SP8034A

® PRELIMINARY SP8034A 250 V/µs APC Amplifier with Integrated Photodiode and Gain Adjust Capability FEATURES ■ Slew Rate of 250V/us ■ 7ns Settling Time to 1% for 1.5V Step ■ 10 mV Output Offset Voltage ■ 20uV/°C Output Offset Drift ■ Digital Gain Select ■ +/- 6 dB External Gain Adjust VCC GAIN SEL RGCOM GND 1 2 3 4 SP8034A 8 Pin COB 8 7 6 5 VOUT VREF RGAIN2 RGAIN1 DESCRIPTION The SP8034A represents the next generation APC amplifier with integrated photodetector. This device monitors the light intensity of the laser diode in CD-R, CD-RW, DVD-R, DVD-RW and DVD-RAM assemblies by sensing the laser power with an integrated photodiode. The amplified signal from the APC contains the laser power information. This signal is subsequently fed back to the laser diode driver to control its power. The on-chip photodetector transforms incident light into a proportional current. This current is then converted to a voltage through a transimpedance amplifier. Adjustable gain is provided in the transimpedance amplifier by means of a gain control loop that is controlled by an external resistor. The external resistor is not part of the signal path, which greatly reduces the effects of all parasitic capacitances and inductances on the flex cable at these pins. The signal is buffered to provide reactive load drive capability. The SP8034A achieves an unparalleled level of performance by combining excellent DC stability and low noise with outstanding AC performance. This level of performance is achieved using a proprietary fully complementary BiCMOS process with fully integrated, on-board photodetectors. The SP8034A is offered with a nominal gain of 2000V/W and is packaged in a 3.0mm x 3.5mm, 8 lead COB package. Gain Select VCC R1 R2 6000 GND 2000 VOUT TIA Gain Control Buffer 6k R1 2000 R2 6000 VREF RGCOM RGAIN1 RGAIN2 Rg1 R g2 Figure 1. Functional Diagram Rev. 5/14/03 SP8034A APC Amplifier with Integrated Photodetector © Copyright 2003 Sipex Corporation 1 ABSOLUTE MAXIMUM RATINGS TJ(MAX) ........................................................................................ 120°C VS(MAX) ............................................................................................... 6V VIN(MAX) .............................................................................................. 6V These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. ELECTRICAL SPECIFICATIONS Unless otherwise noted: +4.5V ≤ VCC ≤ +5.5V, CLOAD = 50pF to GND, RGAIN=400Ω and RLOAD = 1kΩ to VREF. 0°C≤TA≤ +70°C, VREF = 2.1V PARAMETER Supply Voltage Output Sensitivity SP8034A CONDITIONS Any Select Mode. Laser Beam Diameter = 0.70mm, uniform density RGAIN = 950Ω RGAIN = 950Ω Any Select Mode MIN 4.5 TYP MAX UNITS 5 5.5 V 2000 V/W Output Sensitivity Change vs. VCC Output Sensitivity Change vs. Temp Input Optical Power Required to Produce 1.5V Output Swing SP8034A Full Scale Output Voltage Swing(Vp-p) Relative to VREF Voltage Reference Range RGAIN = 400Ω Output Offset Voltage Output Offset Voltage Drift RGAIN = 400Ω RGAIN = 950Ω Output Noise BW: 1kHz to 1MHz Output Noise BW: 1kHz to 100MHz Output Slew Rate Output Settling Time to 1% of Final Value, 1.5V Step Output Overshoot, 1.5V Step Bandwidth (-3db) RGAIN = 400Ω PSRR* Output Offset Voltage RGAIN = 400Ω RGAIN = 950Ω Power Supply Current TA = 25°C Full Temp Gain Adjust Range VCC=+5.0V 150Ω < RGAIN < 950Ω Gain Adjust Range VCC=+4.5V 250Ω< RGAIN < 950Ω Input Voltage Vlow (TTL Level) Vhigh (TTL Level) TJA, 3mm x 3.5mm Package * PSRR = 20 * log ( ∆ VSUPPLY / ∆ VOUT ) 5 0.1 %/V %/°C mW -1.5 1.9 -10 0.75 -1.7 2.1 200 1 3 250 7 2.3 10 25 50 2 5 15 5 V V mV µV/°C µV/°C mV mV V/µs ns % MHz dB dB mA 65 55 50 100 73 75 20 25 +6 +6 0.8 -6 -3 dB dB V V °C/W 2.4 90 Rev. 5/14/03 SP8034A APC Amplifier with Integrated Photodetector © Copyright 2003 Sipex Corporation 2 PIN DESCRIPTION PIN NUMBER 1 2 3 4 5 6 7 8 NAME VCC GAIN RGCOM GND RGAIN1 RGAIN2 VREF VOUT FUNCTION Supply Voltage GAIN Select Common connection point for RGAIN1 and RGAIN2 Power Ground Gain Adjust 1(Gain Select = LOW) Gain Adjust 2 (Gain Select = HIGH) Reference Voltage Output Voltage THEORY OF OPERATION The SP8034A is an Automatic Power Control (APC) circuit for pick-up head applications. The part consists of a photo-detector that converts the light (780nm or 650nm) into current, and active circuitry (transimpedance amplifier and buffer) to convert the current into voltage. The overall transfer characteristics are therefore represented by a Voltage per Watt curve. There are three pins for gain adjust, using two separate