Broadcom
ACPL-C740-EvalKit-UG100
6
ACPL-C740 Evaluation Kit Board
User Guide
Isolated Sigma-Delta Modulator
The shunt resistor mounting pad is designed to accommodate various shunt resistor package types. The Kelvin
connection PCB trace connects from the center of the pad to the inputs of ACPL-C740 through the anti-aliasing filters
(AAFs). Connecting from the center of the pads is usually the optimum location for most shunt resistor designs. The
evaluation board also provides pads P1 and P2 for soldering thick cables to the motor driving board.
Apply an input voltage signal without a shunt resistor.
Connect the audio cable with the audio 3.5-mm jack connected to either a PC, smart phone, tablet, MP3 player, or any
kind of audio player device. Then, connect the crocodile clips to the shunt resistor mounting pads.
Check the 1 kHz sine test signal and supply a 1 kHz sine wave voltage signal to the evaluation board. Other methods
include playing any of the three provided sine wave files on a music player software program from the audio player
devices described previously. Adjust the volume until the signal level is near ±200 mV or ±20,000 ADC counts for best
SNR/SNDR performance.
The performance of SNR/SNDR is dependent on a few factors:
– The evaluation board
– The sigma-delta modulator used, in this case, the ACPL-C740
– Input signal frequency used
– The decimation ratio, which can be set at the application GUI to 256, 128, or 64.
– The input signal level. The ACPL-C740 recommended input voltage range is from –200 mV to 200 mV. To achieve
the best SNR/SNDR, design the maximum input signal range nearest ±200 mV (using the selection of the input
current range and shunt resistor value).
– The input signal source.
shows a comparison of the SNR/SNDR performance between audio signal sources coming from a laptop.
Table 2: SNR/SNDR Comparison
Filter
Configuration
Signal Source from Audio Jack of Laptop
Signal Freq. = 500 Hz
Signal Freq. = 1000 Hz
Signal Freq. = 2000 Hz
SNR(dB)
SNDR(dB)
SNR(dB)
SNDR(dB)
SNR(dB)
SNDR(dB)
Sinc3 DR = 64
not enough sampling sinewave cycles
66
64
61
59
Sinc3 DR = 128
76
73
74
73
70
63
Sinc3 DR = 256
77
75
78
77
73
63
