AN2836 datasheet(27/57 Pages) STMICROELECTRONICS

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AN2836

Designing an application with L6225, L6226, L6227

Doc ID 15084 Rev 1

27/57

Equation 17

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

the pull-up voltage applied to REN.

The external RC network, CEN in particular, must be chosen in order to obtain a reasonably

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

Figure 25 and 26 show both tDISABLE and tDELAY as a function of CEN: at least 100 µs for

tDISABLE are recommended, keeping the delay time below 1÷2 µs at the same time.

The internal open drain can also be turned on if the device experiences an overtemperature

(OVT) condition. The OVT causes 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 circuits (see Figure 1 to Figure 3), all the power DMOS 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 then the power DMOS are turned back on.

4.14

Adjusting the overcurrent detection trip point (L6226 only)

The L6226 allows the user to set the overcurrent detection threshold separately for the two

full bridges connecting two resistors (RCL) to pins PROGCLA and PROGCLB. The OCD

threshold (ISOVER) follows the equations:

●

ISOVER = 2.8 A ±30% at -25 °C < Tj < 125 °C if RCL = 0 Ω (PROGCL connected to

GND)

●

ISOVER =

±10% at -25 °C < Tj < 125 °C if 5 kΩ < RCL < 40 kΩ

Figure 27 shows the OCD threshold versus the RCL value in the range from 5 kΩ to 40 kΩ.

)

OFF

(

OPDR

)

FALL

(

⋅

Figure 25.

Typical disable time vs. CEN for

several values of REN

Figure 26.

Typical delay time vs. CEN

AM01645v1

10 0

1 .10

C EN [n F ]

R EN = 220 k

R EN = 1 0 0 k

R EN = 4 7 k

R EN = 33 k

R EN = 1 0 k

AM01646v1

0.1

C EN [n F ]

11050

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