MAX6638ATC 데이터 시트보기 (PDF) - Maxim Integrated

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MAX6638ATC

Temperature Monitor with Dual Serial Interface

Maxim Integrated 

Temperature Monitor with

Dual Serial Interface

SMBus1 CRC1 = 06h

SMBus2 CRC2 = 05h

ACTUAL DATA

READY FROM

ADC CONVERSIONS

ACTUAL DATA READ

BY SMBus2

SMBus1 START

TIME

CONVERSION

250

500

750

1000

1250

1500

1750

2000 (ms)

CYCLE

CYCLE

CYCLE

CYCLE

CYCLE

CYCLE

CYCLE

CYCLE

CYCLE

SMBus1 DATA AVAILABLE

CYCLE

CYCLE

CYCLE

CYCLE

SMBus2 START

CONVERSION

SHADED BOXES INDICATE EXPECTED ADC CONVERSION CYCLING AND DATA READINGS OF SMBus2 FROM START CONVERSION

Figure 3. An Example of ADC Cycling for Two Conversion Rates Set by Each Controllers on SMBus1 and SMBus2

The MAX6638 allows conversion rates that are 2x multi-

ples of the minimum rate of 0.0625Hz. Figure 2 shows

several different conversion rate settings.

The ADC converts at the higher rate of the two conver-

sions set by SMBus1 and SMBus2 controllers. The con-

troller that sets the higher rate receives a new

conversion at the higher conversion-rate time. The con-

troller that sets the lower rate receives the most recent

conversion result at the lower conversion-rate timing.

Figure 3 shows an example of this. SMBus1 initiates the

ADC converter by selecting conversion rate 06h (4Hz)

prior to SMBus2 initiating a conversion. Then SMBus2

initiates conversions of 05h (2Hz) independent of the

process initiated by SMBus1. The controller accesses

data at its programmed time set by the initiated conver-

sion time. The data presented to SMBus2 is always

ready at the anticipated time, but the data is actually

the result of a previous conversion sequence driven by

the higher conversion rate set by SMBus1.

The first SMBus channel that activates a conversion

sequence always establishes the MAX6638 conversion

cycling. The ADC conversion rates increase and

decrease as set by each of the SMBus controllers with

the higher conversion rate always dominating.

Increasing the conversion rate with the ADC cycling

increases the rate the MAX6638 performs cycles with-

out losing sync of the previously established cycle tim-

ing. A decrease in conversion rate reduces the ADC

cycling to the lower rate without losing sync with the

previously set cycle pattern. The ADC cycling pattern is

only reset following a POR event or upon exiting the

standby mode through one of the SMBus controllers’

initiation of cycling or single-shot conversion.

Low-Power Standby Mode

Standby mode reduces the supply current to 3µA (typ)

by disabling the ADC and timing circuitry when both

SMBus controller channels enable standby mode.

Standby mode is enabled only when both SMBus con-

trollers request standby mode. Set each of the RUN bits

to 1 in each corresponding configuration register (see

Tables 3 and 5) to enter standby mode. When one

SMBus controller channel is set to standby mode, the

other conversion rate is automatically set to the active

channel’s conversion rate and mode. The MAX6638

retains all data in the registers and each SMBus inter-

face is active and listening for SMBus commands.

Standby mode is not a shutdown mode. With activity on

either SMBus, the device draws more supply current

(see the Typical Operating Characteristics). In standby

mode, the MAX6638 performs an ADC conversion

sequence through the one-shot command, regardless

of either of the RUN bit statuses, upon receipt of a one-

shot command from either SMBus controller.

If the device receives standby commands from both

SMBus controllers during a conversion, the conversion

cycle truncates, and the data from that conversion is

not latched into a temperature register. The previous

data does not change and remains available.

Supply current drawn during the 32ms conversion period

is 800µA (typ). Slowing down the conversion rate reduces

the average supply current (see the Typical Operating

Characteristics). Between conversions, the conversion

rate timer consumes 40µA (typ) of supply current.

SMBus Interface

From a software perspective, the MAX6638 appears as a

set of byte-wide registers that contain temperature data,

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