Rainbow-electronics MAX6656 Manual do Utilizador descarregar pdf (Página 6)

MAX6655/MAX6656

ADC Conversion Sequence

Each time a conversion begins, all channels are con-

verted, and the results of the measurements are avail-

able after the end of conversion. A BUSY status bit in

the Status Byte shows that the device is actually per-

forming a new conversion; however, even if the ADC is

busy, the results of the previous conversion are always

available. The conversion sequence for the MAX6655

(MAX6656) is External Diode 1, External Diode 2,

Internal Diode, V

IN3

, V

IN2

), V

IN1

, V

IN2

The ADC always converts at maximum speed, but the

time between a sequence of conversions is adjustable.

The Conversion Rate Control Byte (Table 1) shows the

possible delays between conversions. Disabling voltage

or temperature measurements with the Configuration

Byte makes the ADC complete the conversion

sequence faster.

Low-Power Standby Mode

Standby mode disables the ADC and reduces the sup-

ply current drain to 3µA (typ). Enter standby mode by

forcing STBY low or through the RUN/STOP bit in the

Configuration Byte register. Hardware and software

standby modes behave identically; all data is retained

in memory, and the SMBus interface is alive and listen-

ing for reads and writes. Standby mode is not a shut-

down mode. Activity on the SMBus draws extra supply

current (see Typical Operating Characteristics).

Enter hardware standby mode by forcing STBY low. In

a notebook computer, this line may be connected to

the system SUSTAT# suspend-state signal. The STBY

low state overrides any software conversion command.

If a hardware or software standby command is

received while a conversion is in progress, the conver-

sion cycle is truncated, and the data from that conver-

sion is not latched into the Temperature Reading

available.

Supply current during the 125ms conversion is typically

550µA. Between conversions, the instantaneous supply

current is about 25µA, due to the current consumed by

the conversion-rate timer. With very low supply voltages

(under the POR threshold), the supply current is higher

due to the address input bias currents.

Dual Remote/Local Temperature Sensors and

Four-Channel Voltage Monitors

6 _______________________________________________________________________________________

Write Byte Format

Read Byte Format

Send Byte Format Receive Byte Format

Slave Address: equiva-

lent to chip-select line of

a 3-wire interface

Command Byte: selects which

Data Byte: data goes into the register

set by the command byte (to set

thresholds, configuration masks, and

sampling rate)

Slave Address: equiva-

lent to chip-select line

Command Byte: selects

which register you are

reading from

Slave Address: repeated

due to change in data-

flow direction

Data Byte: reads from

the register set by the

command byte

Data Byte: writes data to the

last read byte or write byte

transmission

Data Byte: reads data from

the register commanded

by the last read byte or

write byte transmission;

also used for SMBus alert

response return address

S = Start condition

P = Stop condition

Shaded = Slave transmission

A = Not acknowledged

ACK

7 bits

ADDRESS ACK

8 bits

DATA ACK P

8 bits

S COMMANDWR

ACK

7 bits

ADDRESS ACK S ACK

8 bits

DATA

7 bits

ADDRESS RD

8 bits

PS COMMAND A

ACK

7 bits

ADDRESS

8 bits

COMMAND ACK PS

ACK

7 bits

ADDRESS RD

8 bits

DATA PS

Figure 1. SMBus/I

C Protocols

1 2 3 4 5 6 7 8 9 10 11 ... 17 18

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