Datasheet MAX16126, MAX16127 (Analog Devices) - 10

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MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
TERM Connection
The TERM connection has an internal switch to IN.
UV FAULT SUPPLY CURRENT VS. SUPPLY VOLTAGE
In shutdown (SHDN = GND), this switch is open. By 2.0 connecting the voltage threshold resistive divider to 1.8 TERM instead of directly to IN, power dissipation in the resistive divider can be eliminated and the shutdown 1.6 supply current reduced. 1.4 TA = +125°C
Reverse-Voltage Protection
1.2 TA = +25°C 1.0 TA = -40°C The MAX16126/MAX16127 integrate reverse-voltage protection, preventing damage to the downstream circuitry 0.8 CURRENT(mA) LY caused by battery reversal or negative transients. The 0.6 devices can withstand reverse voltage to -36V without SUPP 0.4 damage to themselves or the load. During a reverse- 0.2 voltage condition, the two external n-channel MOSFETs 0 are turned off, protecting the load. Connect a 0.1µF 0 10 20 30 ceramic capacitor from IN to GND, connect 10µF from the SUPPLY VOLTAGE (V) load to GND, and minimize the parasitic capacitance from GATE to GND to have a fast reserve-battery voltage-tran-
Applications Information
sient protection. During normal operation, both MOSFETs are turned on and have a minimal forward voltage drop,
Automotive Electrical Transients
providing lower power dissipation and a much lower
(Load Dump)
voltage drop than a reverse-battery protection diode. Automotive circuits generally require supply voltage protection from various transient conditions that occur in
Supply Current During Fault Conditions
automotive systems. Several standards define various During fault conditions, the MAX16126/MAX16127 pulses that can occur. Table 1 summarizes the pulses supply current is higher than normal operation. When a from the ISO 7637-2 and ISO 16750-2 specification. fault condition occurs, the MAX16126/MAX16127 pulls the Most of the pulses can be mitigated with capaci- gate low but keeps the charge pump active. This results tors and zener clamp diodes (see the Typical in increased supply because the charge pump tries hard Operating Characteristics and also the Increasing the to bring up the gate. See Figures below for supply current Input Voltage Protection Range section). The load dump during overvoltage and undervotlage fault conditions. (pulse 5a and 5b) occurs when the alternator is charging the battery and a battery terminal gets disconnected. Due to the
OV FAULT MODE SUPPLY CURRENT VS.
sudden change in load, the alternator goes out of regulation
SUPPLY VOLTAGE
and the bus voltage spikes. The pulse has a rise time 2.0 of about 10ms and a fall time of about 400ms, but can 1.8 extend out to 1s or more depending on the characteris- tics of the charging system. The magnitude of the pulse 1.6 T depends on the bus voltage and whether the system is 1.4 A = +125°C T unsuppressed or uses central load-dump suppression A = +25°C 1.2 (generally implemented using very large clamp diodes 1.0 TA = -40°C built into the alternator). Table 1 lists the worst-case CURRENT(mA) Y 0.8 values from the ISO 7637-2 specification. SUPPL 0.6 Cold crank (pulse 4) occurs when activating the starter motor in cold weather with a marginal battery. Due to the 0.4 large load imposed by the starter motor, the bus voltage 0.2 sags. Since the MAX16126/MAX16127 can operate down 0 to 3V, the downstream circuitry can continue to operate 0 10 20 30 through a cold-crank condition. If desired, the undervoltage SUPPLY VOLTAGE (V) threshold can be increased so that the MOSFETs turn www.analog.com Analog Devices │ 10