AN901 Datasheet, PDF (10/25 Pages) STMicroelectronics – Electromagnetic compatibility

AN901
2.10. VSNS Voltage Divider
For the purpose of selecting sense resistors R5 and R6, the entire dc-dc converter can be modeled as a non-
inverting amplifier as shown in Figure 5. Notice that the non-inverting input, supply voltage (V+), and output voltage
of the amplifier correspond to the internal 1.05 V reference, V_IN, and V_OUT of the dc-dc converter.
Figure 5. Simplified V_OUT Gain Model
Assuming infinite DC gain and applying KCL at the inverting input of the amplifier, V_OUT can be expressed by:
V_OUT = 1.05_^RR-----⁵⁶-- + 1_ + R5  I_VSNS
Equation 30.
where I_VSNS represents the input offset current at VSNS pin. From Equation 30, it can be observed that a very
large R5 could reduce the output voltage accuracy.
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Rev. 0.1