CS5480 datasheet(27/70 Pages) CIRRUS

27 / 70 page

CS5480

DS980F3

5.9 Phase Sequence Detection

Polyphase meters using multiple CS5480 devices may

be configured to sense the succession of voltage

zero-crossings and determine which phase order is in

service. The phase sequence detection within CS5480

involves counting the number of OWR samples from a

starting point to the next voltage zero-crossing rising

edge or falling for each phase. By comparing the count

for each phase, the phase sequence can be easily

determined: the smallest count is first, and the largest

count is last.

The phase sequence detection and control register

PSDC provides the count control, zero-crossing

direction and count results. Writing '0' to bit DONE and

'10110' to bits CODE[4:0] of the PSDC register followed

by a falling edge on the RX pin will initiate the phase

sequence detection circuit. The RX pin must be held low

for a minimum of 500ns. When the device is in UART

mode, it is recommended that a 0xFF command be

written to all parts to start the phase sequence

detection. Multiple CS5480 devices in a polyphase

meter must receive the register writing and the RX

falling edge at the same time so that all CS5480 devices

starts to count simultaneously. Bit DIR of PSDC register

specifies the direction of the next zero crossing at which

the count stops. If bit DIR is '0', the count stops at the

next negative-to-positive zero crossing. If bit DIR is '1',

the count stops at the next positive-to-negative zero

crossing. When the count stops, the DONE bit will be

set by the CS5480, and then the count result of each

phase may be read from bits PSCNT[6:0] of the PSDC

If the PSCNT[6:0] bits are equal to 0x00, 0x7F or

greater than 0x64 (for 50Hz) or 0x50 (for 60Hz), then a

measurement

error

has

occurred,

and

the

measurement results should be disregarded. This could

happen when the voltage input signal amplitude is lower

than the amplitude specified in the VZXLEVEL register.

To determine the phase order, the PSCNT[6:0] bit

counts from each CS5480 are sorted in ascending

order. Figure 18 and Figure 19 illustrate how phase

sequence detection is performed.

Phase sequences A, B, and C for the default rising edge

transition are illustrated in Figure 18. The PSCNT[6:0]

bits from the CS5480 on phase A will have the lowest

count, followed by the PSCNT[6:0] bits from the

CS5480 on phase B with the middle count, and the

PSCNT[6:0] bits from the CS5480 on phase C with the

highest count.

Phase sequences C, B, and A for rising edge transition

are illustrated in Figure 19. The PSCNT[6:0] bits from

the CS5480 on phase C will have the lowest count,

followed by the PSCNT[6:0] bits from the CS5480 on

phase B with the middle count, and the PSCNT[6:0] bits

from the CS5480 on phase A with the highest count.

5.10 Temperature Measurement

The CS5480 has an internal temperature sensor, which

is designed to measure temperature and optionally

compensate for temperature drift of the voltage

reference. Temperature measurements are stored in

the Temperature register (T), which, by default, is

configured to a range of ±128 degrees on the Celsius

(°C) scale.

Figure 18. Phase Sequence A, B, C for Rising Edge Transition

-2

Phase A Channel

-2

Phase B Channel

-2

Phase C Channel

Write 0x16 to

PSDC Register

Start on the Falling

Edge on the RX Pin

Stop

Phase C Count

Phase B Count

Phase A Count

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