ANALOG DEVICES Single and4 Channel, 201s, 10-bitADC With On-Chip TemperatureSensor Preliminary Specifications AD7416/AD7417/AD7418 FEATURES 10-Bit ADC with 20ps Conversion Time Single and Four Single-ended Analog Input Channels On-Chip Temperature Sensor -55C to 125C On-Chip Track/Hold On-Chip Reference (2.5V +1%) Over-Temperature Indicator Automatic Power Down at the end of a Conversion Wide Operating Supply Range 2.7V to5.5V I?C Compatible Serial Interface Selectable Serial Bus Address Allows Connection of up to 8 AD7416/AD7417s to a Single Bus Superior Replacement for LM75 APPLICATIONS Data Acquisition Systems with Ambient Temperature Monitoring Industrial Process Control Automotive Battery Charging Applications Personal Computers GENERAL DESCRIPTION The AD7417 and AD7418 are 10-Bit, single and 4 Channel A/D Converter with an On-Chip Temperature Sensor that can operate from a single 2.7V to 5.5Vs power supply. The devices contain a 10ys successive- approximation converter based around a capagitor DAC, a 5 Channel Multiplexer, an On-Chip Temperature Sensor, an On-Chip Clock Oscillator, an On-Chip: Track/Hold, and an On-Chip Reference (2.5V). Ehe:AD7416 is a temperature monitoring only devige:in an SO-8 package The On-Chip Temperature:Sensor on the AD7417 can be accessed via multiplexer chainel 0. When the multiplexer channel 0 is selected and a conversion is initiated the resulting ADC code at the end of the conversion gives a measurement of the ambient temperature (41C @ 25C). On-chip registers can be programmed with high and low temperature limits, and an open-drain Overtemperature Indicator output (OTT) is provided, which becomes active when a programmed limit is exceeded A configuration register allows programming of the sense of the OTI output (active high or active low) and its operating mode (Comparator or Interrupt). A programmable fault queue counter allows the number of Prelim A 1/98 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. FUNCTIONAL BLOCK DIAGRAM REFIN VDD Lf) f) TEMP SENSOR REF 2.5V VIN1 |__| CHARGE REDISTRIBUTION DAC DATA OUT if CONTROL SDL Vin2 SAMPLING LOGIC ce MUX CAPACITOR INTERFACE. SDA VIN3 P-L VIN4 oO I VBALANCE ia" fe OO CO 0 NC NC GND CONVST xO AL AD7417.Functional Block Diagram out of limit mieasurements that must occur before triggering the TI output to be set, to prevent spurious triggering: .of the OTI output in noisy environments. An: I?C-compatible serial interface allows the AD7416/17/ 18 "registers to be written to and read back. The three LSBs of the AD7416/17s serial bus address can be slected, which allows up to 8 AD7416/17s to be connected to a single bus. The AD7417 is available in a Narrow Body 0.15" 16 Lead mall Outline IC (SOIC) and in a 16 Lead, Tiny Shrink Small Outline Package (TSSOP).The AD7418 is available in SOIC and 8-lead MicroSmall Outline (uSOIC). PRODUCT HIGHLIGHTS 1. The AD7416/17/18 have an On-Chip Temperature Sensor which allows an accurate measurement of the ambient temperature (+1C @ 25C, 42C over temperature) to be made. The measurable temperature range is -55C to +125C. An Over-Temperature Indicator is implemented by carrying out a digital comparison of the ADC code for channel 0 (temperature sensor) with the contents of the On-Chip Over Temperature Register. 2. The AD7417 offers a space saving 10-Bit A/D solution with 4 external voltage input channels, an On-Chip Temperature Sensor, an On-Chip reference and Clock Oscillator. 