SG1549Y Microsemi Corporation, SG1549Y Datasheet - Page 4

• Manufacturer Part Number: SG1549Y
• Description: Current Sense Latch
• Manufacturer: Microsemi Corporation

Rev 1.1a
Copyright
D Package Pb-free transition DC:0440 100% Pb-free Matte Tin Lead Finish
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
required to eliminate high frequency transients. It must be remembered
that the 500 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.
CONNECTION DIAGRAMS & ORDERING INFORMATION
Note 1. Contact factory for JAN and DESC product availability.
APPLICATION NOTES
8-PIN CERAMIC DIP
Y - PACKAGE
8-PIN PLASTIC DIP
M - PACKAGE
Package
1994
SC
, a small low-pass filter as shown in Figure 3 is often
(continued)
Part No.
SG1549Y/883B
SG1549Y/DESC
SG1549Y
SG2549Y
SG3549Y
SG2549M
SG3549M
Temperature Range
-55 C to 125 C
-55 C to 125 C
-55 C to 125 C
-25 C to 85 C
-25 C to 85 C
0 C to 70 C
0 C to 70 C
Ambient
2. All parts are viewed from the top.
4
(See Notes Below)
FIGURE 4 — POWER BOOST AND CURRENT CONTROL WITH THE SG1627
FIGURE 2 — CURRENT CONTROL FOR A BUCK REGULATOR WITH
Connection Diagram
M Package: RoHS / Pb-free 100% Matte Tin Lead Finish
M Package: RoHS Compliant / Pb-free Transition DC: 0503
FIGURE 3 — A PUSH-PULL CONVERTER WITH LOW-LINE
— LO CM INPUT
— HI CM INPUT
+ LO CM INPUT
+ HI CM INPUT
SG1549/SG2549/SG3549
EMITTER CURRENT SENSING
CONSTANT DRIVE CURRENT
11861 Western Avenue
1
2
3
4
8
7
6
5
[phone]
+V
CLOCK RESET
HI OUTPUT
LO OUTPUT
S
Garden Grove, CA 92841
FAX: [phone]