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SUMMIT
MICROELECTRONICS, Inc. Laser Diode Adaptive Power Controller
SML2108
PRELIMINARY
FEATURES
! Integrated Bias Current Monitor " Monitors & Measures Laser Temperature Directly " Eliminates Need for External Thermistor & Thermal Coupling Issues " Alarm Output on Over-temperature Condition ! Adaptive Modulation Control (AMC) " Adjusts Modulation Current as a Function of the Laser Temperature " 8 x 8 Programmable Compensation Table " 256 Independent Compensation Values " Integrated 8-Bit Modulation Control DAC ! Flexible Biasing Architecture " Bias Control and Modulation Control: 0 to 10mA / 0 to 100 mA Source, 0 to 100mA Sink ! Automatic Power Control (APC) with Integrated 10-Bit Programmable Offset " Automatic Initial Bias Optimization ! Electronic Calibration Through 2-wire Interface ! 3V or 5V Operation
DESCRIPTION
The SML2108 is an adaptive power controller for laser diodes. It is the industry's first integrated device that can directly monitor and measure a laser diode's temperature, and provide a variable modulation current. The SML2108's integrated active feedback loop is used to calibrate and control the mean and modulation power of high speed, high power laser diodes. Inherent manufacturing tolerances introduce variations of performance in laser diodes. These variations, combined with parametric changes over the laser's extreme temperature range and laser ageing, call for an efficient temperature compensation scheme. Using an internal digital control loop and a programmable nonvolatile compensation lookup table, the SML2108 provides the most optimum adaptive power control with a minimum number of external components. The SML2108 removes the need for any manual calibration of the laser control circuit, which is currently the industry standard practice. All calibration values are programmed through the 2-wire communication interface, which can be controlled by most production ATE equipment. Programming of configuration, control and calibration values by the user can be simplified with the interface adapter and Windows GUI software obtainable from Summit Microelectronics. The SML2108 is available in 48 lead TQFP.
SIMPLIFIED APPLICATION DIAGRAM
VDD LASER DIODE IN+ IN- LASER MODULATION DRIVER MODSET VDD VDD AUTOMON SDA Interface SCL MODN IMOD MONITOR DIODE
BIASN DETECT
SML2108
VSS
2053 SAD 1.0
(c)SUMMIT MICROELECTRONICS, Inc., 2000 * 300 Orchard City Dr., Suite 131 * Campbell, CA 95008 * Phone 408-378-6461 * FAX 408-378-6586 * www.summitmicro.com Characteristics subject to change without notice 2053 2.2 11/07/00
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SML2108
PRELIMINARY
FUNCTIONAL BLOCK DIAGRAM
DETECT 12 VCC
CAP1 11
CAP2 10 VDD
A0
1
A1 2 A2 3
SDA 4 SCL 5 (All Rs 100k) AUTOMON 6 CE# 48 Config
8-Bit ADC
NV Scaling & Offset
NV POR
POR Reg
2
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+ 5 ADC Read & Alarm Reg 8 NV Look-up Table 8-Bit DAC
10-Bit NV Reg
10-Bit DAC Reg
10-Bit DAC
- BIAS P EXT TEMP BIAS N 13 VSS A 14 VSS D 7 RDY ALERT# MOD P MOD N VSS
2053 BD 2.1
SUMMIT MICROELECTRONICS, Inc.
SML2108
PRELIMINARY
PIN CONFIGURATION
48-Pin TQFP
CE# VDD VDD BIASP BIASP MODP MODP VDD VDD VSS VSS 48 47 46 45 44 43 42 41 40 39 38 37
A0 A1 A2 SDA SCL AUTOMON RDY# ALERT# EXT TEMP CAP2 CAP1 DETECT
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24
36 35 34 33 32 31 30 29 28 27 26 25
MODN MODN BIASN BIASN VSS VSS VSS VSS BIASN BIASN MODN MODN
VSSA VSSD VDD VDD BIASP BIASP MODP MODP VDD VDD VSS VSS
2053 PCon 2.0
PIN DESCRIPTIONS
DETECT (12) This is the analog input from the laser monitor photodiode for the integrator circuit. There is an on-board resistance of 2M between the DETECT input and CAP1 pin. CAP1 and CAP2 (11 & 10) Capacitor inputs for an external capacitor in the feedback loop of the Mean Power Control Integrator. There is an onboard capacitance of 500pF. AUTOMON (6) Active high input used to enable the internal auto-monitor function, which provides automatic adjustments to the modulation output currents (MODP and MODN) based on the internal A/D output and the values stored in the nonvolatile lookup table. This pin has an internal 100k pullup. ALERT# (8) Active low, open-drain output. This pin is driven low whenever the bias current increases beyond a predefined nonvolatile threshold. This can be used to predict laser failure.
