Download 简化的 LDO PSRR 测量

Application Report
Application
Report
应用报告
Application
Report
SLAA414
– July 2009
年
ZHCA089–2009
7月
SLAA414
July2009
2009
SLAA414
––July
LDO PSRR Measurement
Simplified
LDO PSRR 测量简化说明
LDOPSRR
PSRRMeasurement
Measurement
Simplified
LDO
Simplified
Sanjay Pithadia and Scot Lester .................................................................... PMP - LP Linear Regulators
和Regulators
PMP
– 低压线性稳压器
Sanjay
Pithadia
Scot Lester
Sanjay
Pithadiaand
andScot
ScotLester
Lester....................................................................
....................................................................作者：
PMP
LPLinear
LinearRegulators
Sanjay
Pithadia
PMP
- -LP
ABSTRACT
ABSTRACT
This application report explains ABSTRACT
different
methods of measuring the Power Supply
This
application
report
explains
different
methods
of measuring
measuring
the Power
Power
Supply
摘要
Rejection
Ratio
(PSRR)
of a Low-Dropout
(LDO) of
regulator
and the
includes
theSupply
pros and
This
application
report
explains
different
methods
Rejection
Ratio
(PSRR)
of
a
Low-Dropout
(LDO)
regulator
and
includes
the
pros
and
cons
of
these
measuring
methods.
Rejection
Ratio
(PSRR)
of
a
Low-Dropout
(LDO)
regulator
and
includes
the
pros
and
本应用报告解释了测量低压差 (LDO) 稳压器的电源抑制比 (PSRR) 的不同测量方法以及这些测量方法的优点
consofofthese
thesemeasuring
measuringmethods.
methods.
cons
及缺点。
What is PSRR?
What
PSRR?
What isisPSRR?
Power Supply Rejection Ratio or Power Supply Ripple Rejection (PSRR) is a measure of a circuit’s power
什么是 PSRR?
Power
Supply
Rejection
Ratiooror
Power
Supply
RippleRejection
Rejection
(PSRR)
ameasure
measure
circuit’s
power
supply’s
rejection
expressed
as
a logSupply
ratio
ofRipple
output
noise
to input
noise.
provides
a measure
of
Power
Supply
Rejection
Ratio
Power
(PSRR)
isisaPSRR
ofofaacircuit’s
power
电源抑制比或电源纹波抑制
是一个电路的电源抑制能力的度量值，表示为输出噪声与输入噪声的对数之比。
提供了
(PSRR)ripple,
supply’s
rejection
expressed
asaalog
log
ratioofofoutput
outputnoise
noiseto
toinput
inputnoise.
noise.
PSRR
provides
ameasure
measure
offrom
how well
a circuit
rejects
of ratio
various
frequencies,
injected
at
its input.
The
ripple acan
bePSRR
either
supply’s
rejection
expressed
as
PSRR
provides
of
一个电路对从它的输入处引入的不同频率的纹波抑制能力的度量值。纹波可以来自输入电源，比如一个
的电源纹波，
how
well
circuit
rejects
ripple,
varioussupply
frequencies,
injectedatatripple
input.
The
ripple50Hz/60Hz
canbe
beeither
either
from
the
input
supply
such ripple,
as
a 50Hz/60Hz
ripple,injected
switching
from
a DC/DC
converter,
orfrom
ripple
how
well
aacircuit
rejects
ofofvarious
frequencies,
itsitsinput.
The
ripple
can
thedue
input
supply
such
asan
50Hz/60Hz
supply
ripple,
switching
ripple
from
DC/DC
converter,
ripple
也可以是来自
转换器的开关纹波，还可以是由于输入电压被电路板上不同的电路块共用所致。在
tosupply
the
sharing
of
input supply
between
different
circuit
blocks
onaathe
board.
