VOLTAGE MARGINIG USING DAC

Question

Hi, 
 We are using AD5676ARUZ-REEL7 DAC in our design for voltage margining the LDO. Kindly help us in margining and also in calculating resistor value (Rdac). 
 We have used TPS7A57 LDO which has only bottom resistor(Rref) for setting the output voltage as mentioned in below image. 
 Provide us solution as soon as possible. 
 
 Thanks 
 S Sathya shree

iandal · Accepted Answer

Hi SS1 
 The LDO output is varied by the Rref present on the pin, so a digipot might be better fit here. For example the AD5290 has 256 positions available for 100kohm should cover the range of values for the TPS7A57 based on Table 8-4. 
 The RDAC value would depend on the LDO output value and the margining range you require. (typical is +/-5%) 
 256 positions equates to around ~390 ohm steps. With an IREF of 50uA, that gives around 19.5mV of delta at the output of the LDO. 
 Best regards, 
 Ian)