Detailed Description
The MAX8516/MAX8517/MAX8518 are low-input, low-
dropout, PMOS regulators capable of delivering up to
1A of output current with as little as 200mV of headroom
from input to output. The PMOS output stage can be dri-
ven from input voltages down to +1.425V without sacri-
ficing stability or transient performance. Since these
regulators have a PMOS output device, supply current
is not a significant function of load or input headroom.
Internal p-Channel Pass Transistor
The MAX8516/MAX8517/MAX8518 feature a 100mΩ (typ)
p-channel MOSFET pass transistor. Unlike similar
designs using pnp pass transistors, p-channel MOSFETs
require no base drive, which reduces quiescent current.
pnp-based regulators also waste considerable current in
dropout when the pass transistor saturates and use high
base-drive currents under large loads. The MAX8516/
MAX8517/MAX8518 do not suffer from these problems
and consume only 340µA (typ) of quiescent current
under heavy loads, as well as in dropout.
Short-Circuit/Thermal Fault Protection
The MAX8516/MAX8517/MAX8518 are fully protected
from a short circuit at the output through current-limiting
and thermal-overload circuitry. In the fault condition
when the output is shorted to ground, the output current
is limited to 2A. Under these conditions, the part quickly
heats up. When the junction temperature reaches
+165°C, the thermal-overload circuitry turns off the
output, allowing the part to cool down. When the junction
temperature cools to +150°C, the output turns back on
and tries to reestablish regulation. Current limiting and
thermal protection continue until the fault is removed. For
continuous operation, do not exceed the absolute maxi-
mum junction-temperature rating of T
J
= +150°C.
Output Voltage Selection
The MAX8516/MAX8517/MAX8518 feature an
adjustable output voltage from 0.5V to 3.4V, using two
external resistors connected as a voltage-divider to FB
as shown in Figure 1. The output voltage is set by the
following equation:
where typically V
FB
= 0.5V. Choose R2 ≤ 5kΩ to opti-
mize quiescent current, accuracy, and high-frequency
power-supply rejection. To simplify resistor selection:
Soft-Start
Inherent soft-start limits inrush current. Peak inrush cur-
rent is dependent on the value of C
OUT
and can be cal-
culated as follows:
Shutdown Mode
The MAX8516/MAX8517/MAX8518 include an enable
input. To shut down the device, pull EN to GND. For
normal operation, connect the EN to IN. During shut-
down, an internal 10kΩ resistor pulls down the output.
Power-OK (MAX8517 Only)
The MAX8517 features a power-OK (POK) output to
indicate the status of the output. POK remains high
when the regulator output is within ±10% of its nominal
output voltage. If the output voltage falls or rises out-
side this range, POK transitions low. This open-drain
output requires an external pullup resistor to IN. An
internal delay circuit prevents POK from switching for
50µs (typ) after the trip threshold is initially reached. If
the part is in shutdown mode, POK is low.
Power-On Reset (MAX8518 Only)
The MAX8518 features a power-on reset (POR) output
that transitions high 140ms (typ) after the output has
risen above 90% of its final value. This open-drain out-
put requires an external pullup resistor to IN. If the part
is in shutdown mode, falls below 90% of the nominal
output voltage, or experiences a short-circuit or thermal
fault, POR immediately transitions low.
