MAX8865R 查看數據表（PDF） - Maxim Integrated

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MAX8865R

Dual, Low-Dropout, 100mA Linear Regulators

Maxim Integrated 

Dual, Low-Dropout, 100mA Linear Regulators

IN

OUT_

OUTPUT

VOLTAGE

MAX8865

R1

20pF

CIN

2µF

BATTERY

MAX8866

SHDN_ SET_

COUT

1µF

RL

GND

R2

Figure 2. Adjustable Output Using External Feedback

Resistors

In preset voltage mode, internal, trimmed feedback

resistors set the MAX886_R outputs to 2.80V, the

MAX886_S outputs to 2.84V, and the MAX886_T out-

puts to 3.15V. Select this mode by connecting SET_ to

ground. If SET_ can’t be grounded in preset voltage

mode, limit impedances between SET_ and ground to

less than 100kΩ. Otherwise, spurious conditions could

cause the voltage at SET_ to exceed the 60mV Dual

Mode threshold.

In adjustable mode, select an output between 1.25V

and 5.5V using two external resistors connected as a

voltage divider to SET_ (Figure 2). The output voltage is

set by the following equation:

VOUT_ = VSET_ (1 + R1 / R2)

where VSET_ = 1.25V. To simplify resistor selection:

R1

=

R2





VOUT _

VSET _

−



1

Choose R2 = 100kΩ to optimize power consumption,

accuracy, and high-frequency power-supply rejection.

The total current through the external resistive feedback

and load resistors should not be less than 10µA. Since

the VSET_ tolerance is typically less than ±25mV, the

output can be set using fixed resistors instead of trim

pots. Connect a 10pF to 25pF capacitor across R1 to

compensate for layout-induced parasitic capacitances.

Shutdown

A low input on a SHDN__ pin individually shuts down one

of the two outputs. In shutdown mode, the selected

pass transistor, control circuit, and all biases are turned

off. When both sections are turned off, the reference

and thermal shutdown are also turned off and the sup-

ply current is typically reduced to 0.16nA. Connect

SHDN__ to IN for normal operation. The MAX8866 output

voltages are actively discharged to ground when indi-

vidual regulators are shut down (see Typical Operating

Characteristics).

Current Limit

The MAX8865/MAX8866 include a current limiter for

each output section that monitors and controls the pass

transistor’s gate voltage, estimating the output current

and limiting it to about 220mA. For design purposes,

the current limit should be considered 120mA (min) to

320mA (max). The outputs can be shorted to ground for

an indefinite time period without damaging the part.

Thermal Overload Protection

Thermal overload protection limits total power dissipa-

tion in the MAX8865/MAX8866. When the junction tem-

perature exceeds TJ = +170°C, the thermal sensor

sends a signal to the shutdown logic, turning off the

pass transistors and allowing the IC to cool. The ther-

mal sensor will turn the pass transistors 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

MAX8865/MAX8866 in the event of fault conditions.

Stressing the device with high load currents and high

input-output differential voltages (which result in elevat-

ed die temperatures above +125°C) may cause a

momentary overshoot (2% to 8% for 200ms) when the

load is completely removed. This can be remedied by

raising the minimum load current from 0µA (+125°C) to

100µA (+150°C). For continuous operation, do not

exceed the absolute maximum junction temperature

rating of TJ = +150°C.

Operating Region and Power Dissipation

Maximum power dissipation of the MAX8865/MAX8866

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 MAX8865/MAX8866 die junction and the surround-

ing air, and θJA is the thermal resistance of the pack-

age to the surrounding air (244°C/W).

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