G768

Global Mixed-mode Technology Inc. G768B Remote/Local Temperature Sensor, 2 Fan Controllers with SMBus Serial Interface and System Reset Circuit Features Measures Two Remote and One Local Temperatures No Calibration Required SMBus 2-Wire Serial Interface Programmable Under/Over-temperature Alarms Supports SMBus Alert Response Accuracy: ±5°C (-40°C to + 125°C, remote) ±3°C (+60°C to + 100°C, remote) +4.5V to +5.5V Supply Range Constant Fan Speed Control Built-in MOSFET switch Internal short-circuit protection PWM control for stable operation Watchdog for fan control Precision Monitoring of 5V Power-Supply Voltage 140ms Min Power-On Reset Pulse Width RESET Output Guaranteed RESET Valid to VCC=1V Power Supply Transient Immunity No External Components needed for reset function Small, 16-Pin SSOP Package General Description The G768B contains a precise digital thermometer, 2 fan controllers, and a system-reset circuit. The G768B is backward compatible with G768, Except that there is an additional watchdog function. This function prevents fan from being out of control when system fails. The thermometer reports the temperature of 2 remote sensors and its own package. The remote sensors are diode-connected transistors typically a low-cost, easily mounted 2N3904 NPN type that replace conventional thermistors or thermocouples. Remote accuracy is ±5°C for multiple transistor manufacturers, 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 (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 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. G768B also contains a 2-channel fan speed controller. It connects directly to the fans and performs closed-loop control of the fan speed independently. The only external component required is a 10µF capacitor per channel. It determines the current fan speed based on the fan rotation pulses and an externally supplied clock. (To be continued) Applications Desktop and Notebook Central Office Computers Telecom Equipment Smart Battery Packs Test and Measurement LAN Servers Multi-Chip Modules Industrial Controls Pin Configuration G768B OUT1 Vcc DXP1 DXN DXP2 RESET GND GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 OUT2 Vcc SMBCLK FG2 SMBDATA ALERT FG1 CLK Ordering Information PART* G768B TEMP. RANGE -10°C to +85°C PIN-PACKAGE 16SSOP 16Pin SSOP Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 1 Global Mixed-mode Technology Inc. It uses pulse width modulation (PWM) method and an on-chip MOSFET to control the fan speed to ±2% of the programmed speed. The desired fan speed is also programmed via SMBusTM. The actual fan speed and fan status can be read via the SMBusTM. Short-circuit protection is implemented to prevent damages to the fan and this IC itself. The G768B also turns on the fans by hardware watchdog system. The fan controller would fully turn on both fans when one of the following conditions happens. 1. when either of the remote temperature is higher than its own TMAX. 2.when either of these two remote diodes is open. 3.when both remote diodes are short G768B The G768B also contains a microprocessor (µP) supervisory circuit used to monitor the power supplies in µP and digital systems. They provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 5V-powered circuits. This circuit asserts a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 140ms after VCC has risen above the reset threshold. The G768B has an active-low RESET output. The reset comparator is designed to ignore fast transients on VCC. Reset threshold of this circuit is set to 4.38V. The G768B is available in a small, 16-pin SSOP surface-mount package. Typical Operating Circuit 10µF IN OUT1 OUT2 10µF IN FAN1 FG FG1 FG2 10µF VCC 10µF VCC FAN2 FG 10k EACH G768B DXP1 DXN SMBCLK SMBDATA ALERT CLK 2N3904 2200pF DXP2 SMBCLK SMBDATA INTERRUPT INTERRUPT TO µC CLOCK 32.768kHz 2N3904 2200pF RESET RESET µP GND Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 2 Global Mixed-mode Technology Inc. Absolute Maximum Ratings Vcc to GND……………….………….…….-0.3V to +6V DXP1, DXP2 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)….