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
Copyright
©
1994
1
11861 Western Avenue
∞
Garden Grove, CA 92841
(714) 898-8121
∞
FAX: (714) 893-2570
L
INFINITY
Microelectronics Inc.
SG1549/SG2549/SG3549
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage, V
S
..................................................... 25V
HI CM Input Voltage ............................................................ 40V
LO Output "off" Voltage ....................................................... 40V
LO Output "on" current ..................................................... 25mA
Note 1. Values beyond which damage may occur.
Operating Junction Temperature
Hermetic (Y Package) .................................................. 150°C
Plastic (N Package) ...................................................... 150°C
Storage Temperature Range ............................ -65°C to 150°C
THERMAL DATA
Y Package:
Thermal Resistance-
Junction to Case
,
θ
JC
.................. 50°C/W
Thermal Resistance-
Junction to Ambient
,
θ
JA
............ 130°C/W
M Package:
Thermal Resistance-
Junction to Case
,
θ
JC
.................. 60°C/W
Thermal Resistance-
Junction to Ambient
,
θ
JA
............. 95°C/W
Note A. Junction Temperature Calculation: T
J
= T
A
+ (P
D
x
θ
JA
).
Note B. The above numbers for
θ
JC
are maximums for the limiting
thermal resistance of the package in a standard mount-
ing configuration. The
θ
JA
numbers are meant to be
guidelines for the thermal performance of the device/pc-
board system. All of the above assume no ambient
airflow.
RECOMMENDED OPERATING CONDITIONS
(Note
2)
Input Supply Voltage, V
S
.................................................... 5.0V
HI CM Input Voltage .................................................. 2V to 40V
LO Output "off" Voltage ............................................. 5V to 40V
LO Output "on" Current ............................................. 0 to 10mA
Reset LO Voltage ..................................................... 0V to 0.8V
Note 2. Range over which the device is functional.
Reset HI Voltage .................................................... 2.5V to 5.0V
Operating Ambient Temperature Range
SG1549Y ....................................................... -55°C to 125°C
SG2549Y or M ................................................. -25°C to 85°C
SG3549Y or M .................................................... 0°C to 70°C
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for SG1549 with -55°C
≤
T
A
≤
125°C, SG2549 with
-25°C
≤
T
A
≤
85°C, SG3549 with 0°C
≤
T
A
≤
70°C, and V
S
= 5V. Low duty cycle pulse testing techniques are used which maintains junction and case
temperatures equal to the ambient temperature.)
Parameter
Supply Section
Supply Current
LO CM Input Section
(Note 3)
Threshold Voltage
Input Impedance
HI CM Input Section
(Note 3)
Threshold Voltage
V
PIN 8
= 5V
V
PIN 8
= 20V
Test Conditions
SG1549/2549
SG3549
Units
Min. Typ. Max. Min. Typ. Max.
2
10
80
70
400
300
80
80
70
70
100
100
500
500
100
100
100
100
200
2.0
20
3
15
120
130
600
700
120
120
130
130
300
2.5
40
80
70
400
300
80
80
70
70
2
10
100
100
500
500
100
100
100
100
200
2.0
20
5
15
120
130
600
700
120
120
130
130
300
2.5
40
mA
mA
mV
mV
Ω
Ω
mV
mV
mV
mV
µA
V
µA
Pin 1 & 2 shorted, T
A
= 25°C
pin 1 & 2 shorted
V
PIN 3
= 50mV, T
A
= 25°C
V
PIN 3
= 50mV
V
CM
= 2V, Pin 3 open, T
A
= 25°C
V
CM
= 40V, Pin 3 open, T
A
= 25°C
V
CM
= 2V, Pin 3 open
V
CM
= 40V, Pin 3 open
V
PIN 1
= V
PIN 2
= 40V
Input Current
Clock Reset Section
Min. Trigger Voltage
Input Current
V
PIN 7
= 4V
Note 3. Input threshold voltages and supply current are directly proportional to supply voltage, V
S
.
