Figure 8-4 illustrates inductor current sensing using a shunt resistor. This configuration
continuously monitors the inductor current to provide accurate overcurrent protection across
the operating temperature range. For optimal current sense accuracy and overcurrent
protection, use a
low inductance ±1% tolerance shunt resistor between the inductor and
the output, with a Kelvin connection to the
LM25149
current sense amplifier.
If the peak voltage
signal sensed from ISNS+ to VOUT exceeds the current limit threshold of 60 mV, the current
limit comparator immediately terminates the HO output for cycle-by-cycle current limiting.
Calculate the shunt resistance using Equation 9.
Equation 9. ![GUID-8CB1A352-D0AA-4715-81AE-0F3D64D7A76E-low.gif](/ods/images/SNVSBV5B/GUID-8CB1A352-D0AA-4715-81AE-0F3D64D7A76E-low.gif)
where
- VCS-TH is current sense
threshold of 60 mV.
- IOUT(CL) is the overcurrent
setpoint that is set higher than the maximum load current to avoid tripping the
overcurrent comparator during load transients.
- ΔIL is the peak-to-peak
inductor ripple current.
The soft-start voltage is clamped 150
mV above FB during an overcurrent condition. Sixteen overcurrent events must occur before
the SS clamp is enabled. This makes sure that SS can be pulled low during brief overcurrent
events, preventing output voltage overshoot during recovery.