MAX8869
1A, Microcap, Low-Dropout,
Linear Regulator
6
Maxim Integrated
Detailed Description
The MAX8869 features Dual Mode operation, allowing a
fixed output of +5V, +3.3V, +2.5V, +1.8V, or +1.0V, or
adjustable output from +0.8V to +5.0V. The regulators
are guaranteed to supply 1A of continuous output cur-
rent with only 1µF of output capacitance.
As shown in the functional diagram (Figure 1), the
device has a 0.8V reference, error amplifier, MOSFET
driver, P-channel pass transistor, internal feedback
voltage-divider, soft-start function, reset timer, and Dual
Mode and low V
OUT
comparators.
The 0.8V reference is connected to the error amplifier’s
inverting input. The error amplifier compares this refer-
ence with the selected feedback voltage and amplifies
the difference. The MOSFET driver reads the error sig-
nal and applies the appropriate drive to the P-channel
transistor. If the feedback voltage is high, the pass tran-
sistor’s gate is pulled up, allowing less current to pass
to the output. The low V
OUT
comparator senses when
the feedback voltage has dropped 8% below its
expected level, causing RST to go low.
The output voltage is fed back through either an inter-
nal resistor-divider connected to OUT or an external
resistor network connected to SET. The Dual Mode
comparator examines V
SET
and selects the feedback
path. If V
SET
is below 80mV, the internal feedback path
is used and the output voltage is regulated to the facto-
ry-preset voltage. Otherwise, the output voltage is set
with the external resistor-divider.
Internal P-Channel Pass Transistor
The MAX8869 features a 1A P-channel MOSFET pass
transistor. Unlike similar designs using PNP pass tran-
sistors, P-channel MOSFETs require no base drive,
which reduces quiescent current. PNP-based regula-
tors also waste considerable current in dropout when
the pass transistor saturates and use high base-drive
currents under large loads. The MAX8869 does not suf-
fer from these problems and consumes only 500µA of
quiescent current even in dropout.
Pin Description
PIN NAME FUNCTION
1, 9, 16 N.C. No Connection. Not internally connected.
2, 3, 4, 5 IN
Regulator Input. Connect to power source (+2.7V to +5.5V). Bypass with 1µF or greater
capacitor to GND (see Capacitor Selection and Regulator Stability). Connect all IN inputs
together for proper operation.
6 RST
Reset O utp ut. O p en- d r ai n outp ut i s l ow w hen V
OU T
i s 8% b el ow i ts nom i nal val ue. RST r em ai ns
l ow w hi l e the outp ut vol tag e ( V
OUT
) i s b el ow the r eset thr eshol d and for at l east 3m s after V
OUT
r i ses to w i thi n r eg ul ati on. C onnect a 100kΩ p ul l up r esi stor to O U T to ob tai n an outp ut vol tag e.
7 SHDN
Active-Low Shutdown Input. A logic low reduces the supply current to 0.1µA. Connect SHDN
to IN for normal operation. In shutdown, RST is low and the soft-start capacitor discharges.
8SS
Soft-Start Control. Connect a soft-start capacitor from SS to GND (see Soft-Start Capacitor
Selection). Leave SS open to disable soft-start.
10 GND
Ground. Solder both GND and EP to a large pad or to the circuit-board ground plane to
maximize power dissipation.
11 SET
Voltage-Setting Input. Connect SET to GND for factory-preset output voltage. Connect SET to
an external resistor-divider for adjustable output operation.
12, 13, 14, 15 OUT
Regulator Output. Bypass with a 1µF or greater low-ESR capacitor to GND (see Capacitor
Selection and Regulator Stability). Connect all OUT outputs together for proper operation.
—EP
Exposed Pad. Connect to a large ground plane to maximize thermal performance. Not
intended as an electrical connection point.