4/90 Rev 1.1 2/94
Copyright
©
1994
2
11861 Western Avenue
∞
Garden Grove, CA 92841
(714) 898-8121
∞
FAX: (714) 893-2570
L
INFINITY
Microelectronics Inc.
SG1549/SG2549/SG3549
ELECTRICAL CHARACTERISTICS
(V
S
= 5V, and over recomended operating temperature, unless otherwise specified.)
Parameter
HI Output Section
Off Voltage
On Voltage
LO Output
Off Leakage
On Voltage
Test Conditions
SG1549/2549
SG3549
Units
Min. Typ. Max. Min. Typ. Max.
0
3.2
.01
.3
0.1
2.8
1.0
0.5
0
3.2
.01
.3
0.1
V
V
µA
V
I
L
= 1mA
V
PIN 5
= 40V
I
L
= 5mA
(Note 4)
2.8
1.0
0.5
TYPICAL SWITCHING CHARACTERISTICS
(V
S
= 5V, T
A
= 25°C)
Parameter
Reset Minimum Pulse Width (T
W1
)
Delay from Reset to LO Output (T
D(OFF)
)
LO Input Minimum Pulse Width (T
W2
)
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
Test Conditions
Amplitude = 3.0V
R
L
= 470Ω to V
S
LO CM Amplitude = 200mV
LO CM Amplitude = 200mV, R
L
= 470Ω to V
S
Amplitude = 200mV, V
CM
= 5V
LO CM Input = 200mV
SG1549 Series
Units
Min. Typ. Max.
150 300
ns
ns
300 600
50 300
ns
180 360
ns
300 900
ns
30
60
ns
Note 4: These parameters, although guaranteed, are not tested in production.
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
SC
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
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
C
, and perhaps a diode across R
C
,
will enhance recovery.
FIGURE 1 — HIGH LINE SENSING WITH THE SG1549 IN CONJUNCTION
WITH AN SG1524 PWM CONTROL IC
4/90 Rev 1.1 2/94
Copyright
©
1994
3
11861 Western Avenue
∞
Garden Grove, CA 92841
(714) 898-8121
∞
FAX: (714) 893-2570
L
INFINITY
Microelectronics Inc.
SG1549/SG2549/SG3549
APPLICATION NOTES
(continued)
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
SC
, a small low-pass filter as shown in Figure 3 is often
required to eliminate high frequency transients. It must be remembered
that the 500Ω 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
4.
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.
FIGURE 2 — CURRENT CONTROL FOR A BUCK REGULATOR WITH
CONSTANT DRIVE CURRENT
FIGURE 3 — A PUSH-PULL CONVERTER WITH LOW-LINE
EMITTER CURRENT SENSING
FIGURE 4 — POWER BOOST AND CURRENT CONTROL WITH THE SG1627
CONNECTION DIAGRAMS & ORDERING INFORMATION
Package
8-PIN CERAMIC DIP
Y - PACKAGE
(See Notes Below)
Part No.
SG1549Y/883B
SG1549Y/DESC
SG1549Y
SG2549Y
SG3549Y
SG2549M
SG3549M
Ambient
Temperature Range
-55°C to 125°C
-55°C to 125°C
-55°C to 125°C
-25°C to 85°C
0°C to 70°C
-25°C to 85°C
0°C to 70°C
Connection Diagram
+ HI CM INPUT
— HI CM INPUT
+ LO CM INPUT
— LO CM INPUT
1
2
3
4
8
7
6
5
+V
S
CLOCK RESET
HI OUTPUT
LO OUTPUT
8-PIN PLASTIC DIP
M - PACKAGE
Note 1. Contact factory for JAN and DESC product availability.
4/90 Rev 1.1 2/94
Copyright
©
1994
2. All parts are viewed from the top.
11861 Western Avenue
∞
Garden Grove, CA 92841
(714) 898-8121
∞
FAX: (714) 893-2570
L
INFINITY
Microelectronics Inc.
4
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