1

10

100

1000

-20

-10

0

10

20

30

40

50

FREQUENCY (MHz)

SVA-30206584

100

¼ LMH6523

VCC

0.01 F

0.01 F

0.01 F

0.01 F

40.2

40.2

1 H

1 H

100

¼ LMH6523

VCC

0.01 F

0.01 F

1 H

1 H

VIN

VOUT

SVA-30206583

LMH6523

www.ti.com

SNOSC88 – DECEMBER 2012

CASCADE OPERATION

Figure 49. Schematic for Cascaded Amplifiers

With four amplifiers in one package the LMH6523 is ideally configured for cascaded operation. By using two

amplifiers in series additional gain range can be achieved. The schematic in Figure 49 shows one way to

connect two stages of the LMH6523. The resultant frequency response is shown below in Figure 50. When using

the LMH6523 amplifiers in a cascade configuration it is important to keep the signal level within reasonable limits

at all nodes of the signal path. With over 40dB of total gain it is possible to amplify signals to clipping levels if the

gain is not set correctly.

Figure 50. Frequency Response of Cascaded Amplifiers

DIGITAL CONTROL

The LMH6523 will support two modes of control, parallel mode and serial mode (SPI compatible). Parallel mode

is fastest and requires the most board space for logic line routing. Serial mode is compatible with existing SPI

compatible systems.

The LMH6523 has gain settings covering a range of 31 dB. To avoid undesirable signal transients the LMH6523

should not be powered on with large inputs signals present. Careful planning of system power on sequencing is

especially important to avoid damage to ADC inputs.

The LMH6523 was designed to interface with 2.5V to 5V CMOS logic circuits. If operation with 5V logic is

required care should be taken to avoid signal transients exceeding the DVGA supply voltage. Long, unterminated

digital signal traces are particularly susceptible to these transients. Signal voltages on the logic pins that exceed

the device power supply voltage may trigger ESD protection circuits and cause unreliable operation.

Some pins on the LMH6523 have different functions depending on the digital control mode. These functions will

be described in the sections to follow.

Copyright © 2012, Texas Instruments Incorporated

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Product Folder Links: LMH6523