ADRF6601 LDO not powering up

Question

I have the ADRF6601 on a PCB which plugs into a control card. I have two different configurations for plugging the cards together. The control card writes the SPI commands to setup the ADRF6601. In one configuration, the ADRF6601 comes up as expected and I get the downconversion that I expected. In the other configuration, I do not get the downconversion I expect. The 3p3_LDO and VCO_LDO are at 0 volts. 
 What would cause the LDO regulators to be off? Is there another way besides through a SPI command to turn them off? I am wondering if my second configuration has an issue with the SPI bus and the ADRF6601 is not being programmed properly. 
 Thanks, 
 Mark

rachana.kaza@analog.com · Accepted Answer

HI Mark, 
 Typically the 1.8v regulator is always on to support the SPI port. The other LDOs are usually controlled via the SPI port. I would think that the default condition for both of those regulators would be On at power up . you might want to try a hard reset, and then try toggling them via the SPI. 
 either the spi or the 5V input to the regulator has not been supplied. 
 
 Warm Regards, 
 Rachana

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ADRF6601 LDO not powering up

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