SUMMIT MICROELECTRONICS, Inc.
SDA, SCL (4 & 5) Data and Clock lines, respectively, whose function and use are based on the industry standard I2C interface. Lookup table values, configuration data, and D/A and A/D registers may all be accessed via these two pins of the SML2108. These pins have internal 100k pullups. A0, A1, A2 (1, 2, & 3) Address Pins for the interface provided to allow multiple devices on a single bus. These pins have internal 100k pullups. RDY# (7) Active low, open-drain output. This pin is driven low whenever the internal A/D is performing a conversion, or while the on-board EEPROM is being programmed. EXT TEMP (9) Temperature input (or no connection). This pin can be programmed as an input to the ADC and can interface a temperature sensor. The EXT TEMP pin is multiplexed with the bias current to provide a means of configuring the input to the ADC. When EXT TEMP is programmed as the
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PRELIMINARY
input to the ADC using bit 5 of Register 1, the converted value of the current entering this pin is used as the address of the EEPROM lookup table. In this configuration the modulation current can be controlled by temperature rather than the bias current. Refer to the application example on using the EXT TEMP pin. If this option is not used the pin should be left floating. VSSA, VSSD (13 & 14) Analog and digital low-side supplies for on-board circuitry. Must be at same potential as all other VSS pins. VDD (15, 16, 21, 22, 39, 40, 45, 46, & 47) High-side supply for the Bias and Modulation currents and power supply input for the chip. CE# (48) The chip enable input is active low and provides an additional method of enabling the serial interface. The state of this pin has no effect on the auto-monitor function. This pin has an internal 100k pullup.
BIASP (17, 18, 43, & 44) High-side mean bias control current. Current source output range is programmable, with the optional ranges of 0 to 100mA or 0 to 10mA. BIASN (27, 28, 33, & 34) Low-side mean bias control current. Current sink input range is 0 to 100mA. MODP (19, 20, 41, &42) High-side modulation control current. Current source output range is programmable, with optional ranges of 0 to 100mA or 0 to 10mA. MODN (25, 26, 35, &36) Low-side modulation control current. Current sink input range is 0 to 100mA.
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PRELIMINARY
ABSOLUTE MAXIMUM RATINGS*
Temperature Under Bias ...................... -55C to 125C Storage Temperature ........................... -65C to 150C Lead Solder Temperature (10 secs) ................... 300 C *COMMENT
Stresses 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 outside those listed in the operational sections of this specification is not implied. Exposure to any absolute maximum rating for extended periods may affect device performance and reliability.
ELECTRICAL TABLES
(Over Recommended Operating Conditions; Voltages are relative to GND) Symbol S/N THD Parameter Signal to Noise ratio Total harmonic distortion Peak harmonic intermodulation distortion 2nd Order 3rd Order Conditions TA = 25C Min. 70 -80 -80 -80 Typ. Max. Units dB dB dB dB
Typical ADC Performance
DC Accuracy
Resolution Reolution for which no missing codes are guaranteed Relative accuracy DNL Positive full scale error VSS = 5V Unipolar offset error VSS = 2.7V to 3.6V 8 1/2 1 2 2 2 8 Bits Bits LSB LSB LSB LSB LSB
2053 Elect Table A
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PRELIMINARY
Symbol VDD ID ILO ILI VOL VOH VIL VIH fINT tPUS
Parameter Supply voltage Supply current Input leakage current Output low voltage Output high voltage Input low voltage Input high voltage Integrator loop frequency Power up stabilization time
Conditions Maximum bias and modulation current Bias and modulation current outputs open VIN = 0V to VDD IOL = 2mA VDD = 5V, IOL = -400A VDD < 4.5V, IOL = -100A
Min. 3
Typ.
