Cirrus Logic CS5464 - Manual (Page 17)

CS5464
DS682F3 17
5. PIN DESCRIPTIONS
5.1 Analog Pins
The CS5464 has three differential inputs: VIN
IIN1,
and IIN2
 are the voltage, current1, and current2 inputs,
respectively. A single-ended power fail monitor input,
voltage reference input, and voltage reference output
are also available.
5.1.1 Voltage Inputs
The output of the line voltage resistive divider or trans-
former is connected to the VIN+ and VIN- input pins of
the CS5464. The voltage channel is equipped with a
10x, fixed-gain amplifier. The full-scale signal level that
can be applied to the voltage channel is ±250mV. If the
input signal is a sine wave, the maximum RMS voltage
is 250mVp /

2

176.78mVRMS which is approxi-
mately 70.7% of maximum peak voltage.
5.1.2 Current1 and Current2 Inputs
The output of the current-sensing resistor or transform-
er is connected to the IIN1+ (IIN2+) and IIN1- (IIN2-) in-
put pins of the CS5464. To accommodate different
current-sensing elements, the current channel incorpo-
rates a programmable gain amplifier (PGA) with two se-
lectable input gains. The full-scale signal level for the
current channels is ±50mV or ±250mV. If the input sig-
nal is a sine wave, the maximum RMS voltage is
35.35mVRMS or 176.78mVRMS which is approximate-
ly 70.7% of maximum peak voltage.
5.1.3 Power Fail Monitor Input
An analog input (PFMON) is provided to determine
when a power loss is imminent. By connecting a resis-
tive divider from the unregulated meter power supply to
the PFMON input, an interrupt can be generated, or the
Low Supply Detected (LSD) Status register bit can be
monitored to indicate low-supply conditions. The PF-
MON input has a comparator that trips around the level
of the voltage reference input (VREFIN).
5.1.4 Voltage Reference Input
The CS5464 requires a stable voltage reference of
2.5 V applied to the VREFIN pin. This reference can be
supplied from an external voltage reference or from the
VREFOUT output. A bypass capacitor of at least 0.1
F
is recommended at the VREFIN pin.
5.1.5 Voltage Reference Output
The CS5464 generates a 2.5 V reference (VREFOUT).
It is suitable for driving the VREFIN pin, but has very lit-
tle fan-out and is not recommended for driving external
circuits.
5.1.6 Crystal Oscillator
An external quartz crystal can be connected to the XIN
and XOUT pins as shown in Figure
6 . To reduce system
cost, each pin is supplied with an on-chip, phase-shift-
ing capacitor to ground.
.
Alternatively, an external clock source can be connect-
ed to the XIN pin.
5.2 Digital Pins
5.2.1 Reset Input
The active-low RESET pin, when asserted, will halt all
CS5464 operations and reset internal hardware regis-
ters and states. When de-asserted, an initialization se-
quence begins, setting default register values.
5.2.2 CPU Clock Output
A logic-level clock output (CPUCLK) is provided at the
crystal frequency to drive an external CPU or microcon-
troller clock. Two phase choices are available.
5.2.3 Interrupt Output
The INT pin indicates an enabled Internal Status regis-
ter (Status) bit is set. Status register bits indicate condi-
tions such as data ready, modulator oscillations, low
supply, voltage sag, current faults, numerical overflows,
and result updates.
5.2.4 Energy Pulse Outputs
The CS5464 provides three pins (E1, E2, E3) for pulse
energy outputs. These pins can also be used to output
other conditions, such as voltage sign, power fail moni-
tor, or energy channel in use.
Figure 6. Oscillator Connections
Oscillator
Circuit
DGND
XIN
XOUT
C1
C1 = 22 pF
C2
C2 =