CS5461 datasheet(27/46 Pages) CIRRUS

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CS5461

DS546PP2

From this equation the value of ‘PR’ is shown as:

Therefore the Pulse-Rate Register is set to

~420.875 Hz, or 0x00349C.

EXAMPLE #2: The required number of pulses per

unit energy present at EOUT is specified to be

500 pulses/kW-hr;

given

that

the

maximum

line-voltage is 250 V (RMS) and the maximum

line-current is 20 A (RMS). In such a situation, the

nominal line voltage and current do not determine

the appropriate pulse-rate setting. Instead, the max-

imum line levels must be considered. As before, the

given maximum line-voltage and line-current lev-

els are used to determine KV and KI:

KV = 150 mV / 250 V = 0.0006

KI = 150 mV / 20 A = 0.0075

Ω

Again the sensor gains are calculated such that the

maximum line-voltage and line-current levels will

measure as 0.6 in the RMS Voltage Register and

RMS Current Register.

With voltage and current channel input ranges set

to 10x, the required Pulse-Rate Register setting is

determined using the following equation:

Therefore PR = ~1.929 Hz.

Note that the Pulse-Rate Register cannot be set to a

frequency of exactly 1.929 Hz. The closest setting

that the Pulse-Rate Register can obtain is

0x00003E = 1.9375 Hz. To improve the accuracy,

either gain register can be programmed to correct

for the round-off error in PR. This value would be

calculated as

When MCLK/K is not equal to 4.096 MHz, the re-

sult for ‘PR’ that is calculated for the Pulse-Rate

4.096 MHz / (MCLK/K).

For

MCLK/K

3.05856 MHz the result is scaled by 4.096/3.05856

to get a final PR result of ~2.583 Hz.

5.6 Auto-Boot Mode Using EEPROM

When the CS5461 MODE pin is left unconnected,

the CS5461 is in normal operating mode, called

host mode. When this pin is set to logic high, the

CS5461 auto-boot mode is enabled. In auto-boot

mode, the CS5461 is configured to request a mem-

ory download from an external serial EEPROM.

Auto-Boot mode allows the CS5461 to operate

without the need for a microcontroller.

5.6.1 Auto-Boot Configuration

Figure 13 shows the typical connections between

the CS5461 and a serial EEPROM for proper au-

to-boot operation. In this mode, CS and SCLK are

driven outputs. During the auto-boot sequence, the

CS5461 drives CS low, provides a clock output on

SCLK, and drives out-commands on SDO. It re-

ceives the EEPROM data on SDI. The serial EE-

PROM

must

programmed

with

the

user-specified commands and register data that will

be used by the CS5461 to change any of the default

Vnom

250mV

------------------

Inom

250mV

------------------

--------------------------------------------

100Hz

132mV

250mV

------------------

112.5mV

250mV

-----------------------

------------------------------------------------

500

pulses

kW hr

⋅

------------------

1hr

3600s

--------------

1kW

1000W

------------------

250mV

------------------

250mV

------------------

⋅⋅

⋅

Ign or Vgn

1.929

-------------

1.00441

≅

0x404830

CS5461

EEPROM

/EOUT

/EDIR

MODE

SCK

SDI

SDO

/CS

SCK

/CS

Connector to Calibrator

VD+

5 K

Mech. Counter

Stepper Motor

Figure 13. Typical Interface of EEPROM to CS5461

CS5461 Datasheet(PDF) 27 Page - Cirrus Logic

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