G766 Global Mixed-mode Technology Inc. Remote Temperature Sensor with SMBus Serial Interface Features General Description Single Channel: Measures Remote CPU Tem- The G766 is a precise digital thermometer that reports the temperature of a remote sensor. 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 ±3°C for multiple transistor manufacturers, with no calibration needed. The G766 can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor. perature No Calibration Required SMBus 2-Wire Serial Interface Programmable Under/Overtemperature Alarms Supports SMBus Alert Response Accuracy: ±3°C (+60°C to +100°C, remote) 3µA (typ) Standby Supply Current 300µA (max) Supply Current in Auto- Convert Mode +3V to +5.5V Supply Range Small, 10-Pin MSOP Package The 2-wire serial interface accepts standard System Management Bus (SMBusTM) Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read temperature data. The data format is 7 bits plus sign, with each bit corresponding to 1°C, in twos-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 G766 is available in a small, 10-pin MSOP surface-mount package. Applications Desktop and Notebook Computers Smart Battery Packs LAN Servers Industrial Controls Central Office Telecom Equipment Test and Measurement Multi-Chip Modules Ordering Information Pin Configuration PART* TEMP. RANGE PIN PACKAGE G766 -55°C to +125°C 10-MSOP Typical Operating Circuit 3V TO 5.5V G766 0.1 µF ADD0 1 10 ADD1 2 9 SMBDATA GND 3 8 SMBCLK 200Ω ALERT Vcc DXP STBY SMBCLK SMBDATA DXN 4 7 STBY DXN 2N3904 DXP 6 5 Vcc ALERT 2200pF 10k EACH CLOCK DATA INTERRUPT TO µC ADD0 ADD1 GND 10 Pin MSOP Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 1 G766 Global Mixed-mode Technology Inc. Absolute Maximum Ratings ESD Protection (all pins, human body model)…..2000V Continuous Power Dissipation(TA = +70°C) MSOP (derate 5.6mW/°C above +70°C)….......444mW Operating Temperature Range………-55°C to +125°C Junction Temperature…………………….……..+150°C Storage temperature Range………….-65°C to +165°C Lead Temperature (soldering, 10sec)…….……....+300°C Vcc to GND………….…….……..……….-0.3V to +6V DXP, ADD to GND……..…….…-0.3V to (Vcc + 0.3V) DXN to GND……………..……………..-0.3V to +0.8V SMBCLK, SMBDATA, ALERT , STBY to GND ……………………………………………..…-0.3V to +6V SMBDATA, ALERT Current………….-1mA to +50mA DXN Current……………………..………………….±1mA 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 CONDITIONS MIN TYP MAX UNITS ADC and power supply Temperature Resolution (Note 1) Monotonicity guaranteed Initial Temperature Error, TA = +60°C to +100°C Local Diode (Note 2) TA = 0°C to +85°C Temperature Error, Remote Di- TR = +60°C to +100°C ode (Notes 2 and 3) TR = -55°C to +125°C Temperature Error, Local Diode (Notes 1 and 2) TA = +60°C to +100°C TA = 0°C to +85°C Including long-term drift 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 8 -2 -3 -3 2 3 3 -5 -2.5 -3.5 3.0 5 2.5 3.5 5.5 2.6 1.0 SMBus static Hardware or software standby, SMBCLK at 10kHz Logic inputs forced to Vcc or GND Conversion Time 94 Conversion Rate Timing Error Auto-convert mode -25 Remote-Diode Source Current Address Pin Bias Current 2.8 50 1.7 50 2.95 3 10 2.5 210 125 °C V V mV V mV 156 ms 25 % High level 80 100 120 8 10 160 12 Ver 1.0 Dec 11, 2001 °C µA Low level ADD0, ADD1; momentary upon power-on reset DXP forced to 1.5V °C µA 4 Auto-convert mode, average measured over 4sec. Logic inputs forced 16 conv/sec to VCC or GND From stop bit to conversion complete (both channels) Average Operating Supply Bits µA µA TEL: 886-3-5788833 http://www.gmt.com.tw 2 G766 Global Mixed-mode Technology Inc. Electrical Characteristics (continued) (Vcc = + 3.3V, TA = 0 to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS SMBus Interface Logic Input High Voltage STBY , SMBCLK, SMBDATA; Vcc = 3V to 5.5V Logic Input Low Voltage STBY , SMBCLK, SMBDATA; Vcc = 3V to 5.5V 2.2 0.8 Logic Output Low Sink Current ALERT , SMBDATA forced to 0.4V 6 ALERT Output High Leakage Current Logic Input Current ALERT forced to 5.5V Logic inputs forced to Vcc or GND -1 SMBus Input Capacitance SMBus Clock Frequency SMBCLK Clock Low Time SMBCLK Clock High Time SMBCLK, SMBDATA (Note 4) tLOW , 10% to 10% points tHIGH , 90% to 90% points SMBus Start-Condition Setup Time SMBus Repeated Start-Condition Setup Time tSU : STA , 90% to 90% points SMBus Start-Condition Hold Time tHD: STA , 10% of SMBDATA to 90% of SMBCLK SMBus