MAX16126 Datasheet, PDF (11/19 Pages) Maxim Integrated Products – Load-Dump/Reverse-Voltage Protection Circuits

MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Table 1. Summary of ISO7637 Pulses
NAME
Pulse 1
Pulse 2a
Pulse 3a
Pulse 3b
Pulse 4
Pulse 5a
Pulse 5b
DESCRIPTION
Inductive load disconnection
Inductive wiring disconnection
Switching transients
Cold crank
Load dump (unsuppressed)
Load dump (suppressed)
PEAK VOLTAGE (V) (max)^*
12V SYSTEM
-100
50
-150
100
-7
-6
87
(Varies, but less than pulse 5a)
*Relative to system voltage.
DURATION
1ms to 2ms
0.05ms
0.2Fs
100ms (initial)
Up to 20s
400ms (single)
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:
V_TRIPLOW
=
(V_TH
-
V_TH-HYS)^{}
R _TOTAL
R2 + R3


V_TRIPHIGH
=
V_TH^{}
R
TOTAL
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:
R3 = ^{VTH × R TOTAL}
V_TRIPHIGH
3) Calculate R2 based on R_TOTAL, R3, and the desired
lower trip point:
R2 = ^{(VTH - VTH-HYS) × RTOTAL} - R3
V_TRIPLOW
4) Calculate R1 based on R_TOTAL, R2, and R3:
R1 = R _TOTAL - R2 - R3
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