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(R)
Advanced
SP8024/8025/8026
200V/s Integrated APC Amplifier
with Gain Adjust & Differential Output
FEATURES Slew Rate of 200V/s Fast Settling Time - 10ns Gain Switch 2V Output Swing Low Offset Voltage: < 10mV Low Offset Drift: < 20V/C 12dB External Gain Adjust Range
VCC GAIN RCOM GND
1 2 3 4
SP8024/25/26
8 Pin COB
8 7 6 5
VOUT + VOUT RGAIN2 RGAIN1
DESCRIPTION The SP8024, SP8025, and SP8026 are high-speed, differential output APC amplifiers that integrate the photodiode and adjustable gain block on one chip. This allows the user to control the laser power of the system in high-speed DVDRW, DVDRAM and CDRW systems. The wide 2V output swing also allows better system performance. FUNCTIONAL DIAGRAM
GAIN VCC GND
31
TIA
2463
Buffer
VOUT+ 1VP-P
50pF 1k
850 Rf1 Rf2 850
31
(Flexible Flat Cable)
VOUTBuffer
2463
1VP-P
50pF
1k
RGCOM RG1
RGAIN1 RG2
RGAIN2
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
1
ABSOLUTE MAXIMUM RATINGS
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. TJ(MAX) ........................................................................................ 120C VS(MAX) ............................................................................................... 6V VIN(MAX) .............................................................................................. 6V
ELECTRICAL SPECIFICATIONS
Unless otherwise noted: VCC = +5.0V, CLOAD = 50pF to GND, RGAIN=262 and RLOAD = 1k. -20CTA +85C, nominal gain
PARAMETER Supply Voltage Nominal Output Sensitivity SP8024 SP8025 SP8026 Input Optical Power Required to Produce 2 V Output Swing SP8024 SP8025 SP8026 Full Scale Output Voltage Swing(Vp-p) Output Common Mode Voltage Differential Output Offset Voltage Differential Output Offset Voltage Drift Differential Output Noise Differential Output Noise Differential Output Slew Rate Differential Output Settling Time to 1% of Final Value, 2V Step Output Overshoot, 2V step Bandwidth (-3db) PSRR Power Supply Current Gain Adjust Range Input Voltage Vlow(TTL Level) Vhigh(TTL Level) TJA, 3mm x 3.5mm Package
CONDITIONS Any Select Mode ODB Gain
MIN 4.5
TYP 5 1000 2000 3000
MAX UNITS 5.5 V V/W
Any Select Mode ODB Gain 2 1 0.666 1.9 -10 -20 BW: 1kHz to 1MHz BW: 1kHz to 100MHz 200 1 3 250 10 15 5 65 4.5V < VCC < 5.5V TA = 25C Full Temp No Load < 5% Overshoot, 150 < RGAIN < 1350 -9 60 100 65 20 25 3 dB 2 VCC/2 10 20 2 5 mW
V V mV V/C mV mV V/s ns % MHz dB mA
0.8 2.2 75
V V C/W
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
2
PIN DESCRIPTION
PIN NUMBER 1 2 3 4 5 6 7 8 NAME VCC GAIN RCOM GND RGAIN1 RGAIN2 VOUTVOUT+ FUNCTION Supply Voltage Gain Select Common connection point for RGAIN1 and RGAIN2 Power Ground Gain Adjust 1 Gain Adjust 2 Output Voltage Output Voltage +
THEORY OF OPERATION Internal Operation The SP8024/25/26 APC circuits have an integrated photo detector and are designed with three nominal sensitivities of 1mV/W, 2mV/ W and 3mV/W respectively. Each part's sensitivity can also be adjusted continuously and independently for two different gain modes via two external resistors over a range of 12dB. The two gain modes are controlled by a TTL compatible logic input. This logic input also normalizes the internal photo detector's responsivity for 650nm and 780nm laser wavelengths. The logic pin selects between the two external gain setting resistors to allow independent control and settings for the two gain functions. The 8024 APC family uses two stages of gain to optimize for speed and offset. The two stages consist of a differential trans-impedance amplifier (TIA), and a differential gain adjust amplifier. TIA The first stage is a differential trans-impedance amplifier (TIA) for converting the photo detector output current to a balanced differential voltage. This topology allows for fast settling of the photo detector and also cancels offset effects. The TIA has no external components. Variable Gain Amplifier This stage is used to vary the gain of the system. It provides selection for two different gain setting resistors, RGAIN1 and RGAIN2, at pins 5 and 6 via internal MOSFET switches S1 and S2. The logic input at pin 2 controls the selection of the two external gain set resistors.
