MIC384 datasheet(12/21 Pages) MICREL

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MIC384

Micrel

MIC384

September 2000

is in shutdown mode, and the interrupt status will not be

retained. Since entering shutdown mode stops A/D conver-

sions, the MIC384 is incapable of detecting or reporting

temperature events of any kind while in shutdown. Diode

faults require one or more A/D conversion cycles to be

recognized, and therefore will not be reported either while the

device is in shutdown (see "Diode Faults" above).

Fault_Queue

Fault queues (programmable digital filters) are provided in

the MIC384 to prevent false tripping due to thermal or

electrical noise. The two bits in CONFIG[4:3] set the depth of

Fault_Queue. Fault_Queue then determines the number of

consecutive temperature events (TEMPx > T_SETx, or TEMPx

< T_HYSTx) which must occur in order for the condition to be

considered valid. There are separate fault queues for each

zone. As an example, assume the part is in comparator

mode, and CONFIG[4:3] is programmed with 10

The

measured temperature in zone one would have to exceed

T_SET1 for four consecutive A/D conversions before /INT

would be asserted or the S1 status bit set. Similarly, TEMP1

would then have to be less than T_HYST1 for four consecu-

tive conversions before /INT would be reset. Like any filter,

the fault queue function also has the effect of delaying the

detection of temperature events. In this example, it would

take 4 x t

CONV to detect a temperature event. The depth of

Fault_Queue vs. D[4:3] of the configuration register is shown

in Table 4.

]

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Table 4. Fault_Queue Depth Settings

Interrupt Generation

Assuming the MIC384 is in interrupt mode and interrupts are

enabled, there are seven different conditions that will cause

the MIC384 to set one of the status bits, S0, S1, or S2, in

CONFIG and assert its /INT output. These conditions are

listed in Table 5. When a temperature event occurs, the

corresponding status bit will be set in CONFIG. This action

cannot be masked. However, a temperature event will only

generate an interrupt signal on /INT if it is specifically enabled

by the interrupt mask bit (IM =0 in CONFIG). Following an

interrupt, the host should read the contents of the configura-

tion register to confirm that the MIC384 was the source of the

interrupt. A read operation on

any register will cause /INT to

be de-asserted. This is shown in Figure 5. The status bits will

only be cleared once CONFIG has been read.

Since temperature-to-digital conversions continue while /INT

is asserted, the measured temperature could change be-

tween the MIC384’s assertion of /INT and the host’s re-

sponse. It is good practice for the interrupt service routine to

read the value in TEMPx, to verify that the over-temperature

or under-temperature condition still exists. In addition, more

than one temperature event may have occurred simulta-

neously or in rapid succession between the assertion of /INT

and servicing of the MIC384 by the host. The interrupt service

routine should allow for this eventuality. Keep in mind that

clearing the status bits and deasserting /INT is not sufficient

to allow further interrupts to occur. TEMPx must become less

than T_HYSTx if the last event was an over-temperature

condition, or greater than T_SETx if the last event was an

under-temperature condition, before /INT can be asserted

again.

Putting the device into shutdown mode will de-assert /INT

and clear the status bits (S0, S1, and S2). This should not be

done before completing the appropriate interrupt service

routine(s).

Polling

The MIC384 may either be polled by the host, or request the

host’s attention via the /INT pin.

In the case of polled

operation, the host periodically reads the contents of CONFIG

to check the state of the status bits. The act of reading

CONFIG clears the status bits. If more than one event that

sets a given status bit occurs before the host polls the

MIC384, only the fact that at least one such event has

occurred will be apparent to the host. For polled systems, the

interrupt mask bit should be set (IM = 1). This will disable

interrupts from the MIC384 and prevent the /INT pin from

sinking current.

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