…………………………….4000V G768B ESD Protection (other pins, human body model).2000V Continuous Power Dissipation (T A= +70°C) SSOP (de-rate 8.30mW/°C above +70°C)…….………667mW Operating Temperature Range………-10°C to +85°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 = + 5V, TA = 60°C, unless otherwise noted.) PARAMETER Temperature Sensor Temperature Resolution(Note 1) CONDITIONS Monotonicity guaranteed MIN TYP MAX UNITS 8 -5 -3 5 3 3.5 5 2.8 50 1.7 50 3 200 250 300 94 -25 120 15 4.5 125 160 20 5 2 0.2 0.5 0.8 2.4 350 1.8 0.7 1.1 300 350 156 25 200 25 5.5 5 0.25 µA ms % µA 5.5 2.95 2.5 10 µA Bits °C °C V V mV V mV Temperature Error, Remote Diode (Notes 2 TR = 0°C to +125°C and 3) TR = 60°C to +100°C Temperature Error, Local Diode (Notes 1 and 2) Supply-Voltage Range Under-voltage Lockout Threshold Under-voltage Lockout Hysteresis Power-On Reset Threshold POR Threshold Hysteresis Standby Supply Current Vcc input, disables A/D conversion, rising edge Vcc , falling edge SMBus static Logic inputs forced to Vcc or Hardware or software GND standby, SMBCLK at 10kHz Auto-convert mode, average 0.25 conv/sec measured over 4sec. Logic 2.0 conv/sec inputs forced to Vcc or GND From stop bit to conversion complete(all channels) Auto-convert mode DXP forced to 1.5V High level Low level VCC Both fans’ speed = 0rpm Each channel Each channel VIL VIH Each channel VCC=5V VCC=5V VCC=5V Including long-term drift TA = +60°C to +100°C -3.5 4.5 2.6 1.0 Average Operating Supply Current Conversion Time Conversion Rate Timing Error Remote-Diode Source Current Fan Controller Supply voltage Shutdown current MOSFET on resistance Short-circuit current limit Input logic low Input logic high Average Output current FG input Positive-going threshold voltage FG input Negative-going threshold voltage FG input Hysteresis voltage V µA Ω A V V mA V V V Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 3 Global Mixed-mode Technology Inc. Electrical Characteristics (continued) (Vcc = + 5V, TA = 60°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 Logic Input Current SMBus Input Capacitance SMBus Clock Frequency 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 Start-Condition Setup Time SMBus Data Valid to SMBCLK Rising-Edge Time SMBus Data-Hold Time SMBCLK Falling Edge to SMBus Data-Valid Time G768B MIN 2.4 0.8 6 1 -2 5 DC 4.7 4 4.7 500 4 4 800 0 1 100 2 CONDITIONS SMBCLK, SMBDATA; Vcc = 4.5V to 5.5V SMBCLK, SMBDATA; Vcc = 4.5V to 5.5V ALERT , SMBDATA forced to 0.4V ALERT forced to 5.5V Logic inputs forced to Vcc or GND SMBCLK, SMBDATA (Note 4) 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 SMBDATA to 10% of SMBDATA tSU: DAT , 10% or 90% of SMBDATA to 10% of SMBCLK tHD : DAT(Note 5) Master clocking in data TYP MAX UNITS V V mA µA µA pF kHz µs µs µs ns µs µs ns µs µs Electrical Characteristics (continued) (VCC =full range, TA= 60°C, unless otherwise noted.) PARAMETER Reset Threshold Reset Active Timeout Period RESET Output Voltage Low RESET Output Voltage High SYMBOL VTH VOL VOH CONDITIONS MIN 4.2 TYP 4.4 340 MAX 4.5 0.4 UNITS V ms V V VCC=VTH min ISINK =3.2mA VCC>VTH max ISOURCE =5.0mA VCC-1.5 Note 1: Guaranteed but not 100% tested. Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the G768B 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 ±3°C error limits for the +60°C to +100°C temperature range. See Table3. Note 3: A remote diode is any diode-connected transistor from Table1. TR is the junction temperature of the remote diode. See Remote Diode Selection for remote diode forward voltage requirements. Note 4: 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. Note 5: 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. Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 4 Global Mixed-mode Technology Inc. Pin Description PIN 1 2,15 3 G768B NAME OUT1 Vcc DXP1 FUNCTION PWM output, connect to fan 1 Supply Voltage Input , 4.5V to 5.5V. Bypass to GND with a 0.1µF capacitor. Combined Current Source and A/D Positive Input for remote-diode channel 1. Do not leave DXP1 floating; tie DXP1 to DXN if no remote diode on channel 1 is used. Place a 2200pF capacitor between DXP1 and DXN for noise filtering. Combined Current Sink and A/D Negative Input. DXN is common negative node of both remote diodes on channel 1 and 2. The traces of DXP1-DXN and DXP2-DXN pairs should be routed independently. The common DXN should be connected together as close as possible to the IC. DXN is internally connected to the GND pin for signal ground use. Combined Current Source and A/D Positive Input for remote-diode channel 2. Do not leave DXP2 floating; tie DXP2 to DXN if no remote diode on channel 2 is used. Place a 2200pF capacitor between DXP2 and DXN for noise filtering. RESET Output remains low while VCC is below the reset threshold, and for 240ms after VCC rises above 4 DXN 5 DXP2 6 7,8 9 10 11 12 13 14 16 RESET GND CLK FG1 ALERT SMBDATA FG2 SMBCLK OUT2 the reset threshold. Ground Clock input for fan speed measurement. Fan1 pulse input. SMBus Alert (interrupt) Output, open drain. SMBus Serial-Data Input / Output, open drain. Fan2 pulse input. SMBus Serial-Clock Input. PWM output, connect to fan 2. Detailed Description The G768B (patents pending) is a 4-in-1 IC. It consists of one temperature sensor, 2 fan speed controllers and provides system-reset function. The temperature sensor is designed to work in conjunction with an external micro-controller (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 a 12-bit serial analog-to-digital converter (ADC) with a sophisticated front end, the G768B contains a switched current source, a multiplexer, an ADC, an SMBus interface, 2 fan controllers, a reset circuit 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. 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. All channels are converted automatically once the conversion process has started, either in free-running or single-shot mode. If one of the three channels is not used, the device still performs all measurements, and the user can simply ignore the results of the unused channel. If the remote diode channel is unused, tie DXPx to DXN rather than leaving the pins open. The DXN input is internally connected to the ground node inside the chip to set up the analog to digital (A/D) inputs for a differential measurement. The worst-case DXP-DXN differential input voltage range is 0.25V to 0.95V. Excess resistance in series with the remote diode causes about +1/2°C error per ohm. Likewise, 200µV of offset voltage forced on DXP-DXN causes about 1°C error. Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 5 Global Mixed-mode Technology Inc. G768B CLK FAN CONTROL OUT2 FG2 OUT1 FG1 FAN CONTROL VCC CONTROL LOGIC SMBUS REGISTERS SMBCLK SMBDATA ALERT DXP1 DXP2 DXP2 DXN + + MUX + INTERNAL GROUND + ADC RESET CIRCUIT RESET Fig 1. Functional Diagram A/D Conversion Sequence If a Start command is written (or generated automatically in the free-running auto-convert mode), all three channels are converted, and the results of all 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. Accuracy has been experimentally verified for all of the devices listed in Table 1. The G768B 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 200A; 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 G768B's effective accuracy. The thermal time constant of the SSOP-16 package is about 140sec in still air. For the G768B 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 current across the sensor package do not interfere with measurement accuracy. Self-heating can significantly affect the 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, and both fans are working at low speeds. Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER Philips Motorola(USA) National Semiconductor(USA) MODEL NUMBER PMBS 3904 MMBT3904 MMBT3904 Note:Transistors must be diode-connected (base short -ed to collector). Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 6 Global Mixed-mode Technology Inc. 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. 