Table 1: Gain Select Logic Truth Table
Gain Select Pin 2 0 or Open 1 Rexternal, Pin 3 to: RG1 - Pin 5 RG2 - Pin 6 Gain Factor (x) 6.25 6.25 Sensitivity (mV/W) RG1 = RG2 = 262
SP8024 SP8025 SP8026
1 1
2 2
3 3
The gain of this balanced amplifier topology is given by: GAIN = 1 + Rf1 + Rf2 REXT
where RGAIN is external and Rf1 = Rf2 = 850 in feedback. The nominal gain is defined as 6.25.
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
3
THEORY OF OPERATION : Continued Variable Gain Amplifier: continued There are internal buffering resistors and a MOSFET switch resistance in series with the external Rgain. These internal resistances add up to a nominal value of 62. Therefore the true gain equation is: GAIN = 1 + Rf1 + Rf2 REXT + 62 with the internal compensation of the amplifier, instability occurs. This instability appears as overshoot in the transient response. The stray capacitance at pins 5 and 6 should be kept below 1pF. This stage also allows the part to drive high capacitive loads. The maximum load capacitance is 50pF bulk. The actual load is typically a flexible ribbon cable (FLEX) that acts like a transmission line. This presents a distributed capacitive load plus inductance and resistance. In this case care should be taken to match the characteristic impedance of the line at the far end to avoid standing waves and ringing. The buffer is designed to drive 1k to ground. However, this resistor can be adjusted in value to accommodate the characteristic impedance of the signal trace.
This gives a nominal external Rgain value of 324 - 62 = 262 for a gain of 6.25. The constraints on this stage are the parasitic capacitances associated with the input pins. The resistors used for setting the system gain are actually subminiature potentiometers. They are used for calibrating out systematic variations in the optical path. Pins 5 and 6 connect to the summing node of the gain stage through MOSFET switches. When a capacitor is added to the summing node of an inverting amplifier it creates a pole in the response. If this pole increases enough to interfere
SP8026 Differential APC Sensitivity versus Gain Set Resistor
6.0 5.0 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -4.0 -5.0 -6.0 -7.0 -8.0 -9.0 -10.0 -11.0 -12.0 REXT RGAIN Sensitivity 6.0 5.7 5.3 5.0 4.7 4.3 4.0 3.7 3.3 3.0 2.7 2.3 2.0 1.7 1.3 1.0 0.7 0.3 0.0 2200
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Resistance ()
Figure 1. System Gain versus Gain Set Resisitor
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
4
System Sensitivity (mV/W)
Gain (dB)
Layout and Routing Considerations Special care must be taken when designing the Flex or PCB for this part. The output peak current requirement is in the order of 12.5mA when driving 50pF of capacitive load with a slew rate of 200V/s 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 should be as close to the part as possible. This capacitor should be 0.1F ceramic. C2 is optional to improve decoupling and is recommended to be 1F tan-
talum. The layout of the PCB is pictured here. Note the wide and short traces on the supply lines. The traces for the gain resistors R1 and R2 are kept as short as possible to avoid excessive parasitics. Any parasitics on these nodes will limit the performance of the system. R1 and R2 are subminiature potentiometers in the application. This is a single layer board done on 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.
Top
Figure 2. Test and Evaluation PCB Layout for COB 8 Lead Package
Bottom
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
5
+5V + C1 0.1F VCC GAIN GAIN RGCOM GND 1 2 3 4 8 VOUT+ VOUTRGAIN2 RGAIN1 RL2 1k + +
VOUT+
RL1 1k
CL1 50pF
SP8024 SP8025 SP8026
7 6 5
CL2 50pF
VOUTRG1 262
RG2 262
Figure 3. Test and Evaluation Schematic
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
6
PACKAGE : 8 PIN COB
0.090
1 2 3 4
8 7 6
b
0.600
D e
5
S H TOP VIEW E
5 ( 2X)
F L
PIN SIDE VIEW
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 0.28/0.48 0.075/0.275
DETECTOR SIZE
0.35mm
D E e H L F S
0.70mm
Detector Area
8 PIN COB (3.5mm x 3.0mm)
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
(c) Copyright 2003 Sipex Corporation
7
ORDERING INFORMATION
Part Number Temperature Range Package Type
SP8024 ................................................... -20C to +85C .............. 8 lead COB (3.0mm x 3.5mm) SP8025 ................................................... -20C to +85C .............. 8 lead COB (3.0mm x 3.5mm) SP8026 ................................................... -20C to +85C .............. 8 lead COB (3.0mm x 3.5mm)
Corporation
ANALOG 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. 6/02/03 SP8024, 25, 26 200V/s Integrated APC Amplifier (c) Copyright 2003 Sipex Corporation
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