IRS20124SPBF datasheet(21/27 Pages) IRF

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IRS20124S(PbF)

DT/SD pin

DT/SD pin provides two functions: 1) setting dead-

time and 2) shutdown. The IRS20124 determines

its operation mode based on the voltage applied

to the DT/SD pin. An internal comparator

translates which mode is being used by comparing

internal reference voltages. Threshold voltages for

each mode are set internally by a resistive voltage

divider off Vcc, negating the need of using a precise

absolute voltage to set the mode.

Vcc

0.89xVcc

0.57xVcc

0.36xVcc

0.23xVcc

Shutdown

45nS

35nS

25nS

15nS

Operational Mode

VDT

Dead-time

Deadtime Settings vs VDT Voltage

Design Example

Table 1 shows suggested values of resistance for

setting the deadtime. Resistors with up to 5%

tolerance can be

used if these

listed values are

followed.

Vcc

COM

DT/SD

>0.5mA

IRS20124

Table 1. Suggested

Resistor Values for Deadtime

Settings

Shutdown

Since IRS20124 has internal deadtime generation,

independent inputs for HO and LO are no longer

provided. Shutdown mode is the only way to turn

off both MOSFETs simultaneously to protect them

from over current conditions. If the DT/SD pin de-

tects an input voltage below the threshold, V

DT4,

the IRS20124 will output 0 V at both HO and LO

outputs, forcing the switching output node to go

into a high impedance state.

Over Current Sensing

In order to protect the power MOSFET, IRS20124

has a feature to detect over-current conditions,

which can occur when speaker wires are shorted

together. The over-current shutdown feature can

be configured by combining the current sensing

function with the shutdown mode via the DT/SD pin.

Load Current Direction in Class D

Audio

Application

In a Class D audio amplifier, the direction of the

load current alternates according to the audio in-

put signal. An over current condition can therefore

happen during either a positive current cycle or a

negative current cycle. It should be noted that

External Resistor

Deadtime

mode

(Ω)

DT/SD

(V)

DT1

<10k

Open

1.00 (Vcc)

DT2

3.3k

8.2k

0.71 (Vcc)

DT3

5.6k

4.7k

0.46 (Vcc)

DT4

8.2k

3.3k

0.29 (Vcc)

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