G781

Global Mixed-mode Technology Inc. ±1°C Remote and Local Temperature Sensor with SMBus Serial Interface Features Two Channels: Measures Both Remote and Local Temperatures No Calibration Required SMBus 2-Wire Serial Interface Programmable Under/Overtemperature Alarms Supports SMBus Alert Response Accuracy: ±1°C (+60°C to +100°C, remote) ±3°C (+60°C to + 100°C, local) 320µA (typ) Average Supply Current During Conversion +3V to +5.5V Supply Range Small 8-Lead SO Package G781 General Description The G781 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 replace conventional thermistors or thermocouples. Remote accuracy is ±1°C 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 0.125°C, 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 G781 is available in a small, 8-pin SOP surface-mount package. Applications Desktop and Notebook Computers Smart Battery Packs LAN Servers Industrial Controllers Central Office Telecom Equipment Test and Measurement Multi-Chip Modules Ordering Information PART* G781 TEMP. RANGE -20°C to +120°C PIN-PACKAGE 8-SOP Pin Configuration Typical Operating Circuit 3V TO 5.5V 0.1µF G781 VCC DXP DXN THERM THERM 1 2 3 4 8 7 6 5 SMBCLK SMBDATA ALERT DXN DXP VCC 10kΩ EACH CLOCK DATA INTERRUPT TO µC SMBCLK SMBDATA ALERT THERM GND GND 2N3904 2200pF 8 Pin SOP Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 1 Global Mixed-mode Technology Inc. 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 G781 body model).……………………………………….2000V ESD Protection (other pins, human body model)..2000V Continuous Power Dissipation (T A = + 70°C) ..SOP (derate 8.30mW/°C above +70°C)…………......667mW Operating Temperature Range………-20°C to +120°C Junction Temperature………………….………..+150°C Storage temperature Range………….-65°C to +165°C Lead Temperature (soldering, 10sec)……..……...+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Electrical Characteristics (VCC = + 3.3V, TA = 0°C to +85°C, 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 VCC, falling edge POR Threshold Hysteresis 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 SMBus static Hardware or software standby, SMBCLK at 10kHz 0.5 conv/sec 8.0 conv/sec CONDITIONS TR = +60°C to +100°C, VCC = 3.0V to 3.6V TR = 0°C to +125°C (Note 2) TA = +60°C to +100°C TA = 0°C to +85°C (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 µA +1 +3 +3 +5 5.5 °C °C V V mV V mV µA ms sec µA From stop bit to conversion complete (both channels) Conversion-Rate Control Byte=04h, 1Hz DXP forced to 1.5V High level Low level Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 2 Global Mixed-mode Technology Inc. Electrical Characteristics (continued) (VCC = + 3.3V, TA = 0 to +85°C, unless otherwise noted.) PARAMETER SMBus Interface Logic Input High Voltage Logic Input Low Voltage Logic Output Low Sink Current ALERT Output High Leakage Current G781 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 µA µA pF kHz ms µs µs µs ns µs µs ns ns µs 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 Logic Input Current SMBus Input Capacitance SMBus Clock Frequency SMBus Timeout SMBCLK Clock Low Time SMBCLK Clock High Time SMBus Start-Condition Setup Time SMBus Repeated Start-Condition Setup Time 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 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 tSU : STA , 90% to 90% points 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. Pin Description PIN 1 2 3 4 5 6 7 8 NAME VCC DXP DXN GND FUNCTION Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF 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. Ground THERM Open-drain output. Requires pull-up to VCC. ALERT SMBus Alert (interrupt) Output, open drain SMBDATA SMBus Serial-Data Input / Output, open drain SMBCLK SMBus Serial-Clock Input Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 3 Global Mixed-mode Technology Inc. Detailed Description The G781 is a temperature sensor designed to work in conjunction with an external microcontroller (µC) or other intelligence in thermostatic, process-control, or monitoring applications. The µC is typically a powermanagement or keyboard controller, generating SMBus serial commands by “bit-banging” generalpurpose input-output (GPIO) pins or via a dedicated SMBus interface block. Essentially an serial analog-to digital converter (ADC) with a sophisticated front end, the G781 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. G781 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 +0.6°C error per ohm. Likewise, 240µV of offset voltage forced on DXP-DXN causes about 1°C error. VCC MUX DXP DXN + + REMOTE LOCAL 2 + ADC CONTROL LOGIC SMBUS 7 SMBDATA SMBCLK DIODE FAULT READ WRITE 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 Figure 1. Functional Diagram Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 4 Global Mixed-mode Technology Inc. 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 goodquality, diode-connected small-signal transistor. The G781 can also directly measure the die temperature 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 10µA; check to ensure this is true at the highest expected temperature. The forward voltage must be less than 0.95V at 300µA; 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 100Ω. 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. Thermal Mass and Self-Heating Thermal mass can seriously degrade the G781’s effective accuracy. The thermal time constant of the SOP- package is about 140 in still air. For the G781 junction temperature to settle to within +1°C after a sudden +100°C 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 G781 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 320µA plus 0.4V x 1mA. Package theta J-A is about 120°C /W, so with VCC = 3.3V and no copper PC board heat-sinking, the resulting temperature rise is: dT = 1.45mW x 120°C /W = 0.17°C Even with these contrived circumstances, it is difficult to introduce significant self-heating errors. 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). ADC Noise Filtering The ADC is an integrating type with inherently good noise rejection. Micropower 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 +1°C to 10°C, depending on the frequency and amplitude. PC Board Layout Place the G781 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. Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 5 Global Mixed-mode Technology Inc. 