Hi Engineer Zone Team
This is a lengthy post in order to give the full details of our application and problems.
AD9517-1 Application description.
We are using the AD9517-1ABCPZ in manual reference switchover mode and also to generate various frequencies as shown in the attached block diagram. REF1 is a 10MHz GPS derived signal from a GPS receiver and REF2 is a 10MHz signal from a highly stable VCTCXO (Euroquartz VEM42T33-10). The signals REF1 & REF2 that are applied to the AD9517-1 are both 3.3V LVCMOS signals and terminated by 10kW resistor to ground reference. We use an external VCO, CVCO55CC-0775-0800 from Crystek, that is tunable in the range 775MHz to 800MHz together with an external loop filter. The AD9517-1 outputs a 777.6MHz LVPECL at OUT0 and it is used as the clock reference to the DDS AD9910. It also outputs a 2.4MHz LVDS signal at OUT6, using 324 divider, and this output is used as the main clock reference to an FPGA. All other outputs are powered down.
AD9517-1 problem description.
We have been using the AD9517-1 since 2011 and so far, used 3156 of these devices in our products. Except for one initial development issue concerning the reference switch over we did not have any other problems with the device for the past 13 years. Although there have been six PCB revisions in the past 13 years to mainly include the features requested by the customers, the circuitry or the PCB layout concerning the AD9517-1 has not changed since its first usage. In the last batch of the PCBs, we are encountering the following issues.
- Does not detect the REF2, but detects the REF1, despite both REF1 & REF2 are present.
- Indicates that the REF1 is present when actually REF1 is absent & REF2 is present.
- Indicates that both REF1 and REF2 are present when actually both were absent.
- Some devices fail to communicate through the SPI interface and cannot be programmed.
- The Part ID code, obtained from the read only register 0x003, which uniquely identifies the dash version of the device, does not correspond to the part marking. We only use the AD9517-1 and expect the ID code to be always 0x51 but we do also get 0x11, 0x53, 0xD3 corresponding to AD9917-0, AD9517-3 & AD9517-4 respectively. In addition to the above-mentioned device codes, we also encountered a device with 0xF1 code, which does not correspond to any device in the AD9517 family. Note the majority of the devices read the correct ID code of 0x51. I have attached image of the register 0x003 readback values obtained through the Saleae Logic Analyzer. Also attached are the photos of the package marking that have different Part ID code.
Note that, in accessing the Part ID value from the AD9517, we perform only the essential minimum SPI transactions on power up. Specifically,
WRITE to 0x0000 the value 0x99 - use SDO, use long instructions.
WRITE to 0x0004 the value 0x01 - readback active registers.
WRITE to 0x0232 the value 0x01 - update all registers.
Some of the important register settings are given below but the entire register setting is also attached.
Note here:
REF1 = External 10MHz Reference.
REF2 = Internal 10MHz Reference.
Register address:
0x017 Bits [7:2] = Status Pin Control = 111000 = Status of REF2 frequency, active low.
0x017 Bits [1:0] = Antibacklash pulse width = 00 = 2.9ns (default value).
0x01A Bit [6] = Reference frequency monitor threshold = 0 = Frequency valid if above the highest frequency threshold.
0x01A Bits [5:0] = LD pin control = 111101 = Digital lock detect (DLD), active low.
0x01B Bit [7] = VCO frequency monitor = 1 = Enables VCO frequency monitor.
0x01B Bit [6] = REF2 frequency monitor = 1 = Enables REF2 frequency monitor.
0x01B Bit [5] = REF1 frequency monitor = 1 = Enables REF1 frequency monitor.
0x01B Bits [4:0] = REFMON pin control = 10111 = Status of REF1 frequency, active low.
0x01C Bit [7] = Disable switchover deglitch = 0 = Enables switchover deglitch circuit (default).
0x01C Bit [6] = Select REF2 = 0 = Selects REF1 (default).
0x01C Bit [5] = Use REF_SEL pin = 1 = Uses REF_SEL pin.
0x01C Bits [4:3] = Reserved = 00 = Default value.
0x01C Bit [2] = REF2 Power-on = 1 = REF2 Power on.
0x01C Bit [1] = REF1 Power-on = 1 = REF1 Power on.
0x01C Bit [0] = Differential reference = 0 = Single-ended reference mode (default).
We have written to all the necessary registers and also verified that the readback values are consistent with that was written.
Please see attached a screenshot of the above register configuration values.
REFMON (monitors REF1) and STATUS (monitors REF2) output pins drive LEDs, through an inverter, for visual indication and their state on this output pins are also monitored by the CPU. In the event where either reference is absent the CPU uses the REF_SEL input pin to switch between the two references that is available. By default, REF1 is the preferred reference as it is the more accurate GPS signal.
I have also attached the schematic page of the AD9517-1 for your reference.
Our parts are generally purchased through an authorized distributor such as Avent, Arrow, element14, X-on, Digikey etc. The last batch of these components, which we have issues with, were bought from Wide Star International Electronics Limited, a company based in China. The main reason was that they offered the shortest lead time at a competitive cost.
Engineer Zone Question
Can the Part ID differ for the same dash version of the device?
Can there be a device with Part ID, 0xF1, that does not match any dash version of the device?
I do believe that the various issues mentioned above may all stem from one common problem and not separate problems manifesting suddenly.
Thanks, is advance for finding the problem, solutions and advice.
Regards
Diva
