MAX8860 查看數據表（PDF） - Maxim Integrated

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MAX8860

Low-Dropout, 300mA Linear Regulator in µMAX

Maxim Integrated 

Low-Dropout, 300mA

Linear Regulator in µMAX

Choose R2 = 100kΩ to optimize power consumption,

accuracy, and high-frequency power-supply rejection.

Ensure that the total current through the external resis-

tive feedback and load resistors is not less than 10µA.

Since the VSET tolerance is typically less than ±20mV,

set the output using fixed resistors instead of trim pots.

In preset voltage mode, connect SET to GND. Keep

impedances between SET and ground to less than

100kΩ. Otherwise, spurious conditions can cause VSET

to exceed the 60mV Dual Mode threshold.

Shutdown

Drive SHDN low to place the MAX8860 in shutdown

mode. In shutdown mode, the pass transistor, control

circuit, reference, and all biases are turned off, reduc-

ing the supply current to typically 10nA. Connect SHDN

to IN for normal operation.

Current Limit

The MAX8860 includes short-circuit protection. It includes

a current limiter that controls the pass transistor’s gate

voltage to limit the output current to about 770mA. For

design purposes, the minimum current limit is 330mA.

Thermal Overload Protection

Thermal overload protection limits total power dissipa-

tion in the MAX8860. When the junction temperature

(TJ) exceeds +170°C, the thermal sensor sends a sig-

nal to the shutdown logic, turning off the pass transistor

and allowing the IC to cool. The pass transistor turns on

again after the IC’s junction temperature typically cools

by 20°C, resulting in a pulsed output during continuous

thermal overload conditions.

Thermal overload protection is designed to protect the

MAX8860 against fault conditions. Stressing the device

with high-load currents and high input-output differen-

tial voltages (which result in die temperatures above

+125°C) may cause a momentary overshoot (2% to 8%

for 200ms) when the load is completely removed.

Remedy this by raising the minimum load current from

0 (+125°C) to 100µA (+150°C). This is accomplished

with an external load resistor. For continuous operation,

do not exceed the absolute maximum junction tempera-

ture rating of +150°C.

Operating Region and

Power Dissipation

Maximum power dissipation of the MAX8860 depends

on the thermal resistance of the case and circuit board,

the temperature difference between the die junction

and ambient air, and the rate of air flow. The power dis-

sipated by the device is:

P = IOUT (VIN - VOUT)

The maximum power dissipation is:

PMAX = (TJMAX - TA) / θJA

where: TJMAX = +150°C

TA is the ambient temperature

θJA = 244°C/W

The MAX8860’s pins perform the dual function of provid-

ing an electrical connection as well as channeling heat

away from the die. Use wide circuit-board traces and

large, solid copper polygons to improve power dissipa-

tion. Using multiple vias to buried ground planes further

enhances thermal conductivity.

Reverse Battery Protection

The MAX8860 has a unique protection scheme that lim-

its the reverse supply current to less than 1mA when

either VIN or VSHDN falls below GND. The circuitry

monitors the polarity of these two pins, disconnecting

the internal circuitry and parasitic diodes when the

applied voltage is reversed. This feature prevents the

device from overheating and damaging an improperly

installed battery.

Integrator Circuitry

The MAX8860 uses an external 33nF compensation

capacitor for minimizing load- and line-regulation errors

and for lowering output noise. When the output voltage

shifts due to varying load current or input voltage, the

integrator capacitor voltage is raised or lowered to

compensate for the systematic offset at the error ampli-

fier. Compensation is limited to ±5% to minimize tran-

sient overshoot when the device goes out of dropout,

current limit, or thermal shutdown.

Fault-Detection Circuitry

When the output voltage goes out of regulation—such

as during dropout, current limit, or thermal shutdown—

FAULT goes low. In addition, the fault-detection circuitry

detects when the input-to-output voltage differential is

insufficient to ensure good load and line regulation at

the output. When the input-to-output voltage differential

is less than 130mV for a load current of 200mA, FAULT

also goes low. The differential threshold is designed to

be always higher than and track with the dropout volt-

age, and to scale proportionally with load current (see

Fault Detect Threshold vs. Load Current graph in the

Typical Operating Characteristics).

The FAULT pin is an open-drain N-channel MOSFET. To

create a voltage level output, connect a pull-up resistor

from FAULT to OUT. To minimize current consumption,

make this resistor as large as practical. A 100kΩ resistor

works well for most applications.

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