Max. 5.5
Units V mA
2 1 10 0.4 2.4 VDD - 0.2 -0.1 0.7 x VDD 0.3 x VDD 0.5 1
A A V V V V V kHz ms
Output leakage current VOUT = 0V to VDD
Integrator time constant is less than 10ms 0 390.6
10
Analog Inputs
DETECT DETECT input to ADC IEXT TEMP Full scale current input N-channel modulation current P-channel modulation current N-channel bias current P-channel bias current 10-Bit DAC output Open drain ALERT output is active 1.5 V A
Analog Outputs
IMODN IMODP IBIASN IBIASP VDAC 0 0 0 0 0 -100 100 -100 100 1.5 mA mA mA mA V
Digital Outputs
ALERT ALERT output 5 mA
2053 Elect Table B
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SML2108
PRELIMINARY
DEVICE OPERATION
General Description The SML2108 is an adaptive power controller for laser diodes with an active feedback loop used to calibrate and control the mean and modulation power of high speed, high power laser diodes. Inherent manufacturing tolerances introduce variations of performance in laser diodes. These variations, combined with parametric changes over the laser's extreme temperature range and laser ageing, call for an efficient compensation solution. The SML2108, with a minimum number of external components, is designed to compensate for these tolerances using a digital control loop and a programmable nonvolatile calibration lookup table. Figure 1 illustrates the usefulness of the SML2108. The figure shows the output light power of a laser diode versus its operating current. Depicted in the graph are typical laser diode characteristics at two different temperatures. At the first temperature (T1), the laser requires an average bias current of IBIAS1. The modulation current needed to switch the laser between its on and off state is labeled IMOD1. The ratio of light power of its on state divided by the light power of its off state is referred to as the extinction ratio. Ideally the laser will maintain a constant extinction ratio over its entire operating temperature range, as the receiver module is calibrated to this level. Running the laser driver at a higher extinction ratio indicates that power is being wasted, whereas operating at a lower extinction ratio indicates that data may possibly be lost. When the laser is operated at a second temperature (T2) the required bias current is shown as IBIAS2. To maintain a constant extinction ratio as in the T1 curve the laser requires a modulation of IMOD2. The SML2108 is the industry's first integrated device capable of providing a variable modulation current based on a function of either the bias current or an external temperature. This ability to be able to compensate the modulation output current enables the system designer to optimize the extinction ratio of the laser driver module. The SML2108 has been specified to remove the need for any manual calibration of the laser control circuit. All calibration values are programmed through an industry standard 2-wire communication interface, whose protocol and function can be controlled by most production ATE equipment. Bias Current -- Mean Power Control The SML2108 bias current outputs (BIASP and BIASN) establish the average power being delivered to an external laser diode. The output of the laser diode is separately monitored using a local back-face diode, the output of which is tied to the DETECT pin of the SML2108. When coupled with the on-board integrator this feedback loop becomes the mean power control for the laser diode. The output block of the mean power control is shown in Figure 2.
Light Power
(On) 1 T1 T2
1BIAS1
1BIAS2
(Off) 0
Total 1
1MOD2 1MOD1
2053 Fig01
Figure 1. Laser Current Increase Caused by Temperature Increase, Constant Light Power Out
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The built-in integration time constant is nominally 1ms. This is accomplished by using an internal 2M resistor and 500pF capacitor. The time constant can be modified by adding external capacitance between the CAP1 and CAP2 terminals, and/or by adding external resistance between the DETECT and CAP1 terminals. For stability reasons it is not recommended that the time constant be decreased to less than 100us. The output of an internal 10-Bit DAC biases the positive terminal of the integrating amplifier. This DAC provides an analog reference to the integrator which is useful for initial calibration of the laser module. The full-scale value of the DAC output is 1.5V. 10-Bit Bias Control D/A The 10-Bit D/A determines the reference voltage of the non-inverting terminal of the integrating amplifier in the mean power control loop. Associated with this DAC are a 10-Bit volatile register and a 10-Bit nonvolatile (NV) register. The content of the volatile register determines the DAC output voltage. The DAC output voltage is given by the following relation:
VDD
IBIAS Source 0 to 10 mA or 0 to 100 mA ADC Input From MPC Integrator BIAS CONTROL BIASP
BIASN IBIAS Sink 0 to 100 mA
2053 Fig02
Figure 2. Output Block 1: Mean Power Control
VDD IMOD Source 0 to 10 mA or 0 to 100 mA MODP
OV =
X x 1.5V 1024
where X = the decimal equivalent of the 10-Bit data stored in the volatile register. Note that the DAC output voltage is not directly accessible external to the chip. However, when the SML2108 is placed in a typical application circuit, the mean power control feedback loop forces the voltage at the DETECT pin to be the same as the DAC output. On device power-up the volatile register may be loaded with all zeroes, or it may be loaded from the contents of the 10Bit nonvolatile register. Access to the 10-Bit volatile register is obtained via the 2wire interface at slave address 1001BIN, word address 0. Refer to Figures 9, 10, 12, and 13 for details on programming and reading data from the 10-Bit register. When writing to the volatile register the new DAC output will become valid immediately at the end of the write command. Reading the volatile register has no effect on the DAC output. Reading or writing the volatile register has no effect on the contents of the nonvolatile register. The 10-Bit NV register can only be accessed indirectly through the volatile register. The command sequence to communicate with the NV register is the same as that of
