MAX8865T/S/R, MAX8866T/S/R
Dual, Low-Dropout, 100mA Linear Regulators
10 ______________________________________________________________________________________
Reverse Battery Protection
The MAX8865/MAX8866 have a unique protection
scheme that limits the reverse supply current to less
than 1mA when either V
IN
or V
SHDN_ _
falls below
ground. The circuitry monitors the polarity of these
pins, disconnecting the internal circuitry and parasitic
diodes when the battery is reversed. This feature pre-
vents the device from overheating and damaging the
battery.
__________Applications Information
Capacitor Selection and
Regulator Stability
Normally, use two 1µF surface-mount ceramic capaci-
tors on the input and a 1µF surface-mount ceramic
capacitor on each output of the MAX8865/MAX8866.
Larger input capacitor values and lower ESR provide
better supply-noise rejection and transient response. A
higher-value input capacitor (10µF) may be necessary
if large, fast transients are anticipated and the device is
located several inches from the power source. Improve
load-transient response, stability, and power-supply
rejection by using large output capacitors. For stable
operation over the full temperature range, with load cur-
rents of 100mA, a minimum of 1µF is recommended
(see the Region of Stable C
OUT
ESR vs. Load Current
graph in the
Typical Operating Characteristics
).
Noise
The MAX8865/MAX8866 exhibit 350µV
RMS
noise during
normal operation. When using the MAX8865/MAX8866
in applications that include analog-to-digital converters
of greater than 12 bits, consider the ADC’s power-sup-
ply rejection specifications (see the Output Noise DC to
1MHz photo in the
Typical Operating Characteristics
).
Power-Supply Rejection and Operation
from Sources Other than Batteries
The MAX8865/MAX8866 are designed to deliver low
dropout voltages and low quiescent currents in battery-
powered systems. Power-supply rejection is 60dB at low
frequencies and rolls off above 400Hz. As the frequency
increases above 100kHz, the output capacitor is the
major contributor to the rejection of power-supply noise
(see the Power-Supply Rejection Ratio vs. Frequency
graph in the
Typical Operating Characteristics
.
When operating from sources other than batteries,
improve supply-noise rejection and transient response
by increasing the values of the input and output capac-
itors, and using passive filtering techniques (see the
supply and load-transient responses in the
Typical
Operating Characteristics
).
Load-Transient Considerations
The MAX8865/MAX8866 load-transient response
graphs (see
Typical Operating Characteristics
) show
two components of the output response: a DC shift of
the output voltage due to the different load currents,
and the transient response. Typical overshoot for step
changes in the load current from 0mA to 50mA is
12mV. Increasing the output capacitor’s value and
decreasing its ESR attenuates transient spikes.
Cross-Regulation
Cross-regulation refers to the change in one output
voltage when the load changes on the other output. For
the MAX8865/MAX8866, cross-regulation for a 0mA to
50mA load change on one side results in less than 1mV
change of output voltage. If the power dissipation on
one output causes the junction temperature to exceed
125°C, ensure regulation of the other output with a mini-
mum load current of 100µA.
Input-Output (Dropout) Voltage
A regulator’s minimum input-output voltage differential (or
dropout voltage) determines the lowest usable supply volt-
age. In battery-powered systems, this will determine the
useful end-of-life battery voltage. Because the
MAX8865/MAX8866 use P-channel MOSFET pass transis-
tors, their dropout voltages are a function of R
DS(ON)
multi-
plied by the load currents (see
Electrical Characteristics
).
___________________Chip Information
TRANSISTOR COUNT: 259
