Datasheet LTC6101, LTC6101HV (Analog Devices) - 10

link to page 10 LTC6101/LTC6101HV
APPLICATIONS INFORMATION Useful Gain Configurations
Peak dissipation is 200mW. If a 5mΩ sense resistor is employed, then the effective current error is 30mA, while
Gain RIN ROUT VSENSE at VOUT = 5V IOUT at VOUT = 5V
the peak sense voltage is reduced to 10mV at 2A, dis- 20 499 10k 250mV 500µA sipating only 20mW. 50 200 10k 100mV 500µA The low offset and corresponding large dynamic range of 100 100 10k 50mV 500µA the LTC6101 make it more flexible than other solutions in
Selection of External Current Sense Resistor
this respect. The 150µV typical offset gives 60dB of dy- namic range for a sense voltage that is limited to 150mV The external sense resistor, RSENSE, has a significant effect max, and over 70dB of dynamic range if the rated input on the function of a current sensing system and must be maximum of 500mV is allowed. chosen with care. First, the power dissipation in the resistor should be
Sense Resistor Connection
considered. The system load current will cause both heat Kelvin connection of the IN– and IN+ inputs to the sense and voltage loss in RSENSE. As a result, the sense resis- resistor should be used in all but the lowest power ap- tor should be as small as possible while still providing plications. Solder connections and PC board interconnec- the input dynamic range required by the measurement. tions that carry high current can cause significant error Note that input dynamic range is the difference between in measurement due to their relatively large resistances. the maximum input signal and the minimum accurately One 10mm x 10mm square trace of one-ounce copper reproduced signal, and is limited primarily by input DC is approximately 0.5mΩ. A 1mV error can be caused by offset of the internal amplifier of the LTC6101. In addition, as little as 2A flowing through this small interconnect. RSENSE must be small enough that VSENSE does not exceed This will cause a 1% error in a 100mV signal. A 10A load the maximum input voltage specified by the LTC6101, even current in the same interconnect will cause a 5% error under peak load conditions. As an example, an application for the same 100mV signal. By isolating the sense traces may require that the maximum sense voltage be 100mV. from the high-current paths, this error can be reduced If this application is expected to draw 2A at peak load, by orders of magnitude. A sense resistor with integrated RSENSE should be no more than 50mΩ. Kelvin sense terminals will give the best results. Figure 2 Once the maximum R illustrates the recommended method. SENSE value is determined, the mini- mum sense resistor value will be set by the resolution or V+ dynamic range required. The minimum signal that can be accurately represented by this sense amp is limited by the RIN input offset. As an example, the LTC6101B has a typical RSENSE input offset of 150µV. If the minimum current is 20mA, a +IN –IN sense resistor of 7.5mΩ will set V + – SENSE to 150µV. This is LOAD the same value as the input offset. A larger sense resistor V+ V– will reduce the error due to offset by increasing the sense voltage for a given load current. Choosing a 50mΩ RSENSE will maximize the dynamic range OUT LTC6101 VOUT and provide a system that has 100mV across the sense ROUT resistor at peak load (2A), while input offset causes an 6101 F02 error equivalent to only 3mA of load current.
Figure 2. Kelvin Input Connection Preserves Accuracy Despite Large Load Current
Rev I 10 For more information www.analog.com Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION REVISION HISTORY TYPICAL APPLICATION RELATED PARTS