sp8034 Exar Corporation, sp8034 Datasheet - Page 4

• Manufacturer Part Number: sp8034
• Description: 250 V/?s Apc Amplifier With Integrated Photodiode And Gain Adjust Capability
• Manufacturer: Exar Corporation

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.
Rev. 5/21/03
Figure 5. Test Circuit - Cload = 50p, V
GAIN
+5V
C1
0.1µF
+
GAIN
GND
V
GND
R
CC
GCOM
GAIN
GND
V
CC
1
2
3
4
PIN
R2
R1
CC
SP8034 APC Amplifier with Integrated Photodetector
Figure 4. Evaluation Board.
= 5V, Gain = 0V, Rgain = 400.
S P8034
R
400
R
400
G1
G1
RL
V
V
®
O
REF
CR
8
7
6
5
LAYOUT AND ROUTING CONSIDERATIONS
4
V
V
R
R
OUT
REF
GAIN2
GAIN1
This capacitor should be 0.1µF ceramic. C2 is
optional to improve decoupling and is recom-
mended 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 R
R
cessive parasitics. Any parasitics on these nodes
will limit the performance of the system. R
and R
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 V
the traces associated with the gain-setting
resistors.
GAIN
GAIN
2 are kept as short as possible to avoid ex-
OUT
Depends
on FPC
RS
+ and V
2 are subminiature potentiometers in
OUT
RL
1k
© Copyright 2003 Sipex Corporation
+
- are routed away from
+
CL1
50pF
C2
0.1µF
V
V
OUT
REF
GAIN
1 and
GAIN
1