This is a design circuit for the physical implementation of the LED current sense circuitry assuming the thermal fold back circuitry is a simple current source. This circuit is based on the LM3424 uses an external current sense resistor (RSNS) placed in series with the LED load to convert the LED current (ILED) into a voltage (VSNS). This is the figure of the circuit.
The HSP and HSN pins are the inputs to the high-side sense amplifier which are forced to be equal potential (VHSP=VHSN) through negative feedback. For matching and noise performance, the suggested signal current ICSH is approximately 100 μA. This current does not flow in the LEDs and will not affect either the off-state LED current or the regulated LED current. ICSH can be above or below this value, but the high-side amplifier offset characteristics may be affected slightly. [Schematic’s circuit source: National Semiconductor, Inc]
The HSP and HSN pins are the inputs to the high-side sense amplifier which are forced to be equal potential (VHSP=VHSN) through negative feedback. For matching and noise performance, the suggested signal current ICSH is approximately 100 μA. This current does not flow in the LEDs and will not affect either the off-state LED current or the regulated LED current. ICSH can be above or below this value, but the high-side amplifier offset characteristics may be affected slightly. [Schematic’s circuit source: National Semiconductor, Inc]
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