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參數(shù)資料
| 型號： | OPA832DBVR |
| 英文描述： | Low-Power, Single-Supply, Fixed-Gain Video Buffer Amplifier |
| 中文描述： | 低功耗，單電源，固定增益視頻緩沖放大器 |
| 文件頁數(shù)： | 19/26頁 |
| 文件大小： | 471K |
| 代理商： | OPA832DBVR |
"#$
SBOS266B JUNE 2003 REVISED SEPTEMBER 2004
www.ti.com
19
DC ACCURACY AND OFFSET CONTROL
The balanced input stage of a wideband voltage-feedback
op amp allows good output DC accuracy in a wide variety
of applications. The power-supply current trim for the
OPA832 gives even tighter control than comparable
products. Although the high-speed input stage does
require relatively high input bias current (typically 5
μ
A out
of each input terminal), the close matching between them
may be used to reduce the output DC error caused by this
current. This is done by matching the DC source
resistances appearing at the two inputs. Evaluating the
configuration of Figure 3 (which has matched DC input
resistances), using worst-case +25
°
C input offset voltage
and current specifications, gives a worst-case output
offset voltage equal to:
(NG = noninverting signal gain at DC)
±
(NG
×
V
OS(MAX)
)
±
(R
F
×
I
OS(MAX)
)
=
±
(2
×
10mV)
±
(400
×
1.5
μ
A)
=
±
10.6mV
A fine-scale output offset null, or DC operating point
adjustment, is often required. Numerous techniques are
available for introducing DC offset control into an op amp
circuit. Most of these techniques are based on adding a DC
current through the feedback resistor. In selecting an offset
trim method, one key consideration is the impact on the
desired signal path frequency response. If the signal path
is intended to be noninverting, the offset control is best
applied as an inverting summing signal to avoid interaction
with the signal source. If the signal path is intended to be
inverting, applying the offset control to the noninverting
input may be considered. Bring the DC offsetting current
into the inverting input node through resistor values that
are much larger than the signal path resistors. This will
insure that the adjustment circuit has minimal effect on the
loop gain and hence the frequency response.
THERMAL ANALYSIS
Maximum desired junction temperature will set the
maximum allowed internal power dissipation, as
described below. In no case should the maximum junction
temperature be allowed to exceed 150
°
C.
Operating junction temperature (T
J
) is given by
T
A
+ P
D
×
is the sum of quiescent power (P
DQ
) and additional
power dissipated in the output stage (P
DL
) to deliver load
power. Quiescent power is simply the specified no-load
supply current times the total supply voltage across the
part. P
DL
will depend on the required output signal and
load; though, for resistive loads connected to
mid-supply (V
S
/2), P
DL
is at a maximum when the output
is fixed at a voltage equal to V
S
/4 or 3V
S
/4. Under this
condition, P
DL
= V
S2
/(16
×
R
L
), where R
L
includes
feedback network loading.
JA
. The total internal power dissipation (P
D
)
Note that it is the power in the output stage, and not into the
load, that determines internal power dissipation.
As a worst-case example, compute the maximum T
J
using
an OPA832 (SOT23-5 package) in the circuit of Figure 3
operating at the maximum specified ambient temperature
of +85
°
C and driving a 150
load at mid-supply.
P
D
= 10V
×
3.9mA + 5
2
/(16
×
(150
|| 400
)) = 53.3mW
Maximum T
J
= +85
°
C + (0.053W
×
150
°
C/W) = 93
°
C.
Although this is still well below the specified maximum
junction temperature, system reliability considerations
may require lower ensured junction temperatures. The
highest possible internal dissipation will occur if the load
requires current to be forced into the output at high output
voltages or sourced from the output at low output voltages.
This puts a high current through a large internal voltage
drop in the output transistors.
BOARD LAYOUT GUIDELINES
Achieving optimum performance with a high-frequency
amplifier like the OPA832 requires careful attention to
board layout parasitics and external component types.
Recommendations that will optimize performance include:
a) Minimize parasitic capacitance
to any AC ground for
all of the signal I/O pins. Parasitic capacitance on the
output and inverting input pins can cause instability: on the
noninverting input, it can react with the source impedance
to cause unintentional bandlimiting. To reduce unwanted
capacitance, a window around the signal I/O pins should
be opened in all of the ground and power planes around
those pins. Otherwise, ground and power planes should
be unbroken elsewhere on the board.
b) Minimize the distance
( < 0.25”) from the power-supply
pins to high-frequency 0.1
μ
F decoupling capacitors. At the
device pins, the ground and power-plane layout should not
be in close proximity to the signal I/O pins. Avoid narrow
power and ground traces to minimize inductance between
the pins and the decoupling capacitors. Each power-
supply connection should always be decoupled with one
of these capacitors. An optional supply decoupling
capacitor (0.1
μ
F) across the two power supplies (for
bipolar operation) will improve 2nd-harmonic distortion
performance. Larger (2.2
μ
F to 6.8
μ
F) decoupling
capacitors, effective at lower frequency, should also be
used on the main supply pins. These may be placed
somewhat farther from the device and may be shared
among several devices in the same area of the PC board.
c) Careful selection and placement of external
components will preserve the high-frequency perfor-
mance.
Resistors should be a very low reactance type.
Surface-mount resistors work best and allow a tighter
overall layout. Metal film or carbon composition
axially-leaded resistors can also provide good high-
frequency performance. Again, keep their leads and PC
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| OPA832DBVT | 制造商:BB 制造商全稱:BB 功能描述:Low-Power, Single-Supply, Fixed-Gain Video Buffer Amplifier |
| OPA832ID | 功能描述:視頻放大器 Lo-Pwr Single-Supply Fixed-Gain Video Bfr RoHS:否 制造商:ON Semiconductor 通道數(shù)量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
| OPA832IDBVR | 功能描述:視頻放大器 Lo-Pwr Single-Supply Fixed-Gain Video Bfr RoHS:否 制造商:ON Semiconductor 通道數(shù)量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
| OPA832IDBVRG4 | 功能描述:視頻放大器 Lo-Pwr Single-Supply Fixed-Gain Video Bfr RoHS:否 制造商:ON Semiconductor 通道數(shù)量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
| OPA832IDBVT | 功能描述:視頻放大器 Lo-Pwr Single-Supply Fixed-Gain Video Bfr RoHS:否 制造商:ON Semiconductor 通道數(shù)量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
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