rev 1.1a 03/17/2005 microsemi inc. copyright ? 1994 11861 western avenue garden grove, ca 92841 1 (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
rev 1.1a copyright ? 1994 11861 western avenue garden grove, ca 92841 2 (714) 898-8121 fax: (714) 893-2570 operating junction temperature hermetic (y package) .................................................. plastic (n package) ...................................................... storage temperature range ............................ 150 c 150 c -65 c to 150 c input supply voltage, v s ..................................................... hi cm input voltage ............................................................ lo output "off" voltage ....................................................... lo output "on" current ..................................................... 25v 40v 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 , q jc .................. 50c/w thermal resistance- junction to ambient , q ja ............ 130c/w m package: thermal resistance- junction to case , q jc .................. 60c/w thermal resistance- junction to ambient , q ja ............. 95c/w thermal data note a. junction temperature calculation: t j = t a + (p d x q ja ). note b. the above numbers for q jc are maximums for the limiting thermal resistance of the package in a standard mount- ing configuration. the q 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. min. trigger voltage input current 2.0 20 2.5 40 2.0 20 v m a v cm = 2v, pin 3 open, t a = 25c v cm = 40v, pin 3 open, t a = 25c v cm = 2v, pin 3 open v cm = 40v, pin 3 open v pin 1 = v pin 2 = 40v threshold voltage input current 100 100 500 500 80 70 400 300 80 70 400 300 120 130 600 700 100 100 500 500 120 130 600 700 mv mv w w sg3549 sg1549/2549 test conditions parameter units v pin 8 = 5v v pin 8 = 20v supply current supply section 2 10 3 15 2 10 note 3. input threshold voltages and supply current are directly proportional to supply voltage, v s . 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 c -25 c to 85 c 0 c to 70 c note 2. range over which the device is functional. input supply voltage, v s .................................................... 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 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.) min. typ. max. min. typ. max. 5 15 ma ma lo cm input section (note 3) pin 1 & 2 shorted, t a = 25c pin 1 & 2 shorted v pin 3 = 50mv, t a = 25c v pin 3 = 50mv threshold voltage input impedance hi cm input section (note 3) 100 100 100 100 200 120 120 130 130 300 80 80 70 70 120 120 130 130 300 mv mv mv mv m a 100 100 100 100 200 80 80 70 70 clock reset section v pin 7 = 4v 2.5 40 rohs peak package solder reflow temp (40 sec. max. exp.)....... 260c (+0, -5)
rev 1.1a copyright ? 1994 11861 western avenue garden grove, ca 92841 3 (714) 898-8121 fax: (714) 893-2570 lo output 1.0 0.5 .01 .3 1.0 0.5 v pin 5 = 40v i l = 5ma off leakage on voltage sg1549/sg2549/sg3549 typical switching characteristics (note 4) (v s = 5v, t a = 25 c) 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 ns ns ns ns ns ns 300 600 300 360 900 60 150 300 50 180 300 30 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 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 sg1524s 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. electrical characteristics (v s = 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 r l = 470 w to v s lo cm amplitude = 200mv lo cm amplitude = 200mv, r l = 470 w to v s amplitude = 200mv, v cm = 5v lo cm input = 200mv off voltage on voltage 0 3.2 0.1 v v 0 3.2 0.1 i l = 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 .3 m a v
rev 1.1a copyright ? 1994 11861 western avenue garden grove, ca 92841 4 (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 sg1524s 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 500 w 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. ambient temperature range part no. package connection diagram 8-pin ceramic dip y - package 8 7 6 5 2 1 3 4 hi cm input + hi cm input + lo cm input lo cm input clock reset +v s lo output hi output sg1549y/883b -55 c to 125 c sg1549y/desc -55 c to 125 c sg1549y -55 c to 125 c sg2549y -25 c to 85 c sg3549y 0 c to 70 c connection diagrams & ordering information (see notes below) 8-pin plastic dip m - package sg2549m -25 c to 85 c m package: rohs / pb-free 100% matte tin lead finish sg3549m 0 c to 70 c m package: rohs compliant / pb-free transition dc: 0503 note 1. contact factory for jan and desc product availability. 2. all parts are viewed from the top. d package pb-free transition dc:0440 100% pb-free matte tin lead finish
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