Start-Condition Setup Time tSD: STO , 90% of SMBDATA to 10% of SMBDATA SMBus Data Valid to SMBCLK Rising-Edge Time SMBus Data-Hold Time SMBCLK Falling Edge to SMBus Data-Valid Time tSU: DAT , 10% or 90% of SMBDATA to 10% of SMBCLK tHD : DAT (Note 5) V V mA 1 µA 1 µA 5 DC 4.7 4 100 pF kHz µs µs 4.7 500 4 4 µs ns µs µs 800 ns 0 µs Master clocking in data 1 µs Electrical Characteristics (Vcc = + 3.3V, TA = -5.5 to + 125°C, unless otherwise noted.) (Note 6) PARAMETER CONDITIONS ADC and power supply Temperature Resolution(Note 1) Initial Temperature Error, Local Diode ( Note 2) Temperature Error, Remote Diode (Notds2 and 3) Supply-Voltage Range Conversion Time Conversion Rate Timing Error SMBus Interface Monotonicity guaranteed 8 TA = +60°C to +100°C TA = -55°C to +125°C TR = +60°C to +100°C TR = -55°C to +125°C -2 -3 -3 -5 2 3 3 5 3.0 5.5 From stop bit to conversion complete Auto-convert mode Logic Input Low Voltage Logic Output Low Sink Current Vcc = 3V Vcc = 5.5V STBY, SMBCLK, SMBDATA; Vcc = 3V to 5.5V ALERT, SMBDATA forced to 0.4V ALERT Output High Leakage Current Logic Input Current Logic inputs forced to Vcc or GND Logic Input High Voltage MIN TYP MAX UNITS STBY, SMBCLK, SMBDATA Bits 62 -25 25 2.2 2.4 0.8 -2 °C V ms % V 6 ALERT forced to 5.5V °C V mA 1 µA 2 µA Note1 : Guaranteed but not 100% tested. Note2 : Quantization error is not included in specifications for temperature accuracy. For example, if the G766 device temperature is exactly +66.7°C, or +68°C (due to the quantization error plus the +1/2°C offset used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to 100°C temperature range. See Table2. Note3 : 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. Note4 : The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus. Note5 : Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of SMBCLK’s falling edge. Note6 : Specifications from -55°C to +125°C are guaranteed by design, not production tested. Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 3 Global Mixed-mode Technology Inc. G766 Pin Description PIN NAME FUNCTION 1 ADD0 2 ADD1 SMBus Slave Address Select pin SMBus Address Select pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance (>50pF) at the address pins when floating may cause address-recognition problems. 3 4 GND DXN 5 DXP 6 Vcc 7 8 9 10 Ground Combined Current Sink and A/D Negative Input. 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. Supply Voltage Input , 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series resistor is recommended but not required additional noise filtering. Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode. Low = standby mode, high = operate mode. SMBCLK SMBus Serial-Clock Input SMBDATA SMBus Serial-Data Input / Output, open drain STBY ALERT SMBus Alert (interrupt) Output, open drain Detailed Description ADC and Multiplexer The ADC is an averaging type that integrates over a 60ms period (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. The G766 (patents pending) 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 power-management or keyboard controller, generating SMBus serial commands by “bit-banging” general-purpose input-output (GPIO) pins or via a dedicated SMBus interface block. Essentially an 8-bit serial analog-to digital converter (ADC) with a sophisticated front end, the G766 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 four over/under-temperature alarm registers. 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. Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 4 G766 Global Mixed-mode Technology Inc. STBY ADD0 ADD1 VCC ADDRESS DECODER MUX DXP 2 + DXN + REMOTE + ADC 7 SMBUS SMBDATA CONTROL LOGIC LOCAL SMBCLK READ WRITE DIODE FAULT 8 8 REMOTE TEMPERATURE DATA REGISTER COMMAND BYTE (INDEX) REGISTER 8 HIGH-TEMPETATURE THRESHOLD (REMOTE HIGH) STATUS BYTE REGISTER LOW-TEMPETATURE THRESHOLD (REMOTE CONFIGURATION BYTE REGISTER ) LOW CONVERSION RATE REGISTER DIGITAL COMPARATOR (REMOTE) ALERT S Q R 8 SELECTED VIA SLAVE ADD = 0001 100 ALERT RESPONSE ADDRESS REGISTER Figure 1. Functional Diagram 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. grated 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 100µA; 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. Remote-Diode Selection Temperature accuracy depends on having a good-quality, diode-connected small-signal transistor. Accuracy has been experimentally verified for all of the devices listed in Table 1. The G766 can also directly measure the die temperature of CPUs and other inte- Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 5 Global Mixed-mode Technology Inc. Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER traces such as +12VDC. Leakage currents from PC board contamination must be dealt with carefully, since a 20MΩ leakage path from DXP to ground causes about +1°C error. MODEL NUMBER Philips PMBS3904 Motorola(USA) National Semiconductor(USA) MMBT3904 MMBT3904 G766 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. Note:Transistors must be diode-connected (base shorted to collector). Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. ADC Noise Filtering The ADC is an integrating type with inherently good noise rejection, especially of low-frequency signals such as 60Hz/120Hz power-supply hum. Micropower operation places constraints on high-frequency noise rejection; therefore, careful PC board layout and proper external noise filtering are required for highaccuracy remote measurements in electrically noisy environments. 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 200µV of voltage error at DXP-DXN to cause a +1°C measurement error. So, most parasitic thermocouple errors are swamped out. 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. 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. 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(see Typical Operating Characteristics). 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 Place the G766 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. PC Board Layout Checklist Place the G766 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- 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. necting to GND. Place the noise filter and the 0.1µF Vcc bypass capacitors close to the G766. Add a 200Ω resistor in series with Vcc for best Route the DXP and DXN traces in parallel and in close proximity to each other, away from any high-voltage noise filtering (see Typical Operating Circuit). Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 6 Global Mixed-mode Technology Inc. Activate hardware standby mode by forcing the STBY pin low. In a notebook computer, this line may be connected to the system SUSTAT# suspend-state signal. The STBY pin low state overrides any software conversion command. If a hardware or 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. GND 10 MILS 10 MILS DXP MINIMUM 10 MILS G766 DXN 10 MILS GND Supply-current drain during the 125ms conversion period is always about 450µA. 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. 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 (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 unterminated. SMBus Digital Interface From a software perspective, the G766 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. 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 + 1°C error. Low-Power Standby Mode Standby mode disables the ADC and reduces the supply-current drain to less than 10µA. Enter standby mode by forcing the STBY pin low or via the RUN/STOP bit in the configuration byte register. Hardware and software standby modes behave almost identically: all data is retained in memory, and the SMB interface is alive and listening for reads and writes. The only difference is that in hardware standby mode, the one-shot command does not initiate a conversion. The G766 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 7bits plus sign in twos-complement form for each channel, with each data bit representing 1°C (Table 2), transmitted MSB first. Measurements are offset by +1/2°C to minimize internal rounding errors; for example, +99.6°C is reported as +100°C. 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 G766 can be forced to perform A/D conversions via the one-shot command, despite the RUN/STOP bit being high. Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 7 G766 Global Mixed-mode Technology Inc. Write Byte Format S ADDRESS ACK WR COMMAND 7 bits ACK DATA 8 bits ACK P 8 bits 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 ACK COMMAND 7 bits ACK S 8bits ADDRESS RD ACK DATA 7bits /// P 8 bits 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 ACK WR COMMAND 7 bits ACK P /// P 8 bits Command Byte: sends command with no data , usually used for one-shot command Receive Byte Format S ADDRESS ACK RD DATA 7 bits 8 bits 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 Table 2. Data Format (Twos-Complement) TEMP. (°C) ROUND TEMP. (°C) +130.00 +127 0 111 1111 +127.00 +126.50 +126.00 +25.25 +127 +127 +126 +25 0 0 0 0 111 111 111 001 1111 1111 1110 1001 +0.50 +0.25 +0.00 -0.25 +1 +0 +0 +0 0 0 0 0 000 000 000 000 0001 0000 0000 0000 -0.50 -0.75 -1.00 -25.00 +0 -1 -1 -25 0 1 1 1 000 111 111 110 0000 1111 1111 0111 -25.50 -54.75 -55.00 -65.00 -25 -55 -55 -65 1 1 1 1 110 100 100 011 0110 1001 1001 1111 -70.00 -65 1 011 1111 registers for each A/D channel. If either measured temperature equals or exceeds the corresponding alarm threshold value, an ALERT interrupt is asserted. DIGITAL OUTPUT DATA BITS SIGN MSB LSB The power-on-reset (POR) state of both THIGH registers is full scale (0111 1111, or +127°C). The POR state of both TLOW registers is 1100 1001 or -55°C. Thermostat Mode Thermostat mode changes the function of the ALERT output from a latched interrupt-type output to a selfclearing thermostat for fan control. This output simply responds to the current temperature. If the current temperature is above THIGH, ALERT activates and does not go inactive until the temperature drops below TLOW. Enable thermostat mode through the configuration register, with one bit to enable the feature and another bit to set the output polarity (active high or active low). The ALERT thermostat comparison is made after each conversion, or at the end of any SMBus transaction. For example, if the limit is changed while the device is in standby mode, the ALERT output responds correctly according to the last valid A/D result. Upon entering thermostat mode, the ALERT output is reset so that if the temperature is in the hysteresis band ALERT initially goes inactive. The power-on reset (POR) state disables thermostat mode. Alarm Threshold Registers Four registers store alarm threshold data, with high-temperature (THIGH) and low-temperature (TLOW ) Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 8 G766 Global Mixed-mode Technology Inc. Diode Fault Alarm ALERT Interrupts There is a continuity 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. 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. 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 continuity 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. If the remote channel is shorted (DXP to DXN or DXP to GND), the ADC reads 0000 0000 so as not to trip either the THIGH or TLOW alarms at their POR settings. In applications that are never subjected to 0°C in normal operation, a 0000 0000 result can be checked to indicate a fault condition in which DXP is accidentally short circuited. Similarly, if DXP is short circuited to VCC, the ADC reads +127°C for both remote and local channels, and the device alarms. 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 3). Table 3. Read Format for Alert Response Address (0001 100) BIT NAME 7(MSB) ADD7 6 ADD6 5 ADD5 4 ADD4 3 ADD3 2 ADD2 1 ADD1 0(LSB) 1 FUNCTION Provide the current G766 slave address that was latched at POR (Table 8) Logic 1 Table 4. Command-Byte Bit Assignments REGISTER COMMAND POR STATE FUNCTINON RLTS 00h 0000 0000* Read local temperature: returns latest temperature RRTE RSL RCL RCRA 01h 02h 03h 04h 0000 0000* N/A 0000 0000 0000 0111 Read remote temperature: returns latest temperature Read status byte (flags, busy signal) Read configuration byte Read conversion rate byte RFU RFU RRHI RRLS 05h 06h 07h 08h N/A N/A 0111 1111 1100 1001 Reserved for future use Reserved for future use Read remote THIGH limit Read remote TLOW limit WCA WCRW WLHO WLLM 09h 0Ah 0Bh 0Ch N/A N/A N/A N/A Write configuration byte Write conversion rate byte Write local THIGH limit Write local TLOW limit WRHA WRLN OSHT 0Dh 0Eh 0Fh N/A N/A N/A Write remote THIGH limit Write remote TLOW limit One-shot command (use send-byte format) *If the device is in hardware standby mode at POR, both temperature registers read 0°C. Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 9 G766 Global Mixed-mode Technology Inc. Configuration Byte Functions The configuration byte register (Table 5) is used to mask (disable) interrupts and to put the device in software standby mode. This register’s contents can be read back over the serial interface. 