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 +1°C to 10°C, depending on the frequency and amplitude (see Typical Operating Characteristics). PC Board Layout Place the G768B 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 +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 20MΩ leakage path from DXP to ground causes about +1°C error. Route the 2 pairs of DXP1-DXN and DXP2-DXN traces independently (Figure 2a). Connect the common DXN as close as possible to the DXN pin on IC (Figure 2a). Connect guard traces to GND on either side of the DXP-DXN traces (Figure 2b). 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 200µV of voltage error at DXP-DXN to cause a +1°C measurement error. So, most parasitic thermocouple Ver 1.3 Oct 28, 2002 G768B 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 steelwork will. Placing a copper ground plane between the DXP-DXN traces and traces carrying high-frequency noise signals do not help reduce EMI. PC Board Layout Checklist Place the G768B 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 connecting to GND. Route two DXPx-DXN pairs independently Connect the common DXN as close as possible to the DXN pin on IC. Place the noise filter and the 0.1F Vcc bypass capacitors close to the G768B. GND DXP1 DXP1 DXN DXP1 DXN G768B DXN DXP2 DXP2 GND Chip Boundary Fig 2(a) Connect the common DXN as close as possible to the DXN pin on IC. GND 10 MILS 10 MILS DXP MINIMUM 10 MILS DXN 10 MILS GND Fig 2 (b) Recommended DXP/DXN PC TEL: 886-3-5788833 http://www.gmt.com.tw 7 Global Mixed-mode Technology Inc. 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. 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 via the RUN/STOP bit in the configuration byte register. In standby mode, all data is retained in memory, and the SMB interface is alive and listening for reads and writes. This is valid for temperature sensor only. 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 G768B can be forced to perform temperature measurement via the one-shot command, despite the RUN/STOP bit being high. Supply-current drain during the 125ms conversion period is always about 500µA. 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). Fan Controller The fan speed is measured by counting the number of the CLK pin period between the rising edges of two fan speed pulses on FG pin. In this way, we are actually measuring the period of the fan speed. To avoid the cost of doing division to obtain the speed, this count number, N, is used in the PWM control algorithm, thus, the desired fan speed should be programmed by writing the corresponding count number. The count number is given by: G768B N = (CLK x 30) / (rpm x P) N : Count Number P : FG pulses number per revolution of fan. For CLK = 32768Hz, P = 2 ⇒N = 491520 / rpm For CLK = 16384Hz, P = 2 ⇒N = 245762 / rpm Some selected count numbers are shown below Table 2. Count numbers for P=2 rpm 968 1935 2000 3000 4000 5000 6000 7000 8000 9000 10000 20000 30000 CLK=32768Hz --254 246 164 123 98 82 70 61 55 49 25 16 CLK=16384Hz 254 127 123 82 61 49 41 35 31 27 25 12 8 To stop the fan, program the fan speed register to 255. This also makes the fan controller into power saving mode. Controlling Fan at Lower Speed For stably controlling fans at lower rotataion speed, three schemes are recommended as below: 1.Use larger decoupling capacitors between FAN_OUT and GND. 2.Shunt a capacitor of 1µF-2µF on FG pin to GND. 3.Use fans with open-collector FG outputs. When controlling fans under lower rotation speed, the output voltage of FAN_OUT would be too low for fan to generate recognizable FG signals. Using decouple capacitors on FAN_OUT and FG is to increase the SNR on FG pins. While Using fans with open-collector FG outputs can thoroughly solve the problem, because the logic high level of FG would be fixed to 5V. Reset Immunity Negative-Going VCC Transients In addition to issuing a reset to the microprocessor (µP) during power-up, power-down, and brownout conditions, the G768B is relatively immune to short duration negative-going VCC transients (glitches). Typically, for the G768B, a VCC transient that goes 100mV below the reset threshold and lasts 20µs or less will not cause a reset pulse. A 0.1µF bypass capacitor mounted as close as possible to the VCC pin provides additional transient immunity. Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 8 Global Mixed-mode Technology Inc. Ensuring a Valid Reset Output Down to VCC = 0V W hen VCC falls below 1V, the G768B RESET output no longer sinks current-it becomes an open circuit. Therefore, high-impedance CMOS logic inputs connected to RESET can drift to undetermined voltages. This presents no problem in most applications, since most µP and other circuitry is inoperative with VCC below 1V. However, in applications where RESET must be valid down to 0V, adding a pull-down resistor to RESET causes any stray leakage currents to flow to ground, holding RESET low (Figure 3). R1's value is not critical; 100kΩ is large enough not to load RESET and small enough to pull RESET to ground. Interfacing to Ps with Bi-directional Reset Pins Ps with bi-directional reset pins (such as the Motorola 68HC11 series) can connect to the G768B reset output. If, for example, the G768B RESET output is asserted high and the µP wants to pull it low, indeterminate logic levels may result. To correct this, connect a 4.7kΩ resistor between the G768B RESET output and the µP reset I/O (Figure 4). Buffer the G768B RESET output to other system components. Benefits of Highly Accurate Reset Threshold Most µP supervisor Ics have reset threshold voltages between 5% and 10% below the value of nominal supply voltages. This ensures a reset will not occur within 5% of the nominal supply, but will occur when the supply is 10% below nominal. When using Ics rated at only the nominal supply ±5% this leaves a zone of uncertainty where the supply is between 5% and 10% low, and where the reset may or may not be asserted. The G768B use highly accurate circuitry to ensure that reset is asserted close to the 5% limit, and long before the supply has declined to 10% below nominal. G768B SMBus Digital Interface From a software perspective, the G768B appears as a set of byte-wide registers that contain temperature data, alarm threshold values, fan speed data, 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 and fan control channel within the device responds to the same SMBus slave address for normal reads and writes. The G768B employs four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte (Figure 5). 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 over-write 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 (Table3), 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. BUFFER BUFFERED RESET TO OTHER SYSTEM COMPONENTS VCC VCC 4.7k G768B RESET µP RESET GND GND Fig 4. Interfacing to µPs with Bi-directional Reset I/O VCC G768B RESET R1 100k GND Fig 3. RESET Valid to VCC = Ground Circuit Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 9 Global Mixed-mode Technology Inc. Write Byte Format S Address 7 bits G768B 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 sampling rate) Read Byte Format S Address WR 7 bits ACK Command 8 bits ACK S Address 7 bits 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 Fig 5. SMBus Protocols Table 3. Data Format (Twos-Complement) ROUND DIGITAL OUTPUT TEMP. TEMP. DATA BITS (°C) (°C) SIGN MSB LSB +130.00 +127.00 +126.50 +126.00 +25.25 +0.50 +0.25 +0.00 -0.25 -0.50 -0.75 -1.00 -25.00 -25.50 -54.75 -55.00 -65.00 -70.00 +127 +127 +127 +126 +25 +1 +0 +0 +0 +0 -1 -1 -25 -25 -55 -55 -65 -65 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 111 111 111 111 001 000 000 000 000 000 111 111 110 110 100 100 011 011 1111 1111 1111 1110 1001 0001 0000 0000 0000 0000 1111 1111 0111 0110 1001 1001 1111 1111 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 (0111 1111, or +127°C). The POR state of both TLOW registers is 1100 1001 or -55°C. Diode Fault Alarm 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. Ver 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 10 Global Mixed-mode Technology Inc. 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. 