LM5145 datasheet(27/69 Pages) TI

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DCR

OUT(CL)

1 s

(s)

1 s R

˜ ¨

(12)

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

thus reducing the susceptibility of noise pickup from the switch node. Carefully observe the guidelines found in

Section 12.1 to make sure that noise and DC errors do not corrupt the differential current sense signals applied

between the CS and VOUT pins.

9.3.15 Hiccup Mode Current Limiting (RES)

The LM25143 includes an optional hiccup mode protection function that is enabled when a capacitor is

connected to the RES pin. In normal operation, the RES capacitor is discharged to ground. If 512 cycles of

cycle-by-cycle current limiting occurs, SS is pulled low and the HO and LO outputs are disabled (see Figure 9-6).

A 20-μA current source begins to charge the RES capacitor. When the RES voltage increases to 1.2 V, RES

is pulled low and the SS capacitor begins to charge. The 512-cycle hiccup counter is reset if four consecutive

switching cycles occur without exceeding the current limit threshold. Separate hiccup counters are provided for

each channel, but the RES pin is shared by both channels. One channel can be in hiccup protection while

the other operates normally. In the event that both channels are in an overcurrent condition triggering hiccup

protection, the last hiccup counter to expire pulls RES low and starts the RES capacitor charging cycle. Both

channels then restart together when VRES = 1.2 V. If RES is connected to VDDA at power up, the hiccup function

is disabled for both channels.

1.2 V RES threshold

IRES = 20 A

0 V

RES

Current Limit

detected

ISS = 21 A

VREF = 0.6 V

Current Limit persists

during 512 consecutive

clock cycles

tRES

tSS

Hiccup delay

– no switching

Soft-start time

VFB + 150 mV

Figure 9-6. Hiccup Mode Timing Diagram

Use Equation 13 to calculate the RES capacitance.

RES

(nF)

17 t

(ms)

(13)

where

• tRES is the specified hiccup delay as shown in Figure 9-6.

9.3.16 High-Side and Low-Side Gate Drivers (HO1/2, LO1/2, HOL1/2, LOL1/2)

The LM25143 contains N-channel MOSFET gate drivers and an associated high-side level shifter to drive the

external N-channel MOSFET. The high-side gate driver works in conjunction with an external bootstrap diode,

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LM25143

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