From IMOD DAC
MOD CONTROL
MODN IMOD Sink 0 to 100 mA
2053 Fig03
Figure 3. Output Block 2: IMOD
the volatile register, except word address 2 is used instead of 0. When reading the NV register, the data is first transferred into the volatile register where it may be accessed by the serial interface. Note that upon this transfer the DAC output will change immediately to reflect the new data. Similarly, when writing to the NV register,
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PRELIMINARY
the data is first placed in the volatile register. At the conclusion of the write command an internal nonvolatile write sequence initiates the storage of the volatile contents into the NV register. Note that when modifying the 10-Bit DAC output, the mean power control loop will become temporarily disrupted. It may be several milliseconds before the bias current has settled to its steady state value. Until then its value will be undefined. Modulation Current -- Auto-Monitor Control The laser bias current, which relates directly to laser temperature, can be monitored using an on-board, current-sensing A/D converter. In the auto-monitor mode the 8-Bit output of the converter is used as an address to the EEPROM lookup table. The subsequent 8-Bit data output from the lookup table becomes the input for the compensation DAC. The 8-Bit compensation DAC output is a current in the range of 0 to 100mA and is used to control the modulation current MODP and MODN. The output block of the modulation current control is shown in Figure 3. The lookup table provides an arbitrary mapping from bias current to modulation current. The input range to the ADC may be scaled and/or offset to provide maximum resolution within the appropriate conversion space. The sample interval is programmable from 10s to 1s. Refer to the ADC section for further details about configuring the A/D. The interface is used to program the configuration registers as well as lookup table values. Lookup Table A 2k-Bit (256 x 8) memory array of on-board EEPROM comprises the internal lookup table. This array is accessed via the 2-wire serial interface using a slave address of 1010BIN. (Note: 1010BIN is the default, however this may be set to 1110BIN, depending upon the contents of Configuration Register 2.) Refer to the Bus Interface section for details on programming and reading data from the device. In the auto-monitor mode the content of the array represents the transfer function between the A/D output and the final value of modulation current. Using a lookup table to implement this function allows arbitrary functions, and even nonlinear relations, to be easily realized. Also, the use of a lookup table allows each device to be customized
to normalize overall module operation. Although the memory may normally be read and written as a standard memory, a security feature exists in the configuration settings that will prevent any external access to the array. Additionally, if the auto-monitor feature is not used, then the modulation output current may be programmed to a fixed value, and the array may be used as a standard memory to store device settings, board identification values, production dates, etc. 8-Bit Current Output D/A The 8-Bit D/A defines the modulation output current. Associated with this DAC are an 8-Bit volatile register and an 8-Bit nonvolatile (NV) register. The content of the volatile register determines the DAC output current. The DAC output current is given by the following relation:
OC =
X x 100mA 256
where X = the 8-Bit data stored in the volatile register. On device power-up the volatile register may be loaded with all zeroes or it may be loaded from the contents of the 8Bit nonvolatile register. Access to the 8-Bit volatile register is obtained via the 2wire interface at slave address 1001BIN, word address 4. Refer to Figures 8 and 11 for details on programming and reading data from the 8-Bit register. When writing to the volatile register, the new DAC output will become valid immediately at the end of the write command. Reading the volatile register has no effect on the DAC output. Reading or writing the volatile register has no effect on the contents of the nonvolatile register. The 8-Bit NV register can only be accessed indirectly through the volatile register. The command sequence to communicate with the NV register is the same as that of the volatile register, except word address 6 is used instead of 4. When reading the NV register the data is first transferred into the volatile register where it may be accessed by the serial interface. Note that upon this transfer the DAC output will change immediately to reflect the new data. Similarly, when writing to the NV register, the data is first placed in the volatile register. At the conclusion of the write command, an internal nonvolatile write sequence initiates the storage of the volatile contents into the NV register.
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PRELIMINARY
ADC SCALING AND OFFSET The ADC can be customized to monitor a particular range of bias current by programming Register 0. Bits 3 and 2 control the scaling of the ADC while bits 1 and 0 control the ADC offset. The four graphs (Figures 4, 5, 6, & 7) illustrate the ADC scale values, according to the two bit code. In each Graph the curves are differentiated by the ADC offset values. Note: if using IBIASP with the maximum current option set to 10 mA, divide the x-axis value by 10 (i.e., 75 = 7.5, etc.). These combinations of scales and offsets allow the resolution to be maximized over a given range of current. For example, if the bias current is known to be in the range of 30mA to 70mA the choice would be the Half scale graph (code 10BIN) and the 1/4 offset curve (code 01BIN) to maximize the resolution of the ADC. Note that these graphs assume a full scale bias current of 100mA. When the ADC is configured to receive input from the EXT TEMP pin full scale current becomes 390.6A, which limits the internal 1/256 scale factor between bias current and the ADC input current.
