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SS8018
1C Remote and Local Temperature Sensor with SMBus Serial Interface n FEATURES
n n n n n n
n DESCRIPTION
The SS8018 is a precise digital thermometer that reports the temperature of both a remote sensor and its own package. The remote sensor is a diode-connected transistor - typically a low-cost, easily mounted 2N3904 NPN type that replaces a conventional thermistor or thermocouple. Remote accuracy is 1C with no calibration needed. The remote channel can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor. The 2-wire serial interface accepts standard System Management Bus (SMBus) Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read temperature data. The data format is 11bits plus sign, with each bit corresponding to 0.125C, in two's-complement format. Measurements can be done automatically and autonomously, with the conversion rate programmed by the user or programmed to operate in a single-shot mode. The adjustable rate allows the user to control the supply current drain. The SS8018 is available in a small 8-pin SOP surface-mount package.
n n n
Two channels: measures both remote and local temperatures No calibration required SMBus 2-wire serial interface Programmable under/over-temperature alarms SMBus alert response supported Accuracy: 1C (+60C to +100C, remote) 3C (+60C to + 100C, local) Average supply current during conversion of 320A (typ) Supply range of +3V to +5.5V Small 8-lead SO package
n APPLICATIONS
Desktop and Notebook Computers Smart Battery Packs LAN Servers Industrial Controllers Central Office Telecom Equipment Test and Measurement Multi-Chip Modules
n ORDERING INFORMATION
SS8018XX PACKING TYPE TR: TAPE & REEL Example: SS8018TR a SS8018 shipped in tape & reel packing
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n ABSOLUTE MAXIMUM RATINGS
VCC to GND...................................................................................-0.3V to +6V DXP to GND...................................................................................-0.3V to VCC + 0.3V DXN to GND...................................................................................-0.3V to +0.8V SMBCLK, SMBDATA, ALERT to GND................................................-0.3V to +6V SMBDATA, ALERT Current...............................................................-1mA to +50mA DXN Current...................................................................................1mA ESD Protection (SMBCLK, SMBDATA, ALERT , human body model)........2000V ESD Protection (other pins, human body model).....................................2000V Continuous Power Dissipation (T A = +70C) ..................................SOP (derate 8.30mW/C above +70C).......................................................667mW Operating Temperature Range.........................................................-20C to +120C Junction Temperature.....................................................................+150C Storage temperature Range.............................................................-65C to +165C Lead Temperature (soldering, 10sec).....................................................+300C
n ELECTRICAL CHARACTERISTICS
(VCC = + 3.3V, TA = 0C to +85C, unless otherwise noted.) PARAMETER
Temperature Error, Remote Diode (Note 1) Temperature Error, Local Diode Supply-Voltage Range Undervoltage Lockout Threshold VCC input, disables A/D conversion, rising edge Undervoltage Lockout Hysteresis Power-On Reset Threshold POR Threshold Hysteresis SMBus static Standby Supply Current Average Operating Supply Current Conversion Time Conversion Rate Timing Remote-Diode Source Current Logic inputs forced to VCC or GND Auto-convert mode. Logic inputs forced to VCC or GND Hardware or software standby, SMBCLK at 10kHz 0.5 conv/sec 8.0 conv/sec VCC, falling edge
CONDITIONS
TR = +60C to +100C, VCC = 3.0V to 3.6V TR = 0C to +125C (Note 2) TA = +60C to +100C TA = 0C to +85C (Note 2)
MIN TYP MAX UNITS
-1 -3 -3 -5 3.0 2.8 50 1.7 50 3 4 35 320 125 1 176 11 A +1 +3 +3 +5 5.5 C C V V mV V mV
A ms sec A
From stop bit to conversion complete (both channels) Conversion-Rate Control Byte=04h, 1Hz DXP forced to 1.5V High level Low level
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n ELECTRICAL CHARACTERISTICS (cont.)
