LPC47M192 datasheet(136/228 Pages) SMSC

136 / 228 page

SMSC DS – LPC47M192

Page 136

Rev. 03/30/05

DATASHEET

Temperature High Limit 1 or 2 register and Remote Temperature Low Limit 1 or 2 register, then the Remote Temp

Error 1 or 2 status bit is set in the Interrupt Status Register 1.

There are Remote Diode Fault status 1 and 2 bits in the Status Register 2 (0x42). The LPC47M192 automatically

sets the associated diode fault bit to 1 when there is an open circuit fault on the Remote x+ or Remote x- thermal

diode input pins. The occurrence of either a short (D+ and D- shorted together) or open circuit fault will cause 80h to

be loaded into the associated reading register, which will cause the corresponding remote temp error bit to be set.

This will cause the THERM# pin to become active if enabled. This same operation applies (including the diode

fault bit getting set) for the following board design error conditions: D+ shorted to VCC, D- shorted to VCC,

D+ shorted to ground. The diode fault bit will also be set if D- is shorted to ground, however, the part will

give a valid temperature reading (with some error), so the out of limit bit will not be set and therefore the

THERM# pin will not go active for this condition.

. Before a remote diode conversion is updated, the status of the

remote diode is checked.

The temperature change is computed by measuring the change in Vbe at two different operating points of the diode

to which the Dx+ and Dx- pins are connected. But accuracy of the measurement also depends on non-ideality factor

of the process the diode is manufactured on. See “Appendix A – Thermal Diode Parameters” for relationship

between the non-ideality factor and the change in Vbe.

Note

: Since digital boards can be electrically noisy environments that may interfere when measuring very small

voltages from a remote diode sensor, special layout considerations should be made. See “Layout Considerations”

below.

7.18.3.9.3

Temperature Data Format

Temperature data can be read from the three temperature registers. One is the Ambient Temperature Reading

Diode Temperature Reading 2 register (0x52).

The following table shows the corresponding format of the temperature digital data, represented by an 8-bit, two’s

complement word with an LSB equal to 1.0

0C.

Temperature

Digital Output

+125

0111 1101

+25

0001 1001

+1.0

0000 0001

0000 0000

-1.0

1111 1111

-25

1110 0111

-40

1101 1000

7.18.3.9.4

Offset Register

Offset Register 1 is used for internal or remote temperature 1 reading.

The Offset Register 1 (1Fh) contain a 2's

complement value which is added (or subtracted if the number is negative) to the temperature reading. The default

value in the offset register is zero, so initially zero is always added to the temperature reading. This offset register is

configured for the external temperature channel by default. It may be switched to the internal channel by setting bit 4

of the Special Function Register to 1.

7.18.3.9.5

Second Offset Register

The Offset Register 2 at 1Eh is for second remote diode temperature reading.

This register contains a 2's

complement value which is added (or subtracted if the number is negative) to the second external temperature

reading. Note that the default value in the offset register is zero, so initially zero is always added to the second

temperature reading. This offset register only applies to remote diode temperature reading 2. No configuration bit is

required.

7.18.3.10 Thermal / Voltage Interrupt Pin

The THERM# function is multiplexed on A0/RESET#/THERM#/XNOR_OUT pin. This function is used as an interrupt

output for out-of-limit temperature events. It can also be enabled for out-of-limit voltage events.

LPC47M192 Datasheet(PDF) 136 Page - SMSC Corporation

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