MCP9902 datasheet(12/50 Pages) MICROCHIP

12 / 50 page

MCP9902/3/4

DS20005382C-page 12

 2015-2016 Microchip Technology Inc.

For CPU substrate transistors that require the BJT

transistor model, the ideality factor behaves slightly

differently

than

for

discrete

diode-connected

transistors. Refer to Table 4-4 when using a CPU

substrate transistor.

4.11

Diode Faults

The MCP9902/3/4 detects several “diode fault” mech-

anisms, defined as one of the following: an open

between DP and DN, a short from VDD to DP, or a

short from VDD to DN. When each temperature mea-

surement is made, the device checks for a diode fault

on the external diode channel(s). When a diode fault is

detected, the ALERT/THERM2 pin asserts (unless

masked, see Register 5-20) and the temperature data

reads 00h in the MSB and LSB registers (note: the low

limit will not be checked).

If a short occurs across DP and DN or a short occurs

from DP to GND, the low limit status bit is set and the

ALERT/THERM2 pin asserts (unless masked). This

condition is indistinguishable from a temperature

measurement of 0.000°C (-64°C in extended range)

resulting in temperature data of 00h in the MSB and LSB

registers.

If a short from DN to GND occurs (with a diode-con-

nected transistor), temperature measurements will

continue as normal with no alerts.

The External Diode Fault Register (Register 5-19)

indicates which of the external diodes caused the

FAULT bit in the Status Register to be set. This

4.12

Consecutive Alerts

The MCP9902/3/4 contains multiple consecutive alert

counters. One set of counters applies to the

ALERT/THERM2 pin and the second set of counters

applies to the THERM pin. Each temperature measure-

ment channel has a separate consecutive alert counter

for each of the ALERT/THERM2 and THERM pins. All

counters are user programmable and determine the

number of consecutive measurements that a tempera-

ture channel(s) must be out-of-limit or reporting a diode

fault before the corresponding pin is asserted.

The Consecutive Alert register determines how many

times an out-of-limit error or diode fault must be

detected in consecutive measurements before the

ALERT/THERM2 or THERM pin is asserted. Addition-

ally, the Consecutive Alert register controls the SMBus

Time-out functionality.

An out-of-limit condition (i.e., HIGH, LOW or FAULT)

occurring on the same temperature channel in consec-

utive measurements will increment the consecutive

alert counter. The counters will also be reset if no

out-of-limit condition or diode fault condition occurs in a

consecutive reading.

When the ALERT/THERM2 pin is configured as an

interrupt, when the consecutive alert counter reaches

its programmed value, the following will occur: the

STATUS bit(s) for that channel and the last error

condition(s)

(i.e.,

E1HIGH,

E2LOW

and/or

TABLE 4-3:

IDEALITY FACTOR LOOK-UP

TABLE (DIODE MODEL)

Setting Factor Setting Factor Setting

Factor

08h

0.9949

18h

1.0159

28h

1.0371

09h

0.9962

19h

1.0172

29h

1.0384

0Ah

0.9975

1Ah

1.0185

2Ah

1.0397

0Bh

0.9988

1Bh

1.0200

2Bh

1.0410

0Ch

1.0001

1Ch

1.0212

2Ch

1.0423

0Dh

1.0014

1Dh

1.0226

2Dh

1.0436

0Eh

1.0027

1Eh

1.0239

2Eh

1.0449

0Fh

1.0040

1Fh

1.0253

2Fh

1.0462

10h

1.0053

20h

1.0267

30h

1.0475

11h

1.0066

21h

1.0280

31h

1.0488

12h

1.0080

22h

1.0293

32h

1.0501

13h

1.0093

23h

1.0306

33h

1.0514

14h

1.0106

24h

1.0319

34h

1.0527

15h

1.0119

25h

1.0332

35h

1.0540

16h

1.0133

26h

1.0345

36h

1.0553

17h

1.0146

27h

1.0358

37h

1.0566

TABLE 4-4:

SUBSTRATE DIODE IDEALITY

FACTOR LOOK-UP TABLE

(BJT MODEL)

Setting Factor Setting Factor Setting Factor

08h

0.9869

18h

1.0079

28h

1.0291

09h

0.9882

19h

1.0092

29h

1.0304

0Ah

0.9895

1Ah

1.0105

2Ah

1.0317

0Bh

0.9908

1Bh

1.0120

2Bh

1.0330

0Ch

0.9921

1Ch

1.0132

2Ch

1.0343

0Dh

0.9934

1Dh

1.0146

2Dh

1.0356

0Eh

0.9947

1Eh

1.0159

2Eh

1.0369

0Fh

0.9960

1Fh

1.0173

2Fh

1.0382

10h

0.9973

20h

1.0187

30h

1.0395

11h

0.9986

21h

1.0200

31h

1.0408

12h

1.0000

22h

1.0213

32h

1.0421

13h

1.0013

23h

1.0226

33h

1.0434

14h

1.0026

24h

1.0239

34h

1.0447

15h

1.0039

25h

1.0252

35h

1.0460

16h

1.0053

26h

1.0265

36h

1.0473

17h

1.0066

27h

1.0278

37h

1.0486

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