(VCC = + 3.3V, TA = 0 to +85C, unless otherwise noted.) PARAMETER
SMBus Interface Logic Input High Voltage Logic Input Low Voltage Logic Output Low Sink Current
ALERT Output High Leakage Current
CONDITIONS
STBY , SMBCLK, SMBDATA; Vcc = 3V to 5.5V STBY , SMBCLK, SMBDATA; Vcc = 3V to 5.5V
ALERT , SMBDATA forced to 0.4V ALERT forced to 5.5V
MIN TYP MAX UNITS
2.4 0.8 6 1 -2 5 100 30 4.7 4 4.7 500 4 4 800 300 1 2 V V mA A A pF kHz ms s s s ns s s ns ns s
Logic Input Current SMBus Input Capacitance SMBus Clock Frequency SMBus Timeout SMBCLK Clock Low Time SMBCLK Clock High Time SMBus Start-Condition Setup Time
Logic inputs forced to VCC or GND SMBCLK, SMBDATA SMBCLK low time for interface reset tLOW , 10% to 10% points tHIGH , 90% to 90% points
SMBus Repeated Start-Condition Setup Time tSU : STA , 90% to 90% points SMBus Start-Condition Hold Time SMBus Stop-Condition Setup Time SMBus Data Valid to SMBCLK Rising-Edge Time SMBus Data-Hold Time SMBCLK Falling Edge to SMBus Data-Valid Time tHD: STA , 10% of SMBDATA to 90% of SMBCLK tSD: STO , 90% of SMBCLK to 10% of SMBDATA tSU: DAT , 10% or 90% of SMBDATA to 10% of SMBCLK tHD : DAT Master clocking in data
Note 1: A remote diode is any diode-connected transistor from Table1. TR is the junction temperature of the remote of the remote diode. See Remote Diode Selection for remote diode forward voltage requirements. Note 2: Guaranteed by design but not 100% tested.
n PIN DESCRIPTIONS
PIN
1 2 3 4 5 6 7 8
NAME
VCC DXP DXN
FUNCTION
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1F capacitor. Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave DXP floating; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. Combined Current Sink and A/D Negative Input. Open-drain output. Requires pull-up to VCC. Ground SMBus Alert (interrupt) Output, open drain SMBus Serial-Data Input / Output, open drain SMBus Serial-Clock Input
THERM
GND
ALERT SMBDATA SMBCLK
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n BLOCK DIAGRAM
VCC MUX DXP DXN + +
REMOTE LOCAL
2 + ADC CONTROL LOGIC
READ WRITE
7 SMBUS
SMBDATA SMBCLK
DIODE FAULT
8
8
11
REMOTE TEMPERATURE DATA REGISTER
LOCAL EMPERATURE DATA REGISTER
8
COMMAND BYTE (INDEX) REGISTER
11
HIGH-TEMPETATURE THRESHOLD (REMOTE HIGH)
HIGH-TEMPETATURE THRESHOLD (LOCALT HIGH )
8
STATUS BYTE REGISTER
LOW-TEMPETATURE THRESHOLD (REMOTE LOW)
LOW-TEMPETATURE THRESHOLD (LOCAL T LOW )
CONFIGURATION BYTE REGISTER
11
DIGITAL COMPARATOR (REMOTE)
8
CONVERSION RATE REGISTER
DIGITAL COMPARATOR (LOCAL)
ALERT
Q R S
SELECTED VIA SLAVE ADD = 0001 100
ALERT RESPONSE ADDRESS REGISTER
THERM
COMPARATOR THERM LIMIT AND HYSTERESIS REGISTER
n PIN CONFIGURATION
SS8018
VCC DXP DXN THERM 1 2 3 4 8 7 6 5 SMBCLK SMBDATA ALERT
n TYPICAL APPLICATION
3V TO 5.5V 0.1F
VCC
10k EACH
DXP
SMBCLK SMBDATA
CLOCK DATA INTERRUPT TO C
DXN 2N3904 2200pF
ALERT THERM GND
GND
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n APPLICATIONS INFORMATION
The SS8018 is a temperature sensor designed to work in conjunction with an external microcontroller (C) or other intelligence in thermostatic, process-control or monitoring applications. The C is typically a powermanagement or keyboard controller, generating SMBus serial commands by "bit-banging" general-purpose input-output (GPIO) pins or via a dedicated SMBus interface block. Essentially a serial analog-to-digital converter (ADC) with a sophisticated front end, the SS8018 contains a switched current source, a multiplexer, an ADC, an SMBus interface and associated control logic (Figure 1). Temperature data from the ADC is loaded into two data registers, where it is automatically compared with data previously stored in several over/under-temperature alarm registers. ADC and Multiplexer The ADC is an averaging type that integrates over a 60ms period (each channel, typical), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes, measures their forward voltages, and computes their temperatures. Both channels are automatically converted once the conversion process has started, either in free-running or single-shot mode. If one of the two channels is not used, the device still performs both measurements, and the user can simply ignore the results of the unused channel. If the remote diode channel is unused, tie DXP to DXN rather than leaving the pins open. 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 +0.6C error per ohm. Likewise, 240V of offset voltage forced on DXP-DXN causes about 1C error. A/D Conversion Sequence If a Start command is written (or generated automatically in the free-running auto-convert mode), both channels are converted, and the results of both measurements are available after the end of conversion. A BUSY status bit in the status byte shows that the device is actually performing a new conversion; however, even if the ADC is busy, the results of the previous conversion are always available. Remote Diode Selection Temperature accuracy depends on having a good- quality, diode-connected small-signal transistor. The SS8018 can also directly measure the die temperature
