ADF5901 datasheet(25/27 Pages) AD

25 / 27 page

ADF5901

Data Sheet

Rev. A | Page 24 of 26

5. Write 0x809FE560 to Register R0 to power Tx1 on, Tx2 off,

and LO on.

6. Write 0x809FED60 to Register R0 to set the Tx1 amplitude

calibration (400 µs).

7. Write 0x89FE5A0 to Register R0 to power Tx1 off, Tx2 on,

and LO on.

8. Write 0x809FF5A0 to Register R0 to set the Tx2 amplitude

calibration (400 µs).

9. Write 0x2800B929 to Register R9.

10. Write 0x809F25A0 to Register R0 to disable the R and N

counters.

TEMPERATURE SENSOR

The ADF5901 has an on-chip temperature sensor that can be

accessed on the ATEST pin or as a digital word on DOUT

following an ADC conversion. The temperature sensor operates

over the full operating temperature range of −40°C to +105°C.

The accuracy can be improved by performing a one-point

calibration at room temperature and storing the result in

memory.

With the temperature sensor on the analog test bus and test bus

connected to the ATEST pin (Register 4 set to 0x0000A064) the

ATEST voltage can be converted to temperature with the

following equation:

(

)

GAIN

OFF

ATEST

Temperatur

−

(



(3)

where:

VATEST is the voltage on the ATEST pin.

VOFF = 0.699 V, the offset voltage.

VGAIN = 6.4 × 10−3, the voltage gain.

The temperature sensor result can be converted to a digital

word with the ADC and readback on DOUT with the following

sequence:

1. Write 0x809FA5A0 to Register R0 to enable the counters.

2. Write 0x00012064 to Register R4 to connect the analog test

bus to the ADC and VTEMP to the analog test bus.

3. Write 0x00028C82 to Register R2 to start the ADC

conversion.

4. Write 0x018902C3 to Register R3 to set the output ADC

data to DOUT.

5. Read back DOUT.

6. Write 0x809F25A0 to Register R0 to disable R and N

counters.

Convert the DOUT word to temperature with the following

equation:

(

)

(

)

GAIN

OFF

LSB

ADC

Temperatur

−

(



(4)

where:

ADC is the ADC code read back on DOUT.

VLSB = 7.33 mV, the ADC LSB voltage.

VOFF = 0.699 V, the offset voltage.

VGAIN = 6.4 × 10−3, the voltage gain.

RF SYNTHESIS: A WORKED EXAMPLE

The following equation governs how to program the ADF5901:

RFOUT = (INT + (FRAC/225)) × (fREF) × 2

(5)

where:

RFOUT is the RF frequency output.

INT is the integer division factor.

FRAC is the fractionality.

fREF = REFIN × ((1 + D)/(R × (1 + T)))

(6)

where:

REFIN is the reference frequency input.

D is the reference doubler bit, DB10 in Register R7 (0 or 1).

R is the reference division factor.

T is the reference divide by 2 bit, DB11 in Register R7 (0 or 1).

For example, in a system where a 24.125 GHz RF frequency

output (RFOUT) is required and a 100 MHz reference frequency

input (REFIN) is available, fREF is set to 50 MHz.

From Equation 6,

fREF = (100 MHz × (1 + 0)/(1 × (1 + 1)) = 50 MHz

From Equation 5,

24.125 GHz = 50 MHz × (N + FRAC/225) × 2

Calculating the N and FRAC values,

N = int(RFOUT/(fREF × 2)) = 241

FRAC = FMSB × 213 + FLSB

FMSB = int(((RFOUT/(fREF × 2)) − N) × 212) = 1024

FLSB = int(((((RFOUT/(fREF × 2)) − N) × 212) − FMSB) × 213) = 0

where:

FMSB is the 12-bit MSB FRAC value in Register R5.

FLSB is the 13-bit LSB FRAC value in Register R6.

int() makes an integer of the argument in parentheses.

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