Internal P-Channel Pass Transistor
The MAX1963/MAX1976 feature a 0.33
(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. PNP-based regulators also waste consid-
erable current in dropout when the pass transistor
saturates and use high base-drive currents under large
loads. The MAX1963/MAX1976 do not suffer from these
problems and consume only 90μA (typ) of quiescent
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 1.5k
resistor pulls OUT to GND,
RESET
is actively pulled
low, and the supply current drops below 1μA.
RESET
Output
The MAX1963/MAX1976 microprocessor (μP) supervisory
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 MAX1963/MAX1976 monitor and control the pass
transistor
’
s gate voltage, limiting the output current to
450mA (min). If the output exceeds I
LIM
, the MAX1963/
MAX1976 output voltage drops.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX1963/MAX1976. When the junction tem-
perature exceeds T
J
= +165
°
C, a thermal sensor turns
off the pass transistor, allowing the IC to cool. The ther-
mal 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
MAX1963/MAX1976 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 MAX1963/MAX1976 maximum power dissipation
depends on the thermal resistance of the IC package
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 dissipation is:
P
MAX
= (T
J(MAX)
- T
A
) / (
θ
JC
+
θ
CA
)
where (T
J(MAX)
- T
A
) is the temperature difference
between the MAX1963/MAX1976 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.
M
Low-Input-Voltage, 300mA LDO Regulators
with
RESET
in SOT and TDFN
_______________________________________________________________________________________
7
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
(POWER DISSIPATION LIMIT)
(V
IN
- V
OUT
) (V)
M
2.5
2.0
1.5
1.0
0.5
100
200
300
400
0
0
3.0
MAXIMUM RECOMMENDED
OUTPUT CURRENT 6-PIN SOT23
T
A
= +85
°
C
T
A
= +70
°
C
Figure 2. Power Operating Regions for the 6-Pin SOT23:
Maximum Output Current vs. Input Voltage
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
(POWER DISSIPATION LIMIT)
(V
IN
- V
OUT
) (V)
M
2.5
2.0
1.5
1.0
0.5
100
200
300
400
0
0
3.0
MAXIMUM RECOMMENDED
OUTPUT CURRENT 6-PIN TDFN
T
A
= +85
°
C
Figure 3. Power Operating Regions for the 6-Pin TDFN:
Maximum Output Current vs. Input Voltage