MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
_______________________________________________________________________________________ 7
______________________________________________________________Pin Description
OUT2 Voltage-Set Input. Connect to GND for the factory-preset output voltage. Connect to a resistive
divider from OUT2 to GND for adjustable output voltage.
SET27
Secondary Regulator Supply Input (2.5V to 11.5V). Bypass with a 1µF, low-ESR capacitor to GND.IN29
Secondary Regulator Shutdown Input. A logic-low input turns off the secondary regulator and the
reference.
SHDN2
10
Ground. Connect to a ground plane to maximize thermal dissipation.GND4, 5, 12, 13
Secondary Regulator Output. Bypass with a 2.2µF low-ESR (< 0.5Ω) capacitor to GND. To improve
load-transient response and noise performance, use a higher-value, lower-ESR capacitor.
OUT26
Power-Good Output. This open-drain output is low when V
OUT1
is out of regulation (V
OUT1
is 4%
lower than its nominal value).
PWROK13
PIN
Main Regulator Shutdown Input. A logic low turns off the main regulator and power-good comparator.
SHDN1
2
Main Regulator Supply Input (2.5V to 11.5V). Bypass with a 1µF, low-ESR capacitor to GND.IN11
FUNCTIONNAME
11 REF2 Secondary Reference Output. Bypass with a 0.1µF capacitor to GND.
14 OUT1
Main Regulator Output. Bypass with a 3.3µF, low-ESR (< 0.5Ω) capacitor to GND. To improve load-
transient response and noise performance, use a higher-value, lower-ESR capacitor.
15 SET1
OUT1 Voltage Set Input. Connect to GND for the factory-preset output voltage. Connect to a
resistive divider from OUT1 to GND for adjustable output voltage.
_______________Detailed Description
The MAX8862 features Dual Mode™ operation, allow-
ing a fixed output of 4.95V (L), 3.175V (T), or 2.85V (R),
or an adjustable output from 2V to 11V. The regulator’s
outputs, OUT1 and OUT2, supply 250mA and 100mA,
respectively.
The block diagram (Figure 1) shows the contents of
each regulator. Note that the main regulator provides a
power-good indicator, and the secondary regulator’s
reference output voltage is available at REF2.
The 1.25V bandgap reference is connected to the error
amplifier’s inverting input. The error amplifier compares
this reference with the selected feedback voltage and
amplifies the difference. The MOSFET driver reads the
error signal and applies the appropriate drive to the
P-channel transistor. If the feedback voltage is lower
than the reference, the pass transistor’s gate is pulled
lower, allowing more current to pass and increase the
output voltage. If the feedback voltage is too high, the
pass transistor’s gate is pulled up, allowing less current
to pass to the output.
The output voltage is fed back through either an
internal resistor voltage divider connected to OUT1/
OUT2, or an external resistor network connected to
SET1/SET2. The Dual Mode comparator examines
V
SET1
/V
SET2
and selects the feedback path. If this volt-
age is below 40mV, internal feedback is used and the
output voltage is regulated to the factory-preset volt-
age.
Internal P-Channel Pass Transistor
The MAX8862’s P-channel pass transistor provides
several advantages over similar designs using PNP
pass transistors, including longer battery life.
The P-channel MOSFET requires no continuous base
current, thereby reducing quiescent current consider-
ably. PNP regulators normally waste a considerable
amount of current in dropout when the pass transistor
saturates; they also use high base-drive currents under
large loads. The MAX8862 does not suffer from these
problems: it consumes only 200µA of quiescent current
for both regulators under light and heavy loads, as well
as in dropout.
No connect. There is no internal connection to this pin.N.C. 8, 16
