Datasheet

www.ti.com Setup and Operation
7. Plug the 10 pin female end of the ribbon cable from the USB Interface board into J6 on the LMH6518
evaluation board. The ribbon cable pin 1 should connect to J6 pin 1 (J6 pin 1 has square pad on the
board bottom, and a “1” silk-screened on the top side of the board, for easy identification). Table 1
shows the connections to the USB interface board (for reference only).
Table 1. USB Interface Board/ LMH6518 Evaluation Board Interconnect Detail
Name Function LMH6518 Evaluation Board Pin (J6) USB Interface Board (X4)
Ground Ground 1 “GND”, pin 2
CS Chip Select 3 A7, pin 1
DO
(1)
Data out (LMH6518 SDIO pin) 4 A0, pin 15
SCLK Clock 5 A6, pin 3
DI
(1)
Data In (LMH6518 SDIO pin) 7 L7, pin 6
(1)
DI and DO are tied together on the LMH6518 evaluation board, and connected to LMH6518 SDIO pin for bidirectional data read
or write.
8. Plug the USB Interface board to a free USB port, with the other end mating with the USB port on the
USB Interface board, and launch the LMH6518 software, if not already. If a pop-up window appears,
click “yes to upload the correct setup to the USB Interface board and you are now ready to control the
LMH6518. When the application is running, you should see “USB Connected All ACK” in the Status
Bar at the bottom-left of the LMH6518 software window shown in Figure 3. If the status bar message
does not appear, un-plug the USB cable and reapply to reinitiate the USB Interface board and until the
proper message appears.
3.2 LMH6518 Evaluation Board Setup
Refer to the board schematic and layout documents.
1. Jumper Placement: The LMH6518 evaluation board generates the 3.3 V logic supply on board
(Jumper JP3, pins 1-2 shorted powers the LMH6518 off the on-board 3.3 V source.
NOTE: JP3, pin 1 has a ”1” silk-screened next to it on the top side of the board). The output
common mode voltage (Main and Auxiliary outputs both) are set to about 1.2V using an
onboard voltage divider (R
1
, and R
2
) from V
CC
(+5 V). R
21
and R
22
(0 Ω resistors) tie this 1.2 V
level to both main and auxiliary common mode inputs (“V
CM
” and “V
CM_AUX
” that are pins 13
and 16, respectively).
2. Outputs: The main outputs of the LMH6518 appear at J1 and J2 (SMA connectors). These connectors
can be tied directly to a Texas Instruments Gsample/second ADC (ADC081500), or equivalent, for DC
coupled data acquisition. Done this way, pin 9 of J6 (V
CMO
) can be tied to the common mode output
control of the ADC to allow the ADC to control the LMH6518 output common mode voltage. Note that
R
3
= 10K and C
1
= 1 nF would need to be installed on the evaluation board for this kind of testing. In
addition, move R
21
and R
22
(0Ω resistors) to R
23
and R
24
in order to disconnect the onboard 1.2 V
reference and instead allow the ADC to control the main and auxiliary common mode voltages.
The auxiliary outputs, that can be terminated in 100 Ω on board by installing R
4
(100 Ω), appear at J8
and J7. Note that the auxiliary outputs (used for trigger function in oscilloscope applications) are very
similar to the main outputs, with the exception of slightly higher distortion levels. The auxiliary outputs
are available at J8 and J7 SMA connectors.
J1, and J2 (and also J7, and J8) differential impedance should be close to 100 Ω with minimal parasitic
effects when being measured. As these outputs are all at approximately 1.2 V common mode level,
they cannot be terminated in DC coupled 50 Ω (similar to an oscilloscope input) directly. AC coupled
50 Ω terminated instrumentation (such as S parameter analyzers) can be connected to these SMA
outputs directly for observation. With single ended Hi-Z input instrument observation, the LMH6518
outputs should be terminated in 100 Ω differential, as shown in Figure 2 (beware of the loading effect
of such an observation on the LMH6518 outputs).
3
SNOA535B–October 2008–Revised May 2013 AN-1906 LMH6518 Evaluation Board
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