InLDO
the的情况下，
case
of
LDOs,
the
input
such
as
aa50Hz/60Hz
supply
ripple,
switching
ripple
from
DC/DC
converter,
ororripple
DC/DC
PSRR
due
theis
sharing
anof
input
supply
between
differentcircuit
circuitcompared
blockson
onthe
board.
thecase
case
LDOs,
PSRR
a measure
the supply
regulated
output
voltage
ripple
tothe
the
inputInIn
voltage
ripple
over
a wide
due
totothe
sharing
ofofan
input
different
blocks
board.
the
ofof(dB)
LDOs,
是一个在较大的频率范围内（通常为
），稳定的输出电压纹波相比于输入电压纹波的度量值，用分贝
来表示
10Hz 至between
1MHz
PSRR
measure
theregulated
output
voltage
ripple
compared
to
the
input
voltage
ripple
over
a
wide
frequency
range (10Hz
toregulated
1MHz
is
common)
and
is
expressed
in
decibels
(dB).
The
PSRR
is
very
critical
PSRR
isisaameasure
ofofthe
output
voltage
ripple
compared
to
the
input
voltage
ripple
over
a
wide
其大小。在许多音频和射频应用中，
是一个非常重要的参数。
PSRR
frequency
range
(10Hzaudio
1MHz
iscommon)
common)
andisisexpressed
expressedinindecibels
decibels(dB).
(dB).The
ThePSRR
PSRRisisvery
verycritical
critical
parameter
in many
andisRF
applications.
frequency
range
(10Hz
toto1MHz
and
parameter
in
many
audio
and
RF
applications.
parameter
in
many
audio
and
RF
applications.
计算The
的基本公式是：
PSRR
basic
equation for PSRR is:
The
basic
equationfor
forPSRR
PSRR
The basic equation
is:is:
Ripple
Input
PSRR = 20 log
RippleInput
Ripple
Input
Ripple
Output
PSRR==20
20log
log
PSRR
(1)
RippleOutput
Ripple
Output
(1)
(1)
在过去，
性能，但目前
已经拥有了在 5MHz
下 PSRR >TI
的 LDO >
LDO 稳压器件都具有较差的高频
TI performance,
40dB
LDO。在
TI PSRR
Historically
LDOs have poor highPSRR
frequency
PSRR
but currently
has的LDOs
with
数据表中，关于
曲线图很重要的一点是，
的坐标轴是反向的（如图
所示）。
被计算为抑制能力，因此它本应
Historically
LDOs
have
poor
high
frequency
PSRR
performance,
but
currently
TI
has
LDOs
with
PSRR
PSRR
PSRR
1
PSRR
40dB at LDOs
5MHz.have
One poor
important
point regarding
PSRR graphs
TI LDO TI
datasheet
is that
PSRR
Historically
high frequency
PSRRthe
performance,
butincurrently
has LDOs
with the
PSRR
>>
40dB
at
5MHz.
One
important
point
regarding
the
PSRR
graphs
in
TI
LDO
datasheet
is
that
the
PSRR
是个负数；然而，图中显示它是一个正数，这说明一个更高的数值表示了更高的噪声抑制。
axis
inverted
Figurepoint
1). The
PSRR the
is calculated
as rejection
so itdatasheet
should beisathat
negative
number;
40dB
at is
5MHz.
One(See
important
regarding
PSRR graphs
in TI LDO
the PSRR
axis
inverted
(See
Figure
1).
Thepositive
PSRRisnumber
iscalculated
calculated
asrejection
soititshould
should
beaahigher
negative
number;
however,
the(See
graph
shows
itThe
as
so that
arejection
higher so
number
denotes
noise
rejection.
axis
isisinverted
Figure
1).
PSRR
as
be
negative
number;
however,
the
graph
shows
it
as
positive
number
so
that
a
higher
number
denotes
higher
noise
rejection.
however, the graph shows it as positive number so that a higher number denotes higher noise rejection.