255 Offset 00 01 10 11 224 192
ADC OUTPUT
255 224 192
ADC OUTPUT
160 128 96 64 32 0
160 128 96 64 32 0
Offset 00 01 10 11
0
10
20
30
40
50
60
70
80
90 100
2053 Fig04
0
10
20
30
40
50
60
70
80
90 100
2053 Fig05
IBIAS (mA)
IBIAS (mA)
Figure 4. Full Scale (code 11BIN) with Offset
Figure 5. Half Scale (code 10BIN) with Offset
255 224 192
ADC OUTPUT
255 224 192 Offset 00 01 10 11
ADC OUTPUT
160 128 96 64 32 0
160 128 96 64 32 0
Offset 00 01 10 11
0
10
20
30
40
50
60
70
80
90 100
2053 Fig06
0
10
20
30
40
50
60
70
80
90 100
2053 Fig07
IBIAS (mA)
IBIAS (mA)
Figure 6. Quarter Scale (code 01BIN) with Offset
10
Figure 7. Tenth Scale (code 00BIN) with Offset
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PRELIMINARY
REGISTERS
REGISTER BIT MAPS The SML2108 has three user programmable, nonvolatile configuration registers. Register 0 This register is used to configure the 8-Bit ADC that monitors the bias current. Bit 7 enables the ADC alert to be latched, which will hold the ALERT pin low until the alert is reset. Bits 6, 5, and 4 are used to set the sample interval of the ADC. The input to the ADC can be scaled and offset to provide maximum resolution over the bias current. Bits 3 and 2 are used to set the full scale range of the ADC, while bits 1 and 0 are used to set the ADC offset. See the Table. Register 1 This register controls multiple functions. Bit 7 disables the alert during a manual analog-to-digital conversion of the bias current. Bit 6 selects the action that will reset an alert from the ADC. When this bit is set to a 0 any device read or write will reset the alert. When set to a 1 the alert will be reset by a low AUTOMON signal. Bit 5 is used to toggle the source of the ADC input between the IBIAS current and the EXT TEMP signal. Bit 2 initializes the input of the 10 bit DAC to either zero or a stored value from a nonvolatile register when the device is powered up. Bit 1 initializes the input of the 8 bit DAC to either zero or a stored value from a nonvolatile register when the device is powered up. Bit 0 sets the maximum P-channel bias current (IBIASP) and modulation current (IMODP) to either 10mA or 100mA. Register 2 This register controls several functions related to the bus interface. Bits 7 and 6 control the read and write access to the configuration registers. It is imperative that register 2 be programmed properly to prevent an inadvertent lockout. Bit 5 determines whether the memory array is available or locked. Bit 4 selects the device type address for accessing the memory array, while bit 3 determines whether the device must receive a bus address that corresponds to the biasing of the address pins. Bit 2 is used to enable an alert condition on the ADC to shut down the bias current. Bits 1 & 0 are unused.
7 ADC Alert 0 1
6
5
4
3
2
1
0 Function Alert not latched Alert latched 5s 20s 160s 1.28ms 6.25ms 25ms 200ms 1.6s sample interval " " " " " " " " " " " " " "
ADC Sample Interval x 0 0 0 0 1 1 1 1 x 0 0 1 1 0 0 1 1 x 0 1 0 1 0 1 0 1
ADC Range
ADC Offset
x
x x x
x
0 0 1 x x x 1
0 1 0 1 0 0 1 0 1 0 1 1 Register 0
1/10 full scale bias current 1/4 full scale bias current 1/2 full scale bias current Full scale bias current No offset 1/4 of full scale bias current offset 1/2 of full scale bias current offset 3/4 of full scale bias current offset
2053 Reg0 1.0
x
x
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7 Alert 0 1
6 Alert Reset x 0 1
5 ADC Input
4
3
2 10-Bit DAC
1 8-Bit DAC
0 IBIASP Function Alert not allowed during manual conversion
Unused
x x 0 1 x x 0 1 x x
Alert allowed during manual conversion Alert reset by Read or Write Alert reset by Low on AUTOMON pin IBIASN or IBIASP current input to ADC EXT TEMP pin input to ADC Input to DAC is zero on power up Input to DAC is from nonvolatile register on power up 0 x 1 x 0 1 Input to DAC is zero on power up Input to DAC is from nonvolatile register on power up Max current is 10mA: IBIASP , IMODP Max current is 100mA: IBIASP , IMODP
2053 Reg1 1.0
x x x
Register 1
7
6
5
4
3
2
1
