To use the ESD diode forward-drop approach, we need a diode on the chip to which we can ap电感器生产ply forward bias and measure its voltage. That can easily be done on most chips with an ESD diode connected between a pin and t模压电感he supply voltage. Because the measured data gives us the diode voltage, we must also consider the relationship between a diode voltage and temperature.4
Diode voltage decreases with a nearly constant slope 功率电感and negligible deviation. If plotted with respect to temperature, the result would look like the plot in Figure 5.
Figure 5. The forward voltage for a diode biased at constant current varies with temperature.
In Figure 5, TA is the ambient temperature and VDA is the diode voltage at ambient temperature. We, therefore, know one point on the graph and its slope. Slope can be derived by measuring the diode voltage at different temperatures in a temperature-controlled oven. Alternatively, you can use a number like 2mV/K, which is valid with minimal error for a wide range of diode currents.4 These numbers should apply to any other chip as well, but for accuracy it is always better to measure the slope associated with the current intended for biasing the diode. Any temperature can now be represented in terms of the diode voltage:
(Eq. 27)
Where:
T is the temperature for which the diode voltage is VD.
s is the slope of the graph (s < 0).
Substituting this ex中山电感厂pression in Equations 11 and 12 yields the following:
VD = sθJAP + VDA + (VDi - sθJAP - VDA)e-kAt (Eq. 28) VD = VDA + sθJAP(1 - e-kAt) (Eq. 29)
Substituting in Equations 18, 19, and 20 also yields:
(Eq. 30)
(Eq. 31)
(Eq. 32)
To apply our RC network properly for curve fitting the measured voltage-transient data for the diode, now we only need to set the magnitude of the current source as:
lS = sPG (Eq. 33)
Because s < 0, you can realize Equation 33 by reversing the current source direction and setting its magnitude to |sPG|.
We can demonstrate a practical application of the RC simulation model using the equations derived above and a linear LED driver like the MAX16828/MAX16815. These chips operate up to 40V using few external components, and the MAX16828 supplies an LED string with up to 200mA (Figure 6差模电感). The MAX16815 is pin-compatible with the MAX16828 and similar in function, but maximum output current is 100mA instead of 200mA.
Figure 6. Typical application circuit for the
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