3. The Automatic Power Down feature enables the AD7416/17/18 to achieve superior Power performance. At slower throughput rates the part can be programmed to operate in a low power shutdown mode allowing further savings in power consumption. Analog Devices, Inc., 1995 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703AD7416/7417/7418 AD7417-SPECIFICATIONS' Preliminary Information (Voo = +2.7V to +5.5V, GND = 0 V, REF\y = +2.5 V. ) Parameter A Version|B Version| S Version| Units Test Conditions/Comments DC ACCURACY Any Channel Resolution 10 10 10 Bits Minimum Resolution for Which No Missing Codes are Guaranteed 10 10 10 Bits Relative Accuracy +1 +1 +1 LSB max Differential Nonlinearity +1 +1 +1 LSB max Gain Error? +2 +2 +2 LSB max | External Reference +10 +10 +20/-10 LSB max | Internal Reference Gain Error Match? +1/2 +1/2 +1/2 LSBmax | AD7417 only Offset Error? +2 +2 +2 LSB max Offset Error Match +1/2 +1/2 +1/2 LSBmax | AD7417 only ANALOGINPUTS Input Voltage Range VREF VREF VREF V max 0 0 0 V min Input Leakage Current +1 +1 +1 pA max Input Capacitance 10 10 10 pF max TEMPERATURE SENSOR! Measurement Error External Reference Vapr = 2.5V Ambient Temperature 25C +2 +1 +2 C max Tin to Tmax +3 +2 +3 2 nyrax Measurement Error* On-chip Reference Ambient Temperature 25C $2.25 +2.25 +2.25 fC typ Tin to TMax +3 +3 +6 C typ Temperature Resolution 1/4 1/4 la C/LSB REFERENCE INPUT? REF, Input Voltage Range* 2.625 2.625 2.625 V max 25V+5% 2.375 2.375 2.375 V min 2.5V -5% Input Impedance 40 40 40 kQ min Input Capacitance 10 10 10 pFmax ON-CHIP REFERENCE Nominal 2.5V Reference Error? +25 +25 +50 mV max Temperature Coefficient? 86 80 150 ppm/ C typ Ypp Ybpp O, TEMP TEMP SENSOR CR =] pataout sensor| | 35v Keon Fe DATA OUT REF DAC DAC bet t { | cLock| | CONTROL sol vini pa CONTROL SDL MUX SAMPLING LOGIC Pc MUX LOGIC 2c CAPACITOR INTERFACE. SDA INTERFACE. SDA a et SAMPLING | VBALANCE } CAPACITOR VBALANCE 0 O Oo Oo AGND AO AL OAR AGND coNvsT AO At AD7416 Functional Block Diagram AD7418 Functional Block Diagram Prelim A 1/98Preliminary Information AD7416/7417/7418 Parameter Min Typ Max Units Test Conditions/Comments TEMPERATURE SENSOR AND ADC Accuracy +2.0 a @ TA = -25C to +100C +3.0 C TA = -55C to +125C Resolution 10 Bits Update rate tp 355 Ls OTI Delay 1x ta 6 x tg ms Depends on Fault Queue Setting Supply Current 1.0 mA During Conversions 250 pA Between Conversions 1 LA Shutdown Mode Torr Default Temperature 80 C Tuysr Default Temperature 75 C DIGITAL INPUTS Input High Voltage, Vn; +Vs x 0.7 HVs + 0.4 Vv Input Low Voltage, Vz; -0.3 H+Vs x 0.3 Vv Input High Current, Iny 0.005 1.0 ma Vin'= 5V Input Low Current, Iq, -0.005} -1.0 ma Vin = 0V Input Capacitance, Cry 20 pF All Digital Inputs DIGITAL OUTPUTS Output Low Voltage, Voi 0.4 V Io, = 3mA Output High Current 100 pA Vou = 5V Output Fall Time, ty 250 ns Cy = 400pF, Ip = 3mA OS Output Low Voltage, Vor 0x8 Vv Iour = 4mA AC ELECTRICAL CHARACTERISTICS Serial Clock Period, t, 2.5 Ls See Figure 1 Data In Setup Time to SCL High, t, 50 ns See Figure 1 Data Out Stable after SCL Low, t; 0 ns See Figure 1 SDA Low Setup Time to SCL Low 100 ns See Figure 1 (Start Condition), ty SDA High Hold Time after SCL High 50 ns See Figure 1 (Stop Condition), ts t}_+ SCL uW t SDA DATA IN >| ge SDA DATA OUT Figure 1. Diagram for Serial Bus Timing Prelim A 1/97AD7416/7417/7418 Preliminary Information AD7417 PIN FUNCTION DESCRIPTION Mnemonic Pin Description Ami to Anna 10-7 Analog input channels. The AD7417 has four analog input channels. The input channels are single ended with respect to GND. The input channels can convert voltage signals in the range OV to Vpzr . A channel is selected by writting to the configuration register of the AD7417 - See Control Byte Section. Vpp 14 Positive supply voltage, +2.7V to +5.5V. GND 6 Ground reference for track/hold, comparator and capacitor DAC, and digital cirtcuitry. CONVST 1 This is logic input signal. The convert start signal. The rising edge of this signal powers up the part fully. The pulse should be 4us or else an internal pulse of 4us is used to ensure correct power up. A_ 10-bit analog to digital conversion is initiated on the falling edge of the this signal. The falling edge of this signal places the Track/Hold in hold mode. The Track/Hold goes into track mode again at the end of the conversion. See Operating Mode Section of the data sheet SDA 2 Digital I/O. Serial Bus Bi-directional Data. Open-drain output. SCL Digital Input. Serial Bus Clock. OTI 4 This is a logic output. The Over