0 Function All Registers locked; no Read or Write
Register Access 0 0 1 1 0 1 0 1
Memory Device Pin Alert Access Address Address Action
Unused
x x 0 1 0 1 x x x x
Read all Registers; no Write Write all Registers; no Read Read and Write all Registers EEPROM available EEPROM locked Device Type Adress is 1010BIN Device Type Adress is 1110BIN 0 Responds to address pin biased address only Responds to any bus address 0 1 Bias current unaffected by alert condition Alert condition shuts down bias current
2053 Reg2 1.0
x
x x x
1 x
Register 2
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SML2108
PRELIMINARY
BUS INTERFACE
GENERAL DESCRIPTION The I2C bus is a two-way, two-line serial communication between different integrated circuits. The two lines are: a serial Data line (SDA) and a serial Clock line (SCL). All Summit Microelectronics parts support a 100kHz clock rate, and some support the alternative 400kHz clock. Check the AC Electrical Table for the value of fSCL. The
tR tF tHIGH
SDA line must be connected to a positive supply by a pullup resistor located on the bus. Summit parts have a Schmitt input on both lines. See Figure X1 and Table X1 for waveforms and timing on the bus. One bit of Data is transferred during each Clock pulse. The Data must remain stable when the Clock is high.
tLOW
SCL
tSU:SDA tHD:DAT tSU:DAT tSU:STO
tHD:SDA
tBUF
SDA In
tAA
tDH
SDA Out
2053 Fig08
Figure 8. I2C Data Timing
Symbol fSCL tLOW tHIGH tBUF tSU:STA tHD:STA tSU:STO tAA tDH tR tF tSU:DAT tHD:DAT TI tWR Parameter SCL clock frequency Clock low period Clock high period Bus free time Start condition setup time Start condition hold time Stop condition setup time Clock edge to valid output Data Out hold time SCL and SDA rise time SCL and SDA fall time Data In setup time Data In hold time Noise filter SCL and SDA Write cycle time Noise suppression 250 0 100 5 SCL low to valid SDA (cycle n) SCL low (cycle n+1) to SDA change Before new transmission Conditions Min. 0 4.7 4.0 4.7 4.7 4.0 4.7 0.3 0.3 1000 300 3.5 Max. 100 Units kHz s s s s s s s s ns ns ns ns ns ms
2053 Table01 1.0
Table 1. I2C Data Timing
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Start and Stop Conditions Both Data and Clock lines remain high when the bus is not busy. Data transfer between devices may be initiated with a Start condition only when SCL and SDA are high. A highto-low transition of the Data line while the Clock line is high is defined as a Start condition. A low-to-high transition of the Data line while the Clock line is high is defined as a Stop condition. See Figure 9.
SCL
1
2
3
8
9
SDA Trans SDA Rec ACK
2053 Fig10
Figure 10. Acknowledge Timing
START Condition SCL STOP Condition
In the case of a Read from a Summit part, when the last byte has been transferred to the Master, the Master will leave the Data line high for a NACK. This will cause the Summit part to stop sending data, and the Master will issue a Stop on the clock pulse following the NACK. In the case of a Write to a Summit part the Master will send a Stop on the clock pulse after the last Acknowledge. This will indicate to the Summit part that it should begin its internal non-volatile write cycle. Read and Write The first byte from a Master is always made up of a seven bit Slave address and the Read/Write bit. The R/W bit tells the Slave whether the Master is reading Data from the bus or writing Data to the bus (1 = read, 0 = write). The first four of the seven address bits are called the Device Type Identifier (DTI). The DTI for the SML2108 is 1010. The next three bits are not used in the SML2108 (See Figure 11). The SML2108 will issue an Acknowledge after recognizing a Start condition and its DTI. In the read mode the SML2108 transmits eight bits of data, then releases the SDA line, and monitors the line for an Acknowledge signal. If an Acknowledge is detected, and no Stop condition is generated by the Master, the SML2108 will continue to transmit data. If an Acknowledge is not detected (NACK) the SML2108 will terminate further data transmission. See Figure 12.
