SNVSC75 Data sheet

SNVSC75B April 2023 – September 2025 LM5171-Q1

PRODUCTION DATA

8.6.1.2.12 Channel Current Monitor (IMONx)

For best current monitor accuracy, choose IMONx resistor that the maximum operating voltage on the IMONx pin is less than 3V.

Considering two phase current monitoring with maximum 50A for each channel, and make sure IMONx voltage no more than 3V, R_IMONx is found as:

Equation 100. R_IMONx = 10kΩ

Choose C_IMONx considering delay and voltage ripple. Here we select:

Equation 101. C_IMONx = 10nF

Then the delay of the monitor is determined by the following time constant:

Equation 102.

τ_{I M O N x} = R_{I M O N x} \times C_{I M O N x} = 10 k Ω \times 10 n s = 100 μ s

At full load, the DC component of the monitor voltage is:

Equation 103.

V_{I M O N x} = 2 \times (\frac{I_{m a x} \times R_{C S}}{500 Ω} + 50 μ A) \times R_{I M O N x} = 2 \times (\frac{30 A \times 1 m Ω}{500 Ω} + 50 μ A) \times 10 k Ω = 2.2 V

Considering the inductor ripple current, the IOUT peak to peak ripple current is:

Equation 104.

Δ I M O N x = \frac{I_{p k - p k} \times R_{C S}}{500 Ω} = \frac{23.8 A \times 1 m Ω}{500 Ω} = 47.6 μ A

The RC filter corner frequency is thus given by:

Equation 105.

f_{I M O N x} = \frac{1}{2 π \times R_{I M O N x} \times C_{I M O N x}} = \frac{1}{6.28 \times 10 k Ω \times 10 n F} = 1.59 k H z

The resulting peak-to-peak monitor ripple voltage is approximately determined by:

Equation 106.

Δ V_{I M O N x} = Δ I M O N x \times (R_{I M O N x}‖ \frac{1}{2 i \times π \times F_{S W} \times C_{I M O N x}}) = 47.6 μ A \times (10 k Ω‖ \frac{1}{2 i \times π \times 100 k H z \times 10 n F}) = 7.5 m V

The peak-to-peak monitor ripple voltage is approximately 0.34% of the full load DC monitor voltage. Increasing C_IMONx attenuates the ripple voltage at the cost of higher monitor delay.