SRK2000D datasheet(10/17 Pages) STMICROELECTRONICS

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Application information

SRK2000

10/17

Doc ID 17811 Rev 2

Equation 2

If VCC_G is not too low (<8÷9 V), its tolerance is not critical because it is related only to that

of VEN_On (±5.6%) and of the external resistors R1, R2 (±1% each is recommended). Then,

some care needs to be taken only as far as the selection of the -12/-25 mV threshold is

concerned: in fact, the large spread of IEN considerably affects the voltage on the EN pin as

the device turns on, a value that can be found by solving the first of (1) for VEN:

Equation 3

A couple of examples clarify the suggested calculation methodology.

Example 1 VCC_G = 10 V, VDVS1,2_Off = - 25 mV.

In this case, VEN must definitely be lower than the minimum value of VEN_Th (= 0.32 V).

From the second of (2), the nominal ratio of R1 to R2 is (10 – 1.8) / 1.8 = 4.555. Substituting

the appropriate extreme values in (3) it must be (4.75 - 7·10-6·R1) / (1 + 4.555) < 0.32;

solving for R1 yields R1 > 425 k

Ω; let us consider an additional 4% margin to take both the

tolerance and the granularity of the R1 and R2 values into account, so that: R1 > 425·1.04 =

442 k

Ω. Choose R1 = 442 kΩ (E48 standard value) and, from the second of (2), R2 =

442/4.555 = 97 k

Ω; use 97.6 kΩ (E48 standard value).

Example 2 VCC_G = 10 V, VDVS1,2_Off = - 12 mV.

In this case, VEN must definitely be higher than the maximum value of VEN_Th (= 0.40 V).

From the second of (2), the nominal ratio of R1 to R2 is (10 – 1.8) / 1.8 = 4.555. Substituting

the appropriate extreme values in (3) it must be (4.25 - 13·10-6·R1) / (1 + 4.555) > 0.4;

solving for R1 yields R1 < 156 k

Ω; with 4% additional margin R1 < 156/1.04 = 150 kΩ.

Choose R1 = 147 k

Ω (E48 standard value) and, from the second of (2), R2 = 147/4.555 =

32.3 k

Ω; use 32.4 kΩ (E48 standard value).

Note:

In both examples the gate drivers are disabled as Vcc falls below 9.75 V (nominal value), as

the voltage on the EN pin falls 45 mV below VEN_On.

⎪

⎩

⎪⎪

⎪

⎨

⎧

−

CCOn

−

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