AN3338 datasheet(27/72 Pages) STMICROELECTRONICS

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AN3338

Electrical characteristics and functions

Equation 2

•

t3: the SD signal reaches the lower threshold Vsd_L_THR and the control unit switches

off the input HIN and LIN. The smart shutdown is disabled (M1 off) and SD can rise up

with a time constant

B, given by:

Equation 3

•

t4: when the SD signal reaches the upper threshold Vsd_H_THR, the system is re-

enabled.

2.3.8

Current sensing shunt resistor selection

As previously discussed, the shunt resistors RSHUNT externally connected between the N

pin and ground (see

Figure 10) are used to realize the overcurrent detection.

When the output current exceeds the short-circuit reference level (ISC), the CIN signal

overtakes the VREF value and the short-circuit protection is active. For a reliable and stable

operation the current sensing resistor should be a high quality, low tolerance non-inductive

type. In fact, stray inductance in the circuit, which includes the layout, the RC filter, and also

the shunt resistor, must be minimized in order to avoid undesired short-circuit detection.

()

⋅

Figure 16. Timing chart of smart shutdown function

AN3338 Datasheet(PDF) 27 Page - STMicroelectronics