshold, V
TH-HYS
is the hysteresis, and V
UV
is the
desired undervoltage threshold.
Use the nearest standard-value resistor that is less
than the calculated value. A lower value for total resis-
tance dissipates more power, but provides slightly better
accuracy.
MOSFET Selection
MOSFET selection is critical to design a proper protec-
tion circuit. Several factors must be taken into account:
the gate capacitance, the drain-to-source voltage rating,
the on-resistance (R
DS(ON)
), the peak power dissipation
capability, and the average power dissipation limit. In
general, both MOSFETs should have the same part num-
ber. For size-constrained applications, a dual MOSFET
can save board area. Select the drain-to-source voltage
so that the MOSFETs can handle the highest voltage that
might be applied to the circuit. Gate capacitance is not
as critical, but it does determine the maximum turn-on
and turn-off time. MOSFETs with more gate capacitance
tend to respond more slowly.
Figure 1. Overvoltage and Undervoltage Window Detector Circuit (MAX16126)
GND
GATE
V
IN
100kI
10nF
SRC OUT
IN OUT
DC-DC
CONVERTER
SHDN
TERM
IN
UVSET
OVSET
GND
R1
R2
R3
MAX16126
0.1µF
FLAG
10µF
100I