MAX15008 Datasheet, PDF (14/23 Pages) Maxim Integrated Products – Automotive 300mA LDO Voltage Regulators with Tracker Output and Overvoltage Protector

Automotive 300mA LDO Voltage Regulators
with Tracker Output and Overvoltage Protector
Overvoltage-Limiter Mode
When operating in overvoltage-limiter mode, the feed-
back path consists of SOURCE, FB_PROT’s internal
comparator, the internal gate charge pump/gate pull-
down, and the external n-channel MOSFET (Figure 2).
This configuration results in the external MOSFET oper-
ating as a hysteretic voltage regulator.
During normal operation, GATE is enhanced 8.1V
above V_IN. The external MOSFET source voltage is
monitored through a resistive voltage-divider between
SOURCE and FB_PROT. When V_SOURCE exceeds the
adjustable overvoltage threshold, an internal pulldown
switch discharges the gate voltage and quickly turns
the MOSFET off. Consequently, the source voltage
begins to fall. The V_SOURCE fall time is dependent on
the MOSFET’s gate charge, the internal charge-pump
current, the output load, and any load capacitance at
SOURCE. When the voltage at FB_PROT is below the
overvoltage threshold by an amount equal to the hys-
teresis, the charge pump restarts and turns the
MOSFET back on. In this way, the OVP controller
attempts to regulate V_SOURCE around the overvoltage
threshold. SOURCE remains high during overvoltage
transients and the MOSFET continues to conduct dur-
ing an overvoltage event. The hysteresis of the
FB_PROT comparator and the gate turn-on delay force
the external MOSFET to operate in a switched on/off
sequence during an overvoltage event.
Exercise caution when operating the MAX15008 in
voltage-limiting mode for long durations. Care must be
taken against prolonged or repeated exposure to
overvoltage events while delivering large amounts of
load current as the power dissipation in the external
MOSFET may be high under these conditions. To pre-
vent damage to the MOSFET, implement proper
heatsinking. The capacitor connected between
SOURCE and ground can also be damaged if the rip-
ple current rating for the capacitor is exceeded.
As the transient voltage decreases, the voltage at
SOURCE falls. For fast-rising transients and very large
MOSFETs, connect an additional capacitor from GATE
to PGND. This capacitor acts as a voltage-divider work-
V_IN
IN
GATE
MAX15008
SOURCE
FB_PROT
SGND
PROTECTOR
OUTPUT
Figure 2. Overvoltage Limiter (MAX15008)
ing against the MOSFET’s drain-to-gate capacitance. If
using a very low gate charge MOSFET, additional
capacitance from GATE to ground might be required to
reduce the switching frequency.
Control Logic
The MAX15008/MAX15010 LDO features two logic
inputs, EN_LDO and HOLD, making these devices suit-
able for automotive applications. For example, when
the ignition key signal drives EN_LDO high, the regula-
tor turns on and remains on even if EN_LDO goes low,
as long as HOLD is forced low and stays low after initial
regulator power-up. In this state, releasing HOLD turns
the regulator output (OUT_LDO) off. This feature makes
it possible to implement a self-holding circuit without
external components. Forcing EN_LDO low and HOLD
high (or unconnected) places the regulator into shut-
down mode reducing the supply current to less than
16µA. Table 1 shows the state of OUT_LDO with
respect to EN_LDO and HOLD. Leave HOLD uncon-
nected or connect directly to OUT_LDO to allow the
EN_LDO input to act as a standard on/off logic input for
the regulator.
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