ADRF6801 and/or ADRF6701 temperature MUXOUT not active when using external LO?

Question

Hello! 
 I'm using an ADRF6801 demodulator in combination with an ADRF6701 modulator. 
 I want to monitor junction temperatures of both chips, so the chips were configured to use the VPTAT temperature proportional voltage output at the MUXOUT pin. 
 This is working properly if both chips are using their internal PLL. 
 But when I let e.g. ADRF6701 be the "LO generator" for the ADRF6801 (or vice versa), then only the active chip (="LO generator") does output the VPTAT voltage. The other one keeps the pin at GND (0V). 
 I did not find any information about such a behaviour in the datasheet. Is this behaviour intended? 
 BR, 
 Markus

MarkusNTHFS · Accepted Answer

Thank you for that hint. I set DB20=1 (charge pump enable) and DB19=1 (3.3V LDO enable) in register 6 (I think that this is what you ment), then VPTAT shows the expected behaviour and output is visible on both chips, in all 3 possible situations. 
 It would be nice if that information made it to the datasheet.)

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ADRF6801 and/or ADRF6701 temperature MUXOUT not active when using external LO?