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. Status Byte Functions The status byte register (Table 6) 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 150ms max after the one-shot conversion is commanded. Command Byte Functions The 8-bit command byte register (Table 4) is the master index that points to the various other registers within the G766. 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. Table 5. Configuration-Byte Bit Assignments BIT NAME POR STATE FUNCTION 7 (MSB) MASK 0 Masks all ALERT interrupts when high. 6 RUN / STOP 0 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. 5 POL 0 4 3 to 0 THERM RFU 0 0 ALERT pin polarity control in thermostat mode. 0 = active low 1 = active high Enables thermostat mode when high. Reserved for future use Table 6. Status-Byte Bit Assignments BIT NAME 7 (MSB) BUSY 6 5 4 3 RFU RFU RHIGH* RLOW* 2 1 0 (LSB) DIODE FAULT RFU RFU FUNCTION A high indicates that the ADC is busy converting. Reserved for future use Reserved for future use 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 fault (open-circuit, shorted diode, or DXP short to GND). Reserved for future use (returns 0) Reserved for future use (returns 0) *These flags stay high until cleared by POR, or until the status byte register is read. Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 10 G766 Global Mixed-mode Technology Inc. Table 7. Conversion-Rate Control Byte DATA CONVERSION RATE (Hz) 00h 0.0125 01h 02h 03h 04h 0.25 0.5 1 2 05h 06h 07h 08h to FFh 4 8 16 RFU sponse slave address (see the Alert Response Address section). 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 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. POR and UVLO The G766 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 1.75V (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). 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. Table 8. Slave Address Decoding (ADD0 and ADD1) Conversion Rate Byte The conversion rate register (Table 7) 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 07h (16Hz). Slave Addresses The G766 appears to the SMBus as one device having a common address for both ADC channels. The device address can be set to one of nine different values by pin-strapping ADD0 and ADD1 so that more than one G766 can reside on the same bus without address conflicts (Table 8). ADD0 ADD1 ADDRESS GND GND GND High-Z GND High-Z Vcc GND 0011 000 0011 001 0011 010 0101 001 High-Z High-Z Vcc Vcc High-Z Vcc GND High-Z 0101 010 0101 011 1001 100 1001 101 Vcc Vcc 1001 110 Note: High-Z means that the pin is left unconnected and floating. Power-Up Defaults: Interrupt latch is cleared. Address select pins are sampled. THIGH and TLOW registers are set to max and min limits, respectively. Device is in normal mode. ( ALERT acts as a latched interrupt output.) The address pin states are checked at POR only, and the address data stays latched to reduce quiescent supply current due to the bias current needed for high-Z state detection. The G766 also responds to the SMBus Alert Re- Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 11 G766 Global Mixed-mode Technology Inc. A B tLOW tHIGH C D G E F H I J K M L SMBCLK SMBDATA tSU:STA tHD:STA tHD:DAT tSU: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 A B tLOW tHIGH 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 C D E F G H J I K SMBCLK SMBDATA tSU:STA tHD:STA tSU:STO tSU:DAT 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 Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 12 G766 Global Mixed-mode Technology Inc. Package Information A 10 A e C L E E1 b 1 DETAIL “A” e 0.076 A2 C SEATING PLANE θ2 A A1 R1 0.25 b D R GAUGE PLANE b b1 θ1 WITH PLATING c1 L θ3 c BASE METAL SYMBOL A A1 A2 b b1 c c1 D E1 e E L θ1 θ2 θ3 R R1 MIN. DIMENSION IN MM NOM. ----0.05 0.81 0.15 0.15 0.13 0.13 2.90 2.90 0.445 0° 0.09 0.09 --------0.86 ----0.20 ----0.15 3.00 3.00 0.50 BSC 4.90 BSC 0.55 ----12 REF 12 REF --------- MAX. MIN. 1.10 0.15 0.91 0.30 0.25 0.23 0.18 3.10 3.10 ----0.002 0.032 0.006 0.006 0.005 0.005 0.114 0.114 0.648 6° 0.0175 0°° --------- 0.004 0.004 JEDEC DIMENSION IN INCH NOM. --------0.034 ----0.008 0.006 0.118 0.118 0.020 BSC 0.193 BSC 0.0217 ----12 REF 12 REF --------- MAX. 0.043 0.006 0.036 0.012 0.010 0.009 0.007 0.122 0.122 0.0255 6° --------- MO-187BA Taping Specification Feed D irection T ypical M S O P P ackage O rientation Ver 1.0 Dec 11, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 13