MAX8863(1998) Просмотр технического описания (PDF) - Maxim Integrated
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MAX8863 Datasheet PDF : 8 Pages
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Low-Dropout, 120mA Linear Regulators
Operating Region and Power Dissipation
Maximum power dissipation of the MAX8863/MAX8864
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 = IOUT (VIN -
VOUT). The resulting maximum power dissipation is:
PMAX = (TJ - TA) / θJA
where (TJ - TA) is the temperature difference between
the MAX8863/MAX8864 die junction and the surround-
ing air, and θJA is the thermal resistance of the chosen
package to the surrounding air.
The GND pin of the MAX8863/MAX8864 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
The MAX8863/MAX8864 have a unique protection
scheme that limits the reverse supply current to less
than 1mA when either VIN or VSHDN 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.
VIN > 5.5V Minimum Load Current
When operating the MAX8863/MAX8864 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 MAX8863/MAX8864.
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.
Noise
The MAX8863/MAX8864 exhibit 350µVRMS noise during
normal operation. When using the MAX8863/MAX8864
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 MAX8863/MAX8864 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.
Ripple 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 MAX8863/MAX8864 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.
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
MAX8863/MAX8864 use a P-channel MOSFET pass
transistor, their dropout voltage is a function of RDS(ON)
multiplied by the load current (see Electrical
Characteristics).
___________________Chip Information
TRANSISTOR COUNT: 148
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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