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AD5932 Frequency generation issue

Question asked by Vengeful on Jun 2, 2017
Latest reply on Jun 9, 2017 by musach

Hi, 

 

I currently have this device in a designed circuit. It is being clocked by a 8Mhz source. 

The settings for this design follow the application note AN-1044 but values modified for this specific design.

 

Configured device for CTRL pin toggled externally; DAC enable, MSBout enable

Fstart set to 1Mhz

Fdelta set to 0.1Mhz

Number of increments set to 50

uint8_t AD5932_CONF_0[3] = { SS3_AD5932, (0x00 | 0x0F), 0xFF};
uint8_t AD5932_CONF_1[3] = { SS3_AD5932, (AD5932_FREQ_ST_LB | 0x00), 0x00};// F start L
uint8_t AD5932_CONF_2[3] = { SS3_AD5932, (AD5932_FREQ_ST_HB | 0x02), 0x00};// F start H
uint8_t AD5932_CONF_3[3] = { SS3_AD5932, (AD5932_FREQ_LB | 0x03), 0x33}; //F delta low
uint8_t AD5932_CONF_4[3] = { SS3_AD5932, (AD5932_FREQ_HB | 0x00), 0x33 };//F delta high
uint8_t AD5932_CONF_5[3] = { SS3_AD5932, (AD5932__NO_INC | 0x00), 0x20 };// Number of steps

 

However with the following being sent, this device just simply does not start at 1Mhz when the pin is toggled and the increments are most definitely not 0.1Mhz. 

 

By sending the conf 1,2,3,4,5, it does not have any effect on the test. It seems as if the device only responds to the first configuration (CONF_0)! To test that it only considers the first configuration, I enable auto increment instead of CTRL pin toggle. Then start the scan by raising that pin high, I can clearly see it starting the scan and increment. 

 

I am not sure why it would reject the next bunch of settings. 

The scan almost always starts at 250Khz and then creeps to toward 4Mhz where it stays. 

 

The device is commanded from an I2C to SPI expander chip, all other devices respond perfectly well. 

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