SG1549

4/90 Rev 1.1 2/94

INFINITY

Microelectronics Inc.

1994

11861 Western Avenue

∞

Garden Grove, CA 92841

(714) 898-8121

∞

FAX: (714) 893-2570

SG1549/SG2549/SG3549

CURRENT SENSE LATCH

DESCRIPTION

This monolithic integrated circuit is an analog latch device with digital reset. It was

specifically designed to provide pulse-by-pulse current limiting for switch-mode power

supply systems, but many other application are also feasible. Its function is to provide

a latching switch action upon sensing an input threshold voltage, with reset accom-

plished by an external clock signal. This device can be interfaced directly with many

kinds of pulse width modulating control IC's, including the SG1524, SG1525A and

SG1527A.

The input threshold for the latch circuit is 100mV, which can be referenced either to

ground or to a wide-ranging positive voltage. There are high and low-going output

signals available, and both the supply voltage and clock signal can be taken directly

from an associated PWM control chip.

With delays in the range of 200 nanoseconds, this latch circuit is ideal for fast reaction

sensing to provide overall current limiting, short circuit protection, or transformer

saturation control.

FEATURES

•••••

Current sensing with 100mV

threshold

•••••

Common-mode input at ground or

to 40V

•••••

Complementary outputs

•••••

Automatic reset from PWM clock

•••••

180ns delay

•••••

Interface direct to SG1524,

SG1525A, SG1527A

HIGH RELIABILITY FEATURES

- SG1549

♦

Available to MIL-STD-883

♦

LMI level "S" processing available

♦

Radiation data available

BLOCK DIAGRAM

SCHEMATIC

4/90 Rev 1.1 2/94

INFINITY

Microelectronics Inc.

1994

11861 Western Avenue

∞

Garden Grove, CA 92841

(714) 898-8121

∞

FAX: (714) 893-2570

Operating Junction Temperature

Hermetic (Y Package) ..................................................

Plastic (N Package) ......................................................

Storage Temperature Range ............................

150

-65

C to 150

Input Supply Voltage, V

.....................................................

HI CM Input Voltage ............................................................

LO Output "off" Voltage .......................................................

LO Output "on" current .....................................................

25V

40V

25mA

ABSOLUTE MAXIMUM RATINGS

(Note 1)

SG1549/SG2549/SG3549

Note 1. Values beyond which damage may occur.

Y Package:

Thermal Resistance-

Junction to Case

.................. 50°C/W

Thermal Resistance-

Junction to Ambient

............ 130°C/W

M Package:

Thermal Resistance-

Junction to Case

.................. 60°C/W

Thermal Resistance-

Junction to Ambient

............. 95°C/W

THERMAL DATA

Note A. Junction Temperature Calculation: T

= T

+ (P

Note B. The above numbers for

are maximums for the limiting

thermal resistance of the package in a standard mount-

ing configuration. The

numbers are meant to be

guidelines for the thermal performance of the device/pc-

board system. All of the above assume no ambient

airflow.

Min. Trigger Voltage

Input Current

2.0

2.5

2.0

= 2V, Pin 3 open, T

= 25°C

= 40V, Pin 3 open, T

= 25°C

= 2V, Pin 3 open

= 40V, Pin 3 open

PIN 1

= V

PIN 2

= 40V

Threshold Voltage

Input Current

100

500

400

300

400

300

120

130

600

700

100

500

120

130

600

700

Ω

SG3549

SG1549/2549

Test Conditions

Parameter

Units

PIN 8

= 5V

PIN 8

= 20V

Supply Current

Supply Section

Note 3. Input threshold voltages and supply current are directly proportional to supply voltage, V

5.0V

2V to 40V

5V to 40V

0 to 10mA

0V to 0.8V

Reset HI Voltage ....................................................

Operating Ambient Temperature Range

SG1549Y .......................................................

SG2549Y or M .................................................

SG3549Y or M ....................................................

2.5V to 5.0V

-55

C to 125

-25

C to 85

C to 70

Note 2. Range over which the device is functional.

Input Supply Voltage, V

....................................................

HI CM Input Voltage ..................................................

LO Output "off" Voltage .............................................

LO Output "on" Current .............................................

Reset LO Voltage .....................................................

RECOMMENDED OPERATING CONDITIONS

(Note 2)

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1549 with -55

≤

125

C, SG2549 with

-25

≤

C, SG3549 with 0

≤

C, and V

= 5V. Low duty cycle pulse testing techniques are used which maintains junction and case

temperatures equal to the ambient temperature.)

Min. Typ. Max. Min. Typ. Max.

LO CM Input Section

(Note 3)

Pin 1 & 2 shorted, T

= 25°C

pin 1 & 2 shorted

PIN 3

= 50mV, T

= 25°C

PIN 3

= 50mV

Threshold Voltage

Input Impedance

HI CM Input Section

(Note 3)

100

200

120

130

300

120

130

300

100

200

Clock Reset Section

PIN 7

= 4V

2.5

4/90 Rev 1.1 2/94

INFINITY

Microelectronics Inc.

1994

11861 Western Avenue

∞

Garden Grove, CA 92841

(714) 898-8121

∞

FAX: (714) 893-2570

LO Output

1.0

0.5

.01

1.0

0.5

PIN 5

= 40V

= 5mA

Off Leakage

On Voltage

SG1549/SG2549/SG3549

TYPICAL SWITCHING CHARACTERISTICS

(Note 4)

= 5V, T

= 25

Reset Minimum Pulse Width (T

)

Delay from Reset to LO Output (T

D(OFF)

)

LO Input Minimum Pulse Width (T

)

Delay from LO Input to LO Output (T

D(ON)

)

Delay from HI Input to LO Output (T

D(ON)

)

Delay from HI Output to LO Output

300

600

300

360

900

150

300

180

300

Min. Typ. Max.

