Buck converter for the ISL8117 track an external voltage level

Question

Hello community, I'm working on a project about Buck Converter using ISL8117. 
 I'm using it with Input voltage Vin = 24 V . Output voltage Vout is adjustable. Vout_min = 3V. Vout_max = 21V . 
 The ISL8117 will be set up to track an external voltage level Vmaster . Voltage level Vmaster is the output of external DAC. Vmaster_min = 0V. Vmaster_max = 10V. A resistive divider is connected between the Vmaster and ground. The center point of the divider will be connected to the SS/TRK pin of the ISL8117. The voltage at SS/TRK pin ( Vtrk) is greater than 0.6V when the master rail reaches regulation. Output voltage Vout = Vout_min = 3V, when Vtrk = 0,6V. Output voltage Vout = Vout_max = 21V, when Vtrk = 4,2V. What is the maximum voltage Vtrk at SS/TRK pin for tracking control mode ISL8117? Does value Vtrk = 4,2V is legal level for tracking control mode ISL8117? 
 Thank you.

AB_RENESAS · Accepted Answer

Hi, 
 Kindly share your schematic with resistor value 
 Thanks 
 Ab

Slalom · Answer

ISL8117_v01.pdf Digital adjustment Vout ISL8117

AB_RENESAS · Answer

Hi, 
 Please below table from datasheet 
 
 Also ,set the tracking resistive divider ratio exactly the same as the ISL8117 output resistive divider. For your case its different. 
 Thanks 
 AB

AB_RENESAS · Answer

Hi, 
 Looks like you purpose is to use controller&rsquo;s SPI signal to control ISL8117&rsquo;s output to track a voltage rail. For same the Vmaster signal should adjust the FB pin voltage not SS/TRK to adjust ISL8117&rsquo;s Vout..SS/TRK pin is not for this purpose . Kindly find below diagram as reference .R value deepends on the controller DA signal. maybe start with 10k, 
 
 Thanks 
 AB

Buck converter for the ISL8117 track an external voltage level

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