MAX8869 MAXIM [Maxim Integrated Products], MAX8869 Datasheet - Page 6

• Manufacturer Part Number: MAX8869
• Description: 1A, Microcap, Low-Dropout, Linear Regulator Foldback Output Current Limit
• Manufacturer: MAXIM [Maxim Integrated Products]

1A, Microcap, Low-Dropout,
Linear Regulator
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
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
6
12, 13, 14, 15
_______________________________________________________________________________________
2, 3, 4, 5
1, 9, 16
PIN
10
11
—
6
7
8
OUT
NAME
SHDN
comparators.
GND
N.C.
OUT
RST
SET
SS
EP
IN
Detailed Description
OUT
comparator senses when
No Connection. Not internally connected.
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.
Reset O utp ut. O p en- d r ai n outp ut i s l ow w hen V
l ow w hi l e the outp ut vol tag e ( V
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.
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.
Soft-Start Control. Connect a soft-start capacitor from SS to GND (see Soft-Start Capacitor
Selection). Leave SS open to disable soft-start.
Ground. Solder both GND and EP to a large pad or to the circuit-board ground plane to
maximize power dissipation.
Voltage-Setting Input. Connect SET to GND for factory-preset output voltage. Connect SET to
an external resistor-divider for adjustable output operation.
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.
Exposed Pad. Connect to a large ground plane to maximize thermal performance. Not
intended as an electrical connection point.
OUT
) i s b el ow the r eset thr eshol d and for at l east 3m s after V
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
path. If V
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.
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.
FUNCTION
SET
OU T
Internal P-Channel Pass Transistor
is below 80mV, the internal feedback path
i s 8% b el ow i ts nom i nal val ue. RST r em ai ns
SET
and selects the feedback
Pin Description
OUT