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Global Mixed-mode Technology Inc.
Two Remote Temperature Sensors and One Fan Controller with SMBus Serial Interface and System Reset Circuit
Features
Measures Two Remote Temperatures No Calibration Required SMBus 2-Wire Serial Interface Programmable Under/Over-temperature Alarms Programmable Thermal Shutdown Signal Supports SMBus Alert Response Accuracy: 5C (-40C to + 125C, remote) 3C (+60C to + 100C, remote) +4.5V to +5.5V Supply Range Fan speed control range: 3,000 to 30,000 rpm Fan speed accuracy: 2% Built-in MOSFET switch Internal current-limit and over-temperature protection for fan control Watchdog for fan control Alarm for fan failure Precision Monitoring of 5V Power-Supply Voltage 340ms Typical 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
G768D
General Description
The G768D contains a precise digital thermometer, a fan controller, and a system-reset circuit. Except for one less fan controller, G768D is backward compatible with G768B. G768D has 2 more functions, fan-failure detection and programmable thermal shutdown signal. The thermometer reports the temperature of 2 remote sensors. 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 5C 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 1C, 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. G768D also contains a 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 10F capacitor per channel. It determines the current fan speed based on the fan rotation pulses and an externally supplied 32.768KHz clock.
Applications
Desktop and Notebook Central Office Computers Telecom Equipment Smart Battery Packs Test and Measurement LAN Servers Multi-Chip Modules Industrial Controls
Pin Configuration
G768D
FANVCC Vcc DXP1 DXN DXP2 RESET DGND AGND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 TH_SHUT Vcc SMBCLK NC SMBDATA ALERT FG CLK
Ordering Information
PART NUMBER
G768D
TEMP. RANGE
-55C to +125C
PIN-PACKAGE
16SSOP
16Pin SSOP
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It uses LDO 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 accepted frequency of fan rotation pulses is 100~1000Hz, which corresponds to 3,000 to 30,000 rpm for a typical fan that produces two pulses per revolution. The G768D also turns on the fans by hardware watchdog system. The fan controller would fully turn on the fan when any 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.
G768D
The G768D also contains a microprocessor (P) supervisory circuit used to monitor the power supplies in P 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 G768D 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 4.4V typical. The G768D is available in a small, 16-pin SSOP surface-mount package.
Typical Operating Circuit
IN 1F FANVCC TH_SHUT
FAN1
FG FG
VCC
10F 10k EACH
G768D
DXP1 DXN SMBCLK SMBDATA ALERT CLK 2N3904 2200pF DXP2 SMBCLK SMBDATA INTERRUPT TO C CLOCK 32.768kHz
2N3904
2200pF
RESET
RESET
P
GND
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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 C L K , F G , S M B C L K , S M B D A T A , ALERT t o GND................................................-0.3V to +6V SMBDATA, ALERT Current...............-1mA to +50mA DXN Current.............................................1mA ESD Protection (SMBCLK, SMBDATA, ALERT , hu-
G768D
man body model)...........................................2000V ESD Protection (other pins, human body model)...2000V Continuous Power Dissipation (T A= +70C) SSOP (de-rate 8.30mW/C above +70C)............667mW Operating Temperature Range...-55C to +125C Junction Temperature......................+150C Storage temperature Range.........-65C to +165C Lead Temperature (soldering, 10sec)..........+300C
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 = 60C, unless otherwise noted.) PARAMETER
Temperature Sensor Temperature Resolution (Note 1)
CONDITIONS
Monotonicity guaranteed
MIN TYP MAX UNITS
8 -5 -3 5 3 3 5 2.8 50 1.7 50 3 200 250 300 94 -25 120 15 4.5 125 160 20 5 2 0.2 0.5 300 350 156 25 200 25 5.5 5 0.25 0.7. 1.0 32.768 600 500 A ms % A 5.5 2.95 2.5 10 A Bits C C V V mV V mV
Temperature Error, Remote Diode (Notes 2 TR = 0C to +125C and 3) TR = 60C to +100C 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 Fan speed = 0rpm Including long-term drift TA = +60C to +100C
-3 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 Clock frequency FANVCC over-current trig FANVCC current limit FG input Positive-going threshold voltage FG input Negative-going threshold voltage FG input Hysteresis voltage
V A A V V KHz mA mA
VIL VIH CLK
VCC=5V VCC=5V VCC=5V
1 0.7 0.3
V V V
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Electrical Characteristics (continued)
(VCC = + 5V, TA = 60C, 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 RisingEdge Time SMBus Data-Hold Time SMBCLK Falling Edge to SMBus Data-Valid Time
G768D
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 A A pF KHz s s s ns s s ns s s
Electrical Characteristics (continued)
(VCC =full range, TA= 60C, 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 G768D device temperature is exactly +66.7C, or +68C (due to the quantization error plus the +1/2C offset used for rounding up) and still be within the guaranteed 3C error limits for the +60C to +100C 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.
