Cirrus Logic CDB5451A - Manual (Page 7)

CDB5451A
DS458DB3 7
differential signal. Using voltage channel #1 as an
example (see Figure 2), note that HDR10 sets the
input to the positive side of the first voltage channel
input (VIN1+ pin). HDR13 sets the input to the
negative side of the first voltage channel input
(VIN1- pin). In a single-ended input configuration,
HDR13 would be set to the “AGND” setting, and
HDR10 would be set to “VIN1+” and would conduct
the single-ended signal. In a differential input con-
figuration, HDR13 would be set to “VIN1-” and
HDR10 would be set to “VIN1+” and this pair of in-
puts would form the differential input pair into the
VIN1+ and VIN1- pins of the CS5451A.
WARNING: DANGER! One of the possible appli-
cations for the CS5451A includes data acquisition
for a power metering system. However, the user
should not attempt to directly connect any lead
from a high-voltage power line to the evaluation
board inputs, even if the current/voltage levels are
gain reduced by resistive dividers and/or shunts.
Because the ground terminal of the parallel cable
(from the PC) is near or at earth ground potential,
the ground node on the evaluation board will also
be forced to earth ground potential. Serious dam-
age and even personal injury can occur if a “hot”
voltage main is connected to any point on the eval-
uation board, including the analog input connec-
tors. Such power line signals must be isolated by
current/voltage transformers and reduced in mag-
nitude before they can be safely applied to the
evaluation board.
Several patch-circuit areas are provided near the
voltage/current input headers, in case the user
wants to connect special sensor circuitry to the an-
alog inputs (such as transformers, shunt resistors,
etc., for monitoring a 3-phase power line). For
each of the three channels, a Shunt Resistor or
Current Transformer can be mounted in these ar-
eas and connections can be made to the individual
current-channel input pairs. Likewise, for each of
the three voltage channels, a Voltage Divider or
Voltage Transformer can be inserted to drive the
CS5451A’s three voltage input pairs. Note from
Figure 2 that a simple R-C network filters each
sensor’s output to reduce any noise that might be
coupled into the input leads. The 3 dB corner of the
filter is approximately 50 kHz differential and com-
mon mode.
Other header options listed in Table 2 allow the
user to set the source of the input clock signal and
the source of the voltage reference (VREFIN) in-
put, etc. The voltage reference options and clock
input options are discussed next.
2.3.2 Voltage Reference Input
To supply the CS5451A with a suitable 1.2 V volt-
age reference input at the VREFIN pin, the evalu-
ation board provides three voltage reference
options: on-chip, on-board, and external. See
HDR14 as shown in Figure 1. Table 3 illustrates
the available voltage reference settings for
HDR14. With HDR14’s jumpers in position “VRE-
HDR15
Controls the source for the CS5451A XIN clock
input. Set to on-board 4.000
MHz crystal (U1).
HDR16 This header should always be shorted. Short this header
HDR17
Determines whether the main analog supply will be
powered from the A- post, or from the regulated 3V
voltage (generated from the +5V_IN) post input.
Set to A-
HDR18
Choose whether the digital circuitry will be powered
by main analog supply, or powered by separate dig-
ital supply (through VD+ post).
Set to main analog
supply
Name Function Description Default Setting Default Jumpers
Table 2. Default Header Settings (Continued)
O O EXT XIN
O O DGND
O O 4.0096 MHz
OSC
O O
O O +5V_IN
O O A+
O O
O O
VD+
V+