250MHz to 4000MHz Dual,
Analog Voltage Variable Attenuator
9
                     Detailed Description
The MAX19790 is a dual, general-purpose analog volt-
age  variable  attenuator  (VVA)  designed  to  interface 
with 50I systems operating in the 250MHz to 4000MHz 
frequency  range.  Each  attenuator  includes  a  control 
circuit that provides 22dB of attenuation range with a 
linear control slope of 10dB/V. Both attenuators share a 
common analog control and can be cascaded together 
to yield 44dB of total dynamic range, with a combined 
linear control slope of 20dB/V.
               Applications Information
Analog Attenuation Control
A single input voltage at the CTRL pin adjusts the attenu-
ation of the device. Up to 22dB of attenuation-control 
range is provided per attenuator. At the insertion-loss 
setting, the attenuators loss is approximately 2.4dB.
If  a  larger  attenuation-control  range  is  desired,  the   
second on-chip attenuator can be connected in series to 
provide an additional 22dB of gain-control range.
Note  that  the  CTRL  pin  simultaneously  adjusts  both 
on-chip  attenuators.  The  CTRL  input  voltage  drives  a 
high-impedance load (> 50kI). It is suggested that a 
current-limiting resistor be included in series with this 
connection, to limit the input current to less than 40mA, 
should the control voltage be applied when V
CC
 is not 
present. A series resistor of greater than 200I provides 
complete protection for +5.0V control voltage ranges. 
Note: To ensure the reliability of the device, limit CTRL 
input voltages to a +1.0V to +4.0V range when V
CC
 is 
present.
Layout Considerations
A  properly  designed  PCB  is  an  essential  part  of  any  
RF/microwave circuit. Keep RF signal lines as short as 
possible  to  reduce  losses,  radiation,  and  inductance. 
For  best  performance,  route  the  ground-pin  traces 
directly to the exposed pad underneath the package. 
This pad MuST be connected to the ground plane of 
the board by using multiple vias under the device to 
provide the best RF and thermal conduction path. Solder 
the exposed pad on the bottom of the device package 
to a PCB.
Power-Supply Bypassing
Proper voltage-supply bypassing is essential for high-
frequency  circuit  stability.  Bypass  each  V
CC
  pin  with 
capacitors placed as close as possible to the device. 
Place the smallest capacitor closest to the device. See 
the Typical Application Circuit and Table 1 for details.
Table 1. Typical Application Circuit Component Values
*C8 can be used to provide additional filtering. Depending on the external driver used on the CTRL line, this capacitance could 
slow down the response time.
DESIGNATION    QTY
DESCRIPTION
C1, C3, C5
3
220pF Q5%, 50V C0G ceramic 
capacitors (0402)
Murata GRM1555C1H221J
C2, C4
2
0.01FF Q10%, 25V X7R ceramic 
capacitors (0402)
Murata GRM155R71E103K
C6
1
1000pF Q5%, 50V C0G ceramic 
capacitor (0402)
Murata GRM1555C1H102J
C7
1
0.1FF Q10%, 16V X7R ceramic 
capacitor (0603)
Murata GRM188R71C104K
C8*
0
Not installed, ceramic capacitor 
(0603) 
DESIGNATION    QTY
DESCRIPTION
C9
1
22pF Q5%, 50V C0G ceramic 
capacitor (0402)
Murata GRM1555C1H220J
R1, R2
2
10I Q5% resistors (0402)
Any
R3, R4
2
0I resistors (0402)
Note: In cases where V
CTRL
 is 
applied before or removed after 
V
CC
, use R4 = 200I.
U1
1
Analog attenuator IC
Maxim MAX19790ETX+
Note: U1 has an exposed pad 
conductor, which requires it to be 
solder-attached to a grounded 
pad on the PCB to ensure a 
proper electrical/thermal design.