Temperature Indicator (OTT) is set logic low if the result of a conversion on channel 0 (Temperature Sensor) is greater that an eight bit word in the Over Temperature Register (OTR). The signal is reset at the end of a serial read operation, i.e. a rising RD/ WR edge when CS is low. AO Digital Input. The lowest programmable bit of:,the Serial Bus Address Al Digital Input. The middle programmable bitof the Serial Bus Address A2 Digital Input. The highest programmable bit of the Serial Bus Address REF yw 5 This is an analog input. An external"2,5V reference can be connected to the AD7417 at this pin. To enable the on-chip reference, the REF, pin should be tied to AGND. If an external reference is connected to the AD7417 the internal reference will shut_down. NC 1,16 No Connection. PIN CONFIGURATION SOIC/TSSOP NY nc] @ lie] we SDAL2 75] CONVST scL] 3 AD7417 74] VDD ort TOP ri3] Ao REFIN Ce VIEW FZ] AL (Not to Scale) env LE 7] a2 Aint [4] 10) AIN3 Aine (2! Po) Aina -4- Prelim A 1/98Preliminary Information AD7416/7417/7418 AD7416 AND AD7418 PIN FUNCTION DESCRIPTION Mnemonic | Pin Description Vpp 7 (AD7418) Analog input channel. The input channel is single ended with respect to GND . The 8 (AD7416) input channel can convert voltage signals in the range OV to 2.5V . The input channel is selected by writting to the Address register of the AD7818 - See Control Byte Section. REF yy 6 (AD7418) This is an analog input. An external 2.5V reference can be connected to the AD7418 at this pin. To enable the on-chip reference the REFpy pin should be tied to AGND. If an external reference is connected to the AD7418 the internal reference will shut down. Ain 5 (AD7418) AO 7 (AD7416) Digital Input. The lowest programmable bit of the Serial Bus Address Al 6 (AD7416) Digital Input. The middle programmable bit of the Serial Bus Address A2 5 (AD7416) Digital Input. The highest programmable bit of the Serial Bus Address GND 4 Analog and Digital Ground. CONVST | 8 (AD7418) This is logic input signal. The convert start signal. The rising edge of this signal powers up the part fully. The pulse should: be:4us or else an internal pulse of 4us is used to ensure correct power up. A 1}0-bitanalog to digital conversion is initiated on the falling edge of the this signal. The:,falling edge of this signal places the Track/Hold in hold mode. The Track/Holdsgoes into track mode again at the end of the conversion. See Operating Mode'Section of the data sheet. OTI 3 This is a logic output. The, Qver Temperature Indicator (OTT) is set logic low if the result of a conversion onchannel 0 (Temperature Sensor) is greater that an eight bit word in the Over temperature register (OTR). The signal is reset by a serial read operation. SDA 1 Digital I/O. Serial, Bus Bi-directional Data. Open-drain output. SCL 2 Digital Input;, Serial clock Bus. spa @ TJ Yop spa @ J] cCONVST scL [) apn7416 [2] ao sc. [) ap7418 [FJ Vaa am = | a or TE) perin eno Paz cup Py ain Prelim A 1/97 -5-AD7416/7417/7418 INTERNAL REGISTER STRUCTURE The AD7417/18 has seven internal registers, as shown in figure 2. Six of these are data registers and one is an address pointer register. the AD7416 has two registers less, not having an ADC register or a Config2 register. TEMPERATURE VALUE REGISTER P (READ-ONLY ADDRESS 00H) CONFIGURATION REGISTER (READ/WRITE ADDRESS 01H) THyst SET-POINT REGISTER (READ/WRITE ADDRESS 02H) TonSET-POINT REGISTER <P} (READ/WRITE ADDRESS 03H) ADDRESS POINTER REGISTER (SELECTS DATA REGISTER! FOR READ/WRITE) ADC REGISTER (READ ONLY - ADDRESS 04H) ADDRESS DATA CONFIG 2 REGISTER (READ/WRITE > ADDRESS 05H) SERIAL BUS SDA INTERFACE + SCL Figure 2. AD7417/18 Register Structure ADDRESS POINTER REGISTER The Address Pointer Register is an 8-bit register, which stores an address that points to one of the six data registers. The first data byte of every serial write operation to the AD7416/17/18 is the address of one of the data registers, which is stored in the Address Pointer. Register, and