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Pin Description
PIN
1 2,15 3
G768D
NAME
FANVCC VCC DXP1
FUNCTION
Output connected to VCC of fan. Supply Voltage Input, 4.5V to 5.5V. Bypass to GND with a 0.1F 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 340ms after VCC rises above
4
DXN
5
DXP2
6 7 8 9 10 11 12 13 14 16
RESET
DGND AGND CLK FG ALERT SMBDATA NC SMBCLK TH_SHUT
the reset threshold. Digital Ground. Analog Ground. 32.768KHz clock input for fan controller. Fan pulse input. SMBus Alert (interrupt) Output, open drain. SMBus Serial-Data Input / Output, open drain. SMBus Serial-Clock Input. Thermal Shutdown Output, push-pull output.
Detailed Description The G768D (patents pending) is a 3-in-1 IC. It consists of one temperature sensor, 1 fan speed controller and provides system-reset function. The temperature sensor is designed to work in conjunction with an external micro-controller (C) or other intelligence in thermostatic, process-control, or monitoring applications. The C is typically a powermanagement or keyboard controller, generating SMBus serial commands by "bit-banging" general-purpose input-output (GPIO) pins or via a dedicated SMBus interface block. Essentially a 12-bit serial analog-to-digital converter (ADC) with a sophisticated front end, the G768D contains a switched current source, a multiplexer, an ADC, an SMBus interface, one fan controller, 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). The multiplexer automatically steers bias currents through two remote 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 two 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 +1/2C error per ohm. Likewise, 200V of offset voltage forced on DXP-DXN causes about 1C error.
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FANVCC FG THERMAL SHUTDOWN LOGIC
G768D
TH_SHUT
FAN CONTROL
VCC
VCC
CLK CONTROL LOGIC SMBUS REGISTERS
SMBCLK SMBDATA ALERT
DXP1 DXP2 DXN
+ + MUX + ADC RESET CIRCUIT RESET
INTERNAL GROUND
Fig 1. Functional Diagram A/D Conversion Sequence If a Start command is written (or generated automatically in the free-running auto-convert mode), both two channels are converted, and the results of both measurements are available after the end of conversion. A BUSY status bit in the status byte shows that the device is actually performing a new conversion; however, even if the ADC is busy, the results of the previous conversion are always available. Remote-Diode Selection Temperature accuracy depends on having a good-quality, diode-connected small-signal transistor. Accuracy has been experimentally verified for all of the devices listed in Table 1. The G768D 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 10A; 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 100. Tight specifications for forward current gain (+50 to +150, for example) indicate that the manufacturer has good process controls and that the devices have consistent VBE characteristics. Thermal Mass and Self-Heating Thermal mass can seriously degrade the G768D's effective accuracy. The thermal time constant of the SSOP-16 package is about 140sec in still air. For the G768D junction temperature to settle to within +1C after a sudden +100C change requires about five time constants or 12 minutes. The use of smaller packages for remote sensors, such as SOT23s, improves the situation. Take care to account for thermal gradients between the heat source and the sensor ,and ensure that stray air current across the sensor package do not interfere with measurement accuracy. 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).
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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 highaccuracy remote measurements in electrically noisy environments. High-frequency EMI is best filtered at DXP and DXN with an external 2200pF capacitor. This value can be increased to about 3300pF(max), including cable capacitance. Higher capacitance than 3300pF introduces errors due to the rise time of the switched current source. Nearly all noise sources tested cause the ADC measurements to be higher than the actual temperature, typically by +1C to 10C, depending on the frequency and amplitude (see Typical Operating Characteristics). PC Board Layout Place the G768D as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4 in. to 8 in. (typical) or more as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily introduce +30C error, even with good filtering, Otherwise, most noise sources are fairly benign. Route the DXP and DXN traces in parallel and in close proximity to each other, away from any high-voltage traces such as +12VDC. Leakage currents from PC board contamination must be dealt with carefully, since a 20M leakage path from DXP to ground causes about +1C 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 3V/C, and it takes about 200V of voltage error at DXP-DXN to cause a +1C measurement error. So, most parasitic thermocouple errors are swamped out.
