MAX8877 Maxim, MAX8877 Datasheet - Page 6

• Manufacturer Part Number: MAX8877
• Description: Low-Noise / Low-Dropout / 150mA Linear Regulators with 2982 Pinout
• Manufacturer: Maxim

The MAX8877/MAX8878 are low-noise, low-dropout,
low-quiescent-current linear regulators designed pri-
marily for battery-powered applications. The parts are
available with preset output voltages ranging from 2.5V
to 5V, in 100mV increments. These devices can supply
loads up to 150mA. As illustrated in Figure 1, the
MAX8877/MAX8878 consist of a 1.25V reference, error
amplifier, P-channel pass transistor, and internal feed-
back voltage divider.
The 1.25V bandgap reference is connected to the error
amplifier’s inverting input. The error amplifier 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 volt-
age is too high, the pass-transistor gate is pulled up,
allowing less current to pass to the output. The output
voltage is fed back through an internal resistor voltage
divider connected to the OUT pin.
An external bypass capacitor connected to the BP pin
reduces noise at the output. Additional blocks include a
current limiter, reverse battery protection, thermal sen-
sor, and shutdown logic. The MAX8878 also includes
an auto-discharge function, which actively discharges
the output voltage to ground when the device is placed
in shutdown mode.
Low-Noise, Low-Dropout, 150mA Linear
Regulators with ‘2982 Pinout
Figure 1. Functional Diagram
6
_______________Detailed Description
_______________________________________________________________________________________
* AUTO-DISCHARGE, MAX8878 ONLY
SHDN
GND
MAX8878
MAX8877
IN
PROTECTION
REVERSE
BATTERY
SHUTDOWN
POWER-ON
CONTROL
THERMAL
SENSOR
AND
1.25V
REF
The MAX8877/MAX8878 are supplied with factory-set
output voltages from 2.5V to 5.0V, in 100mV increments.
Except for the MAX887_EUK29 and the MAX887_EUK32
(which have an output voltage preset at 2.84V and
3.15V, respectively), the two-digit suffix allows the cus-
tomer to choose the output voltage in 100mV increments.
For example, the MAX8877EUK33 has a preset output
voltage of 3.3V (see Expanded Ordering Information ).
The MAX8877/MAX8878 feature a 1.1Ω typical
P-channel MOSFET pass transistor. This provides sever-
al advantages over similar designs using PNP pass tran-
sistors, including longer battery life. The P-channel
MOSFET requires no base drive, which reduces quies-
cent current considerably. PNP-based regulators waste
considerable current in dropout when the pass transistor
saturates. They also use high base-drive currents under
large loads. The MAX8877/MAX8878 do not suffer from
these problems and consume only 100µA of quiescent
current whether in dropout, light-load, or heavy-load
applications (see the Typical Operating Characteristics ).
The MAX8877/MAX8878 include a current limiter, which
monitors and controls the pass transistor’s gate voltage,
limiting the output current to 390mA. For design purposes,
consider the current limit to be 160mA minimum to 500mA
maximum. The output can be shorted to ground for an
indefinite amount of time without damaging the part.
ERROR
AMP
Internal P-Channel Pass Transistor
MOS DRIVER
WITH I
LIMIT
*
N
Output Voltage
Current Limit
P
OUT
BP