SG1549 Series

Test Conditions

Parameter

Units

DYNAMIC TEST CIRCUIT

SWITCHING WAVEFORMS

APPLICATION NOTES

HIGH LINE SENSING - The SG1549 will provide current sensing in the

positive supply line in the typical SG1524 single-ended switching

regulator application shown in Figure 1. The HI CM sense circuitry can

be used with input voltages between 2 and 40 volts.

A value for R

is determined by dividing the 100mV input threshold by

the peak current desired. High-frequency noise, or switching transients,

can usually be eliminated by a small capacitor between pins 3 and 4.

Current control may be accomplished by either the HI OUTPUT pin

connected to the SG1524’s Shutdown pin, or the LO OUTPUT pin

connected directly to the Compensation Terminal. In either case,

activation of the current sense latch will tend to discharge the compen-

sation capacitor, C

, which may cause slow recovery from pulse limiting.

If this feature is desired, the LO OUTPUT pin may be used to discharge

a soft-start network instead of coupling directly to the SG1524. If it is not

desired, the use of a small value of C

, and perhaps a diode across R

will enhance recovery.

ELECTRICAL CHARACTERISTICS

= 5V, and over recomended operating temperature, unless otherwise specified.)

Min. Typ. Max. Min. Typ. Max.

SG3549

SG1549/2549

Test Conditions

Parameter

Units

Amplitude = 3.0V

= 470

Ω

to V

LO CM Amplitude = 200mV

LO CM Amplitude = 200mV, R

= 470

Ω

to V

Amplitude = 200mV, V

= 5V

LO CM Input = 200mV

Off Voltage

On Voltage

3.2

0.1

3.2

0.1

= 1mA

2.8

Note 4: These parameters, although guaranteed, are not tested in production.

FIGURE 1 — HIGH LINE SENSING WITH THE SG1549 IN CONJUNCTION

WITH AN SG1524 PWM CONTROL IC

HI Output Section

2.8

.01

4/90 Rev 1.1 2/94

INFINITY

Microelectronics Inc.

1994

11861 Western Avenue

∞

Garden Grove, CA 92841

(714) 898-8121

∞

FAX: (714) 893-2570

SG1549/SG2549/SG3549

APPLICATION NOTES

(continued)

FIGURE 2 — CURRENT CONTROL FOR A BUCK REGULATOR WITH

CONSTANT DRIVE CURRENT

FIGURE 4 — POWER BOOST AND CURRENT CONTROL WITH THE SG1627

FIGURE 3 — A PUSH-PULL CONVERTER WITH LOW-LINE

EMITTER CURRENT SENSING

Another method of introducing the current shutdown signal is shown in

Figure 2 where the SG1524 is used to activate a constant drive current

to the high-current switch, in this case an SM600. The 2N2222 forms a

constant current generator when driven from the SG1524’s 5.0 volt

reference through a 1K resistor. This transistor is then switched off by

the LO OUTPUT transistor in the SG1549, achieving the fastest re-

sponse to the output of the regulator.

LOW LINE SENSING - In many types of feed-forward or push-pull

converters, current protection may be provided by sensing in an emitter

resistor referenced to ground on the primary side of an output trans-

former. The fast-reacting SG1549 can easily sense secondary overload

as reflected back to the primary and, additionally, provide protection

from unbalanced transformer saturation.

When using the LO CM inputs, the HI CM inputs should be shorted

together. While the LO CM inputs may be connected directly across a

sense resistor, R

, a small low-pass filter as shown in Figure 3 is often

required to eliminate high frequency transients. It must be remembered

that the 500

Ω

input impedance at the LO CM terminals will cause the use

of R1 to increase the effective threshold; however, this also offers the

possibility of an easily adjustable threshold by incorporating a potenti-

ometer at the input.

Coupling the output signal from the SG1549 to the control chip may be

done in several ways including the use of either the Compensation or

Shutdown pins on the SG1524 as described earlier.

Another convenient way to tie the output of the SG1549 into the PWM

control in higher power applications is by using the SG1627 Dual

Interface Driver and connecting the LO OUTPUT terminal of the Sg1549

directly to the two Non-Inverting inputs of the SG1627 as shown in Figure

And finally, keep in mind that the LO OUTPUT terminal of the SG1549

will easily drive most high-speed optical couplers should some type of

isolation between current sense and shutdown control be required.

Ambient

Temperature Range

Part No.

Package

Connection Diagram

8-PIN CERAMIC DIP

Y - PACKAGE

— HI CM INPUT

+ HI CM INPUT

+ LO CM INPUT

— LO CM INPUT

CLOCK RESET

LO OUTPUT

HI OUTPUT

SG1549Y/883B

-55

C to 125

SG1549Y/DESC

-55

C to 125

SG1549Y

-55

C to 125

SG2549Y

-25

C to 85

SG3549Y

C to 70

CONNECTION DIAGRAMS & ORDERING INFORMATION

(See Notes Below)

8-PIN PLASTIC DIP

M - PACKAGE

SG2549M

-25

C to 85

SG3549M

C to 70

Note 1. Contact factory for JAN and DESC product availability.

2. All parts are viewed from the top.