MIC280_06 Datasheet, PDF(8/23 Page) Micrel Semiconductor – Precision IttyBitty Thermal Supervisor

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MIC280_06 Datasheet, PDF (8/23 Pages) Micrel Semiconductor – Precision IttyBitty Thermal Supervisor

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MIC280

(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

+127Â°C

0111 1111

+125Â°C

0111 1101

+25Â°C

0001 1001

+1Â°C

0000 0001

0Â°C

0000 0000

â1Â°C

1111 1111

â25Â°C

1110 0111

â125Â°C

1000 0011

â128Â°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, is reported in registers TEMP1h, the high-order byte,

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

bytes are left-justiï¬ed 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

conï¬guration 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 ï¬lters) 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 ï¬lter, 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 conï¬guration

Micrel

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 ICâs, 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.

Normally when a temperature event occurs, the corresponding

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-

sponse Address 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,

Low Byte

0.0000

0.0625

0.1250

0.2500

0.5625

0.9375

Resolution

9 BITS

10 BITS

11 BITS

Binary

Hex

Binary

Hex

Binary Hex

0000 0000 00

0010 0000 20

0000 0000 00

0100 0000 40

1000 0000 80

1100 0000 C0

1110 0000 E0

Table 4: Digital Temperature Format, Low Bytes

12 BITS

Binary Hex

0000 0000 00

0001 0000 10

0010 0000 20

0100 0000 40

1001 0000 90

1111 0000 F0

MIC280

May 2006

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