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 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 Table 4. Command-Byte Bit Assignments REGISTER RRTE2 RRTE1 RSL RCL RCRA RRHI2 RRLS2 RRHI1 RRLS1 W CA W CRW W RHA2 W RLN2 W RHA1 W RLN1 OSHT SET_CNT1 ACT_CNT1 FAN_STA1 SET_CNT2 ACT_CNT2 FAN_STA2 CHIP_TMP TMAX1 THYST1 TMAX2 THYST2 G768B rupt output pin is open-drain so that device 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. COMMAND 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h 11h 12h 20h 21h 22h 30h 31h 32h 33h 34h POR STATE 0000 0000b 0000 0000b N/A 0000 0000b 0000 0010b 0111 1111b (127) 1100 1001b(-55) 0111 1111b (127) 1100 1001b (-55) N/A N/A N/A N/A N/A N/A N/A 1111 1111b 1111 1111b 10b 1111 1111b 1111 1111b 10b 0000 0000b 0100 0110b (70) 0011 1100b (60) 0100 0110b (70) 0011 1100b (60) FUNCTION Read 2nd remote temperature: returns latest temperature Read 1st remote temperature: returns latest temperature Read status byte (flags, busy signal) Read configuration byte Read conversion rate byte Read 2nd remote THIGH limit Read 2nd remote TLOW limit Read 1st remote THIGH limit Read 1st remote TLOW limit Write configuration byte Write conversion rate byte Write 2nd remote THIGH limit Write 2nd remote TLOW limit Write 1st remote THIGH limit Write 1st remote TLOW limit One-shot command (use send-byte format) Write 1st fan programmed speed register Read 1st fan actual speed register Read 1st fan status register Write 2nd fan programmed speed register Read 2nd fan actual speed register Read 2nd fan status register On-chip temperature 1st remote Tmax 1st remote Thyst 2nd remote Tmax 2nd remote Thyst 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 Ver: 1.3 Oct 28, 2002 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. TEL: 886-3-5788833 http://www.gmt.com.tw 11 Global Mixed-mode Technology Inc. Command Byte Functions The 8-bit command byte register (Table 4) is the master index that points to the various other registers within the G768B. 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. Thermal Configuration Byte Functions The configuration byte register (Table 5) is used to mask (disable) interrupts and to put the device in software standby mode. The lower six bits are internally set to (XX1111), making them "don't care" bits. Write Table 5. Configuration-Byte Bit Assignments BIT NAME POR STATE 7 (MSB) 6 5-0 MASK RUN / STOP G768B zeros to these bits. This register's contents can be read back over the serial interface. Thermal Status Byte Functions The thermal status byte register (02h) (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 DXPx-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. FUNCTION 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 RFU Table 6. Status-Byte Bit Assignments BIT 7(MSB) 6 5 4 3 2 1 0(LSB) NAME BUSY RHIGH2* RLOW2* RHIGH1* RLOW1* OPEN* RFU RFU FUNCTION A high indicates that the ADC is busy converting. A high indicates that the 2nd diode high-temperature alarm has activated. A high indicates that the 2nd diode low-temperature alarm has activated. A high indicates that the 1st diode high-temperature alarm has activated. A high indicates that the 1st diode low-temperature alarm has activated. A high indicates a remote-diode continuity (open-circuit) fault. 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. Table 7. Conversion-Rate Control Byte DATA 00h 01h 02h 03h 04h 05h 06h 07h 08h to FFh CONVERSION RATE (Hz) 0.0625 0.125 0.25 0.5 1 2 4 8 RFU Temperature Sensor Average Supply Current (µA TYP, at Vcc = 5V) 30 33 35 48 70 128 225 425 - Ver: 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 12 Global Mixed-mode Technology Inc. Table 8. RLTS and RRTE Temp Register Update Timing Chart OPERATING MODE Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert Auto-Convert G768B TIME UNTIL RLTS AND RRTE ARE UPDATED 156ms max 156ms max When current conversion is complete (1-shot is ignored) 20sec 10sec 5sec 2.5sec 1.25sec 625ms 312.5ms 237.5ms 156ms 156ms CONVERSION INITIATED BY: Power-on reset 1-shot command, while idling between automatic conversions 1-shot command that occurs during a conversion Rate timer Rate timer Rate timer Rate timer Rate timer Rate timer Rate timer Rate timer NEW CONVERSION RATE (CHANGED VIA WRITE TO CRW) N/A (0.25Hz) N/A N/A 0.0625Hz 0.125Hz 0.25Hz 0.5Hz 1Hz 2Hz 4Hz 8Hz N/A N/A Software Standby RUN/STOP bit Software Standby 1-shot command 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. 