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of CPUs and other integrated circuits having on-board temperature-sensing diodes. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range can be violated. The forward voltage must be greater than 0.25V at 10A; check to ensure this is true at the highest expected temperature. The forward voltage must be less than 0.95V at 300A; check to ensure this is true at the lowest expected temperature. Large power transistors don't work at all. Also, ensure that the base resistance is less than 100. Tight specifications for forward-current gain (+50 to +150, for example) indicate that the manufacturer has good process controls and that the devices have consistent Vbe characteristics. Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER
Philips Motorola(USA) National Semiconductor (USA)
MODEL NUMBER
PMBS3904 MMBT3904 MMBT3904
Note: Transistors must be diode-connected (base shorted to collector). Thermal Mass and Self-Heating Thermal mass can seriously degrade the SS8018's effective accuracy. The thermal time constant of the SOP package is about 140 seconds in still air. For the SS8018 junction temperature to settle to within +1C after a sudden +100C change requires about five time constants or 12 minutes. The use of smaller packages for remote sensors, such as SOT23s, improves the situation. Take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. Self-heating does not significantly affect measurement accuracy. Remote-sensor self-heating due to the diode current source is negligible. For the local diode, the worst-case error occurs when auto-converting at the fastest rate and simultaneously sinking maximum current at the ALERT output. For example, at an 8Hz rate and with ALERT sinking 1mA, the typical power dissipation is VCC x 320A plus 0.4V x 1mA. Package R(J-A) is about 120C /W, so with VCC = 3.3V and no copper PC board heat-sinking, the resulting temperature rise is: dT = 1.45mW x 120C /W = 0.17C Even with these contrived circumstances, it is difficult to introduce significant self-heating errors.
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ADC Noise Filtering The ADC is an integrating type with inherently good noise rejection. Micro-power operation places constraints on high-frequency noise rejection; therefore, careful PC board layout and proper external noise filtering are required for high-accuracy remote measurements in electrically noisy environments. High-frequency EMI is best filtered at DXP and DXN with an external 2200pF capacitor. This value can be increased to about 3300pF (max), including cable capacitance. Higher capacitance than 3300pF introduces errors due to the rise time of the switched current source. Nearly all noise sources tested cause the ADC measurements to be higher than the actual temperature, typically by +1C to 10C, depending on the frequency and amplitude. PC Board Layout Place the SS8018 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4 in. to 8 in. (typical) or more as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily introduce +30C error, even with good filtering; otherwise, most noise sources are fairly benign. Route the DXP and DXN traces in parallel and in close proximity to each other, away from any high-voltage traces such as +12VDC. Leakage currents from PC board contamination must be dealt with carefully, since a 10M leakage path from DXP to ground causes about +1C error. Connect guard traces to GND on either side of the DXP-DXN traces (Figure 2). With guard traces in place, routing near high-voltage traces is no longer an issue. Route through as few vias and cross-unders as possible to minimize copper/solder thermocouple effects. When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. In general, PC board-induced thermocouples are not a serious problem, A copper-solder thermocouple exhibits 3V/C, and it takes about 240V of voltage error at DXP-DXN to cause a +1C measurement error. So, most parasitic thermocouple errors are swamped out. Use wide traces. Narrow ones are more inductive and
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tend to pick up radiated noise. The 10 mil widths and spacing recommended on Figure 2 aren't absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical.
