SA56004GD datasheet(20/36 Pages) NXP

20 / 36 page

SA56004X_5

Product data sheet

Rev. 05 — 22 May 2008

20 of 36

NXP Semiconductors

SA56004X

Digital temperature sensor with overtemperature alarms

7.10.1 Serial interface reset

If the SMBus master attempts to reset the SA56004X while the SA56004X is controlling

the data line and transmitting on the data line, the SA56004X must be returned to a known

state in the communication protocol. This may be accomplished in two ways:

1. When the SDATA is LOW, the SA56004X SMBus state machine resets to the SMBus

idle state if SCLK is held LOW for more than 35 ms (maximum TIMEOUT period).

According to

SMBus speciﬁcation 2.0, all devices are required to time-out when the

SCLK line is held LOW for 25 ms to 35 ms. Therefore, to insure a time-out of all

devices on the bus, the SCLK line must be held LOW for at least 35 ms.

2. When the SDATA is HIGH, the master initiates an SMBus START. The SA56004X will

respond properly to a SMBus START condition only during the data retrieving cycle.

After the START, the SA56004X will expect an SMBus Address byte.

Simpliﬁed system diagram

(1) Typical value; placed close to temperature sensor.

Fig 10. Simpliﬁed system diagram

VDD

SCLK

D+

SDATA

−

ALERT

T_CRIT

GND

SA56004X

002aad201

shielded twisted pair

100 nF

2.2 nF(1)

VDD

FAN CONTROL

CIRCUIT

+5 V

remote sensor

2N3904 (NPN), 2N3906 (PNP),

or similar standalone, ASIC or

microprocessor thermal diode

10 k

Ω

10 k

Ω

10 k

Ω

10 k

Ω

VDD

CLOCK

DATA

INT

SMBus

CONTROLLER

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