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 driven
from input voltages down to +1.425V without sacrificing
stability or transient performance. Since these regulators
have a PMOS output device, supply current is not a sig-
nificant 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 lim-
ited 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 contin-
ue until the fault is removed. For continuous operation, do
not exceed the absolute maximum junction-temperature
rating of TJ = +150°C.
Output Voltage Selection
The MAX8516/MAX8517/MAX8518 feature an adjust-
able 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:
OUT FB R1
V V 1 R2
= +
where typically VFB = 0.5V. Choose R2 ≤ 5kΩ to optimize
quiescent current, accuracy, and high-frequency power-
supply rejection. To simplify resistor selection:
OUT
V
R1 R 2 1
V−
=
Soft-Start
Inherent soft-start limits inrush current. Peak inrush cur-
rent is dependent on the value of COUT and can be cal-
culated as follows:
OUT
INRUSH LOAD C (µF)
I I 66
= +
Shutdown Mode
The MAX8516/MAX8517/MAX8518 include an enable
input. To shut down the device, pull EN to GND. For nor-
mal operation, connect the EN to IN. During shutdown, an
internal 10kΩ resistor pulls down the output.
Power-OK (MAX8517 Only)
The MAX8517 features a power-OK (POK) output to indi-
cate the status of the output. POK remains high when the
regulator output is within ±10% of its nominal output volt-
age. If the output voltage falls or rises outside 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 output
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.
Figure 1. Typical Application Circuit
MAX8516
MAX8517
MAX8518
1µF
4.7µF
ENABLE
SHUTDOWN
IN
IN
POK (MAX8517) OR
POR (MAX8518)
EN GND
FB
OUT
OUT
100kΩ*
R1
R2
ADJUSTABLE
OUTPUT
*FOR MAX8517 AND MAX8518
+1.425V TO +3.6V
MAX8516/MAX8517/
MAX8518
1.425V to 3.6V Input, 1A,
0.2V Dropout LDO Regulators
www.maximintegrated.com Maxim Integrated
│
7