Each channel of the LM5170-Q1 has an independent bidirectional, high accuracy, and high-speed differential current sense amplifier. The differential current sense polarity is determined by the DIR command. The amplifier gain is 50, such that a smaller current sense resistor can be used to reduce power dissipation. The amplified current sense signal is used to perform the following functions:

• Applied to the inverting input of the error amplifier for current loop regulation.
• Used to reconstruct the channel current monitor signal at the IOUT1 and IOUT2 pins.
• Monitored by the cycle-by-cycle peak current limit comparator for instantaneous overcurrent protection.
• Sensed by the current zero cross detector to operate the synchronous rectifiers in diode emulation mode.

The current sense resistor Rcs should be selected for 50-mV current sense voltage when the channel DC current reaches the rated level. The CS1A, CS1B, CS2A, and CS2B pins should be Kelvin connected for accurate sensing.

It is very important that the current sense resistors are non-inductive. Otherwise the sensed current signals are distorted even if the parasitic inductance is only a few nH. Such inductance may not affect the current regulation during continuous conduction mode, but it does affect current zero cross detection, and hence the performance of diode emulation mode under light load. As a consequence, the synchronous rectifier gate pulse is truncated much earlier than the inductor current zero crossing, causing the body diode of the synchronous rectifier to conduct unnecessarily for a longer time. See the Section 8.3.15 for details.

If the selected current sense resistor has parasitic inductance, see the Section 9.1 for methods to compensate for this condition and achieve optimal performance.