AN892 Datasheet, PDF (7/16 Pages) Silicon Laboratories – DESIGN GUIDE FOR ISOLATED DC/DC USING THE

AN892
2.7. VSNS Voltage Divider
For the purpose of selecting sense resistors (R5/R6), the entire dc-dc converter can be modelled as a non-
inverting amplifier as shown in Figure 4. Notice that the non-inverting input, supply voltage (V+), and output voltage
of the amplifier correspond to the internal 1.05V reference, V_IN, and V_OUT of the dc-dc converter.
V_IN
I_VSNS
+ ^{V+ POWER STAGE}
-
V-
V_REF
VSNS
R5
1.05V
V_OUT
C10
R_LOAD
R6
Figure 4. Simplified V_OUT Gain Model
Assuming infinite DC gain and applying KCL at the inverting input of the amplifier, V_OUT can be expressed as:
V_OUT = 1.05_^RR-----⁵⁶-- + 1_ + R5  I_VSNS
Equation 25.
where I_VSNS represents the input offset current at VSNS pin. From Equation 25, it can be observed that a very
large R5 could reduce the output voltage accuracy.
Rev. 0.1
7