SDA In
2053 Fig09
Figure 9. I2C Start and Stop Timing Protocol The protocol defines any device that sends data onto the bus as a Transmitter, and any device that receives data as a Receiver. The device controlling data transmission is called the Master, and the controlled device is called the Slave. In all cases the Summit Microelectronic devices are slave devices, since they never initiate any data transfers. Acknowledge Data is always transferred in 8-Bit bytes. Acknowledge (ACK) is used to indicate a successful data transfer. The Transmitting device will release the bus after transmitting eight bits. During the ninth clock cycle the Receiver will pull the SDA line low to Acknowledge that it received the eight bits of data (See Figure 10). The termination of a Master Read sequence is indicated by a non-Acknowledge (NACK), where the Master will leave the Data line high.
SCL
1
2
3
4
5
6
7
8
9
SDA
1
0
1
0
x
x
x
R/W
ACK
2053 Fig11
Figure 11. Typical Master Address Byte Transmission
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Master SDA Slave
S T A R T
R / W 1010xxxR A C K xxxxxxx
A C K xx xx
N A C K
S T O P
Optional
2053 Fig12
Figure 12. Read
S T A R T
Master SDA Slave
R / W 1 0 1 0 x x xW A C K xxxxxxxx A C K xx xx A C K
S T O P
2053 Fig13
Figure 13. Write In the write mode the SML2108 receives eight bits of data, then generates an Acknowledge signal. It will continue to generate ACKs until a Stop condition is generated by the Master. See Figure 13. Random Address Read Random address Read operations allow the Master to access any memory location in a random fashion. This operation involves a two-step process. First, the master issues a write command which includes the start condition and the Slave address field (with the R/W bit set to Write) followed by the address of the word it is to read. This procedure sets the internal address counter of the SML2108 to the desired address. After the word address acknowledge is received by the Master, it immediately reissues a start condition followed by another Slave address field with the R/W bit set to Read. The SML2108 will respond with an Acknowledge and then transmit the 8 data bits stored at the addressed location. At this point, the Master does not acknowledge the transmission, but does generate a Stop condition. The SML2108 discontinues data transmission. Sequential READ Sequential Reads can be initiated as either a current address Read or a random access Read. The first word is transmitted as with the other byte read modes (current address byte Read or random address byte Read). However, the Master now responds with an Acknowledge, indicating that it requires additional data. The SML2108 continues to output data for each Acknowledge received. The Master terminates the sequential Read operation by not responding with an Acknowledge, and issues a Stop condition. During a sequential read operation the internal address counter is automatically incremented with each Acknowledge signal. For Read operations all address bits are incremented, allowing the entire array to be read using a single Read command. After a count of the last memory address the address counter will `roll-over' and the memory will continue to output data. The protocol for reading and writing to the registers and the lookup table are illustrated in Figures 14 through 24.
SUMMIT MICROELECTRONICS, Inc.
2053 2.2 11/07/00
15
SML2108
PRELIMINARY
TIMING DIAGRAMS
Master SDA Slave
S T A R T
Device R/ Address W 1010xxx0 A C K Word Address A C K
Data Byte n
Data Byte n+1
Data Byte n+15
S T O P
A C K
A C K
A C K
A C K
2053 Fig14
Figure 14. Look-up Table Page/Byte Write
Master SDA Slave
S T A R T
Device R/ Address W 1010xxx0 A C K Word Address A C K
S T A R T
A Device R/ C Address W K 1010xxx1 Data Byte
N A C K
S T O P
2053 Fig15
Figure 15. Look-up Table Random Address Read with Dummy Write
Master SDA Slave
S T A R T
Device R/ Address W 1010xxx0 A C K Word Address A C K
S T A R T
Device R/ Address W 1010xxx1 A C K
First Data Byte
A C K
A C K
Last Data Byte
N A C K
S T O P
2053 Fig16
Figure 16. Look-up Table Sequential Read with Dummy Write
16
2053 2.2 11/07/00
SUMMIT MICROELECTRONICS, Inc.