selects the data register to which subsequent data bytes are written. Only the three LSB's of this registerare used to select a data register. TABLE 1. ADDRESS POINTER REGISTER Preliminary Information TEMPERATURE VALUE REGISTER (ADDRESS 00H) The temperature value register is a 16-bit, read-only register that whose 10 MSBs store the temperature reading from the ADC in 10-bit twos complement format. Bits 5 to 0 are unused. TABLE 3. TEMPERATURE VALUE REGISTER D15 D14D13D12D11D10 DI D8 D7 D6 MSB B8 B7 B6 B5 B4 B3 3B2 Bl LSB The temperature data format is shown in Table 4. This shows the full theoretical range of the ADC from -128C to +127C, but in practice the temperature measurement range is limited to the operating temperature range of the device. TABLE 4. TEMPERATURE:,DATA FORMAT P7* P6* P5* P4* P3*. P2 Pl PO 0 0 0 0 0 Register Select *P3 to P7 must be set to 0 TABLE 2. REGISTER ADDRESSES P2 Pl PO Registers Temperature Value (Read only) Config Register (Read/write) Tori ADC (AD7417/18) Bete |/OlTol]o!]c Oo ]Re [RK Ilo]so 0 1 0 Tuyse (Read/Write) 1 0 1 Config2(AD7417/18) Temperature Digital Output -128 C 10 0000 0000 -125 C 10 0000 1100 -100,,.2C 10 0111 0000 -75 C 10 1101 0100 -50 C 11 0011 1000 -25 C 11 1001 1100 -0.25 C 11 1111 1111 0C 00 0000 0000 +0.25 C 00 0000 0001 +10 C 00 0010 1000 +25 C 00 0110 0100 +50 C 00 1100 1000 +75 C 01 0010 1100 +100 C 01 1001 0000 +125 C 01 1111 0100 +127 C 01 1111 1100 CONFIGURATION REGISTER (ADDRESS 01H) The Configuration Register is an 8-bit, read/write register, which is used to set the operating modes of the AD7416/17/18. The various functions controlled by this register are explained later. Bits D7 to D5 are used for production testing and should be kept at 0 for normal operation. Bits D4 and D3 are used to set the length of the fault queue. D2 sets the sense of the OTI output. D1 selects Comparator or Interrupt mode of operation, and DO selects Shutdown mode. -6- Prelim A 1/98Preliminary Information AD7416/7417/7418 TABLE 5. CONFIGURATION REGISTER D7 D6 D5|D4 D3 D2 D1 DO TABLE 7. FAULT QUEUE SETTINGS Channel Fault OTI Cmp/ | Shut- D4 D3 Number of Faults Selection Queue | Polarity | Int down 0 0 1(Power-up default) Ton SET POINT REGISTER (ADDRESS 03H) 0 1 2 The Tor Set Point Register is a 16-bit, read/write register 1 0 4 whose 9 MSBs store the Toy, set point in twos 1 1 6 complement format. Bits 6 to 0 are unused. TABLE 8. SET POINT REGISTERS D15 | D14;D13|D12 D1l P10 D9| D8} D7 MSB | B8 |B7 B6 B5 B4 |B3 |B2 |Bl Tyyst SET POINT REGISTER (ADDRESS 02H) The Tyysr Set Point Register is a 16-bit, read/write register whose 9 MSBs store the Tyysr set point in twos complement format. Bits 6 to 0 are unused. CONFIG2 REGISTER (ADDRESS 04H) A second configuration register is included in the AD7417/18 for the functionality of the CONVST pin. It is an 8 bit register with bits D5 to DO being left at 0. Bit D7 determines whether the 7417/18 should be operated in its default mode, performing conversions every 355us D7 D6 D5D4D3D2D1D0 0 0 0 0 0 0 or in CONVST pin mode, where conversions will start when the CONVST pin is used only. When Testl bit is 0 the IC filters are enabled (default). A 1 disables the filters. Conversion Mode Testl ADC VALUE REGISTER (ADDRESS ,.05H) The ADC value register is a 16-bit;,, read. only register that whose 10 MSB's store the value produced by the ADC in binary format. Bits 5 to 0:are unused. D15 D14D13D12D11D10 D9 D8 D7 D6 MSB B8 B7 B6 B5 B4 B3 B2 Bl LSB TABLE 6. CHANNEL SELECTION FOR AD7417/18 D7 D6 D5 Select 0 0 0 Temperature 0 0 1 CH1 0 1 0 CH2 0 1 1 CH3 1 0 0 CH4 Prelim A 1/97 SERIAL BUS INTERFACE Control of the AD7416/17/18 is carried out via the IC- compatible serial bus. The AD7416/17/18 is connected to this bus as a slave device, under the control of a master device, e.g. the processor. SERIAL BUS ADDRESS Like all I?C-compatible: devices, the AD7416/17/18 have a 7-bit serial address.;.The four MSBs of this address for the 7416 are set to 10013:the 