GND 10 MILS 10 MILS DXP MINIMUM 10 MILS DXN 10 MILS GND
Figure 2. Recommended DXP/DXN PC Traces Keep in mind that copper can't be used as an EMI shield, and only ferrous materials such as steel work will. Placing a copper ground plane between the DXP-DXN traces and traces carrying high-frequency noise signals does not help reduce EMI. PC Board Layout Checklist n Place the SS8018 close to a remote diode. n Keep traces away from high voltages (+12V bus). n Keep traces away from fast data buses and CRTs. n Use recommended trace widths and spacing. n Place a ground plane under the traces n Use guard traces flanking DXP and DXN and connecting to GND. n Place the noise filter and the 0.1F VCC bypass capacitors close to the SS8018. Twisted Pair and Shielded Cables For remote-sensor distances longer than 8 in., or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6 feet to 12feet (typical) before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. Connect the twisted pair to DXP and DXN and the shield to GND, and leave the shield's remote end un-terminated. Excess capacitance at DX limits practical remote sensor distances (see Typical Operating Characteristics). For very long cable runs, the cable's parasitic capacitance often provides noise filtering, so the 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy; 1 series resistance introduces about + 0.6C error.
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Low-Power Standby Mode Standby mode disables the ADC and reduces the supply-current drain to about 10A. Enter standby mode by forcing high to the RUN /STOP bit in the configuration byte register. Software standby mode behaves such that all data is retained in memory, and the SMB interface is alive and listening for reads and writes. Software standby mode is not a shutdown mode. With activity on the SMBus, extra supply current is drawn (see Typical Operating Characteristics). In software standby mode, the G781 can be forced to perform A/D conversions via the one-shot command, despite the RUN /STOP bit being high. If software standby command is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into either temperature reading register. The previous data is not changed and remains available. Supply-current drain during the 125ms conversion period is always about 320A. Slowing down the conversion rate reduces the average supply current (see Typical Operating Characteristics). In between conversions, the instantaneous supply current is about 25A due to the current consumed by the conversion rate timer. In standby mode, supply current drops to about 3A. At very low supply voltages (under the power-on-reset threshold), the supply current is higher due to the address pin bias currents. It can be as high as 100A, depending on ADD0 and ADD1 settings. SMBus Digital Interface From a software perspective, the SS8018 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, or control bits, A standard SMBus 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. Each A/D channel within the device responds to the same SMBus slave address for normal reads and writes. The SS8018 employs four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte (Figure 3). The shorter Receive Byte protocol allows quicker transfers, provided that the correct data register was previously selected by a Read Byte instruction. Use caution with the shorter protocols in multi-master systems, since a second master could overwrite the command byte without informing the first master. The temperature data format is 11bits plus sign in twos-complement form for remote channel, with each data bit representing 0.125C (Table 2, Table 3), transmitted MSB first. Table 2. Temperature Data Format (Two's-Complement) TEMP. (C)
+127.875 +126.375 +25.5 +1.75 +0.5 +0.125 -0.125 -1.125 -25.5 -55.25 -65.000
SIGN
0 0 0 0 0 0 1 1 1 1 1
DIGITAL OUTPUT DATA BITS MSB LSB
111 111 001 000 000 000 111 111 110 100 011 1111 1110 1001 0001 0000 0000 1111 1110 0110 1000 1111
EXT
111 011 100 110 100 001 111 111 100 110 000
Table 3. Extended Temperature Data Format EXTENDED RESOLUTION
0.000C 0.125C 0.250C 0.375C 0.500C 0.625C 0.750C 0.875C
DATA BITS
0000 0000 0010 0000 0100 0000 0110 0000 1000 0000 1010 0000 1100 0000 1110 0000
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Write Byte Format S ADDRESS
7 bits
WR
ACK
COMMAND
8 bits
ACK
DATA
8 bits
ACK
P
1
Slave Address: equivalent to chip- select line of a 3-wire interface Command Byte: selects which register you are writing to Data byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) Read Byte Format S ADDRESS WR
7 bits
ACK
COMMAND
8bits
ACK
S
ADDRESS
7bits
RD
ACK
DATA
8 bits
///
P
Slave Address: equivalent to chip- select line Command Byte: selects which register you are reading from Slave Address: repeated due to change in data-flow direction Data byte: reads from the register set by the command byte Send Byte Format S ADDRESS
7 bits
WR
ACK
COMMAND
8 bits
ACK
P
Command Byte: sends command with no data , usually used for one-shot command Receive Byte Format S ADDRESS
7 bits
RD
ACK
DATA
8 bits
///
P
Data Byte: reads data from the register commanded by the last Read Byte or Write Byte transmission; also used for SMBus Alert Response return address S = Start condition Shaded = Slave transmission P = Stop condition /// = Not acknowledged Figure 3. SMBus Protocols
