Ramp contorol of AD5560

Question

Hello. 
 I have a few questions about the AD5560. Please tell me. 
 　Q1：Does the AD5560 offer lamp up/down control? 
 　Q2：The datasheet includes the followin statement. 
 　　　&rdquo;The fastest ramp rate is 0.775 V/&micro;s (for a 5 V reference and an 833 kHz clock using a 2032 LSB step size and divider = 1).&rdquo; 
 　　　 How was SR calculated and determined at this time? 
 　　　 This is because when I calculated it, the calculated value was 0.645V/us, which did not match the data sheet value. 
 　　　I calculated as below. 
 　　　　・1step = 16LSB (6.1mV), so it takes about 820steps to reach 5V. 
 　　　　・The update rate is 833 kHz, which is about 1.2 us for 1 step time. 
 　　　　・It takes about 7.74us to reach 5V, so the calculation is now 0.645V/us. 
 
 Best regards.

MacManato · Accepted Answer

Hi, baggio. 
 Thanks for reaching out about AD5560's functionality. Here are my responses to your questions: 
 1. Yes, AD5560 has a ramp function and can be controlled by changing step size, RCLK frequency, clock divider, and start and end codes. 
 
 2. The slew rate, unfortunately, is not calculated that way. Your solution shows maximum slew rate for a 16-LSB step, whereas the datasheet provides for a single 2032-LSB step. 
 
 I don't think 0.775V/us was computed. It is determined by design and characterization. 
 
 Best regards, Mac)

A1DFF · Answer

Hello. I am a user using AD5560.
I had the same question as you while using the ramp function of this chip.
My conclusion is that there is an error in the datasheet.
If you calculate it as 0.775V/1.2us instead of 0.775V/us, the calculation formula for step size and clock divider will be correct.

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Ramp contorol of AD5560