MIC384 datasheet(10/21 Pages) MICREL

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MIC384

Micrel

MIC384

September 2000

Temperature Data Format

The LSB of each register represents one degree Centigrade.

The values are in a two’s complement format, wherein the

most significant bit (D7) represents the sign: zero for positive

temperatures and one for negative temperatures. Table 3

shows examples of the data format used by the MIC384 for

temperatures.

A/D Converter Timing

Whenever the MIC384 is not in its low power shutdown mode,

the internal A/D converter (ADC) attempts to make continu-

ous conversions unless interrupted by a bus transaction

accessing the MIC384.

Upon powering up or coming out of shutdown mode, the ADC

will begin acquiring temperature data starting with the first

external zone, zone 1, then the second external zone, zone

2, and finally the internal zone, zone 0. Results for zone 1 will

be valid after t

CONV1, results for zone two will be ready after

another t

CONV1, and for the local zone tCONV0 later. Figure 4

shows this behavior. The conversion time is twice as long for

external conversions as it is for internal conversions. This

allws the use of a filter capacitor on T1 and/or T2 without a

loss of accuracy due to the resulting longer settling times.

Upon powering up, coming out of shutdown mode, or resum-

ing operation following a serial bus transaction, the ADC will

begin aquiring temperature data with the first external zone

(zone 1), followed by the second external zone (zone 2), and

then the internal zone (zone 0). If the ADC in interrupted by

a serial bus transaction, it will restart the conversion that was

interrupted and then continue in the normal sequence. This

sequence will repeat indefinitely until the MIC384 is shut

down, powered off, or is interrupted by a serial bus transac-

tion as described above.

Power On

When power is initially applied, the MIC384’s internal regis-

ters are set to their default states. Also at this time, the level

on the address input, A0, is read to establish the device’s

slave address. The MIC384’s power-up default state can be

summarized as follows:

• Normal mode operation (i.e., part is not in

shutdown)

• /INT function is set to comparator mode

• Fault queue depth = 1 (FQ=00)

• Interrupts are enabled (IM = 0)

• T_SET0 = 81

°C; T_HYST0 = 76°C

• T_SET1 = 97

°C; T_HYST1 = 92°C

• T_SET2 = 97

°C; T_HYST2 = 92°C

• Initialized to recognize overtemperature faults

Comparator and Interrupt Modes

Depending on the setting of the MODE bit in the configuration

request signal or a thermostatic control signal. Thermostatic

operation is known as

comparator mode. The /INT output is

asserted when the measured temperature, as reported in any

of the TEMPx registers, exceeds the threshold programmed

into the corresponding T_SETx register for the number of

conversions specified by Fault_Queue (described below). In

comparator mode, /INT will remain asserted and the status

bit(s) will remain high unless and until the measured tempera-

ture falls below the value in the T_HYSTx register for

Fault_Queue conversions. No action on the part of the host

is required for operation in comparator mode. Note that

entering shutdown mode will not affect the state of /INT when

the device is in comparator mode.

interrupt mode, once a temperature event has caused a

status bit to be set and the /INT output to be asserted, they will

not be automatically de-asserted when the measured tem-

perature falls below T_HYSTx. They can only be de-asserted

by reading any of the MIC384’s internal registers or by putting

the device into shutdown mode. If the most recent tempera-

ture event was an overtemperature condition, Sx will not be

set again, and /INT cannot be reasserted, until the device has

detected that TEMPx < T_HYSTx. Similarly, if the most

recent temperature event was an undertemperature condi-

tion, Sx will not be set again, and /INT cannot be reasserted,

until the device has detected that TEMPx > T_SETx. This

keeps the internal logic of the MIC384 backward compatible

with that of the LM75 and similar devices. In both modes, the

MIC384 will be responsive to over-temperature events at

power-up. See "Interrupt Generation", below.

Shutdown Mode

Setting the SHDN bit in the configuration register halts the

otherwise continuous conversions by the A/D converter. The

MIC384’s power consumption drops to 1

µA typical in shut-

down mode. All registers may be read from or written to while

in shutdown mode. Serial bus activity will slightly increase the

part’s power consumption.

Entering shutdown mode will not affect the state of /INT when

the device is in comparator mode (MODE = 0). It will retain

its state until after the device exits shutdown mode and

resumes A/D conversions.

However, if the device is shut down while in interrupt mode,

the /INT pin will be unconditionally de-asserted and the

internal latches holding the interrupt status will be cleared.

Therefore, no interrupts will be generated while the MIC384

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