DEMO CIRCUIT 1 1 9 2 Q UICK S TA RT LT6105 G UIDE DESCRIPTION L T6 1 0 5 P re c is io n , G a in S e le c ta b le H ig h S id e Cu rre n t S e n s e A m p lifie r Demonstration Circuit 1192 is a Precision, Gain Selectable High Side Current Sense Amplifier featuring the LT6105. suitable for measuring supply bus loading as they are brought up. W hen provided w ith a negative supply, it is capable ofmonitoring negative supplies. This demo board amplifies a current-sense resistor IRdrop, providing a precision uni-polar output voltage proportional to load current. The LT6105 is pow ered from a supply voltage (from 2.85V up to 36V) w hile it measures current ofa voltage pow er bus (0V to 44V). This device is suitable for measuring battery system current since the monitoring-input current draw s become negligible w hen VCC is pow ered dow n. Its 0V and up input range makes it The key performance characteristics of the LT6105 and DC1192 are show n in the Performance Summary below . PERF ORM ANCE SU M M ARY SYM BOL VIN VCC AV AZ VOUT IM AX ICC IBIAS IINPD tR PARAM ETER M onitored Supply Input Range Amplifier Supply Range Voltage Gain TotalCurrent to Voltage Gain Output Voltage Range M aximum Sense Current V+ (=Vcc) Supply Current VS+ Bias Current VS+ Current during Pow er Dow n VM ON step-response time Design files for this circuit board are available. Call the LTC factory. L, LT, Over-The-Top are registered trademarks ofLinear Technology Corporation. Other product names may be trademarks ofthe companies that manufacture the products. Specifications are at TA = 25°C CONDITIONS M IN -0.3 2.85 RIN1 = RIN2 = 100, ROUT = 4.99k RSENSE = .020 Ohm V+ = 3V Thermallimit ofRSENSE (2W atts) V+= 36V, VS+=3V, VSENSE=0V VS+ = 3V, VSENSE=0V V+= 0V, VS+ =44V, VSENSE=0V IOUT step from 0A to 5A TYP 0… 44 3… 28 50 1 2 150 15 .001 50 M AX 44 36 10 250 25 1 UNITS V V V/V V/A V A µA µA µA µs OPERATING PRINCIPL ES The LT6105 operates by amplifying the voltage drop on a sense resistor placed in series w ith the pow er source ofa load to be monitored. The sense inputs of the amplifier differentially measure the sense-resistor drop to control an internalvariable current source that allow s translation of the input information to a level referenced to VEE (ground in this demo circuit). An internal post-amplifier provides additional gain and buffers the output signal. The post-amplifier gain is established by the pin strap configuration of the part. In DC1192 as shipped, the sense resistor installed is 20mΩ and the resistors set the gain to 50V/V, so the nominal output scaling is 1V per Ampere of load current. Other scalings can be produced by changing the resistors. The DC1192 Schematic diagram is show n in Figure 2. 1 LT6105 Q U ICK START PROCEDU RE Demonstration circuit 1192 is easy to set up to evaluate the performance of the LT6105. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below : 1. W ith pow er off, connect the load driving pow er supply positive to SOURCE and the common to GND. This supply should be in the range of 0V to 44V. If this supply is not equipped w ith an accurate current readout, a DM M (set to measure Amperes) may be connected in series w ith the supply as show n in Figure 1. NOTE. Be sure that the current capacity ofthe DM M is adequate to handle the intended load current. 3. Connect a voltmeter or oscilloscope probe to the Vout terminal, w ith the common connection or ground clip tied to GND. 4. Connect a load to the TO LOAD terminal(positive) and return (negative) to the common of the load driving pow er supply. The load may be a pow er resistor, active load instrument, or other circuit ofinterest. 5. Turn on the pow er supplies. 6. Check for an output voltage that corresponds to the load current: VM ON = 1.0×IO UT. 2. W ith pow er off, connect the amplifier supply positive to VCC and the common to GND. This supply should be in the range of2.85V to 36V. POWER SUPPLY 3.0 + COM POWER SUPPLY 10. +0 COM 1.00 0 DMM 1.00 0 DMM A COM V A COM V LOAD (10Ω) Figure 1. Proper M easurem ent Equipm ent Setup 2 LT6105 3