MAX19794ETX+【PDF 18/25 页】ATTENUATR 46DB 50OHM 4GHZ 36TQFN

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MAX19794

10MHz to 500MHz Dual Analog Voltage Variable

Attenuator with On-Chip 10-Bit SPI-Controlled DAC

Table 1. Attenuator Control Logic States

Detailed Description

The MAX19794 is a dual, general-purpose analog

voltage variable attenuator (VVA) designed to interface

with 50I systems operating in the 10MHz to 500MHz

frequency range. Each attenuator provides 22.4dB of

attenuation range with a linear control slope of 8dB/V.

Both attenuators share a common analog control and can

be cascaded together to yield 44.7dB of total dynamic

range with a combined linear control slope of 16dB/V.

Alternatively, the on-chip, 4-wire SPI-controlled 10-bit

DAC can be used to control both attenuators. In addition,

a step-up/down feature allows user-programmable

attenuator stepping through command pulses without

reprogramming the SPI interface.

Application Information

Attenuation Control and Features

The device has various states that are used to control the

analog attenuator along with some monitoring conditions.

The device can be controlled by an external control

voltage, an internal SPI bus, or a combination of the two.

The various states are described in Table 1. The SPI bus

has multiple registers that are used to control the device

when not configured for the analog only mode. For the

cases where CTRL is used, the control range is 1V to 4V

for V

= 5V, and is 1V to 2.5V for V

= 3.3V.

Up to 22.4dB of attenuation-control range is provided

per attenuator. At the insertion-loss setting, the single

attenuators loss is approximately 1.5dB. If a larger

attenuation-control range is desired, the second on-chip

attenuator can be connected in series to provide an

additional 22.4dB of gain-control range.

The on-chip control driver simultaneously adjusts both

on-chip attenuators. It is suggested that a current-limiting

resistor be included in series with CTRL to limit the input

current to less than 40mA, should the control voltage

be applied when V

is not present. A series resistor

of greater than 200I provides complete protection for

+5.0V control voltage ranges.

Analog Mode Only Control

In Table 1 state (0, 0), the attenuators are controlled

using a voltage applied to the CTRL pin of the device and

the on-chip DAC is disabled. In the case where none of

the features of the SPI bus are needed, the part can be

operated in a pure analog control mode by grounding

pins 14 through 25.

DAC Mode Control

In Table 1 state (1, 0), the attenuators are controlled by

the on chip 10-bit DAC register. See the Register/Mode

section. In this condition, no signal is applied to the CTRL

pin and the load on the CTRL pin should be >100kI. The

DAC is set using the SPI loaded code in the registers

along with the setting of the mode pin.

Analog Mode Control with Alarm Monitoring

In Table 1 state (0, 1), the attenuators are controlled

using a voltage applied to the CTRL pin of the device.

See Register/Mode section. In this condition, the DAC

DAC_LOGIC

RDBK_EN

(D9, REG3)

INTERNAL

SWITCH STATES

ATTENUATOR

10-BIT DAC

S1 = closed

S2, S3, S4 = open

Controlled by external analog voltage on CTRL

(pin 11).

Disabled

S1, S3, S4 = open

S2 = closed

Controlled by on-chip DAC. No voltage applied

to pin 11.

Enabled

S1, S3, S4 = closed

S2 = open

Controlled by external analog voltage on CTRL

(pin 11). CTRL is compared with DAC output.

Comparator drives COMP_OUT (pin 17).

Enabled (update DAC

code to estimate CTRL

voltage on pin 11)

S1, S2 = closed

S3, S4 = open

Controlled by on-chip DAC. The DAC output is

connected to pin 11. Use this state to test the

DAC output. In this condition, no voltage can

be applied to pin 11 and the load on pin 11

must be > 100kI.

Enabled

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