ADL5902ACPZ-R2 datasheet(21/29 Pages) AD

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ADL5902

Data Sheet

Rev. B | Page 20 of 28

BIAS AND POWER-

DOWN CONTROL

LINEAR-IN-dB VGA

(NEGATIVE SLOPE)

IDET

26pF

ADL5902

VREF

2.3V

TEMPERATURE

SENSOR

INLO

INHI

VPOS

POS

TEMP

(BLACK)

GND

(BLACK)

VSET

(BLACK)

VOUT

(BLACK)

VTGT

(BLACK)

VREF

(BLACK)

TEMP

VSET

VOUT

CLPF

COMM

VTGT

VREF

TADJ/PWDN

G = 5

ITGT

60.4Ω

C10

100pF

C12

100pF

VPOS

+5V

(RED)

100pF

0.1µF

100pF

0.1µF

R11

2kΩ

R10

3.74kΩ

R12

301Ω

1430Ω

10µF

RFIN

OPEN

0Ω

R15

OPEN

TC2 PWDN

(BLACK)

Figure 45. Basic Connections for Operation in Measurement Mode

SETTING VTADJ

As discussed in the Theory of Operation section, the output

temperature drift must be compensated by applying a voltage to

the TADJ pin. The compensating voltage varies with frequency.

The voltage for the TADJ pin can be easily derived from a resistor

divider connected to the VREF pin. Table 5 shows the recom-

mended VTADJ for operation from −40°C to +85°C, along with

resistor divider values. Resistor values are chosen so that they

neither pull too much current from VREF (VREF short-circuit

current is 4 mA) nor are so large that the TADJ pin bias current of

3 μA affects the resulting voltage at the TADJ pin.

Table 5. Recommended VTADJ for Selected Frequencies

Frequency

VTADJ (V)

R9 (Ω)

R12 (Ω)

100 MHz

0.5

1430

402

700 MHz to 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

SETTING VTGT

As discussed in the Theory of Operation section, setting the

voltage on VTGT to 0.8 V represents a compromise between

achieving excellent rms compliance and maximizing dynamic

range. The voltage on VTGT can be derived from the VREF pin

using a resistor divider as shown Figure 45 (Resistor R10 and

Resistor R11). Like the resistors chosen to set the VTADJ voltage,

the resistors setting VTGT must have reasonable values that do

not pull too much current from VREF or cause bias current

errors. Also, attention must be paid to the combined current

that VREF must deliver to generate the VTADJ and VTGT voltages.

This current must be kept well below the VREF short-circuit

current of 4 mA.

CHOOSING A VALUE FOR CLPF

CLPF (C9 in Figure 45) provides the averaging function for the

internal rms computation. Using the minimum value for CLPF

allows the quickest response time to a pulsed waveform but

leaves significant output noise on the output voltage signal. By

the same token, a large filter cap reduces output noise but at the

expense of response time.

For non response-time critical applications, a relatively large

capacitor can be placed on the CLPF pin. In Figure 45, a value

of 0.1 μF is used. For most signal modulation schemes, this

value ensures excellent rms measurement compliance and low

residual output noise. There is no maximum capacitance limit

for CLPF.

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