Rev 1.2a

Copyright

© 1997

11861 Western Avenue

∞

∞

∞

∞

∞ Garden Grove, CA 92841

3

(714) 898-8121

∞

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∞ FAX: (714) 893-2570

Fault Logic Outputs (Each output)

V

I

Collector Leakage Current

Collector Saturation Voltage

2.500

25

1

1

0.2

13

AC Line Sense Section

V

V

V

I

I

I

I

Comparator Threshold

Comparator Hysteresis

Input Bias Current

Collector Leakage Current

Collector Saturation Voltage

Emitter Output Voltage

Diode Clamp Voltage

2.440

12

6.0

-0.3

2.560

2

10

0.5

7.5

-1.0

2.440

12

6.0

-0.3

2.500

25

1

1

0.2

13

2

-0.3

3.5

1.0

100

15

100

3.2

72

5

72

I

I

R

+V

Input Offset Voltage

Input Bias Current

Output High Voltage

Output Low Voltage

Large Signal Voltage Gain

Output Source Current

Power Supply Rejection Ratio

mV

µA

V

V

dB

mA

dB

1.250

25

50

0.1

+3.2

1.200

32.5

V

I

I

Comparator Threshold

Comparator Hysteresis

Delay Charging Current

On Saturation Voltage

OFF Clamp Voltage

SG1548/SG2548/SG3548

Min. Typ. Max.

SG3548

SG1548/2548

Test Conditions

Parameter

Units

Min. Typ. Max.

APPLICATION INFORMATION

Note 5. +V

IN

= 4.5V.

Fault Delay Section

1.300

67.5

0.2

+3.6

1.200

32.5

1.250

25

50

0.1

+3.2

1.300

67.5

0.2

+3.6

V

mV

µA

V

V

15

-1.0

1.9

25

3.2

72

5

72

2

-0.3

3.5

1.0

100

15

100

15

-1.0

1.9

25

2.560

2

10

0.5

7.5

-1.0

V

mV

µA

µA

V

V

V

V

µA

V

10

0.5

1

0.2

10

0.5

1

0.2

SETTING THE FAULT TOLERANCE WINDOW

The fault tolerance window is set by applying a voltage less than

the +2.50Vreference to the Lower Threshold input (Pin 1). The

voltage is obtained by a resistor divider from the reference (Pin 3)

to ground. If ±5% tolerance is desired, then 95% of the reference

(+2.375V) is applied to Pin 1. If ±40% is wanted, then 60% of the

reference (+1.50V) is applied. In the example on the back page,

the tolerance is ±5%. The nominal overvoltage and undervoltage

thresholds are centered about the reference at +2.625V and

+2.375V (+2.500V ±0.125V).

SCALING THE MONITORED SUPPLY VOLTAGES

Each positive voltage to be monitored is divided down to +2.50V

with a resistor network and connected to one of the Sense inputs.

Unused Sense inputs should be connected to the reference. This

will not increase the bias current. A variation of the monitored

voltages out of the programmed tolerance range will cause the

appropriate overvoltage or undervoltage fault output to switch

LOW. The effective tolerance on any input may be broadened

with an additional resistor to the voltage reference. The example

on the back page shows a ±10% tolerance on the +5Vsupply

although the SG1548 is programmed for a ±5% tolerance. The

procedure for calculating the resistor value is found in the

SG1548 Application Note.

MONITORING A NEGATIVE VOLTAGE

A negative voltage can be converted to a positive one and

simultaneously scaled to +2.50V by using the internal operational

amplifier as an inverter. Only an input resistor and feedback

resistor are required.

SETTING THE FAULT DELAY

A single capacitor at the Delay pin sets the time an out-of-

tolerance fault must persist before a fault is actually declared.

This feature allows switching noise on the supplies to be rejected.

The delay time is given by: Delay = 25ms/

µF .

AC LINE MONITORING

The AC line voltage can be monitored for single-cycle dropouts

with the few components shown in the example. A half-wave

rectifier charges the capacitor on positive line cycles. After the

positive peak and during the negative line cycle the capacitor

discharges from a fixed voltage controlled by the internal Zener

diode. If a positive cycle is missing, the capacitor discharges to

below the +2.5V trip point of the comparator, causing the output

transistor to turn on.