LM5145 datasheet(22/60 Pages) TI2

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VOUT

Current sense

amplifier

COUT

RDCR

VIN

CS gain = 10

RCS

CCS

VOUT

ISNS

Figure 6-6. Inductor DCR Current Sensing Implementation

Equation 11 shows the voltage drop across the sense capacitor in the s-domain. When the RCSCCS time

constant is equal to LO/RDCR, the voltage developed across the sense capacitor, CCS, is a replica of the inductor

DCR voltage and accurate current sensing is achieved. If the RCSCCS time constant is not equal to the LO/RDCR

time constant, there is a sensing error as follows:

• RCSCCS > LO/RDCR → the DC level is correct, but the AC amplitude is attenuated.

• RCSCCS < LO/RDCR → the DC level is correct, but the AC amplitude is amplified.

VCSs = IOUTCL +∆I2 ×RDCR× 1+S LORDCR

1+sRCSCCS

(11)

Choose the CCS capacitance greater than or equal to 0.1μF to maintain a low-impedance sensing network, thus

reducing the susceptibility of noise pickup from the switch node. Carefully observe Section 7.4.1 to make sure

that noise and DC errors do not corrupt the current sense signals applied between the ISNS and VOUT pins.

6.3.12.3 Hiccup-Mode Current Limiting

The LM25139 includes an internal hiccup-mode protection function. After an overload is detected, 512 cycles of

cycle-by-cycle current limiting occurs. The 512-cycle counter is reset if four consecutive switching cycles occur

without exceeding the current limit threshold. After the 512-cycle counter has expired, the internal soft start is

pulled low, the HO and LO driver outputs are disabled, and the 16384-cycle hiccup counter is enabled. After the

counter reaches 16384, the internal soft start is enabled and the output restarts. The hiccup-mode current limit

is disabled during soft start until after soft start is complete (8ms) and the output voltage has reached half the

regulation value.

LM25139

SLVSJ80 – OCTOBER 2025

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