Datasheet
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
11Maxim Integrated
Table 1. Summary of ISO7637 Pulses
Refer to the ISO7637-2 specification for details on pulse
waveforms, test conditions, and test fixtures.
Setting Overvoltage and Undervoltage
Thresholds (MAX16126)
The MAX16126 uses an external resistive divider to
set the overvoltage and undervoltage thresholds. The
MAX16126 operates in switch mode in which the internal
overvoltage comparator monitors the input voltage. It
uses three resistors in a single resistive divider to set the
undervoltage and overvoltage thresholds. The top of the
resistive divider connects to TERM (see Figure 1).
The MAX16126 includes internal undervoltage and over-
voltage comparators for window detection. GATE is
enhanced and the n-channel MOSFETs are on when
the IN voltage is within the selected window. When the
monitored voltage falls below the lower limit (V
TRIPLOW
)
or exceeds the upper limit (V
TRIPHIGH
) of the window,
the GATE voltage goes to GND, turning off the MOSFETs.
The circuit in Figure 1 shows the MAX16126 enabling the
DC-DC converter when the monitored voltage is in the
selected window.
The resistor values R1, R2, and R3 can be calculated as
follows:
TOTAL
TRIPLOW TH TH-HYS
R
V (V - V )
R2 R3
=
+
TOTAL
TRIPHIGH TH
R
VV
R3
=
where R
TOTAL
= R1 + R2 + R3, V
TH
is the 1.225V OVSET/
UVSET threshold, V
TH-HYS
is the hysteresis.
Use the following steps to determine the values for R1,
R2, and R3:
1) Choose a value for R
TOTAL
, the sum of R1, R2, and R3.
2) Calculate R3 based on R
TOTAL
and the desired upper
trip point:
TH TOTAL
TRIPHIGH
VR
R3
V
×
=
3) Calculate R2 based on R
TOTAL
, R3, and the desired
lower trip point:
TH TH-HYS TOTAL
TRIPLOW
(V - V ) R
R2 - R3
V
×
=
4) Calculate R1 based on R
TOTAL
, R2, and R3:
TOTAL
R1 R - R2 - R3=
*Relative to system voltage.
NAME DESCRIPTION
PEAK VOLTAGE (V) (max)
*
DURATION
12V SYSTEM
Pulse 1 Inductive load disconnection -100 1ms to 2ms
Pulse 2a Inductive wiring disconnection 50 0.05ms
Pulse 3a
Switching transients
-150
0.2Fs
Pulse 3b 100
Pulse 4 Cold crank
-7 100ms (initial)
-6 Up to 20s
Pulse 5a Load dump (unsuppressed) 87
400ms (single)
Pulse 5b Load dump (suppressed) (Varies, but less than pulse 5a)