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AD9508BCPZ-no output

Question asked by Alexrus on Mar 16, 2017
Latest reply on Apr 6, 2017 by Alexrus

Dear colleagues,

during design verification of our PCA we faced up with an AD9508BCPZ unstable operation. 

The input signal is 3.5 Vpp SIN 60 MHz, which is applied to the CLK pos, via a 0.1 uF capacitor. CLKn is bypassed to GND as per datasheet requirement. A correponding part of of the schematics is attached. The divider is configured by a microcontroller via SPI interface. 

The problem is the divider is not configured at operating temperatures lower than room temperature. If cold start (0 - 10 deg C) occurs there is no output signal at corresponding pins of the divider (even before SPI configuration starts, when output signal should be equal input). After a certain time of operation (several minutes, in my opinion, after self heating) an output signal appears (very unstable, it appears/disappears rapidly, but it becomes more stable with input signal amplitude grouth) at output pins with a unit division, as it should be right after start-up. SPI data (coefficient and other settings) is sent to the divider approx. in 2s after power up. If data comes after the divider has an output frequency (equal to input), then the divider configuration is succeeded, otherwise it always failes.

The reason could be, that the divider somewhy cannot recognise input signal and hence no output is presented. 

We've tried different PCAs, input signals (square 3.3V, sin)  and amplitudes (0.3 - 4 Vpp), but could not achieve stable operation. AD9508BCPZ were purchase via official distributor.

 

Please, advise.

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