AD7740 Output frequency instability

Question

Hi, we wanted to use AD7740 for voltage frequency conversion. We are using 1MHz clock generated by microcontroller. However the output frequency is not stable over the VIN range(0-2.5V). We have implemented the same circuit shown in the data sheet except for the clock, in our case the controller output clock is connected to COCKIN pin and CLOCKOUT is left open. Help us resolve this.

FMarasigan · Accepted Answer

Hi Ranjit , 
 The AD7740 requires a stable clock source with a frequency range of 32 kHz to 1 MHz and a duty cycle between 40:60 and 60:40. Since you're using a 1 MHz clock from a microcontroller, ensure that the clock signal meets these requirements. Any deviation in frequency or duty cycle can cause instability in the output frequency. 
 While using an external clock applied to the CLKIN pin is valid, better stability may be achieved by using a crystal oscillator connected between the CLKIN and CLKOUT pins. The on-chip oscillator, when used with a crystal, provides a stable clock signal, which can help improve the performance of the voltage-to-frequency conversion. 
 Thanks, Francis)

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