MAX8873T/S/R, MAX8874T/S/R
Low-Dropout, 120mA Linear Regulators
Operating Region and Power Dissipation
Maximum power dissipation of the MAX8873/MAX8874
depends on the thermal resistance of the case and cir-
cuit board, the temperature difference between the die
junction and ambient air, and the rate of air flow. The
power dissipation across the device is P = I OUT (V IN -
V OUT ). The resulting maximum power dissipation is:
P MAX = (T J - T A ) / θ JA
where (T J - T A ) is the temperature difference between
the MAX8873/MAX8874 die junction and the surround-
ing air, and θ JA is the thermal resistance of the chosen
package to the surrounding air.
The GND pin of the MAX8873/MAX8874 performs the
dual function of providing an electrical connection to
ground and channeling heat away. Connect the GND
pin to ground using a large pad or ground plane.
Reverse Battery Protection
Noise
The MAX8873/MAX8874 exhibit 350μV RMS noise during
normal operation. When using the MAX8873/MAX8874
in applications that include analog-to-digital converters
(ADCs) of greater than 12 bits, consider the ADC’s
power-supply rejection specifications (see the Output
Noise DC to 1MHz photo in the Typical Operating
Characteristics). For devices with lower output noise,
refer to the MAX8877/MAX8878.
Power-Supply Rejection and Operation
from Sources Other than Batteries
The MAX8873/MAX8874 are designed to deliver low
dropout voltages and low quiescent currents in battery-
powered systems. Power-supply rejection is 62dB at
low frequencies and rolls off above 300Hz. As the fre-
quency increases above 20kHz, the output capacitor is
the major contributor to the rejection of power-supply
noise (see the Power-Supply Rejection Ratio vs.
The MAX8873/MAX8874 have a unique protection
Frequency
graph in the
Typical Operating
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 two pins, dis-
connecting the internal circuitry and parasitic diodes
when the battery is reversed. This feature prevents the
device from overheating and damaging the battery.
V IN > 5.5V Minimum Load Current
When operating the MAX8873/MAX8874 with an input
voltage above 5.5V, a minimum load current of 20μA is
required to maintain regulation in preset voltage mode.
When setting the output with external resistors, the min-
imum current through the external feedback resistors
and load must be 30μA.
__________Applications Information
Capacitor Selection and
Regulator Stability
Normally, use a 1μF capacitor on the input and a 1μF
capacitor on the output of the MAX8873/MAX8874.
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 up to 120mA, a minimum of 1μF is recommended.
8
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 by using passive filtering techniques (see the
supply and load-transient responses in the Typical
Operating Characteristics).
Load-Transient Considerations
The MAX8873/MAX8874 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
14mV. Increasing the output capacitor ’s value and
decreasing its ESR attenuates transient spikes.
Input-Output (Dropout) Voltage
A regulator’s minimum input-output voltage differential
(or dropout voltage) determines the lowest usable sup-
ply voltage. In battery-powered systems, this will deter-
mine the useful end-of-life battery voltage. Because the
MAX8873/MAX8874 use a P-channel MOSFET pass
transistor, their dropout voltage is a function of R DS(ON)
multiplied by the load current (see Electrical
Characteristics).
Maxim Integrated