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. Temperature 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 02h (0.25Hz). The G768B looks only at the 3 LSB bits of this register, so the upper 5 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 all channels are available one total conversion time (125ms nominal, 156ms Ver: 1.3 Oct 28, 2002 156ms maximum) after initiating a conversion, whether conversion is initiated via the RUN/STOP bit, one-shot command, or initial power-up. Changing the conversion rate can also affect the delay until new results are available. See Table 8. Programmed fan speed register The programmed fan speed registers (10h for fan 1, 20h for fan 2) are read/write registers. They contain the count number of the desired fan speed. Power up default is FFh. Actual fan speed register The actual fan speed registers (11h for fan 1, 21h for fan 2) are read only. They contain the count number of the actual fan speed. Power up default is FFh. Fan status register The fan status registers (12h for fan1, 22h for fan 2) are read only. Its bit 0 is set to 1 when the actual fan speed is ±20% outside the desired speed. Its bit 1 is set to 1 when fan speed is below 1920 rpm. Power up default is 0000_0010b. Watchdog for fan control Four temperature threshold registers intervene the control of fans. Both pin OUT1 and pin OUT2 go high when one of the remote temperature, DX1 and DX2, rises above the respective Tmax. The control is not released until both temperature values drop below their Thyst. Besides, the fan controller also fully turns on both fans when either of the two remote diodes is open or both are short. The power-up default values for Tmax and Thyst are +70°C and +60°C, respectively. This allows the G768B to be used in the occasion when system fails and loses the fan control of G768B. TEL: 886-3-5788833 http://www.gmt.com.tw 13 Global Mixed-mode Technology Inc. Slave Addresses The G768B appears to the SMBus as one device having a common address for all the ADC and fan control channels. The device address is fixed to be 7Ah for write and 7Bh for read. The G768B also responds to the SMBus Alert Response slave address (see the Alert Response Address section). POR and UVLO The G768B has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the Power-Up Defaults: Interrupt latch is cleared. ADC begins auto /converting at a 0.25Hz rate. Command byte is set to 00h to facilitate quick re- G768B 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). mote Receive Byte queries. THIGH and TLOW registers are set to max and min limits, respectively. 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 6. 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 tSU:STA tHD :STA tSU:DAT tSU:STO tBUF Figure 7. 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 Ver: 1.3 Oct 28, 2002 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 TEL: 886-3-5788833 http://www.gmt.com.tw 14 Global Mixed-mode Technology Inc. Package Information C G768B E1 E L D θ 7° (4X) A2 e b A1 A y Note: 1. Package body sizes exclude mold flash and gate burrs 2. Dimension L is measured in gage plane 3. Tolerance 0.10mm unless other wise specified 4. Controlling dimension is millimeter converted inch dimensions are not necessarily exact. SYMBOLS A A1 A2 b C D E E1 e L y θ MIN 1.35 0.10 ----0.20 0.19 4.80 5.80 3.80 ----0.40 ----0º DIMENSION IN MM NOM 1.60 ----1.45 0.25 ----------------0.64 ------------- MAX 1.75 0.25 ----0.30 0.25 5.00 6.20 4.00 ----1.27 0.10 8º MIN 0.053 0.004 ----0.008 0.007 0.189 0.228 0.150 ----0.016 ----0º DIMENSION IN INCH NOM 0.064 ----0.057 0.010 ----------------0.025 ------------- MAX 0.069 0.010 ----0.012 0.010 0.197 0.244 0.157 ----0.050 0.004 8º Taping Specification Feed Direction Typical SSOP 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: 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 15