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G768D
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 G768D 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 G768D.
GND DXP1 DXN DXP1 DXN
G768D
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
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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; 1 series resistance introduces about + 1C error. Low-Power Standby Mode Standby mode disables the ADC and reduces the supply-current drain to less than 10A. 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 G768D 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 500A. Slowing down the conversion rate reduces the average supply current (see Typical Operating Characteristics). In between conversions, the instantaneous supply current is about 200A due to the current consumed by the system resetting circuit. Fan Controller Since the fan speed is measured by counting the number of 32.768KHz cycles between the rising edges of two fan speed pulses. 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:
N: Count Number
G768D
P: FG pulses number per revolution P=1 N = 983040 / rpm P=2 N = 491520 / rpm P=4 N = 245762 / rpm Some selected count number for P=2 are listed below. Table 2. Rpm
3000 4000 5000 6000 7000 8000 9000 10000 20000 30000
N
164 123 98 82 70 61 55 49 25 16
To stop the fan, program the fan speed register to 255. This also makes the fan controller enter power saving mode. Controlling Fan at Lower Speed For stably controlling fans at lower rotation speed, three schemes are recommended as below: 1.Use larger decoupling capacitors between FANVCC and GND. 2.Shunt a capacitor of 1F-2F on FG pin to GND. 3.Use fans with open-collector FG outputs. When controlling fans under lower rotation speed, the output voltage of FANVCC would be too low for fan to generate recognizable FG signals. Using decouple capacitors on FANVCC 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 (P) during power-up, power-down, and brownout conditions, the G768D is relatively immune to short duration negative-going VCC transients (glitches). Typically, for the G768D, a VCC transient that goes 100mV below the reset threshold and lasts 20s or less will not cause a reset pulse. A 0.1F bypass capacitor mounted as close as possible to the VCC pin provides additional transient immunity.
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Ensuring a Valid Reset Output Down to VCC = 0V When VCC falls below 1V, the G768D 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 P 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; 100k is large enough not to load RESET and small enough to pull RESET to ground. Interfacing to Ps with Bi-directional Reset Pins A P with bi-directional reset pins (such as the Motorola 68HC11 series) can connect to the G768D reset output. If, for example, the G768D RESET output is asserted high and the P wants to pull it low, indeterminate logic levels may result. To correct this, connect a 4.7k resistor between the G768D RESET output and the P reset I/O (Figure 4). Buffer the G768D RESET output to other system components.
G768D
SMBus Digital Interface From a software perspective, the G768D 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 G768D 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 1C (Table3), transmitted MSB first. Measurements are offset by +1/2C to minimize internal rounding errors; for example, +99.6C is reported as +100C.
BUFFER
V CC
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
G 768D
RE SET R1 100k
V CC
VCC 4.7k
G768D
RESET
P
RESET
G ND
GND
GND
Fig 3 RESET Valid to VCC = Ground Circuit
Fig 4. Interfacing to Ps with Bi-directional Reset I/O
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Write Byte Format S Address
7 bits
G768D
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 +127C). The POR state of both TLOW registers is 1100 1001 or -55C. 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.
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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 0C 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 +127C for both 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 WCA WCRW WRHA2 WRLN2 WRHA1 WRLN1 OSHT SET_CNT1 ACT_CNT1 FAN_STA1 TMAX1 THYST1 TMAX2 THYST2 TCRIT1 TCRIT2
G768D
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 31h 32h 33h 34h 35h 36h
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 0100 0110b (70) 0011 1100b (60) 0100 0110b (70) 0011 1100b (60) 0110 1100b (108) 0101 1000b (88)
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 1st remote TMAX 1st remote THYST 2nd remote TMAX 2nd remote THYST Critical temperature for 1st remote temperaure sensor Critical temperature for 2nd remote temperaure sensor
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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. Command Byte Functions The 8-bit command byte register (Table 4) is the master index that points to the various other registers within the G768D. 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 contents are listed in table 5. Bit 7(MASK) is used to mask ALERT interrupt.
