MAX15028 Maxim Integrated Products, MAX15028 Datasheet - Page 8

• Manufacturer Part Number: MAX15028
• Description: (MAX15027 / MAX15028) 1A Low-Dropout Regulators
• Manufacturer: Maxim Integrated Products

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The MAX15027/MAX15028 feature a 75mΩ (typ)
p-channel MOSFET pass transistor. Unlike similar
designs using pnp pass transistors, p-channel MOSFETs
require no base drive, reducing 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
MAX15027/MAX15028 do not suffer from these prob-
lems and consume only 275µA (typ) of quiescent cur-
rent under heavy loads, as well as in dropout.
The MAX15027/MAX15028 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 a maximum of 2A. Under these conditions,
the device quickly heats up. When the junction temper-
ature reaches +165°C (typ), the thermal-overload cir-
cuitry turns off the output, allowing the part to cool
down. When the junction temperature cools to +150°C
(typ), the output turns back on and reestablishes regu-
lation. Current limiting and thermal protection continue
until the fault is removed. For continuous operation, do
not exceed the absolute maximum junction-tempera-
ture rating of T
The MAX15027/MAX15028 feature a soft-start function
that slowly ramps up the output voltage of the regulator
based on the value of the capacitor (C
from SS to GND. Upon power-up, C
a 5µA (typ) current source through SS. The voltage at
SS is compared to the internal 0.5V reference (V
The feedback voltage for regulation (V
of V
(V
rises above V
reference voltage since it is the lower of V
The value of C
time, t
where C
1.425V to 3.6V Input, 1A Low-Dropout
Regulators with BIAS Input
8
REG
_______________________________________________________________________________________
SS
SS
) rises at the same rate. Once V
or V
SS
. Use the following formula to determine C
Internal p-Channel Pass Transistor
is in farads and t
REF
REF
J
SS
. As V
= +150°C.
, the regulation voltage then tracks the
determines the length of the soft-start
C
SS
SS
Thermal Fault Protection
= 10
rises, the regulation voltage
SS
-5
is in seconds.
x t
SS
SS
Short-Circuit/
REG
SS
is charged with
SS
SS
) is the lower
reaches and
Soft-Start
) connected
and V
SS
REF
REF
.
).
.
The MAX15027/MAX15028 include an enable input. To
shut down the IC, drive EN low. In shutdown mode, the
current drawn by BIAS is less than 2µA. This feature is
extremely useful in an automotive application where the
BIAS input is derived from an always-on LDO expecting
to provide minimal dark current. For normal operation,
drive EN high or connect EN to IN (BIAS for MAX15028)
for continuous on operation. During shutdown, an inter-
nal 10kΩ resistor is connected between OUT and GND.
The MAX15027/MAX15028 feature an adjustable output
voltage from 0.5V to V
connected as a voltage-divider to FB as shown in
Figure 1. The output voltage is set by the following
equation:
where typically V
optimize load-transient response for no load to full load
transients, use the resistor-divider as a minimum load
and choose R2 to be 500Ω. To simplify resistor selection:
Figure 1. MAX15028 Typical Application Circuit
SHUTDOWN
1.2V TO 3.6V
ALWAYS-ON
INPUT 3V
ENABLE
TO 5.5V
INPUT
1µF
Programming the Output Voltage
Applications Information
FB
EN
V
BIAS
IN
R
OUT
= 0.5V. Choose R2 to be 10kΩ. Or, to
1
=
MAX15028
R
IN
=
2
V
SS
⎛
⎜
⎝
using two external resistors
FB
V
V
OUT
0.1uF
FB
⎛
⎜
⎝
1
+
GND
OUT
R
−
R
I.C.
FB
Shutdown Mode
1
2
1
⎞
⎟
⎠
⎞
⎟
⎠
R1
R2
OUTPUT
4.7µF