FN6916.0 September 23, 2009 In Figure 50, the circle sources are noise voltages while the diamonds are noise currents and 4kT is 1.6E - 20J. If" />
參數(shù)資料
型號: ISL1539AIRZ
廠商: Intersil
文件頁數(shù): 13/23頁
文件大?。?/td> 0K
描述: IC VDSL2 LINE DVR AMP 24QFN
標準包裝: 90
類型: 驅(qū)動器
驅(qū)動器/接收器數(shù): 4/4
規(guī)程: VDSL2
電源電壓: ±5 V ~ 15 V
安裝類型: 表面貼裝
封裝/外殼: 24-VFQFN 裸露焊盤
供應商設備封裝: 24-QFN(5x4)
包裝: 管件
20
FN6916.0
September 23, 2009
In Figure 50, the circle sources are noise voltages while
the diamonds are noise currents and 4kT is 1.6E - 20J.
If the op amp terms are assumed to be equal for the two
sides of the circuit and two RF and RS resistors are also
equal, and the differential gain is defined as
Ad = 1+2RF/RG, the differential output noise expression
becomes Equation 15.
Putting in numbers for the gain of 10 characterization
circuit (with RS = 50Ω) gives a differential output noise of
eo = 69nV/√Hz. Dividing this by the differential gain of 10
gives an input noise of ei =6.9nV/√Hz which is only
slightly more than the RMS sum of the two 4nV input
voltage noise terms for the op amps themselves
(5.7nV/√Hz).
Board Design Recommendations
The feedback resistors need to be placed as close as
possible to the output and inverting input pins to
minimize parasitic capacitance in the feedback loop. This
includes the RF and RP resistors in the active termination
configuration. Keep the gain resistor also very close to
the inverting inputs for its port and minimize parasitic
capacitances to ground or power planes as well.
Close placement of the supply decoupling capacitors
will minimize parasitic inductance in the supply path.
High frequency load currents are typically pulled
through these capacitors so close placement of 0.01F
capacitors on each of the supply pins will improve
dynamic performance. Higher valued capacitors, 6.8F
typically, can be placed further from the package as
they are providing more of the low frequency
decoupling.
The thermal pad for the ISL1539A should be connected
to either ground or the -VS power plane. The choice of
which plane depends on which one would have the
more accessible thermal area.
While the ISL1539A is relatively robust in driving
parasitic capacitive loads, it is always preferred to get
into any series output resistor needed in the design as
physically close as possible to the output pins. Then
trace capacitance on the other side of that resistor will
have a much smaller effect on loop phase margin.
Protection devices that are intended to steer large load
transients away from the ISL1539A output stage and
into the power supplies or ground should have a short
trace from their supply connections into the nearest
supply capacitor - or should include their own supply
capacitors to provide a low impedance path under fast
transient conditions.
FIGURE 50. OUTPUT NOISE MODEL
-
+
-
+
RS
RG
RF
eN
eO
iN
ii
S
4kTR
S
4kTR
G
R
4kT
F
4kTR
F
4kTR
)
Hz
(nV
() ()
() ()
(
)
f
d
f
i
s
n
d
o
kTR
A
R
i
kTR
R
i
e
A
e
4
2
4
2
+
=
(EQ. 15)
ISL1539A
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