rev. 1.0 1/15 copyright ? 2015 by silicon laboratories an836 an836 current sense amplifier performance comparison: ts1100 vs. maxim MAX9634 1. introduction overall measurement accuracy in current-sense amplifiers is a function of both gain error and amplifier input offset voltage performance. of the two error sources, amplifier input offset voltage can impact the design more so than gain error. if the sense resistor needs to be small to ma ximize power to the load and to minimize power dissipation; then amplifier input offset voltage becomes the dominant error term. to minimize load current sense error, a current-sense amplifier with a lower input offset voltage is required. by comparing the ts1100 against the MAX9634 side-by-side, the ts1100?s 3-to-1 improvement in amplifier input offset voltage translates into a 2x improvement in current measurement accuracy. 2. overview as shown in table 1, the ts1100 family of current sense amplifiers provides an input offset voltage of only 30 v with a gain option of 25, 50, 100, and 200. when compared to the MAX9634, the ts1100 exhibits a factor of three lower input offset voltage. the output voltage is a function of the gain and vsense. however, due to a finite gain error and input offset voltage, vos, the total output volta ge is a function of the gain error, vsense, and vos. this is shown in equations 1 and 2 below. equation 1. equation 2. table 1. ts1100 and MAX9634 data sheet specifications ts1100 MAX9634 ts1100 30 (typ) 100 (typ) gain error (%) 0.1% 0.1% gain options 25 25 50 50 100 100 200 200 v out (ideal) gain v sense ? = v out (actual) gain v sense ? gain gain error ? v sense v os ? ? ?? ? + =
an836 2 rev. 1.0 2.1. performance comparison set-up the ts1100 and the MAX9634 evaluation boards were us ed to perform side-by-side load current measurements. with on-board 50 m ? sense resistors and a 100 ma load currents, a gain of 50 current sense amplifier and 5mv sense resistor voltage should ideally generate a 250 mv output voltage. figures 1 and 2 show the ts1100-50 evaluation board and evaluation board circuit schemati c while figures 3 and 4 show the MAX9634 evaluation board and evaluation board and circuit schematic, resp ectively. figure 5 shows the lab bench setup used to perform the measurements. both set-ups were independent and separate instruments were used to perform the measurements on each evaluation board. in addition, a separate active load was used for each evaluation board. the only common piece of equipment used was the power supply. figure 1. ts1100-50 evaluation board figure 2. ts1100-50 evaluation board circuit schematic
an836 rev. 1.0 3 figure 3. MAX9634 evaluation board figure 4. MAX9634f evaluation board circuit schematic
an836 4 rev. 1.0 figure 5. ts1100 and MAX9634 side-by-side lab bench setup
an836 rev. 1.0 5 2.2. performance comparison results the results are shown in table 2 where vsense, iload, and vout we re measured fo r both devices. 2.3. parasitic resistance considerations because the rsense resistor and trace resistances can vary from board to board, each demo board?s iload was adjusted using its own active load in order to equalize the vsense voltage. in a design, it is im portant to measure the exact sense resistor value and then calculate the necessary load current while taking into account any small trace resistances that can affect the load current measurement. 3. conclusion because its input offset voltage is 3 times lower than th e MAX9634, the ts1100 exhibits an improved load current sense accuracy by a factor of 2 over the MAX9634. av ailable in a pcb-space saving sot23-5 package, the ts1100 consumes less than 1a of supply current, can be used in applications that operate from 2 v to 25 v, and is available in four gain options: 25, 50, 100, and 200. this makes the ts1100 an ideal solution for load current measurement in power conscious applications. see do cumentation on the ts1100 current-sense amplifier and ts9634 current-sense amplifie r. for additional informati on, contact silicon labs. table 2. ts1100 and MAX9634 data sheet specifications ts1100-50 MAX9634f %error = 0.64% %error = 1.28% i load = 100 ma r sense = 50m ? 1% v sense = 5 mv v out (measured) = 248.4 mv v out (ideal) = 250 mv i load = 100 ma r sense = 50m ? 1% v sense = 5 mv v out (measured) = 248.4 mv v out (ideal) = 250 mv
disclaimer silicon laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the silicon laboratories products. characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "typical" parameters provided can and do vary in different applications. application examples described herein are for illustrative purposes only. silicon laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. silicon laboratories shall have no liability for the consequences of use of the information supplied herein. this document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. the products must not be used within any life support system without the specific written consent of silicon laboratories. a "life support system" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. silicon laboratories products are generally not intended for military applications. silicon laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons. trademark information silicon laboratories inc., silicon laboratories, silicon labs, silabs and the silicon labs logo, cmems?, efm, efm32, efr, energy micro, energy micro logo and combinations thereof, "the world?s most energy friendly microcontrollers", ember?, ezlink?, ezmac?, ezradio?, ezradiopro?, dspll?, isomodem ?, precision32?, proslic?, siphy?, usbxpress? and others are trademarks or registered trademarks of silicon laboratories inc. arm, cortex, cortex-m3 and thumb are trademarks or registered trademarks of arm holdings. keil is a registered trademark of arm limited. all other products or brand names mentioned herein are trademarks of their respective holders. http://www.silabs.com silicon laboratories inc. 400 west cesar chavez austin, tx 78701 usa smart. connected. energy-friendly products www.silabs.com/products quality www.silabs.com/quality support and community community.silabs.com
|