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 +30°C 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 10MΩ leakage path from DXP to ground causes about +1°C 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 crossunders 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 3µV/°C, and it takes about 240µV of voltage error at DXP-DXN to cause a +1°C measurement error. So, most parasitic thermocouple errors are swamped out. Use wide traces. Narrow ones are more inductive and 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. 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 Place the G781 close to a remote diode. Keep traces away from high voltages (+12V bus). Keep traces away from fast data buses and CRTs. Use recommended trace widths and spacing. Place a ground plane under the traces Use guard traces flanking DXP and DXN and con necting to GND. Place the noise filter and the 0.1µF VCC bypass capacitors close to the G781. GND G781 10 MILS DXP MINIMUM 10 MILS 10 MILS DXN 10 MILS GND Figure 2. Recommended DXP/DXN PC Traces 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 (typi cal) 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 unterminated. 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; 1Ω series resistance introduces about + 0.6°C error. Low-Power Standby Mode Standby mode disables the ADC and reduces the supply-current drain to about 10µA. 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. Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 6 Global Mixed-mode Technology Inc. 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 320µA. Slowing down the conversion rate reduces the average supply current (see Typical Operating Characteristics). In between conversions, the instantaneous supply current is about 25µA due to the current consumed by the conversion rate timer. In standby mode, supply current drops to about 3µA. 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 100µA, depending on ADD0 and ADD1 settings. SMBus Digital Interface From a software perspective, the G781 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 G781 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 0.125°C (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 G781 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 0.000°C 0.125°C 0.250°C 0.375°C 0.500°C 0.625°C 0.750°C 0.875°C DATA BITS 0000 0000 0010 0000 0100 0000 0110 1000 1010 1100 0000 0000 0000 0000 1110 0000 Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 7 Global Mixed-mode Technology Inc. Write Byte Format S ADDRESS 7 bits G781 DATA 8 bits WR ACK COMMAND 8 bits ACK 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 sam pling 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 Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 8 Global Mixed-mode Technology Inc. Slave Address The G781 appears to the SMBus as one device having a common address for both ADC channels. The G781 device address is set to 1001100. The G781 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 are held low for more than 30ms (typical) during an SMBus communication the G781 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 +85°C). The POR state of both TLOW registers is 0°C. 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(-128°C) so as not to trip either the THIGH or TLOW alarms at their POR settings. G781 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 Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 9 Global Mixed-mode Technology Inc. Command Byte Functions The 8-bit command byte register (Table 5) is the master index that points to the various other registers within the G781. 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. G781 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. Table 5. Command-Byte Bit Assignments REGISTER RLTS RRTE RSL RCL RCRA RLHN RLLI RRHI RRLS W CA W CRW W LHO W LLM W RHA W RLN OSHT RTEXT RTOFS RTOFSEXT RLEXT RHEXT RTTHERM LTTHERM THERMHYST ALERTFQ MFGIO DEVID 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 0101 0101 (85) 0000 0000 0101 0101 (85) 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 THIGH limit Read local TLOW limit Read remote THIGH 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 THERM hysteresis ALERT fault queue code Manufacturer ID Device ID *If the device is in standby mode at POR, both temperature registers read 0°C. Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 10 Global Mixed-mode Technology Inc. Table 6. Configuration-Byte Bit Assignments BIT 7 (MSB) 6 5-0 G781 FUNCTION NAME MASK RUN / POR STATE 0 0 0 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. 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 G781 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. Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 11 Global Mixed-mode Technology Inc. POR AND UVLO The G781 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. Table 9. Alert Fault Queue ALERTFQ VALUE XXXX000X XXXX001X XXXX010X XXXX011X XXXX100X XXXX101X XXXX110X XXXX111X G781 Operation of The THERM Function A local and remote THERM limit can be programmed into the G781 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. FAULT QUEUE NUMBER 1 2 3 3 4 4 4 4 Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 12 Global Mixed-mode Technology Inc. G781 H I J K L M A B tLOW tHIGH C D EF G 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 tLOW tHIGH C D EF G H I J K SMBCLK SMBDATA t SU:STA t HD:STA t SU:DAT t SU:STO t BUF 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 Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 13 Global Mixed-mode Technology Inc. Package Information C G781 E H L D θ 7° (4X) A2 y B A1 A e 8 Pin SOP Package 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 θ MIN. 1.35 0.10 ----0.33 0.19 4.80 3.80 ----5.80 0.40 ----0º 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 8º MIN. 0.053 0.004 ----0.013 0.007 0.189 0.150 ----0.228 0.016 ----0º 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 8º Taping Specification Feed Direction Typical SOP Package Orientation GMT Inc. does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and GMT Inc. reserves the right at any time without notice to change said circuitry and specifications. Ver: 1.0 Oct 02, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 14