SRK2000A データシートの表示（PDF） - STMicroelectronics
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SRK2000A Datasheet PDF : 19 Pages
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SRK2000A
6
Application information
Application information
6.1
6.1.1
EN pin - pin function and usage
This pin can perform three different functions: it sets the threshold VDVS1,2_Off for the drain-
to-source voltage of either synchronous rectifier (SR) Power MOSFET to determine their
turn-off in each conduction cycle; it allows the user to program the UVLO thresholds of the
gate drivers and can be used as Enable (remote on/off control).
Pull-up resistor configuration
At startup, an internal 10 µA current sink (IEN) is active as long as the device supply voltage
VCC is below the startup threshold VCCOn. The moment VCC equals VCCOn (4.5 V typ.), the
voltage VEN on the EN pin determines the turn-off threshold VDVS1,2_Off for the drain voltage
of both synchronous rectifiers during their cycle-by-cycle operation: if VEN < VEN_Th
(= 0.36 V) the threshold is set at -25 mV, otherwise at -12 mV. Once the decision is made,
the setting is frozen as long as VCC is greater than the turn-off level VCCOff (4.25 V typ.).
A simple pull-up resistor R1 to VCC can be used to set VDVS1,2_Off turn-off threshold. The
voltage on the EN pin as the device turns on is given by:
Equation 1
VEN VCCOn IEN R1
Then, considering worst-case scenarios, we have:
Equation 2
R1 633 k VDVS1,2 _ Off 25 mV
R1 296 k VDVS1,2 _ Off 12 mV
Some additional margin (equal to the resistor's tolerance) needs to be considered;
assuming 5% tolerance, the use of the standard values R1 = 680 k in the first case
and R1 = 270 k in the second case, is suggested.
Figure 5. EN pin biased with a pull-up resistor (for logic level MOSFET driving)
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