Shutdown
The MAX8530/MAX8531 have a single shutdown con-
trol input (SHDN). Drive SHDN low to shut down both
outputs, reducing supply current to 10nA. Connect
SHDN to a logic high, or IN, for normal operation.
Internal P-Channel Pass Transistor
The MAX8530/MAX8531 feature two 1Ω P-channel
MOSFET pass transistors. A P-channel MOSFET pro-
vides several advantages over similar designs using
PNP pass transistors, including longer battery life. It
requires no base drive, substantially reducing quies-
cent current. PNP-based regulators waste considerable
current in dropout when the pass transistor saturates
and also use high base-drive currents under heavy
loads. The MAX8530/MAX8531 do not suffer these
problems and consume only 150µA of quiescent cur-
rent whether in dropout, light-load, or heavy-load appli-
cations (see the Typical Operating Characteristics).
Whereas a PNP-based regulator has dropout voltage
that is independent of the load, a P-channel MOSFET’s
dropout voltage is proportional to load current, providing
for low dropout voltage at heavy loads and extremely
low dropout voltage at lighter loads.
Current Limit
The MAX8530/MAX8531 contain two independent cur-
rent limiters, one for each regulator, which monitor and
control the pass transistor’s gate voltage and limit the
output currents to 210mA and 165mA minimum. The
output can be shorted to ground for an indefinite time
without damaging the part.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX8530/MAX8531. When the junction tem-
perature exceeds T
J
= +160°C, the thermal sensor
signals the shutdown logic, turning off the pass transistor
and allowing the IC to cool. The thermal sensor turns the
pass transistor on again after the IC’s junction tempera-
ture cools by 10°C, resulting in a pulsed output during
continuous thermal-overload conditions.
Thermal-overload protection is designed to protect the
MAX8530/MAX8531 in the event of fault conditions. For
continual operation, do not exceed the absolute maxi-
mum junction temperature rating of T
J
= +150°C.
Operating Region and Power Dissipation
The MAX8530/MAX8531s’ maximum power dissipation
depends on the thermal resistance of the case and cir-
cuit board, the temperature difference between the die
junction and ambient air, and the rate of airflow. The
power dissipation across the device is P = I
OUT
(V
IN
-
V
OUT
). Maximum power dissipation:
P
MAX
= (T
J
- T
A
)/(θ
JB
+ θ
BA
)
where T
J
- T
A
is the temperature difference between the
MAX8530/MAX8531 die junction and the surrounding air,
θ
JB
(or θ
JC
) is the thermal resistance of the package, and
θ
BA
is the thermal resistance through the printed circuit
board, copper traces, and other materials to the sur-
rounding air.
The GND pin of the MAX853_ETT__ (6-lead QFN) per-
forms the dual functions of providing an electrical con-
nection to the ground and channeling heat away.
Connect the GND pin and exposed pad to ground
using a large pad or ground plane.
Low-Noise Operation (MAX8531)
An external 0.01µF bypass capacitor at BP, in conjunc-
tion with an internal resistor, creates a lowpass filter
(see the Typical Application Circuit). The MAX8531
exhibits 40µV
RMS
output voltage noise with C
BP
=
0.01µF and C
OUT
= 2.2µF (see the Output Noise
Spectral Density vs. Frequency graph in the Typical
Operating Characteristics).
MAX8530/MAX8531
Dual Low-Dropout Linear Regulators
with
RESET
or Low-Noise Output in UCSP or QFN
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