L9177ATR datasheet(41/55 Pages) STMICROELECTRONICS

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Figure 36. Low side drivers slew rate

GAPGPS00619

IP2

IP1

IN1

IN2

IN1

IP1

Igate

Vgate

Igate

Vgate

VOUT

IOUT

VLVT

80%

20%

not controlled

IOUT

not controlled

At switch-on command the charging current is provided by current generator IP1 and is kept constant until the

output voltage is decreased of roughly 80% of typical battery level. At this point the low side transistor is on and

VLVT signal is set to logic 1 to connect IP2 current generator in parallel with IP1, completing the gate charge

curve and providing maximum gate drive.

When the power transistor is switched-off the gate is discharged quickly using both IN1 and IN2 currents; as soon

as the output voltage reaches roughly 20 % of the nominal battery voltage only IN1 is kept connected to complete

the gate discharging.

In Table 33 the values for IPx and INx current generators are reported for each low side.

As an example Figure 37 shows the resulting slew rate, in typical conditions, of O2H low side driver.

Table 33. Values for IPx and INx current generators for each low side

Low side

IP1

IP2

IN1

IN2

Unit

O2H

243

253

337

µA

INJ

174

180

124

µA

RLY’s

120

µA

119

µA

TACH

µA

L9177A

Low side drivers

DS12175 - Rev 5

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