Output Voltage
The MAX8875 is supplied with factory-set output volt-
ages of 1.5V, 2.5V, 2.7V, 3.0V, 3.3V, or 5.0V. The part
number’s two-digit suffix identifies the nominal output
voltage. For example, the MAX8875EUK33 has a preset
output voltage of 3.3V (see Output Voltage Selector
Guide).
Internal P-Channel Pass Transistor
The MAX8875 features a 1.1Ω (typ) P-channel MOSFET
pass transistor. This provides several advantages over
similar designs using PNP pass transistors, including
longer battery life. The P-channel MOSFET requires no
base drive, which reduces quiescent current signifi-
cantly. PNP-based regulators waste considerable
current in dropout when the pass transistor saturates.
They also use high base-drive currents under large
loads. The MAX8875 does not suffer from these prob-
lems and consumes only 100µA of quiescent current
whether in dropout, light-load, or heavy-load applica-
tions (see Typical Operating Characteristics).
Power-OK Output (POK)
When the output voltage goes out of regulation—as dur-
ing dropout, current limit, or thermal shutdown—POK
goes low. POK is an open-drain N-channel MOSFET. To
obtain a logic-level output, connect a pull-up resistor
from POK to OUT. To minimize current consumption,
make this resistor as large as practical. A 100kΩ resistor
works well for most applications. A capacitor to GND
may be added to generate a power-on-reset (POR)
delay. The POK function is not active during shutdown.
POK also provides a power-on-reset function that can
operate down to V
IN
≤ 1V. See POK Startup Response
in the Typical Operating Characteristics.
Current Limit
The MAX8875 includes a current limiter that monitors
and controls the pass transistor’s gate voltage, limiting
the output current to 390mA (typ). For design purpos-
es, consider the current limit to be 160mA min to
600mA max. The output can be shorted to ground for
an indefinite period of time without damaging the part.
Thermal-Overload Protection
When the junction temperature exceeds T
J
= +170°C,
the thermal sensor signals the shutdown logic, turning
off the pass transistor and allowing the IC to cool. The
thermal sensor will turn the pass transistor on again after
the IC’s junction temperature cools by 20°C, resulting in
a pulsed output during continuous thermal-overload
conditions.Thermal-overload protection is designed to
protect the MAX8875 in the event of fault conditions. For
continuous operation, do not exceed the absolute maxi-
mum junction-temperature rating of T
J
= +150°C.
Operating Region and Power Dissipation
The MAX8875’s maximum power dissipation depends
on the thermal resistance of the case and circuit board,
the temperature difference between the die junction
and ambient air, and the rate of air flow. The power dis-
sipation across the device is P = I
OUT
(V
IN
- V
OUT
). The
maximum power dissipation is:
P
MAX
= (T
J
- T
A
) / (θ
JB
+ θ
BA
)
where T
J
- T
A
is the temperature difference between
the MAX8875 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 MAX8875’s ground pin (GND) performs the dual
function of providing an electrical connection to system
ground and channeling heat away. Connect GND to the
system ground using a large pad or ground plane.
Reverse-Battery Protection
The MAX8875 has a unique protection scheme that lim-
its the reverse supply current to 1mA when either V
IN
or
V
SHDN
falls below ground. The circuitry monitors the
polarity of these two pins and disconnects the internal
circuitry and parasitic diodes when the battery is
reversed. This feature prevents device damage.
__________Applications Information
Capacitor Selection and
Regulator Stability
For stable operation over the full temperature range
and with load currents up to 150mA, use a 1µF (min)
ceramic output capacitor with an ESR <0.2Ω for V
OUT
≥ 2.5V, or an equivalent 3.3µF ceramic output capacitor
for V
OUT
= 1.5V. To reduce noise and improve load-
transient response, stability, and power-supply rejec-
tion, use large output capacitor values, such as 10µF.
Note that some ceramic dielectrics exhibit large capac-
itance and ESR variation with temperature. With
dielectrics such as Z5U and Y5V, it may be necessary
to increase the capacitance by a factor of 2 or more to
ensure stability at temperatures below T
A
= -10°C. With
X7R or X5R dielectrics, 1µF should be sufficient at all
operating temperatures for V
OUT
≥ 2.5V. For a pin-com-
patible, functionally equivalent device for use with a
higher ESR output capacitor, see the MAX8885.
MAX8875
150mA, Low-Dropout Linear Regulator
with Power-OK Output
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