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Slave Address The SS8018 appears to the SMBus as one device having a common address for both ADC channels. The SS8018 device address is set to 1001100. The SS8018 also responds to the SMBus Alert Response slave address (see the Alert Response Address section). One-Shot Register The One-shot register is to initiate a single conversion and comparison cycle when the device is in standby mode and auto conversion mode. The write operation to this register causes one-shot conversion and the data written to it is irrelevant and is not stored. Serial Bus Interface Reinitialization When SMBCLK is held low for more than 30ms (typical) during an SMBus communication, the SS8018 will reinitiate its bus interface and be ready for a new transmission. Alarm Threshold Registers Four registers store alarm threshold data, with high-temperature (THIGH) and low-temperature (TLOW ) registers for each A/D channel. If either measured temperature equals or exceeds the corresponding alarm threshold value, an ALERT interrupt is asserted. The power-on-reset (POR) state of both THIGH registers is full scale (01010101, or +85C). The POR state of both TLOW registers is 0C. Diode Fault Alarm There is a fault detector at DXP that detects whether the remote diode has an open-circuit condition. At the beginning of each conversion, the diode fault is checked, and the status byte is updated. This fault detector is a simple voltage detector. If DXP rises above VCC - 1V (typical) due to the diode current source, a fault is detected and the device alarms through pulling ALERT low while the remote temperature reading doesn't update in this condition. Note that the diode fault isn't checked until a conversion is initiated, so immediately after power-on reset the status byte indicates no fault is present, even if the diode path is broken. If the remote channel is shorted (DXP to DXN or DXP to GND), the ADC reads 1000 0000(-128C) so as not to trip either the THIGH or TLOW alarms at their POR settings.
ALERT Interrupts The ALERT interrupt output signal is latched and can only be cleared by reading the Alert Response address. Interrupts are generated in response to THIGH and TLOW comparisons and when the remote diode is disconnected (for fault detection). The interrupt does not halt automatic conversions; new temperature data continues to be available over the SMBus interface after ALERT is asserted. The interrupt output pin is open-drain so that devices can share a common interrupt line. The interrupt rate can never exceed the conversion rate.
The interface responds to the SMBus Alert Response address, an interrupt pointer return-address feature (see Alert Response Address section). Prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. Alert Response Address The SMBus Alert Response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the Alert Response slave address (0001 100). Then any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus (Table 4). The Alert Response can activate several different slave devices simultaneously, similar to the SMBus General Call. If more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address code wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until serviced (implies that the host interrupt input is level-sensitive). Successful reading of the alert response address clears the interrupt latch. Table 4. Read Format for Alert Response Address (0001 100) BIT NAME
7(MSB) 6 5 4 3 2 1 0(LSB) ADD7 ADD6 ADD5 ADD4 ADD3 ADD2 ADD1 1
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Command Byte Functions The 8-bit command byte register (Table 5) is the master index that points to the various other registers within the SS8018. The register's POR state is 0000 0000, so that a Receive Byte transmission (a protocol that lacks the command byte) that occurs immediately after POR returns the current local temperature data. The one-shot command immediately forces a new conversion cycle to begin. In software standby mode ( RUN /STOP bit = high), a new conversion is begun, after which the device returns to standby mode. If a conversion is in progress when a one-shot command is received in auto-convert mode ( RUN /STOP bit = low) between conversions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses. Configuration Byte Functions The configuration byte register (Table 6) is used to mask interrupts and to put the device in software standby mode. The other bits are empty. Table 5. Command-Byte Bit Assignments REGISTER
RLTS RRTE RSL RCL RCRA RLHN RLLI RRHI RRLS WCA WCRW WLHO WLLM WRHA WRLN OSHT RTEXT RTOFS RTOFSEXT RLEXT RHEXT RTTHERM LTTHERM THERMHYST ALERTFQ MFGIO DEVID
Status Byte Functions The status byte register (Table 7) indicates which (if any) temperature thresholds have been exceeded. This byte also indicates whether or not the ADC is converting and whether there is an open circuit in the remote diode DXP-DXN path. After POR, the normal state of all the flag bits is zero, assuming none of the alarm conditions are present. The status byte is cleared by any successful read of the status, unless the fault persists. Note that the ALERT interrupt latch is not automatically cleared when the status flag bit is cleared. When reading the status byte, you must check for internal bus collisions caused by asynchronous ADC timing, or else disable the ADC prior to reading the status byte (via the RUN /STOP bit in the configuration byte). In one-shot mode, read the status byte only after the conversion is complete, which is approximately 125ms max after the one-shot conversion is commanded.
