LPC47M192 datasheet(137/228 Pages) SMSC

137 / 228 page

SMSC DS – LPC47M192

Page 137

Rev. 03/30/05

DATASHEET

If the internal or remote temperature reading is not within the low or high temperature limits, THERM# will be active

low. It will also be low for the diode pin conditions mentioned in the “External Temperature Measurement” section.

The THERM# pin will remain low while any of the Ambient Temp Error bit or the Remote Temp Error bit in Interrupt

Status 1 Register is set. The THERM# function can be selected by writing a ‘1’ to bit 2 of the Special Function

Block is used on a system, only one can have this function enabled at one time since this will limit the SMBus

address to 0101101, unless external circuitry is provided.

The THERM# pin can be enabled to indicate out-of-limit/equal-limit voltages. Bit 3 of the Special Function register

(4Fh) is used to enable this option. When this bit is set, if one or more of the voltage readings is not within the low or

high limits, THERM# will be active low. This pin will remain low while the associated voltage error bit (+2.5v_Error,

Vccp_Error, +3.3v_Error, +5v_Error, +12v_Error, HVCC_Error, +1.5v_Error or +1.8v_Error) in the Interrupt Status

temperature events only.

The THERM# pin will remain low until Interrupt Status Register 1 and 2 are read. If the temperature or voltage

remains out of limit or equal to the limit, the THERM# will be re-asserted on the next monitoring cycle. THERM# can

also be cleared by issuing an Alert Response Address Call.

The THERM# pin may only become active while the monitor block is operational.

Implementation Note:

In designs using the Hardware Monitor Block of the LPC47M192, all the remote thermal diode inputs must be

properly terminated, even if one or both of the remote temperature sensor channels will not be used to actively

monitor temperatures. These inputs should be terminated with a thermal diode, a transistor or a resistor. If the

channel will never be used to monitor temperature, a resistor can used to allow for proper functioning of the nTHERM

pin. See application note “Using the Hardware Monitor Feature in SMSC Super I/O Devices” for more information.

Unused Analog Voltage Channel inputs should not be left unconnected. This is good design practice, and it will

guarantee proper functioning of the nTHERM pin, if the nTHERM pin is enabled to indicate voltage events. Any

Analog Voltage Measurement Channel that will not be used to actively monitor a power supply must be pulled up to

some nominal voltage. If the nTHERM pin is not enabled to indicate voltage events, unused Analog Voltage Channels

may be grounded.

7.18.3.11 Input Safety

Since the power supply voltages will appear directly at the pins (1.5V – 12V), small external series resistors such as

470 ohm to 1k ohm (see Note) should be put into the lines driving the chip to prevent damaging the traces or power

supplies should an accidental short such as a probe connect two power supplies together. This value should be kept

as small as possible, since raising this resistor will start affecting the accuracy of the internal dividers. These resistors

are recommended, but not necessary.

Note

: The analog input channels on the LPC47M192 are calibrated for 500 ohm resistors. These optional external

resistors should not exceed 1k

Ω.

7.18.3.12 Layout Considerations

To ensure accuracy when measuring analog signals, whether from a voltage divider or remote diode sensor, the

analog components should be located physically as close to the hardware monitoring block as possible. The

following is a list of precautions and suggestions to gain optimal performance from the hardware monitoring block.

Devices that are sources of noise, such as generators, data/address buses and CRTs should be kept as far

away from the hardware monitoring block as possible. (Approximately 4 to 8 inches is adequate).

The Dx+ and Dx- tracks should be kept close together, in parallel with grounded guard tracks on each side.

Using wide tracks will help to minimize inductance and reduce noise pickup. A 10 mil track minimum width

and spacing is recommended. See FIGURE 10.

GND

D+

D-

10 mil.

LPC47M192 Datasheet(PDF) 137 Page - SMSC Corporation

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