JAJSNC5 データシート

JAJSNC5 april 2023 LM5171-Q1

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パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）

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サーマルパッド・メカニカル・データ

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8.2.1.2.12 Channel Current Monitor (IMONx)

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

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

Equation 94. R_IMONx = 10 kΩ

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

Equation 95. C_IMONx = 10 nF

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

Equation 96.

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 97.

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, according to Equation 6, the IOUT peak to peak ripple current is:

Equation 98.

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 99.

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 100.

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.