COMMAND
00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h 11h 12h 13h 14h 19h 20h 21h 22h FEh FFh
POR STATE
0000 0000* 0000 0000* N/A 0000 0000 0000 1000 0000 0000 0000 0000 N/A N/A N/A N/A N/A N/A N/A 0 0 0 0 0 0101 0101 (85) 0101 0101 (85) 0000 1010 (10) 0 0100 0111 0000 0001
FUNCTINON
Read local temperature. It returns latest temperature Read remote temperature. It returns latest temperature Read status byte (flags, busy signal) Read configuration byte Read conversion rate byte Read local TLOW limit Read remote TLOW limit Write configuration byte Write conversion rate byte Write local THIGH limit Write local TLOW limit Write remote THIGH limit Write remote TLOW limit One-shot command (use send-byte format) Remote temperature extended byte Remote temperature offset high byte Remote temperature offset extended byte Remote THIGH limit extended byte Remote TLOW limit extended byte Remote temperature THERM limit Local temperature THERM limit
0101 0101 (85) Read local THIGH limit 0101 0101 (85) Read remote THIGH limit
THERM hysteresis
ALERT fault queue code
Manufacturer ID Device ID
*If the device is in standby mode at POR, both temperature registers read 0C.
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Table 6. Configuration-Byte Bit Assignments BIT
7 (MSB) 6 5-0
NAME
MASK
RUN /
POR STATE
0 0 0
FUNCTION
Masks all ALERT interrupts when high. Standby mode control bit. If high, the device immediately stops converting and enters standby mode. If low, the device converts in either one-shot or timer mode. Reserved for future use
STOP RFU
Table 7. Status-Byte Bit Assignments BIT
7 (MSB) 6 5 4 3 2 1 0 (LSB)
NAME
BUSY LHIGH* LLOW* RHIGH* RLOW* OPEN* RTHRM LTHRM
FUNCTION
A high indicates that the ADC is busy converting. A high indicates that the local high-temperature alarm has activated. A high indicates that the local low-temperature alarm has activated. A high indicates that the remote high-temperature alarm has activated. A high indicates that the remote low-temperature alarm has activated. A high indicates a remote-diode continuity (open-circuit) fault. A high indicates a remote temperature THERM alarm has activated. A high indicates a local temperature THERM alarm has activated.
*These flags stay high until cleared by POR, or until the status byte register is read.
Table 8. Conversion-Rate Control Byte DATA
00h 01h 02h 03h 04h 05h 06h 07h 08h 09h to FFh
CONVERSION RATE (Hz)
0.0625 0.125 0.25 0.5 1 2 4 8 16 RFU
When auto-converting, if the THIGH and TLOW limits are close together, it's possible for both high-temp and low-temp status bits to be set, depending on the amount of time between status read operations (especially when converting at the fastest rate). In these circumstances, it's best not to rely on the status bits to indicate reversals in long-term temperature changes and instead use a current temperature reading to establish the trend direction. For bit 1 and bit 0, a high indicates a temperature alarm happened for remote and local diode respectively. The THERM pin also asserts. These two bits wouldn't be cleared when reading status byte. Conversion Rate Byte The conversion rate register (Table 8) programs the time interval between conversions in free-running auto-convert mode. This variable rate control reduces the supply current in portable-equipment applications. The conversion rate byte's POR state is 08h (16Hz). The SS8018 looks only at the 4 LSB bits of this register, so the upper 4 bits are "don't care" bits, which should be set to zero. The conversion rate tolerance is 25% at any rate setting. Valid A/D conversion results for both channels are available one total conversion time (125ms,typical) after initiating a conversion, whether conversion is initiated via the RUN /STOP bit, one-shot command, or initial power-up.
