AN2839 datasheet(21/40 Pages) STMICROELECTRONICS

21 / 40 page

AN2839

Designing an application with L6228

Doc ID 15104 Rev 1

21/40

where:

Equation 17

tOCD(OFF), tOCD(ON), tD(ON)EN, tD(OFF)EN and ROPDR are device-intrinsic parameters and VDD

is the pull-up voltage applied to REN.

The external RC network, CEN in particular, must be selected to obtain a reasonable fast

OCD intervention (short tDELAY) and a safe disable time (long tDISABLE). Figure 23 and

Figure 24 show both tDISABLE and tDELAY as a function of CEN: at least 100 µs for tDISABLE

are recommended, keeping the delay time between 1 and 2 µs at the same time.

The internal open drain can also be turned on if the device experiences an over-temperature

(OVT) condition. The OVT will cause the device to shut down when the die temperature

exceeds the OVT threshold (TJ > 165 °C typ.). Since the OVT is also connected directly to

the gate-drive circuit (see Figure 1 on page 1), all the Power DMOS’s will shut down, even if

the EN pin voltage is still over Vth(OFF). When the junction temperature falls below the OVT

turn-off threshold (150 °C typ.), the open drain turns off, CEN is recharged up to VTH(ON) and

the Power DMOS’s are turned back on.

1.13

Power management

Even when operating at current levels well below the maximum ratings of the device, the

operating junction temperature must be kept below 125° C.

Figure 25 on page 22 shows the IC’s dissipated power versus the RMS load current in four

different driving sequences, assuming the supply voltage is 24 V.

EN FALL

()

OPDR

TH OFF

()

------------------------------

⋅⋅

Figure 23.

Typical disable time vs. CEN for

several values of REN

Figure 24.

Typical delay time vs. CEN

AM01706v1

10 0

1 .10

C EN [n F ]

R EN = 220 k

R EN = 10 0 k

R EN = 4 7 k

R EN = 33 k

R EN = 1 0 k

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