PDF G768 Data sheet ( Hoja de datos )

Número de pieza	G768
Descripción	Remote/Local Temperature Sensor/ 2 Fan Controllers with SMBus Serial Interface and System Reset Circuit
Fabricantes	ETC
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No Preview Available ! 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 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 1 Vcc 2 DXP1 3 DXN 4 DXP2 5 RESET 6 GND 7 GND 8 16 OUT2 15 Vcc 14 SMBCLK 13 FG2 12 SMBDATA 11 ALERT 10 FG1 9 CLK 16Pin SSOP Ver 1.3 Oct 28, 2002 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 cor- responding 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 ca- pacitor per channel. It determines the current fan speed based on the fan rotation pulses and an exter- nally supplied clock. (To be continued) Ordering Information PART* G768B TEMP. RANGE -10°C to +85°C PIN-PACKAGE 16SSOP TEL: 886-3-5788833 http://www.gmt.com.tw 1 1 page Global Mixed-mode Technology Inc. Pin Description G768B PIN NAME FUNCTION 1 OUT1 PWM output, connect to fan 1 2,15 Vcc 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; 3 DXP1 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 4 DXN 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; 5 DXP2 tie DXP2 to DXN if no remote diode on channel 2 is used. Place a 2200pF capacitor between DXP2 and DXN for noise filtering. 6 RESET RESET Output remains low while VCC is below the reset threshold, and for 240ms after VCC rises above the reset threshold. 7,8 GND Ground 9 CLK Clock input for fan speed measurement. 10 FG1 Fan1 pulse input. 11 ALERT SMBus Alert (interrupt) Output, open drain. 12 SMBDATA SMBus Serial-Data Input / Output, open drain. 13 FG2 Fan2 pulse input. 14 SMBCLK SMBus Serial-Clock Input. 16 OUT2 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 conjunc- tion with an external micro-controller (µC) or other intel- ligence in thermostatic, process-control, or monitoring applications. The µC is typically a power-management or keyboard controller, generating SMBus serial com- mands 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 con- tains 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 con- version 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 5 Page Global Mixed-mode Technology Inc. G768B 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 set- tings. 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 acciden- tally short circuited. Similarly, if DXP is short cir- cuited 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 ad- dress. Interrupts are generated in response to THIGH and TLOW comparisons and when the remote diode is disconnected (for continuity fault detection). The in- terrupt does not halt automatic conversions; new tem- perature data continues to be available over the SMBus interface after ALERT is asserted. The interrupt output 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 in- terrupt is valid by reading the current temperature. Alert Response Address The SMBus Alert Response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the Alert Response slave address (0001 100). Then any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus. Table 4. 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 SET_CNT2 ACT_CNT2 FAN_STA2 CHIP_TMP TMAX1 THYST1 TMAX2 THYST2 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 FUNCTION 0000 0000b Read 2nd remote temperature: returns latest temperature 0000 0000b Read 1st remote temperature: returns latest temperature N/A Read status byte (flags, busy signal) 0000 0000b Read configuration byte 0000 0010b Read conversion rate byte 0111 1111b (127) Read 2nd remote THIGH limit 1100 1001b(-55) Read 2nd remote TLOW limit 0111 1111b (127) Read 1st remote THIGH limit 1100 1001b (-55) Read 1st remote TLOW limit N/A Write configuration byte N/A Write conversion rate byte N/A Write 2nd remote THIGH limit N/A Write 2nd remote TLOW limit N/A Write 1st remote THIGH limit N/A Write 1st remote TLOW limit N/A One-shot command (use send-byte format) 1111 1111b Write 1st fan programmed speed register 1111 1111b Read 1st fan actual speed register 10b Read 1st fan status register 1111 1111b Write 2nd fan programmed speed register 1111 1111b Read 2nd fan actual speed register 10b Read 2nd fan status register 0000 0000b On-chip temperature 0100 0110b (70) 1st remote Tmax 0011 1100b (60) 1st remote Thyst 0100 0110b (70) 2nd remote Tmax 0011 1100b (60) 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 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. Ver: 1.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 11 11 Page

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