SLVSJM3 Data sheet

SLVSJM3 May 2026 ISOS510-SP

ADVANCE INFORMATION

8.1.1.2.2 Sizing R_IN

The input side of ISOS510-SP is current-driven. To limit the amount of current flowing into the AN pin, placing a series resistor, R_IN, in series with the input as shown in Figure 8-1 is recommended.

Depending on how the ISOS510-SP device is being used, the value of R_IN can vary quite a bit. However, at a high level, to make sure the input does not get damaged, the minimum value of R_IN can be calculated for a given input voltage, V_IN, in Equation 3:

Equation 3.

R_{I N} > \frac{V_{I N} - V_{F}}{I_{C (M A X)}}

However, in the use case of a feedback loop, R_IN directly affects the mid-band gain of the loop. Assuming that the TL1431SP has been configured to give a reference voltage, V_REF, of 2.5V and R_PULLUP is 5kΩ, Equation 4 is used to calculate the maximum value of R_IN verifying that the V_COMP voltage on the primary side can be pulled to the saturation voltage of the ISOS510-SP, V_CE(SAT).

Equation 4.

R_{I N} < \frac{(V_{O U T} - V_{R E F} - V_{F}) \times R_{P U L L U P} \times {C T R}_{M I N}}{V_{P U L L U P} - V_{C E (S A T)}} = \frac{(5 V - 2.5 V - 1.2 V) \times 5 k Ω \times 100 %}{10 V - 0.3 V} = 670 Ω

8.1.1.2.2 Sizing RIN

8.1.1.2.2 Sizing R_IN