To check for internal bus collisions, read the status byte. If the least significant seven bits are ones, discard the data and read the status byte again. The status bits LHIGH, LLOW, RHIGH, and RLOW are refreshed on the SMBus clock edge immediately following the stop condition, so there is no danger of losing temperature-related status data as a result of an internal bus collision. The OPEN status bit (diode continuity fault) is only refreshed at the beginning of a conversion, so OPEN data is lost. The ALERT interrupt latch is independent of the status byte register, so no false alerts are generated by an internal bus collision.
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POR AND UVLO The SS8018 has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the data in memory and causing erratic behavior, a POR voltage detector monitors VCC and clears the memory if VCC falls below 1.7V (typical, see Electrical Characteristics table). When power is first applied and VCC rises above 1.7V (typical), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC UVLO comparator, prevents the ADC from converting until there is sufficient headroom (VCC= 2.8V typical).
ALERT Fault Queue To suppress unwanted ALERT triggering the G781 embedded a fault queue function. The ALERT won't assert until consecutive out of limit measurements have reached the queue number. The mapping of fault queue register (ALERTFQ, 22h) value to fault queue number is shown in the Table 9.
Operation of The THERM Function A local and remote THERM limit can be programmed into the SS8018 to set the temperature limit above which the THERM pin asserts low and the bit 1, of status byte will be set to 1 corresponding to remote and local over temperature. These two bits won't be cleared to 0 by reading status byte it the over temperature condition remain. A hysteresis value is provided by writing the register 21h to set the temperature threshold to release the THERM pin alarm state, The releasing temperature is the value of register 19h, 20h minus the value in register 21h. The format of register 21h is 2's complement. The THERM signal is open drain and requires a pull-up resistor to power supply.
Table 9. Alert Fault Queue ALERTFQ VALUE
XXXX000X XXXX001X XXXX010X XXXX011X XXXX100X XXXX101X XXXX110X XXXX111X
FAULT QUEUE NUMBER
1 2 3 3 4 4 4 4
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SS8018
A
B tLOW tHIGH
C
D
EF
G
H
I
J
K
L
M
SMBCLK SMBDATA
tSU:STA tHD:STA tSU:DAT tHD:DAT tSU:STO tBUF
Figure 4. SMBus Write Timing Diagram A = start condition B = MSB of address clocked into slave C = LSB of address clocked into slave D = R/W bit clocked into slave E = slave pulls SMBDATA line low F = acknowledge bit clocked into master G = MSB of data clocked into slave H = LSB of data clocked into slave I = slave pulls SMBDATA line low J = acknowledge clocked into master K = acknowledge clocked pulse L = stop condition data executed by slave M = new start condition
A
B t LOW t HIGH
C
D
EF
G
H
I
J
K
SMBCLK SMBDATA
tSU:STA tHD:STA tSU:DAT tSU:STO tBUF
Figure 5. SMBus Read Timing Diagram A = start condition B = MSB of address clocked into slave C = LSB of address clocked into slave D = R/ W bit clocked into slave E = slave pulls SMBDATA line low F =acknowledge bit clocked into master G = MSB of data clocked into master H = LSB of data clocked into master I = acknowledge clocked pulse J = stop condition K= new start condition
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SS8018
n PHYSICAL DIMENSIONS
8 Pin SOP Package
C
E
H
L D 7 X
(4X)
A2 A1 e B
A
y
Feed Direction Typical SOP Package Orientation
Note: 1. Package body sizes exclude mold flash and gate burrs 2. Dimension L is measured in gage plane 3. Tolerance 0.10mm unless otherwise specified 4. Controlling dimension is millimeter converted inch dimensions are not necessarily exact. SYMBOL
A A1 A2 B C D E e H L y ?
MIN.
1.35 0.10 ----0.33 0.19 4.80 3.80 ----5.80 0.40 ----0
DIMENSION IN MM NOM.
1.60 ----1.45 ----------------1.27 -----------------
MAX.
1.75 0.25 ----0.51 0.25 5.00 4.00 ----6.20 1.27 0.10 8
MIN.
0.053 0.004 ----0.013 0.007 0.189 0.150 ----0.228 0.016 ----0
DIMENSION IN INCH NOM.
0.063 ----0.057 ----------------0.050 -----------------
MAX.
0.069 0.010 ----0.020 0.010 0.197 0.157 ----0.244 0.050 0.004 8
Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties.
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