78M6612 查看數據表（PDF） - Teridian Semiconductor Corporation

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78M6612

Single-Phase, Dual-Outlet Power and Energy Measurement IC

Teridian Semiconductor Corporation 

78M6612 Data Sheet

DS_6612_001

1.2 Analog Front End (AFE)

The AFE functions as a data acquisition system, controlled by the MPU. It consists of an input

multiplexer, a delta-sigma A/D converter, and a voltage reference. The main signals (IA, VA, IB, VB) are

sampled and the ADC counts obtained are stored in CE DRAM where they can be accessed by the CE

and, if necessary, by the MPU.

VREF

IA

VA

IB

MUX

VB

VBAT

VBIAS

TEMP

MUX

MUX

CTRL

EQU

MUX_ALT

CHOP_E

MUX_DIV

VREF

VREF_CAL

VREF_DIS

CROSS

CK32

VBIAS

∆Σ ADC

CONVERTER

V3P3A

-

+

ADC_E

VREF

FIR_DONE

FIR_START

4.9MHz

FIR

FIR_LEN

Figure 2: AFE Block Diagram

1.2.1 Input Multiplexer

The input multiplexer supports up to four input signals that are applied to pins IA, VA, IB, and VB of the

device. Additionally, using the alternate multiplexer selection, it has the ability to select temperature and

the battery voltage. The multiplexer can be operated in two modes:

• During a normal multiplexer cycle, the signals from the IA, IB, VA, and VB pins are selected.

• During the alternate multiplexer cycle, the temperature signal (TEMP) and the battery monitor are

selected, along with the signal sources shown in Table 1. To prevent unnecessary drainage on the

battery, the battery monitor is enabled only with the BME bit (0x2020[6]) in the I/O RAM.

The alternate multiplexer cycles are usually performed infrequently (e.g. every second or so) by the MPU.

In order to prevent disruption of the voltage tracking PLL and voltage allpass networks, VA is not

replaced in the ALT mux selections. Table 1 details the regular and alternative multiplexer sequences.

Missing samples due to an ALT multiplexer sequence are filled in by the CE.

EQU

2

Table 1: Inputs Selected in Regular and Alternate Multiplexer Cycles

Regular MUX Sequence

Mux State

0

1

2

3

IA

VA

IB

VB

ALT MUX Sequence

Mux State

0

1

2

3

TEMP

VA

VBAT

VB

In a typical application, IA and IB are connected to current sensors that sense the current on each branch

of the line voltage. VA and VB are typically connected to voltage sensors through resistor dividers. The

multiplexer control circuit is clocked by CK32, the 32.768 kHz clock from the PLL block, and launches with

each new pass of the CE program. The duration of each multiplexer state depends on the number of

ADC samples processed by the FIR.

8

Rev 2

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