MAX1963A/MAX1976A
Low-Input-Voltage, 300mA LDO Regulators
with
RESET
in SOT and TDFN
_______________________________________________________________________________________ 7
Detailed Description
The MAX1963A/MAX1976A are low-dropout, high-accu-
racy, low-quiescent-current linear regulators designed
primarily for battery-powered applications. These devices
supply loads up to 300mA and are available with preset
output voltages from +0.75V to +3.0V. As illustrated in
Figure 1, the MAX1963A/MAX1976A consist of a refer-
ence, an error amplifier, a p-channel pass transistor, an
internal feedback voltage-divider, and a power-good
comparator.
The reference is connected to the error amplifier, which
compares this reference with the feedback voltage and
amplifies the difference. If the feedback voltage is
lower than the reference voltage, the pass-transistor
gate is pulled lower, which allows more current to pass
to the output and increases the output voltage. If the
feedback voltage is too high, the pass-transistor gate is
pulled up, allowing less current to pass to the output.
Internal p-Channel Pass Transistor
The MAX1963A/MAX1976A feature a 0.33Ω (R
DS(ON)
)
p-channel MOSFET pass transistor. Unlike similar
designs using pnp pass transistors, p-channel
MOSFETs require no base drive, which reduces quies-
cent current. The pnp-based regulators also waste con-
siderable current in dropout when the pass transistor
saturates and use high base-drive currents under large
loads. The MAX1963A/MAX1976A do not suffer from
these problems and consume only 90µA (typ) of quies-
cent current under heavy loads, as well as in dropout.
Shutdown
Pull SHDN low to enter shutdown. During shutdown, the
output is disconnected from the input, an internal 1.5kΩ
resistor pulls OUT to GND, RESET is actively pulled
low, and the supply current drops below 1µA.
RESET
Output
The MAX1963A/MAX1976A microprocessor (µP) supervi-
sory circuitry asserts a guaranteed logic-low reset during
power-up, power-down, and brownout conditions down
to +1V. RESET asserts when V
OUT
is below the reset
threshold and remains asserted for at least t
RP
after V
OUT
rises above the reset threshold of regulation.
Current Limit
The MAX1963A/MAX1976A monitor and control the pass
transistor’s gate voltage, limiting the output current to
450mA (min). If the output exceeds I
LIM
, the MAX1963A/
MAX1976A output voltage drops.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX1963A/MAX1976A. When the junction
temperature exceeds T
J
= +165°C, a thermal sensor
turns off the pass transistor, allowing the IC to cool. The
thermal sensor turns the pass transistor on again after
the junction temperature cools by 15°C, resulting in a
pulsed output during continuous thermal-overload con-
ditions. Thermal-overload protection safeguards the
MAX1963A/MAX1976A in the event of fault conditions.
For continuous operation, do not exceed the absolute
maximum junction-temperature rating of T
J
= +150°C.
Operating Region and Power Dissipation
The MAX1963A/MAX1976A maximum power dissipa-
tion depends on the thermal resistance of the IC pack-
age and circuit board, the temperature difference
between the die junction and ambient air, and the rate
of airflow. The power dissipated in the device is P =
I
OUT
(V
IN
- V
OUT
). The maximum allowed power dissi-
pation is:
P
MAX
= (T
J(MAX)
- T
A
) / (θ
JC
+ θ
CA
)
where (T
J(MAX)
- T
A
) is the temperature difference
between the MAX1963A/MAX1976A die junction and
the surrounding air, θ
JC
is the thermal resistance of the
junction to the case, and θ
CA
is the thermal resistance
from the case through the PC board, copper traces,
and other materials to the surrounding air. For best
heatsinking, expand the copper connected to the
exposed paddle or GND.
The MAX1963A/MAX1976A deliver up to 300mA and
operate with an input voltage up to +3.6V. However,
when using the 6-pin SOT23 version, high output cur-
rents can only be sustained when the input-output dif-
ferential voltage is less than 2V, as shown in Figure 2.
The maximum allowed power dissipation for the 6-pin
TDFN is 1.951W at T
A
= +70°C. Figure 3 shows that the
maximum input-output differential voltage is not limited
by the TDFN package power rating.
Applications Information
Capacitor Selection and
Regulator Stability
Capacitors are required at the MAX1963A/MAX1976A
input and output for stable operation over the full tem-
perature range and with load currents up to 300mA.
Connect a 1µF ceramic capacitor between IN and GND
and a 4.7µF low-ESR ceramic capacitor between OUT
and GND. The input capacitor (C
IN
) lowers the source
impedance of the input supply. Use larger output
capacitors to reduce noise and improve load-transient
response, stability, and power-supply rejection.
The output capacitor’s equivalent series resistance
(ESR) affects stability and output noise. Use output
