MIC280 datasheet(8/23 Pages) MICREL

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MIC280

Micrel

MIC280

November 2004

(D7) represents the sign: zero for positive temperatures and

one for negative temperatures. Table 3 shows examples of

the data format used by the MIC280 for temperatures:

Temperature

Binary

Hex

+127°C

0111 1111

+125°C

0111 1101

+25°C

0001 1001

+1°C

0000 0001

0°C

0000 0000

–1°C

1111 1111

–25°C

1110 0111

–125°C

1000 0011

–128°C

1000 0000

Table 3: Digital Temperature Format, High Bytes

Extended temperature resolution is provided for the external

zone. The high and low temperature limits and the measured

temperature for zone one are reported as 12-bit values stored

in a pair of 8-bit registers. The measured temperature, for

example,isreportedinregistersTEMP1h,thehigh-orderbyte,

and TEMP1l, the low-order byte. The values in the low-order

bytes are left-justiﬁed four-bit binary values representing

one-sixteenth degree increments. The A-D converter resolu-

tion for zone 1 is selectable from nine to twelve bits via the

conﬁguration register. Low-order bits beyond the resolution

selected will be reported as zeroes. Examples of this format

are shown below in Table 4.

FAULT QUEUE

A set of fault queues (programmable digital ﬁlters) are pro-

vided in the MIC280 to prevent false tripping due to thermal

or electrical noise. Two bits, CONFIG[5:4], set the depth of

the fault queues. The fault queue setting then determines

the number of consecutive temperature events (TEMPx >

THIGHx or TEMPx < TLOWx) which must occur in order for

the condition to be considered valid. As an example, as-

sume CONFIG[5:4] is programmed with 10b. The measured

temperature for a given zone would have to exceed THIGHx

for four consecutive A/D conversions before /INT would be

asserted or the status bit set.

Like any ﬁlter, the fault queue function also has the effect

of delaying the detection of temperature events. In this ex-

ample, it would take 4 x tCONV to detect a temperature event.

The fault queue depth vs. CONFIG[5:4] of the conﬁguration

for over-temperature events (CRIT0 and CRIT1) or diode

faults. The fault queue applies only to high-temperature and

low-temperature events as determined by the THIGHx and

TLOWx registers. Any write to CONFIG will result in the fault

queues being purged and reset. Writes to any of the limit

registers, TLOWx or THIGHx, will result in the fault queue for

the corresponding zone being purged and reset.

CONFIG[5:4]

FAULT QUEUE

DEPTH

1 (Default)

Table 5: Fault Queue Depth Settings

Interrupt Generation

There are eight different conditions that will cause the MIC280

to set one of the bits in STATUS and assert its /INT output,

if so enabled. These conditions are listed in Table 6. Unlike

previous generations of thermal supervisor IC’s, there are no

interdependencies between any of these conditions. That is,

if CONDITION is true, the MIC280 will respond accordingly,

regardless of any previous or currently pending events.

Normallywhenatemperatureeventoccurs,thecorresponding

status bit will be set in STATUS, the corresponding interrupt

mask bit will be cleared, and /INT will be asserted. Clearing

the interrupt mask bit(s) prohibits continuous interrupt gen-

eration while the device is being serviced. (It is possible to

prevent events from clearing interrupt mask bits by setting

bits in the lock register. See Table 7 for Lockbit function-

ality.) A temperature event will only set bits in the status

in the interrupt mask register. An interrupt signal will only

be generated on /INT if interrupts are also globally enabled

(IE =1 in CONFIG).

The MIC280 expects to be interrogated using the Alert Re-

sponseAddress once it has asserted its interrupt output. Fol-

lowing an interrupt, a successful response to the A.R.A. or a

read operation on STATUS will cause /INT to be de-asserted.

STATUS will also be cleared by the read operation. Reading

STATUS following an interrupt is an acceptable substitute for

Extended Temperature,

Resolution

Low Byte

9 BITS

10 BITS

11 BITS

12 BITS

Binary

Hex

Binary

Hex

Binary

Hex

Binary

Hex

0.0000

0000 0000

0.0625

0000 0000

0001 0000

0.1250

0000 0000

0010 0000

0.2500

0000 0000

0100 0000

0.5625

1000 0000

1001 0000

0.9375

1000 0000

1100 0000

1110 0000

1111 0000

Table 4: Digital Temperature Format, Low Bytes

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