MAX604 Просмотр технического описания (PDF) - Maxim Integrated

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MAX604

5V/3.3V or Adjustable, Low-Dropout, Low IQ, 500mA Linear Regulators

Maxim Integrated 

5V/3.3V or Adjustable, Low-Dropout,

Low IQ, 500mA Linear Regulators

Output Voltage Selection

The MAX603/MAX604 feature dual-mode operation. In

preset voltage mode, the output of the MAX603 is set to

5V and the output of the MAX604 is set to 3.3V using

internal, trimmed feedback resistors. Select this mode

by connecting SET to ground.

In adjustable mode, an output between 1.25V and 11V

is selected using two external resistors connected as a

voltage divider to SET (Figure 3). The output voltage is

set by the following equation:

VOUT = VSET 1 + RR21

where VSET = 1.20V. To simplify resistor selection:

R1

=

R2





VOUT

VSET



- 1

Since the input bias current at SET is nominally zero,

large resistance values can be used for R1 and R2 to

minimize power consumption without losing accuracy. Up

to 1.5MΩ is acceptable for R2. Since the VSET tolerance

is less than ±40mV, the output can be set using fixed

resistors instead of trim pots.

In preset voltage mode, impedances between SET and

ground should be less than 10kΩ. Otherwise, spurious

conditions could cause the voltage at SET to exceed

the 80mV dual-mode threshold.

Shutdown

A low input on the OFF pin shuts down the MAX603/

MAX604. In the off mode, the pass transistor, control

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

ing the supply current below 2µA. OFF should be con-

nected to IN for normal operation.

Use a fast comparator, Schmitt trigger, or CMOS or TTL

logic to drive the OFF pin in and out of shutdown. Rise

times should be shorter than 1µs. Do not use slow RC

circuits, leave OFF open, or allow the input to linger

between thresholds; these measures will prevent the

output from jumping to the positive supply rail in

response to an indeterminate input state.

Since the OFF threshold varies with input supply volt-

age (see Electrical Characteristics), do not derive the

drive voltage from 3.3V logic. With VIN at 11.5V, the

high OFF logic level needs to be above 4V.

Foldback Current Limiting

The MAX603/MAX604 also include a foldback current

limiter. It monitors and controls the pass transistor’s

gate voltage, estimating the output current and limiting

it to 1.2A for output voltages above 0.8V and VIN - VOUT

IN

OUT

CIN

BATTERY 0.1µF to

10µF

MAX603

MAX604

OFF

SET

GND

OUTPUT

VOLTAGE

R1

COUT RL

10µF

R2

Figure 3. Adjustable Output Using External Feedback Resistors

> 0.7V. For VIN - VOUT < 0.7V (dropout operation), there

is no current limit. If the output voltage drops below

0.8V, implying a short-circuit condition, the output cur-

rent is limited to 350mA. The output can be shorted to

ground for one minute without damaging the device if

the package can dissipate VIN x 350mA without

exceeding TJ = +150°C.

Thermal Overload Protection

Thermal overload protection limits total power dissipa-

tion in the MAX603/MAX604. When the junction temper-

ature exceeds TJ = +160°C, the thermal sensor sends a

signal to the shutdown logic, turning off the pass tran-

sistor and allowing the IC to cool. The thermal sensor

will turn the pass transistor on again after the IC’s junc-

tion temperature cools by 10°C, resulting in a pulsed

output during thermal overload conditions.

Thermal overload protection is designed to protect the

MAX603/MAX604 in the event of fault conditions. For

continual operation, the absolute maximum junction tem-

perature rating of TJ = +150°C should not be exceeded.

Operating Region and Power Dissipation

Maximum power dissipation of the MAX603/MAX604

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:

( ( ) ) P MAX

=





TJ - TA

θJB + θBA





where (TJ - TA) is the temperature difference between

the MAX603/MAX604 die junction and the surrounding

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