7417 are 0101, whilst the three LSBs can be set by the user by connecting the A2 to AO pins to either+Vs or GND. By giving them different addresses, tip to 8 AD7416/17s can be connected to a single, stial bus, or the addresses can be set to avoid conflitswith other devices on the bus. Similarly, the four MSB's6f this address for the AD7418 are 0101, whilst the three "LSB's are all set to zero. The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a START condition, defined as a high to low transition on the serial data line SDA whilst the serial clock line SCL remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the START condition, and shift in the next 8 bits, consisting of a 7-bit address (MSB first) plus a R/W bit, which determines the direction of the data transfer, i.e. whether data will be written to or read from the slave device. The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowledge Bit. All other devices on the bus now remain idle whilst the selected device waits for data to be read from or written to it. if the R/W bit is a 0 then the master will write to the slave device. If the R/W bit is a 1 the master will read from the slave device. 2. Data is sent over the serial bus in sequences of 9 clock pulses, 8 bits of data followed by an Acknowledge Bit from the receiver of data.Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, as a low to high transition when the clock is high may be interpreted as a STOP signal. 3. When all data bytes have been read or written, stop conditions are established. In WRITE mode, the master will pull the data line high during the 10th clock pulse to assert a STOP condition. In READ mode, theAD7416/7417/7418 master device will pull the data line high during the low period before the 9th clock pulse. This is known as No Acknowledge. The master will then take the data line low during the low period before the 10th clock pulse, then high during the 10th clock pulse to assert a STOP condition. Any number of bytes of data may be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation, because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. WRITING TO THE AD7416/17/18 Depending on the register which is being written to, there are three different write for the AD7416/17/18. 1.Writing to the Address Pointer Register for a subsequent read. In order to read data from a particular register, the Address Pointer Register must contain the address of that register. If it does not, the correct address must be written to the Address Pointer register by performing a single-byte write operation, as shown in Figure 3. The write operation consists of the serial bus address followed by the address pointer byte No data is written to any of the data registers. 2.Writing a single byte of data to the Configuration Registers or Tor, Tryst Registers. The Configuration Register is an 8-bit register, so only 1 Preliminary Information one byte of data can be written to it. . If only 8-bit temperature comparisons are required then the temperature LSB can be ignored in Tor; and Tyysr, and only 8 bits need be written to the Tory, and Tyysr registers. Writing a single byte of data to one of these registers consists of the serial bus address, the data register address, written to the Address Pointer Register, followed by the data byte, written to the selected data register.This is illustrated in Figure 4. 3.Writing two bytes of data to the Tor or Tuysr Register If 9-bit resolution is required for the temperature set- points, then two bytes of data must be written to the Tor, and Tyysr registers. This consists of the serial bus address, the register address, written to the address pointer register, followed by two data bytes written to the selected data register. This is illustrated in Figure 5. READING DATA FROM THE AD7416/17/18 Reading data from the AD7416/17/18 is a one or two byte operation. Reading back..the Contents of the Configuration Register is a single byte read operation, as shown in Figure 6, the register';address previously having been set by a single-byte write operation to the address pointer register. Reading data ftom the Temperature Value, Toy, or Tuystr registerg..is..a two-byte operation, as shown in Figure 7. It is also possible to read the most significant bit of a 9/10 bit xegister in this manner. 