LT1776 Wide Input Range, High Efficiency, Step-Down Switching Regulator DESCRIPTION FEATURES n Wide Input Range: 7.4V to 40V The LT 1776 is a wide input range, high efficiency Buck n Tolerates Input Transients to 60V (step-down) switching regulator. The monolithic die in- n 700mA Peak Switch Rating cludes all oscillator, control and protection circuitry. The n Adaptive Switch Drive Maintains Efficiency at High part can accept input voltages as high as 60V and contains Load Without Pulse Skipping at Light Load an output switch rated at 700mA peak current. Current n True Current Mode Control mode control delivers excellent dynamic input supply n 200kHz Fixed Operating Frequency rejection and short-circuit protection. n Synchronizable to 400kHz The LT1776 contains several features to enhance effi- n Low Supply Current in Shutdown: 30m A ciency. The internal control circuitry is normally powered n Available in 8-Pin SO and PDIP Packages via the V pin, thereby minimizing power drawn directly CC U from the V supply (see Applications Information). The IN APPLICATIONS action of the LT1776 switch circuitry is also load depen- n dent. At medium to high loads, the output switch circuitry Automotive DC/DC Converters maintains fast rise time for good efficiency. At light loads, n Cellular Phone Battery Charger Accessories rise time is deliberately reduced to avoid pulse skipping n IEEE 1394 Step-Down Converters behavior. The available SO-8 package and 200kHz switching fre- quency allow for minimal PC board area requirements. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATION V IN Efficiency vs V and I IN LOAD 8V TO 40V 5 90 V IN 1 2 80 SHDN V CC 100m H* 3 5V V SW 70 400mA + + 100m F 39m F 36.5k MBR160 LT1776 10V 63V 1% 60 7 FB 50 6 8 SYNC V C 2200pF 40 V = 10V 12.1k IN 1% V = 20V IN 30 22k 100pF GND V = 30V IN V = 40V 4 IN 20 *43T 30 ON MAGNETICS 1776 F01 1 10 100 1000 MPP 55030 LOAD CURRENT (mA) 1776 TA01 Figure 1 1 EFFICIENCY (%) U ULT1776 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) ORDER PART Supply Voltage (Note 5) .......................................... 60V TOP VIEW NUMBER Switch Voltage (Note 5) ........................................... 60V SHDN 1 8 V C LT1776CN8 SHDN, SYNC Pin Voltage........................................... 7V V FB 2 7 CC LT1776CS8 V Pin Voltage ....................................................... 30V CC V 3 6 SYNC SW LT1776IN8 FB Pin Voltage ........................................................... 3V GND 4 5 V IN LT1776IS8 Operating Junction Temperature Range N8 PACKAGE S8 PACKAGE LT1776C ................................................ 0 C to 125 C 8-LEAD PDIP 8-LEAD PLASTIC SO S8 PART MARKING LT1776I ............................................ 40 C to 125 C T = 125 C, q = 130 C/ W (N8) JMAX JA 1776 T = 125 C, q = 110 C/ W (S8) JMAX JA Storage Temperature Range ................. 65 C to 150 C 1776I Lead Temperature (Soldering, 10 sec).................. 300 C Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25 C. A V = 40V, V open, V = 5V, V = 1.4V unless otherwise noted. IN SW CC C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Power Supplies V Minimum Input Voltage 6.7 7.0 V IN(MIN) l 7.4 V Thermally Limited Continuous Operating Voltage l 40 V I V Supply Current V = 0V 620 800 m A VIN IN C l 900 m A I V Supply Current V = 0V 3.2 4.0 mA VCC CC C l 5.0 mA V V Dropout Voltage (Note 2) 2.8 3.1 V VCC CC Shutdown Mode I V = 0V 30 50 m A VIN SHDN l 75 m A Feedback Amplifier V Reference Voltage 1.225 1.240 1.255 V REF l 1.215 1.265 V I FB Pin Input Bias Current 600 1500 nA IN g Feedback Amplifier Transconductance D lc = 10m A 400 650 1000 m mho m l 200 1500 m mho I , I Feedback Amplifier Source or Sink Current 60 100 170 m A SRC SNK l 45 220 m A V Feedback Amplifier Clamp Voltage 2.0 V CL Reference Voltage Line Regulation 12V V 60V l 0.01 %/V IN Voltage Gain 200 600 V/V Output Switch V Output Switch On Voltage I = 0.5A 1.0 1.5 V ON SW I Switch Current Limit (Note 3) l 0.55 0.70 1.0 A LIM Current Amplifier Control Pin Threshold Duty Cycle = 0% 0.9 1.1 1.25 V Control Voltage to Switch Transconductance 2 A/V 2 U W U W U WW