SML2108
PRELIMINARY
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000100 A C K DDDDDDDD 76543210 A C K
S T O P
2053 Fig17
Figure 17. 8-Bit DAC Volatile Register Write
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000100 A C K
S T A R T
Device R/ Address W 1001xxx1 A C K DDDDDDDD 76543210
N A C K
S T O P
2053 Fig18
Figure 18. 8-Bit DAC Volatile Register Read with Dummy Write
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000110 A C K DDDDDDDD 76543210 A C K
S T O P
2053 Fig19
Figure 19. 8-Bit DAC Non-volatile Register Write
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000110 A C K
S T A R T
Device R/ Address W 1001xxx1 A C K DDDDDDDD 76543210
N A C K
S T O P
2053 Fig20
Figure 20. 8-Bit DAC Non-volatile Register Read with Dummy Write
SUMMIT MICROELECTRONICS, Inc. 2053 2.2 11/07/00
17
SML2108
PRELIMINARY
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000000 A C K DD xxxxxx98 A C K DDDDDDDD 76543210 A C K
S T O P
2053 Fig21
Figure 21. 10-Bit DAC Volatile Register Write
Master SDA Slave
Device R/ Address W 1001xxx0 A C K
Location Address 00000010 A C K DD xxxxxx98 A C K DDDDDDDD 76543210 A C K
S T O P
2053 Fig22
Figure 22. 10-Bit DAC Nonvolatile Register Write
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000000 A C K
S T A R T
Device R/ Address W 1001xxx1 A C K DD xxxxxx98
A C K DDDDDDDD 76543210
N A C K
S T O P
2053 Fig23
Figure 23. 10-Bit DAC Volatile Register Read with Dummy Write
Master SDA Slave
S T A R T
Device R/ Address W 1001xxx0 A C K
Location Address 00000010 A C K
S T A R T
Device R/ Address W 1001xxx1 A C K DD xxxxxx98
A C K DDDDDDDD 76543210
N A C K
S T O P
2053 Fig24
Figure 24. 10-Bit DAC Nonvolatile Register Read with Dummy Write
18
2053 2.2 11/07/00
SUMMIT MICROELECTRONICS, Inc.
SML2108
PRELIMINARY
APPLICATIONS
APPLICATION EXAMPLE USING EXTERNAL TEMPERATURE INPUT The EXT TEMP pin of the SML2108 allows the input of the internal ADC to be driven from an external device, rather than a mirrored version of the bias current. Figure 25 shows an example using a National Semiconductor LM334 to deliver a current into the SML2108 that is proportional to absolute temperature. The scale and offset features of the ADC input can be used to center this current and maximize the full range of the look-up table. For this application the current ISET coming out of the LM334 and into the EXT TEMP pin of the SML2108 is given by the following equation: ISET = 227V / oK / RSET
5V
+ -
LM334
RSET
210 1% ISET
SML2108
EXT TEMP
2053 Fig25
Figure 25. Example of an External Temperature Sensing Device
For example, using a value of 210 for RSET yields a current of 295A at 0oC and 387A at 85oC. Next select scale and offset values of the ADC input that will optimize the current range of the LM334. Nominal fullscale input current of the ADC is 390.6A (= 100mA/256). By setting the input offset to 3/4 scale (293A) and the fullscale range to 1/4 scale (97.6A), then the zero scale of the internal ADC becomes 293A, and the full-scale is 390.6A. This represents a temperature range of approximately -2oC to 88oC using a 210 resistor in the configuration shown. (These settings correspond to configuration Register 0, Bits 3 - 0 set to 7HEX.)
SUMMIT MICROELECTRONICS, Inc.
2053 2.2 11/07/00
19
SML2108
PRELIMINARY
PACKAGE
48 PIN TQFP PACKAGE
8.975 - 9.025 0.353 - 0.355 6.5 - 7.1 0.271 - 0.280
0.02 0.50 BSC
6.5 - 7.1 0.271 - 0.280
8.975 - 9.025 0.353 - 0.355
0.009 0.22
0.003 0.076
DETAIL "A"
0.053 - 0.057 1.35 - 1.45
1 ref
0.063 1.60 max
Pin 1
0.018 - 0.030
A
mm. in.
0.004 - 0.008 0.10 - 0.20
0.45 - 0.75
B
DETAIL "B"
20xx Pckg 1.0
ORDERING INFORMATION
SML2108 Base Part Number
F Package F = 48 Pin TQFP
20
2053 2.2 11/07/00
SUMMIT MICROELECTRONICS, Inc.
SML2108
PRELIMINARY
NOTICE SUMMIT Microelectronics, Inc. reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. SUMMIT Microelectronics, Inc. assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained herein reflect representative operating parameters, and may vary depending upon a user's specific application. While the information in this publication has been carefully checked, SUMMIT Microelectronics, Inc. shall not be liable for any damages arising as a result of any error or omission. SUMMIT Microelectronics, Inc. does not recommend the use of any of its products in life support or aviation applications where the failure or malfunction of the product can reasonably be expected to cause any failure of either system or to significantly affect their safety or effectiveness. Products are not authorized for use in such applications unless SUMMIT Microelectronics, Inc. receives written assurances, to its satisfaction, that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; and (c) potential liability of SUMMIT Microelectronics, Inc. is adequately protected under the circumstances. (c) Copyright 2000 SUMMIT Microelectronics, Inc.
I2C is a trademark of Philips Corporation.
SUMMIT MICROELECTRONICS, Inc. 2053 2.2 11/07/00
21

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