ADL5904

Data Sheet

Rev. B | Page 26 of 27

Table 7. Evaluation Board Configuration Options

Component

Function

Notes

Default Values

RFIN, R1, R2, R3,

R8, R9, R10, L1,

L2, C2, C4, C5

RF input

Apply the RF input signal to the ADL5904 to the SMA connector

labeled RFIN. The ADL5904 RFIN pin (Pin 1) is dc-coupled and is not

internally matched. A broadband 50 Ω match is achieved using an

external 82.5 Ω shunt resistor with a 0.47 µF ac coupling capacitor

placed between the shunt resistor and the RF input. An external

preemphasis network can be built to improve flatness vs. frequency

using the components between R8 and the RFIN SMA connector.

C4= 0.47uF (0402)

R8 = 82.5 Ω (0402)

R2, R9, R10 = 0 Ω (0402)

R1, R3 = open (0402)

L1, L2 = open (0402)

C2, C5 = open (0402)

VCAL, VIN_N,

TPVIN_N, C17,

VCAL threshold

calibration

The output voltage from the threshold calibration pin (VCAL, Pin 3) is

available on the yellow VCAL clip lead. Use the voltage on this pin to

determine the correct threshold voltage that must be applied to Pin 16

(VIN−) to set a particular RF power threshold. This process includes two

steps: first, measure the output voltage on the VCAL yellow clip lead

with no RF signal applied to RFIN (this voltage is approximately 750

mV). Next, apply the RF input power to RFIN, which causes the circuit

to trip, and again measure the voltage on the VCAL yellow clip lead.

The difference between these two voltages is equal to the voltage that

must be applied to VIN− during operation. This voltage can be applied

either to the VIN_N SMA connector or to the TPVIN_N yellow clip lead.

Use C17 to provide noise decoupling of the applied input voltage.

C17 = open (0603)

R6, C3

DECL internal

decoupling

node

A resistor in series with a capacitor to ground must be connected to the

DECL pin (Pin 4).

C3 = 100 nF (0402)

R6 = 4.02 Ω (0402)

VPOS, GND, C7,

C6

Power supply

interface

Apply the 3.3 V power supply for the evaluation board to the VPOS (red)

and GND (black) test loops. The nominal supply decoupling consists of a

100 pF capacitor and a 0.1 µF capacitor, with the 100 pF capacitor

placed closest to the VPOS pin (Pin 5).

C7 = 0.1 µF (0402),

C6 = 100 pF (0402)

VPOS = 3.3 V

VRMS, TP1, R16,

C14

Output

interface

The rms output voltage is available on the VRMS SMA connector or on

the TP1 yellow clip lead.

R16 = 0 Ω (0402)

C14 = 10 nF (0603)

C12

RMS averaging

capacitor

Set the value of the rms averaging capacitor based on the peak to

average ratio and bandwidth of the input signal and based on the

desired output response time and residual output noise.

C12 = 0.1 µF (0402)

Q, Q, QX, QX,

R19, R21, C15,

C16

Threshold

detect output

(Q and Q)

The threshold detect flip flop outputs (Q and Q) are available on the

SMA connectors labeled Q and Q and on the 2-pin headers labeled QX

and QX. To test the response time of Q and Q, remove R19 and R21 and

probe QX and QX with low capacitance FET probes.

C15 = C16 = open (0603)

R19, R21 = 0 Ω (0603)

ENBL, S1, R31

Enable interface

The ADL5904 can be enabled by applying 3.3 V to the ENBL SMA

connector or using the S1 switch. The enable voltage must be equal to

but not greater than the 3.3 V supply voltage.

R31 = 10 kΩ (0603)

RST push-button

switch, R4, C1,

R28

Threshold

detect reset

The threshold detect flip-flop is reset using the RST push-button switch.

The RST switch is connected the VPOS supply voltage through a 1.1 kΩ

resistor (R28). A 100 kΩ pull-down resistor (R4) is connected to the RST

pin, which pulls RST low in the absence of any other stimulus.

The ADL5904 normally powers up with the Q and Q outputs high and

low, respectively. A reset on the power-up circuit can be implemented

by installing a capacitor on C1. When the VPOS supply turns on, RST

goes high momentarily before being pulled low by R4.

R4 = 10 kΩ (0603)

R28 = 1.1 kΩ (0603)

C1 = open (0603)

VIN_N, TPVIN_N,

C17

Threshold

detect level set

The voltage applied to the VIN_N SMA connector or to the TPVIN_N

yellow test loop drives the inverting input of the threshold detect

comparator (VIN−) and thereby defines the RF power level that trips

the threshold detect comparator and flip flop. The threshold detect

voltage can be optionally decoupled using C17.

C17 = open (0603)