G768D
Bit 6 ( RUN /STOP) is to put the device in software standby mode. Setting bit 5 (DET_FAN) with logic 1 can activate the detection of fan failure. Logic 1 in bit 4 (EN_TH_SHUT) makes thermal shutdown function valid and logic 0 disables this function and keep TH_SHUT pin low. Bit 3~0 forms thermal shutdown fault queue. The number of faults these bits decided are listed in table 6. 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.
Table 5. Configuration-Byte Bit Assignments BIT NAME POR STATE
7 (MSB) 6 5 4 3-0 MASK
RUN / STOP
FUNCTION
0 0 0 1 0010b
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. Validation of the fan failure detection. If high, activated. If low, disable. Validation of the fault queue function of thermal shutdown. Fault Queue. Number of faults necessary to detect before setting TH_SHUT output to avoid false tripping due to noise.
DET_FAN EN_TH_SHUT FQ_TH_SHUT
Table 6. Number of Faults assigned by FQ_TH_SHUT FQ_TH_SHUT
0000b 0001b 0010b 0011b 0100b 0101b 0110b 0111b
Number of Faults
1 2 3(Power-up default) 4 5 6 7 8
FQ_TH_SHUT
1000b 1001b 1010b 1011b 1100b 1101b 1110b 1111b
Number of Faults
9 10 11 12 13 14 15 16
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Table 7. Status-Byte Bit Assignments BIT
7(MSB) 6 5 4 3 2 1 0(LSB)
G768D
NAME
BUSY RHIGH2* RLOW2* RHIGH1* RLOW1* OPEN* RFU FAN_FAIL*
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) A high indicates that the fan failure 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 to FFh
CONVERSION RATE (Hz)
0.0625 0.125 0.25 0.5 1 2 4 8 RFU
Temperature Sensor Average Supply Current (A TYP, at VCC = 5V)
30 33 35 48 70 128 225 425 -
Table 9. 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
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
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
Software Standby RUN/STOP bit Software Standby 1-shot command
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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 G768D 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 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 register 10h is read / write register. They contain the count number of the desired fan speed. Power up default is FFh. Actual fan speed register The actual fan speed register 11h is 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 is 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 fan. Pin FANVCC 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 the fan when either of the two remote diodes is open or both are short. The power-up default values for TMAX and THYST are +70C and +60C, respectively. This allows the G768D to be used in the occasion when system fails and loses the fan control of G768D.
G768D
Slave Addresses The G768D 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 G768D also responds to the SMBus Alert Response slave address (see the Alert Response Address section). POR and UVLO The G768D 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). 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 remote Receive Byte queries.
THIGH and TLOW registers are set to max and min limits, respectively
Detection On fan Failure Setting bit 5 (DET_FAN) of CONFIGURATION-BYTE register with logic 1 activates the detection of fan failure. G768D detects fan failure via FG pin. G768D defines fan failure as no transition on FG pin for about 0.5sec or the fan measurement result is 255 counts for consecutive 8 times, it takes about 0.25sec. Once fan failure is detected the ALERT# will be set to logic low and the bit 0 (FAN_FAIL) of STATUS-BYTE will be set to logic high. To clear the ALERT# signal caused by fan failure, the DET_FAN bit should be set to 0 then issue an ARA command on serial bus.
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Thermal Shutdown Signal
When the temperature of DX1 reaches or exceeds the Tcrit1 threshold consecutively for the times equal to the number of faults of the FQ_TH_SHUT registers, TH_SHUT pin becomes logic high. The
same mechanism is duplicated for DX2. There fore, either one of DX1, DX2 continuously over their respective Tcrit, the TH_SHUT will assert logic high to indicate a thermal shutdown event.
G768D
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 SMB Data 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 tSU:DAT t SU:STO t BUF
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 G = MSB of data clocked into master H = LSB of data clocked into master I = acknowledge clocked pulse J = stop condition K= new start condition
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Global Mixed-mode Technology Inc.
Package Information
C
G768D
E1
E L
D 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
MIN
1.35 0.10 ----0.20 0.19 4.80 5.80 3.80 ----0.40 ----0
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 8
MIN
0.053 0.004 ----0.008 0.007 0.189 0.228 0.150 ----0.016 ----0
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 8
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.
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