MAX8862 Просмотр технического описания (PDF) - Maxim Integrated

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MAX8862

Low-Cost, Low-Dropout, Dual Linear Regulator

Maxim Integrated 

Low-Cost, Low-Dropout, Dual Linear Regulator

______________________________________________________________Pin Description

PIN

1

2

3

4, 5, 12, 13

6

NAME

IN1

SHDN1

PWROK1

GND

OUT2

FUNCTION

Main Regulator Supply Input (2.5V to 11.5V). Bypass with a 1µF, low-ESR capacitor to GND.

Main Regulator Shutdown Input. A logic low turns off the main regulator and power-good comparator.

Power-Good Output. This open-drain output is low when VOUT1 is out of regulation (VOUT1 is 4%

lower than its nominal value).

Ground. Connect to a ground plane to maximize thermal dissipation.

Secondary Regulator Output. Bypass with a 2.2µF low-ESR (< 0.5Ω) capacitor to GND. To improve

load-transient response and noise performance, use a higher-value, lower-ESR capacitor.

7

8, 16

9

10

11

14

SET2

N.C.

IN2

SHDN2

REF2

OUT1

OUT2 Voltage-Set Input. Connect to GND for the factory-preset output voltage. Connect to a resistive

divider from OUT2 to GND for adjustable output voltage.

No connect. There is no internal connection to this pin.

Secondary Regulator Supply Input (2.5V to 11.5V). Bypass with a 1µF, low-ESR capacitor to GND.

Secondary Regulator Shutdown Input. A logic-low input turns off the secondary regulator and the

reference.

Secondary Reference Output. Bypass with a 0.1µF capacitor to GND.

Main Regulator Output. Bypass with a 3.3µF, low-ESR (< 0.5Ω) capacitor to GND. To improve load-

transient response and noise performance, use a higher-value, lower-ESR capacitor.

15

SET1

OUT1 Voltage Set Input. Connect to GND for the factory-preset output voltage. Connect to a

resistive divider from OUT1 to GND for adjustable output voltage.

_______________Detailed Description

The MAX8862 features Dual Mode™ operation, allow-

ing a fixed output of 4.95V (L), 3.175V (T), or 2.85V (R),

or an adjustable output from 2V to 11V. The regulator’s

outputs, OUT1 and OUT2, supply 250mA and 100mA,

respectively.

The block diagram (Figure 1) shows the contents of

each regulator. Note that the main regulator provides a

power-good indicator, and the secondary regulator’s

reference output voltage is available at REF2.

The 1.25V bandgap reference is connected to the error

amplifier’s inverting input. The error amplifier compares

this reference with the selected feedback voltage and

amplifies the difference. The MOSFET driver reads the

error signal and applies the appropriate drive to the

P-channel transistor. If the feedback voltage is lower

than the reference, the pass transistor’s gate is pulled

lower, allowing more current to pass and increase the

output voltage. If the feedback voltage is too high, the

pass transistor’s gate is pulled up, allowing less current

to pass to the output.

The output voltage is fed back through either an

internal resistor voltage divider connected to OUT1/

OUT2, or an external resistor network connected to

SET1/SET2. The Dual Mode comparator examines

VSET1/VSET2 and selects the feedback path. If this volt-

age is below 40mV, internal feedback is used and the

output voltage is regulated to the factory-preset volt-

age.

Internal P-Channel Pass Transistor

The MAX8862’s P-channel pass transistor provides

several advantages over similar designs using PNP

pass transistors, including longer battery life.

The P-channel MOSFET requires no continuous base

current, thereby reducing quiescent current consider-

ably. PNP regulators normally waste a considerable

amount of current in dropout when the pass transistor

saturates; they also use high base-drive currents under

large loads. The MAX8862 does not suffer from these

problems: it consumes only 200µA of quiescent current

for both regulators under light and heavy loads, as well

as in dropout.

_______________________________________________________________________________________ 7

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