1 9 START BY MASTER FRAME 1 SERIAL BUS ADDRESS, BYTE ACK. BY AD7416 ACK. BY AD7416 STOP BY MASTER FRAME 2 ADDRESS POINTER REGISTER BYTE Figure 3. Writing to the Address Pojnter Register to select a Data Register for a subsequent Read Operation " ad START BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE ACK. BY AD7416 ACK. BY AD7416 FRAME 2 ADDRESS POINTER REGISTER BYTE 9 scconmuenere [| [|] [LLP LILI LI LIL ACK.BY STOP BY AD7416 | MASTER a FRAME 3 DATA BYTE Figure 4. Writing to the Address Pointer Register followed by a Single Byte of Data to the selected Data Register -8- Prelim A 1/98Preliminary Information AD7416/7417/7418 START BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE ACK. BY AD7416 NO ACK. STOP BY BY MASTER MASTER FRAME 2 DATA BYTE FROM AD7416 Figure 6. Reading a Single Byte of Data from the Configuration Register of \ aX aX ea START BY ACK. BY ACK. BY MASTER AD7416 MASTER FRAME 1 FRAME 2 SERIAL BUS ADDRESS BYTE MOST SIGNIFICANT DATA BYTE FROM AD7416 9 scrccommmeneee |] |] [|] | itty LI LIL soniconmnueneae/'a7 v8 v8 X oa oe X v2 01 X00 / NO ACK. BY STOP BY MASTER, MASTER | FRAME 3 LEAST SIGNIFICANT DATA BYTE FROM AD7416 Figure 7. Reading Two Bytes of Data,from the To7; or Tuysr Register OTI OUTPUT The OTI output is used to indicate that an out-of-limit temperature excursion has occurred. OTI is an open-drain output that can be programmed to be active low by setting bit D2 of the Configuration Register to 0, or active: high by setting bit D2 of the Configuration Register, :t, 1 The OTI output has two operating modes, whith are selected by Bit D1 of the Configuration Register. In the Comparator mode, (D1=0), the OTI, ovitput becomes active when the temperature exceeds, Vigy7)' and remains active until the temperature falls below. Tyysr. This mode allows the AD7416/17/18 to be,usd) as a thermostat, for example to control the operation. of a cooling fan. I I DN a YW ! Tos THYST 7 N77 OS OUTPUT COMPARATOR MODE l l l l t l l | | l l l OS OUTPUT INTERRUPT MODE L_| L_| ! l l ! ! l READ* READ* READ* READ* READ* READ* READ* L *IN INTERRUPT MODE, A READ OPERATION OR SHUTDOWN RESETS THE OS OUTPUT, OTHERWISE THE OS OUTPUT REMAINS ACTIVE INDEFINITELY, ONCE TRIGGERED. Figure 8. Operation of OT! Output (shown active low) Prelim A 1/97 In the Interrupt mode (D1=1), the OTI output becomes active when the temperature exceeds Toy, and remains active even if the temperature falls below Tyysr, until it is reset by a read operation. Once OTI has become active by the temperature exceeding Toy, then been reset, it will remain inactive even if the temperature remains, or subsequently rises again, above Torq. It will not become active again until the temperature falls below Tyysr. It will then remain active until reset by a read operation. Once OTI has become active by the temperature falling below Tuysrs then been reset, it will remain inactive even if the temperature remains, or subsequently falls again, below Tuysr- OTI is also reset when the AD7416/17/18 is placed in shutdown mode, by setting bit DO of the Configuration Register to 1. The OTI output requires an external pullup resistor. This can be connected to a voltage different from +Vgs (for example, to allow interfacing between 5V and 3.3 volt systems) provided that the maximum voltage rating of the OTI output is not exceeded. The value of the pullup resistor depends on the application, but should be as large as possible to avoid excessive sink currents at the OTI output, which can heat the chip and affect the temperature reading. The maximum value of pullup resistor that will meet the output high current specification of the OTI