Datasheet

MAX4207
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
______________________________________________________________________________________ 13
Capacitive Loads
The MAX4207 drives capacitive loads of up to 50pF.
Reactive loads decrease phase margin and can pro-
duce excessive ringing and oscillation. Use an isolation
resistor in series with LOGV1 or LOGV2 to reduce the
effect of large capacitive loads. Recall that the combi-
nation of the capacitive load and the small isolation
resistor limits AC performance.
Power Dissipation
The LOGV1 and LOGV2 amplifiers are capable of
sourcing or sinking in excess of 30mA. Ensure that the
continuous power dissipation rating for the MAX4207 is
not exceeded.
TQFN Package
The 16-lead thin QFN package has an exposed paddle
that provides a heat-removal path, as well as excellent
electrical grounding to the PC board. The MAX4207’s
exposed pad is internally connected to V
EE
, and can
either be connected to the PC board V
EE
plane or left
unconnected. Ensure that only V
EE
traces are routed
under the exposed paddle.
V
EE
GND
REFVOUT
CMVIN
REFIOUT
CMVOUT
REFISET
V
CC
SCALE
LOGV2
OSADJ
LOGV1
REFIIN
LOGIIN
FIBER CABLE
APD
2.7V TO 76V
2.2µH
2.2µF0.22µF
BIAS
REF
CLAMP
OUT
TIA
GND
TO LIMITING
AMPLIFIER
HIGH-SPEED DATA PATH
32pF
V
CC
5MΩ
32pF
330Ω
330Ω
OUTPUT
PHOTODIODE BIAS
0.1µF
I
APD
/10
I
APD
0.1µF
MAX4207
MAX4007
0.1µF
V
EE
Figure 6. Logarithmic Current-Sensing Amplifier with Sourcing Input
Figure 7. Measuring Optical Absorbance
MAX4207
V
EE
GND
REFIIN
LOGIIN
V
CC
CMVIN
REFIOUT
CMVOUT
REFISET
V
CC
V
CC
SCALE
LOGV1
LOGV2
OSADJ
REFVOUT
32pF
330Ω
330Ω
32pF
V
EE