We use HMC531. But the operating temperature of HMC531 will over 85deg when we turn on our system. IC is very hot.
What situation will cause the temperature to rise on HMC531?
If we don't need power output of RFOUT/4, about this pin, may I connect 50 ohms to the ground or let it open?
Does it affect the IC's heat?
Disabling Vcc1 will not impact performance at RFOUT or RFOUT/2 ports. Even with Vcc1 disabled the device will dissipate about 1W. There are a lot of factors with respect to a printed circuit board and…
I may need more information in order to provide much help but yes you can power down VCC1 (pin 6) which will save about 325 mW of power.
RFOUT /4 (pin 4) should either remain open (floating) or if desired you can add a DC blocking capacitor (similar to C4 on evaluation board) after which you can place a shunt 50 ohm resistor to ground. Note that failure to provide DC blocking at pin 4 can result in damage to the device.
1) Is the HMC531 mounted to an ADI evaluation board or your own board?
2) Did you verify that 5.0 V is being provided to VCC1 and VCC2 and that the current draw is correct (if VCC2 isn't used current will drop to 195 mA or so).
3) If mounted to your own board was the recommended footprint used (including the proper size and quantity of thru vias)? Note that the use of blind vias instead of thru vias will negatively impact thermal conductivity.
4) If mounted to your own board what is the quality of the solder joint interface under the HMC531? (X-Ray to confirm there is no (or minimal) voiding.
4) What PCB board material was used and what is the board stackup?
5) Is the board mounted to a heat sink and if so is the pcb board making intimate contact with the heat sink?