output is 30kQ, but higher values may be used if a lower output current is required. For most applications a value of 10kQ will prove suitable. -9-AD7416/7417/7418 The open-drain configuration of OTI allows the OTI outputs of several AD7416s to be wire-ANDed together when in active-low mode. FAULT QUEUE To avoid false triggering of the AD7416/17/18 in noisy environments, a fault queue counter is provided, which can be programmed by bits D3 and D4 of the Configuration Register (see Table 6 on page 5) to count 1, 2, 4 or 6 fault events before OTI becomes active. In order to trigger OTI, the faults must occur consecutively. For example, if the fault queue is set to 4, then four consecutive temperature measurements greater than Toy, (or less than Tyysr) must occur. Any reading that breaks the sequence will reset the fault queue counter, so if there are three readings greater than Toy, followed by a reading less than Toy, the fault queue counter will be reset without triggering OTT. POWER ON DEFAULTS The AD7416/17/18 always powers up with the following defaults: Address pointer pointing to Temperature Value Register Comparator mode Ton = 80C Tuyst = 75C OTI active LOW Fault queue = 1 These default setting allow the AD7416/17/18 to be used as a stand-alone thermostat without any connection to a serial bus. OPERATING MODES The AD7416/17/18 has two possible modes of operation depending on the value of DO in the configuration register. Mode 1 Normal operation of the parts occur when B0=0. In this active mode, a conversion takes place,seyery 355us by generating a power up one shot of ,3usicOnce the conversion has taken place, the: part teturns to a partial powerdown consuming typically:200uA of current until the next conversion occurs. Two situations can arise in this mode on the request of a temperature read. If a read occurs during a conversion, the conversion aborts and a new one starts when the read completes. The temperature value that is read is that of the previous completed conversion. The next conversion will then occur 355us after the new conversion has begun. If a read is called between conversions, then a conversion is initiated when the read completes. After this conversion, the part returns to performing a conversion every 355us. The power dissipation during a conversion is 3mW (Vdd=3V). Taking the conversion time to be 28us the ad7416 dissipates an average of ~240uW. During partial powerdown the power dissipated is 3Vx200uA=600uW. For the remaining 327us of the cycle, an average of 550uW is consumed. Therefore the power consumed over the complete cycle is approximately 800uW. -10- Preliminary Information Mode 2 For applications where temperature measurements are required at a slower rate eg. every second, power consumption of the part can be reduced by writing to the part to go to a full powerdown between reads. The current consumption in full powerdown is typically luA and is initiated when DO=1 in the configuration register. When a measurement is required, a write operation can be performed to tell the part to power up and do a conversion and then the part is written to again to return it to full powerdown mode. Reading the temperature value from the conversion can then be done in the full powerdown stage as the IC bus is always active. Taking the requirement for a temperature measurement every lms as an example, and to btain maximum power efficiency, the part is written,'to,eVery lms to power up and take a conversion, before being written to to power down again afterwards. Therefore because the part is powered up for only approximately 28us of the cycle only (28us/ lms)x3mW=83uWisis the average power dissipated. For the remainder ofthe cycle the part is powered down consuming lyA$dissipating negligible power. The conversion rate, and therefore the power consumption of th:.AID7416/17/18 depends on the rate at which reads are, taking place. As Toy, and Tuysr are two byte reads, the read time with the I?C operating