ADL5902ACPZ-R7 datasheet(17/28 Pages) AD

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ADL5902

Rev. 0 | Page 17 of 28

there is no temperature variation contribution to the absolute value

of VOUT.

For CW signals,

FreqLP ≈ 67.7 × 10−6/(CLPF)

(14)

However, signals with large crest factors include low pseudo-

random frequency content that must be either filtered out or

sampled and averaged out (see the Choosing a Value for CLPF

section for more information).

TEMPERATURE SENSOR INTERFACE

The ADL5902 provides a temperature sensor output with a

scaling factor of the output voltage of approximately 4.9 mV/°C.

The output is capable of sourcing 4 mA and sinking 50 μA

maximum at 25°C. An external resistor can be connected from

TEMP to COMM to provide additional current sink capability.

The typical output voltage at 25°C is approximately 1.4 V.

TEMP

VPOS

COMM

INTERNAL

VPAT

12k

Ω

Figure 38. TEMP Interface Simplified Schematic

VREF INTERFACE

The VREF pin provides an internally generated voltage reference

for the user. The VREF voltage is a temperature stable 2.3 V

reference that is capable of sourcing 4 mA and sinking 50 μA

maximum. An external resistor can be connected from VREF to

COMM to provide additional current sink capability. The

voltage on this pin can be used to drive the TADJ/PWDN and

VTGT pins.

INTERNAL

VOLTAGE

16k

Ω

VREF

VPOS

COMM

Figure 39. VREF Interface Simplified Schematic

TEMPERATURE COMPENSATION INTERFACE

While the ADL5902 has a highly stable measurement output

with respect to temperature using proprietary techniques, for

optimal performance, the output temperature drift must be

compensated for using the TADJ pin. The absolute value of

compensation varies with frequency and VTGT. Table 4 shows the

recommended voltages for VTADJ to maintain a temperature drift

error of typically ±0.5 dB or better over the intended temperature

range (−40°C < TA < +85°C) when driven single-ended and

VTGT = 0.8 V.

Table 4. Recommended VTADJ for Selected Frequencies

Frequency

VTADJ (V)

R9 in Figure 54

(Ω)

R12 in Figure 54

(Ω)

100 MHz

0.5

1430

402

700 MHz

0.4

1430

301

900 MHz

0.4

1430

301

1.9 GHz

0.4

1430

301

2.14 GHz

0.4

1430

301

2.6 GHz

0.45

1430

348

3.5 GHz

0.5

1430

402

5.8 GHz

0.95

1430

1007

The values in Table 4 were chosen to give the best drift

performance at the high end of the usable dynamic range

over the −40°C to +85°C temperature range. There is often a

trade off in setting values, and optimizing for one area of the

dynamic range may mean less than optimal drift performance

at other input amplitudes.

Compensating the device for temperature drift using TADJ

allows for great flexibility. If the user requires minimum

temperature drift at a given input power, a subset of the

dynamic range, or even over a different temperature range than

shown in this data sheet, the VTADJ can be swept while

monitoring VOUT over the temperature at the frequency and

amplitude of interest. The optimal VTADJ to achieve minimum

temperature drift at a given power and frequency is the value of

VTADJ where the output has minimum movement.

2.73

2.75

2.77

2.79

2.81

2.83

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

+125°C

+105°C

+85°C

+55°C

+25°C

–20°C

–40°C

0°C

VTADJ (V)

Figure 40. Effect of VTADJ at Various Temperatures, 2.14 GHz, −10 dBm

Varying VTADJ has only a very slight effect on VOUT at device

temperatures near 25°C; however, the compensation circuit

has more and more effect as the temperature departs farther

from 25°C.

The TADJ pin has a high input impedance and can be conven-

iently driven from an external source or from an attenuated

value of VREF using a resistor divider. Table 4 gives suggested

voltage divider values to generate the required voltage from

VREF. The resistors are shown in the evaluation board schematic

(see Figure 54). VREF does change slightly with temperature and

also input RF amplitude; however, the amount of change is

unlikely to result in a significant effect on the final temperature

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