
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
MAX8885 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 MAX8885
’
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
MAX8885 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 MAX8885
’
s GND pin 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 MAX8885 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
The MAX8885 is designed primarily for applications
using low-cost, high-ESR output capacitors such as
small case-size tantalum electrolytic capacitors. These
capacitors have ESR that can extend as high as 10
,
and their capacitance and ESR can vary widely over
their operating temperature range. For stable operation
over the full operating range, use a 4.7μF (1μF min)
capacitor with ESR > 0.5
(see the Region of Stable
C
OUT
ESR vs. Load Current graph in the
Typical
Operating Characteristics
). Ceramic output capacitors
should not be used with the MAX8885. For a pin-com-
patible, functionally equivalent linear regulator that is
suitable for ceramic output capacitors, refer to the
MAX8875 data sheet.
Bypass the MAX8885
’
s input with a 1μF or greater
capacitor to GND. Place this capacitor close to the
device (<5mm).
M
150mA, Low-Dropout Linear Regulator
with Power-OK Output
_______________________________________________________________________________________
7
SHUTDOWN
LOGIC
ERROR
AMP
1.25V
REF
95%
REF
P
OUT
POK
GND
IN
SHDN
MAX8885
THERMAL
SENSOR
REVERSE
BATTERY
PROTECTION
MOS DRIVER
WITH I
LIMIT
POK
Figure 1. Functional Diagram