Switched load current sensing

Question

Hello, 
 I'm studying a design of a current sense circuit of a switch load (LED for automotive application). 
 The goal is to detect load current defaults, up to 200mA. 
 Switching of the load is managed by a power switch not including current sense function. 
 I think LTC6101 could be a good device for this. 
 My question is where should I place the shunt resistor in relation to the power switch? 
 Upstream or downstream? Low side or high side? 
 Here is follow a schematic which question me... 
 
 Thanks! 
 Martial

maaarmas · Accepted Answer

Hi, Martial! 
 
 The LTC6101 is a high voltage, high side current sense amplifiers. In high side, the shunt resistor must be placed between the power supply and the load wherein in your case is between the power supply and the power switch. 
 
 LT6101 will function with inputs from 1.5V below the +supply to 0.5V above supply and therefore this is optimized to work on high-side current sensing as you want to maintain the part in linear operation in your system. Using it in low-side current sensing, the common-mode voltage may reach below the functional input range putting LT6101 on nonlinear region. 
 
 Additional advantage is that it would allow to detect a load short to ground condition while maintaining the shunt resistor because in low-side, it would appear that the shunt resistor is shorted due to the high voltage. 
 Thank you! 
 
 Regards, 
 Mae)

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Switched load current sensing