ADF4372: The function of internal LDO for VCO

Question

Hello,

I have a question from our customer about the internal LDO for VCO of ADF4372.

Q1. About bit7 of REG002F, "SWITCH_LDO_3P3_5V" usage.
Can he select the voltage, 3.3v or 5v, of VCC_REG_OUT outputs using this register?
If not, could you please explain the purpose of this register and how to use this?

Q2. If Q1 is yes, what voltage for VCC_LDO should be higher than VCC_REG_OUT? (What voltage is needed for the headroom?)

Q3. If REG002F[7] does not affect the output voltage of VCC_REG_OUT, what voltage will be output from VCC_REG_OUT, when 5v be input to VCC_LDO?

Best regards,

y_suzuki

kpeker · Accepted Answer

Hello, 
 
 Firstly, as noted in the datasheet, VCO LDO (internal LDO) is recommended to be disabled for best performance. An external low noise regulator such as LT3045 is recommended. 
 When using internal LDO, VCC_LDO should be 5V or 3.3V and 0x002F[7] should be set accordingly. The LDO output voltage (VCC_REG_OUT) is about 4.5V and about 3V respectively. 
 
 Regards, 
 Kazim)

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ADF4372: The function of internal LDO for VCO