external resistors for two separate gain modes. This allows different adjust for a DVD and a CD mode. The two resistors are each tied from the corresponding RG pin (pin 5 or 6, depending on the mode) to the common gain pin (pin 3). The gain adjust is proportional to the external resistance and is done by means of an analog duplication circuit that translates the resistance value in an active feedback circuit at the transimpedance amplifier. The fact that the external resistor is not in the signal path ensures a better signal quality and immunity to the parasitic capacitance/inductance on the pins 3,5 and 6. In dark condition, the output of the circuit will remain at the externally supplied VREF (1.9V ≥ 2.3V). When light (650nm or 780nm) is received on the photo-diode, the output (VOUT, pin 8) will swing negative with respect to VREF. The output swing is guaranteed to be at least 1.5V from VREF. For example, with VREF at 2V, the output can swing at least as low as 0.5V (absolute). Gain (dB) +6 0 -3 -6 * Sensitivity (mV/mW) 4 2 1.4 1 5000 4500 4000 Sensitivity (V/W) 3500 3000 2500 2000 1500 1000 0 0 100 200 300 400 500 600 700 800 900 1000 Gain Adjust Resistor (Ω) Figure 2. Sensitivity vs. Gain Resistor (Absolute) 100M 95.0M 90.0M 85.0M 80.0M 75.0M 70.0M 65.0M 60.0M 55.0M 50.0M 45.0M 0.0 200 400 RGAIN 600 800 1.0K Figure 3. System Bandwith versus Gain Resistor, VCC = 5V, T = 27C. Ts(nS) 1% 13 12 11 10 BW (MHz) 61 79 87 93 Pin(uW) 380 750 1070 1500 Regain (Ω) 950 400 250 150 * VCC ≥ 5.0V Table 1. Target Gain Set Points for the System. Rev. 5/14/03 SP8034A APC Amplifier with Integrated Photodetector © Copyright 2003 Sipex Corporation 3 LAYOUT AND ROUTING CONSIDERATIONS A major consideration in developing the optical pick-up head system is the extremely small form factor, which is additionally aggravated by the physical locations required by the light path. Special care must be taken when designing the Flex or PCB for this part. The output peak current requirement is in the order of 12.5 mA when driving 50pF of capacitive load with a slew rate of 250V/µs. Therefore care must be taken to provide low inductance, low resistance paths for power and ground and output traces. Supply coupling is also very important. Good supply decoupling is important to ensure the high frequency performance of the system by eliminating supply lead inductance effects. The decoupling capacitor C1, as shown in Figure 5, should be as close to the part as possible. This capacitor should be 0.1µF ceramic. C2 is CL C1 C2 optional to improve decoupling and is recommended to be 1 µF tantalum. The layout of the PCB is pictured here. Note the wide and short traces on the supply lines. The traces for the gain resistors RGAIN1 and RGAIN2 are kept as short as possible to avoid excessive parasitics. Any parasitics on these nodes will limit the performance of the system. RGAIN1 and RGAIN2 are subminiature potentiometers in the application. This is a single layer board using FR4 material. In order to minimize coupling capacitance into the gain setting resistor nodes, it is also critical that VOUT+ and VOUT- are routed away from the traces associated with the gain-setting resistors. VCC GAIN GND R2 GND PIN RL VO VREF CR R1 Figure 4. Evaluation Board. +5V C1 0.1µF + VCC GAIN RGCOM GND 1 2 3 4 RG1 400 ® VOUT RS 8 VOUT 7 VREF Depends on FPC RL 1k + CL1 50pF GAIN + SP8034A 6 RGAIN2 5 RGAIN1 C2 0.1µF VREF RG1 400 Figure 5. Test Circuit - Cload = 50p, VCC = 5V, Gain = 0V, Rgain = 400. Rev. 5/14/03 SP8034A APC Amplifier with Integrated Photodetector © Copyright 2003 Sipex Corporation 4 PACKAGE: 8 PIN COB (3mm x 3.5mm) 0.090mm 1 2 3 4 8 7 6 5 b 0.600mm D e H TOP VIEW E 5° ( 2X) PIN SIDE VIEW L BOTTOM VIEW B A C SIDE VIEW DIMENSIONS in mm Minimum/Maximum A B b C 8–PIN COB 0.90/1.10 .127/.33 0.30/0.50 0.50 nom 2.90/3.10 3.00/3.20 0.75 nom 3.40/3.60 0.40/0.60 DETECTOR SIZE 0.35mm D E e H L 0.70mm Detector Area Rev. 5/14/03 SP8034A APC Amplifier with Integrated Photodetector © Copyright 2003 Sipex Corporation 5 ORDERING INFORMATION Part Number Temperature Range Package Type SP8034A ................................................. -20°C to +85°C .............. 8 lead COB (3.0mm x 3.5mm) Corporation SIGNAL PROCESSING EXCELLENCE Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sales Office 22 Linnell Circle Billerica, MA 01821 TEL: (978) 667-8700 FAX: (978) 670-9001 e-mail: sales@sipex.com Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Rev. 5/14/03 SP8034A APC Amplifier with Integrated Photodetector © Copyright 2003 Sipex Corporation 6