SG29085 データシートの表示（PDF） - Microsemi Corporation

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SG29085

LOW DROPOUT DUAL REGULATOR

Microsemi Corporation 

SG29085/85A

APPLICATION HINTS

EXTERNAL CAPACITORS

To stabilize the outputs and prevent oscillation (perhaps by many

volts) external capacitors are required. The minimum recom-

mended value for the output capacitors is 10µF, although the

actual size and type will likely vary according to the particular

application, e.g., operating temperature range and load. Another

consideration is the effective series resistance (ESR) of the

capacitor. Capacitor ESR will vary by manufacturer. Conse-

quently, some evaluation may be required to determine the

minimum value of the output capacitors. Generally worst case

occurs at the maximum load and minimum ambient temperature.

The size of the output capacitor can be increased to any value

above the minimum. One possible advantage of this would be to

maintain the output voltage during brief periods of negative input

transients

The output capacitors chosen should be rated for the full range

of ambient temperature over which the circuit will be exposed and

expected to operate. For example, many aluminum type electro-

lytic capacitors will freeze at -30°C. The effective capacitance is

reduced to zero in such a situation. Capacitors rated for -40°C

operation must be used in order to maintain regulator stability at

that temperature. Tantalum capacitors satisfy this requirement.

STANDBY OUTPUT

The SG29085/85A differs from most fixed voltage regulators in

that it is equipped with two regulator outputs instead of one. The

additional output is intended for use in systems requiring standby

memory circuits. While the high current regulator output can be

controlled with the ON/OFF pin described below, the standby

remains on under all conditions as long as sufficient input voltage

is applied to the IC. Thus, memory and other circuits powered by

this output remain unaffected by positive line transients, thermal

shutdown, etc.

The standby regulator circuit is designed so that the quiescent

current to the IC is very low (<1.5mA) when the other regulator

output is off.

If the standby output is not required it can be disabled. This is

accomplished by connecting a resistor from the standby output to

the supply voltage, thereby also eliminating the requirement for

a more expensive output capacitor to prevent unwanted oscilla-

tions. The resistor value depends upon the minimum input

voltage expected for a given system.

Since the standby output is shunted with an internal 5.6V zener,

the current through the external resistor should be sufficient to

bias internal resistors up to this point. Approximately 60µA will

suffice, resulting in a 10k external resistor for most applications

(Figure 1).

HIGH CURRENT OUTPUT

VIN

SG29085/85A

RD

10K

STANDBY

OUTPUT

C3

FIGURE 1. Disabling Standby Output to Eliminate C3

The high current regulated output features fault protection

against overvoltage as well as a thermal shutdown feature. If the

input voltage rises above 33V (load dump), the high current

output shuts down automatically. The internal circuitry is thus

protected and the IC is able to survive higher voltage transients

than might otherwise be expected. The thermal shutdown of the

high current output effectively guards against overheating of the

die since this section of the IC is the principle source of power

dissipation on the chip.

ON/OFF SWITCH

The ON/OFF pin is a high impedance low current switch that

controls the main output voltage (pin 2). This is directly compat-

ible with all 5 volt logic families. For use with open collector logic

outputs, a 100Kresistor from this pin to a 5V supply, such as Pin

5, is required.

CONNECTION DIAGRAM & ORDERING INFORMATION (See Note Below)

Package

5-PIN TO-220 PLASTIC

P - PACKAGE

Part No.

SG29085P

SG29085AP

Ambient

Temperature Range

-40°C to 85°C

-40°C to 85°C

Note: 1. All packages are viewed from the top.

Connection Diagram

GND

5 STANBY OUTPUT

4 ON/OFF SWITCH

3 GROUND

2 OUTPUT VOLTAGE (VOUT)

1 INPUT VOLTAGE (VIN)

12/90 Rev 1.1 2/94

Copyright © 1994

LINFINITY Microelectronics Inc.

4

11861 Western Avenue ∞ Garden Grove, CA 92841

(714) 898-8121 ∞ FAX: (714) 893-2570

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