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Block Diagram

THERMAL SHUTDOWN

LOGIC

CONTROL

LOGIC

SMBUS

REGISTERS

MUX

ADC

RESET

CIRCUIT

TH_SHUT

SMBCLK

SMBDATA

ALERT

RESET

+

+

DXP1

DXN

+

INTERNAL GROUND

V

CC

DXP2

THERMAL SHUTDOWN

LOGIC

CONTROL

LOGIC

SMBUS

REGISTERS

MUX

ADC

RESET

CIRCUIT

TH_SHUT

SMBCLK

SMBDATA

ALERT

RESET

+

+

DXP1

DXN

+

INTERNAL GROUND

The SS8017 consists of two temperature sensors, one

on-chip temperature sensor and includes a system-reset

function.

The temperature sensor is designed to work in con-

junction with an external micro-controller (µC) or other

intelligence in thermostatic, process-control, or moni-

toring applications. The µC is typically a powerman-

agement or keyboard controller, generating SMBus

serial commands by "bit-banging" general-purpose in-

put-output (GPIO) pins or via a dedicated SMBus in-

terface block.

Essentially a 12-bit serial analog-to-digital converter

(ADC) with a sophisticated front end, the SS8017 con-

tains a switched current source, a multiplexer, an ADC,

an SMBus interface, a reset circuit and associated

control logic (see block diagram above).

Temperature data from the ADC is loaded into two data

registers, where it is automatically compared with data

previously stored in four over/under-temperature alarm

registers.

ADC and Multiplexer

The ADC is an averaging type that integrates over a

60ms period (each channel, typical).

The multiplexer automatically steers bias currents

through two remote diodes, measures their forward

voltages, and computes their temperatures. All chan-

nels are converted automatically once the conversion

process has started, either in free-running or sin-

gle-shot mode. If one of the two channels is not used,

the device still performs all measurements, and the

user can simply ignore the results of the unused chan-

nel. If the remote diode channel is unused, tie DXPx to

DXN rather than leaving the pins open.

The DXN input is internally connected to the ground

node inside the chip to set up the analog to digital (A/D)

inputs for a differential measurement. The worst-case

DXP-DXN differential input voltage range is 0.25V to

0.95V.

Excess resistance in series with the remote diode

causes about +1/2°C error per ohm. Likewise, 200µV

of offset voltage forced on DXP -DXN causes about 1°C

error.

Detailed Description

SS8017

Rev.2.01 6/06/2003