Internal p-Channel Pass Transistor
The MAX15029/MAX15030 feature a 75mΩ (typ) p-chan-
nel MOSFET pass transistor. Unlike similar designs using
pnp pass transistors, p-channel MOSFETs require no
base drive, reducing quiescent current. pnp-based regula-
tors also waste considerable current in dropout when the
pass transistor saturates and uses high base-drive cur-
rents under large loads. The MAX15029/MAX15030 do
not suffer from these problems and consume only 315μA
(typ) of quiescent current under heavy loads, as well as
in dropout.
Short-Circuit/Thermal-Fault Protection
The MAX15029/MAX15030 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 1A. Under these conditions, the device
quickly heats up. When the junction temperature reaches
+165°C (typ), the thermal-overload circuitry 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 regulation. Current limiting and
thermal protection continue until the fault is removed.
For continuous operation, do not exceed the absolute
maximum junction-temperature rating of TJ = +150°C.
Soft-Start
The MAX15029/MAX15030 feature a soft-start function
that slowly ramps up the output voltage of the regulator
based on the value of the capacitor (CSS) connected
from SS to GND. Upon power-up, CSS is charged with
a 5μA (typ) current source through SS. The voltage at
SS is compared to the internal 0.5V reference (VREF).
The feedback voltage for regulation (VREG) is the lower
of VSS or VREF. As VSS rises, the regulation voltage
(VREG) rises at the same rate. Once VSS reaches and
rises above VREF, the regulation voltage then tracks the
reference voltage since it is the lower of VSS and VREF.
The value of CSS determines the length of the soft-start
time, tSS. Use the following formula to determine CSS.
CSS = 10-5 x tSS
where CSS is in farads and tSS is in seconds.
Shutdown Mode
The MAX15029/MAX15030 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 for continuous on operation.
During shutdown, an internal 10kΩ resistor is connected
between OUT and GND.
Applications Information
Programming the Output Voltage
The MAX15029/MAX15030 feature an adjustable output
voltage from 0.5V to VIN 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 V1
R2
= +
where typically VFB = 0.5V. Choose R2 to be 10kΩ. Or,
to 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:
OUT
V
R1 R2 1
V
= −
Figure 1. MAX15030 Typical Application Circuit
0.1uF
ENABLE
SHUTDOWN
R2
R1
INPUT
1.425V TO 3.6V
ALWAYS-ON
INPUT
3V TO 5.5V
OUTPUT
2.2µF
1µF
IN
BIAS OUT
FB
I.C.
GND
EN
SS
MAX15030
MAX15029/MAX15030 1.425V to 3.6V Input, 500mA Low-Dropout
Regulators with BIAS Input
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