MAX14691 Datasheet, PDF (11/19 Pages) Maxim Integrated Products – High-Accuracy, Adjustable Power Limiter

MAX14691–MAX14693
High-Accuracy, Adjustable Power Limiter
Detailed Description
The MAX14691–MAX14693 adjustable overvoltage,
undervoltage, and overcurrent protection devices guard
systems against overcurrent faults in addition to positive
overvoltage and reverse-voltage faults. When used with
an optional external p-channel MOSFET, the devices
also protect downstream circuitry from voltage faults
up to ±60V. The devices feature a low, 31mΩ, on-resis-
tance integrated FET. During startup, the devices are
designed to charge large capacitances on the output in
a continuous mode for applications where large reservoir
capacitors are used on the inputs to downstream devices.
Additionally, the MAX14691, MAX14692, and MAX14693
feature a dual-stage current-limit mode in which the cur-
rent is continuously limited to 1x, 1.5x, and 2x the pro-
grammed limit, respectively, for a short time after startup.
This enables faster charging of large loads during startup.
The devices feature the option to set the overvoltage-
lockout (OVLO) and undervoltage-lockout (UVLO) thresh-
olds manually using external voltage-dividers or to use
the factory-preset internal thresholds by connecting the
OVLO and/or UVLO pin(s) to GND. The adjustable
overvoltage range of the devices is 6V to 40V, while the
adjustable undervoltage range is 5.5V to 24V. The facto-
ry-preset internal threshold for the devices is 36V (typ),
with the preset internal UVLO threshold being 12V (typ).
The devices’ programmable current-limit threshold can
be set for currents up to 6A in autoretry, latchoff, or
continuous-fault-response mode. When the device is set
to autoretry mode and the current exceeds the threshold
for more than 24ms (typ), the internal FET is turned off
for 720ms (typ), then turned back on. If the fault is still
present, the cycle repeats. In latchoff mode, if a fault is
present for more than 24ms (typ), the internal FET is
turned off until enable is toggled or the power is cycled.
In continuous mode, the current is limited continuously to
the programmed current-limit value. In all modes, FLAG
asserts if V_IN - V_OUT is greater than the FLAG assertion
drop voltage threshold (V_FA).
Startup Control
The devices feature a dual-stage startup sequence that
continuously limits the current to 1x/1.5x/2x the set cur-
rent limit during the startup initial time (t_STI), allowing
large capacitors present on the output of the switch to be
rapidly charged. The MAX14691 limits the current to 1x
the set limit during this period while the MAX14692 and
MAX14693 limit the current to 1.5x and 2x the set limit,
respectively. If the temperature of any device rises to the
thermal-foldback threshold (T_{J_FB}), the device enters
power-limiting mode (Figure 1). In this mode, the device
thermally regulates the current through the switch to
protect itself while still delivering as much current as
possible to the output regardless of the current-limit type
selected. If the output is not charged within the startup
timeout period (t_STO), the switch turns off and IN, EN, or
HVEN must be toggled to resume normal operation.
Overvoltage Lockout (OVLO)
The devices feature two methods for determining
the OVLO threshold. By connecting the OVLO pin
to GND, the preset internal OVLO threshold of 36V
(typ) is selected. If the voltage at OVLO rises above
the OVLO select threshold (V_{OVLO_SEL}), the device
enters adjustable OVLO mode. Connect an exter-
nal voltage-divider to the OVLO pin, as shown in the
Typical Application Circuit to adjust the OVLO threshold.
R3 = 2.2MΩ is a good starting value for minimum current
consumption. Since V_SET is known, R3 has been chosen,
and V_OVLO is the target OVLO value, R4 can then be
calculated by the following equation:
R4 = ^{R3 × VSET}
V_OVLO − V_SET
Undervoltage Lockout (UVLO)
The devices feature two methods for determin-
ing the UVLO threshold. By connecting the UVLO pin
to GND, the preset, internal UVLO threshold of 12V
(typ) is selected. If the voltage at UVLO rises above
the UVLO select threshold (V_{UVLO_SEL}), the device
enters adjustable UVLO mode. Connect an exter-
nal voltage-divider to the UVLO pin, as shown in the
Typical Application Circuit to adjust the UVLO threshold.
R1 = 2.2MΩ is a good starting value for minimum current
consumption. Since V_SET is known, R1 has been chosen,
and V_UVLO is the target value, R2 can then be calculated
by the following equation:
R2 = ^{R1× VSET}
V_UVLO − V_SET
Switch Control
There are two independent enable inputs on the devices:
HVEN and EN. HVEN is a high-voltage-capable input,
accepting signals up to 58V. EN is a low-voltage input,
accepting a maximum voltage of 5V. In case of a fault
condition, toggling HVEN or EN resets the fault. The
enable inputs control the state of the switch based on the
truth table (Table 1).
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