at 100kbit/s would be 270us. This time determines how fast the part can be Operated at. If temperature reads are called too often, then reads will overlap with conversions, aborting them continuously resulting in error. CONVERT START MODE The AD7417/18 has an extra mode, set by writing to the MSB of the config2 register. CONVST Mode. By setting the CONVST mode bit to 1 , conversions will be started using the CONVST pin only. A 3us one shot pulse on the CONVST powers up the device on its rising edge and the falling edge initiates a conversion. If the CONVST mode changes in the middle of a conversion, the conversion will be completed. The part then powers down after the conversion. If the MSB in the register is set to 0 then the part is left in its default mode and any activity on the CONVST pin is ignored. APPLICATIONS INFORMATION SUPPLY DECOUPLING The AD7416/17/18 should be decoupled with a 0.1uF ceramic capacitor between +Vs and GND. This is particularly important if the part is mounted remote from the power supply. Prelim A 1/98Preliminary Information AD7416/7417/7418 MOUNTING THE AD7416 The AD7416/17/18 can be used for surface or air- temperature sensing applications. If the device is cemented to a surface with thermally conductive adhesive, then the die temperature will be within about 0.2C of the surface temperature, thanks to the devices low power consumption. Care should be taken to insulate the back and leads of the device from the air, if the ambient air temperature is different from the surface temperature being measured. The ground pin provides the best thermal path to the die, so the temperature of the die will be close to that of the printed circuit ground track. Care should be taken to ensure that this is in good thermal contact with the surface being measured. As with any IC, the AD7416/17/18 and its associated wiring and circuits must be kept free from moisture to prevent leakage and corrosion, particularly in cold conditions where conditions where condensation is more likely to occur. Water-resistant varnishes and conformal coatings can be used for protection. The small size of the AD7416 package allows it to be mounted inside sealed metal probes, which provide a safe environment for the device. FAN CONTROLLER Figure 9 shows a simple fan controller which will switch on a cooling fan when the temperature exceeds 80C, and switch it off again when the temperature falls below 75C. The AD7416 can be used stand-alone in this application, or with a serial bus interface if different trip temperatures are required. If the AD7416 is used with a bus interface, then the sense of OS can be set to active high, andQJ and R1 can be omitted, and OS connected directly te. the: gate of Q2, with R2 as the pullup resistor. SYSTEM WITH MULTIPLE AD7416S 4+12V 4Vg 3V to 5.5V YS I R2 LOGIC LEVEL 8 s I (8) > 10k > 10kQ MOSFET RATED TO SUIT FAN q CURRENT AA Vvv Qi AD7416 (3}4 2N3904 OR SIMILAR % 6, = THERMOSTAT Figure 10 shows the AD7416 used as a thermostat. The heater will be switched on when the temperature falls below Tyysr, and switch:off again when the temperature rises above Tos. For''this:.application, the OS output should be programmed active Tow, and for comparator mode. 4Vg av to.5V HEATER $ D1 (8) 3 14001 \ oT HEATER ap7416 (3)4 2N3904 SUPPLY OR SIMILAR Figure 10. AD7416 Used as a Thermostat The three LSBs of the AD7416s serial address can be set by the user, allowing 8 different addresses from 1001000 to 1001111. Figure 11 shows a systm sin which 8 AD7416s are connected to a single serial bus, with their OS outputs wire ANDed together to form a.,cofimon interrupt line. This arrangement does mean that each device must be read to determine which one has generated the interrupt, and if a unique interrupt is required for each device, the OS outputs can be connected separately'to the I/O chip. 4Vg 3V to 5.5V SUPER I/O CHIP PROCESSOR Figure 11. Multiple Connection of AD7416s to a Single Serial Bus Prelim A 1/97 -11-