Rainbow Electronics MAX6656 - Manual (Page 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 CC ), V IN1 , V CC (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
register. The previous data is not changed and remains
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
register you are writing to Data Byte: data goes into the register
set by the co mma nd byte ( to se t
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
register commanded by 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 COMMAND WR
ACK
7 bits
ADDRESS ACK S ACK
8 bits
DATA
7 bits
ADDRESS RD
8 bits
P S COMMAND A WR
ACK
7 bits
ADDRESS
8 bits
COMMAND ACK P S WR ACK
7 bits
ADDRESS RD
8 bits
DATA P S A
Figure 1. SMBus/I 2 C Protocols