80
8080
150�mA
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70
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60
10�mA
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PSRR�-�dB
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Figure 1. PSRR Graph of TPS717xx LDOs
Figure1.1.图
PSRR
Graph
TPS717xx
LDOs
Figure
PSRR
Graph
ofof的
TPS717xx
LDOs
1. TPS717xx
LDO
PSRR 曲线图
SLAA414 – July 2009
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July2009
2009
年 7 月 Feedback
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July
ZHCA089
2009
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LDO PSRR Measurement Simplified
1
测量简化说明
1
LDO
PSRR
Measurement
Simplified
1
LDO
PSRR
LDO PSRR Measurement Simplified
1
www.BDTIC.com/TI
Measuring PSRR of LDO
www.ti.com
Measuring PSRR of LDO
The
following
的PSRR
测量
LDO
Measuring
PSRR ofsections
LDO
explain different methods of measuring the PSRR of an LDO.
www.ti.com
www.ti.com
1. Measuring PSRR using LC summing node method:
的PSRRPSRR
测量 of LDO
Measuring
LDO
The basic method of measuring PSRR is shown in Figure 2. In this method, DC voltage and AC
The
following
sectionsLDO
explain
different
methods
measuring
the PSRR
ofthe
an operating
LDO.
以下各节解释了测量一个
的PSRR
的不同方法：
voltages
are summed
together
and
applied
at theofinput
of the LDO.
VDC is
point bias
voltage
and
VAC
is
the
noise
source
used
in
the
test.
Capacitor
C
prevents
VAC
from
shoring
VDC
1.1. 使用
Measuring
PSRR using
LC总和节点法测量
PSRR：LC summing node method:
and inductor L prevents VDC from shorting VAC. So L and C are used for isolating both the sources,
测量
的基本方法如图
所示。在这个方法中，直流电压和交流电压合在一起作为
对VDC产生
ThePSRR
basic
method of measuring
PSRR is shown in Figure 2. In this method,
DC voltage
and
AC
LDO的输入。电容
C防止
VAC
VDC and
VAC, from each2 other.
voltages
are
summed
together
and
applied
at
the
input
of
the
LDO.
VDC
is
the
operating
point
bias
高脉冲影响，电感L防止VDC令VAC发生短路。因此L和C用于隔离两个电源，VDC和VAC。
Thevoltage
L and Cand
willVAC
create
a high
pass
filter used
for VAC
which
will
limit howClow
in frequency
we can
measure
is
the
noise
source
in
the
test.
Capacitor
prevents
VAC
from
shoring
VDC
和C形成一个针对于
点由公式point
VAC的高通滤波器，将限制我们所能测量的
PSRR的最低频率。这个滤波器的
2确定。低于
the Land
PSRR.
The 3dB
point
ofVDC
this filter
determined
Frequencies
below3dB
the
inductor
L prevents
fromisshorting
VAC.by
SoEquation
L and C2.
are
used for isolating
both3dB
the sources,
点的频率将被减弱，使得测量变得更加困难。能被测量的最高频率由
和C的自谐振频率所确定。
will 3dB
start
to
beVAC,
attenuated
which
will make measurements moreLdifficult.
The highest frequency that can
VDC
and
from each
other.
be measured is determined by the self resonant frequencies of the L and C components.
The L and C will create a high pass filter for VAC which will limit how low in frequency we can measure
Fthe
1/ 2Ȇ ¥LC
(2)
PSRR.
The 3dB point of this filter is determined by Equation 2. Frequencies below the 3dB point
min =
will
start
to
be
attenuated
which
will
make
measurements
more
difficult.
The
highest
frequency
that
A drawback to this method is that it works well only for mid-range frequencies (approximately 1 kHz to can
be
measured is determined by the self resonant
frequencies of the L and C components.
500这种方法的缺点是，它只对中频范围内（大约
kHz).
1 kHz 至 500 kHz）的测量是有效的。
Fmin = 1/ 2Ȇ ¥LC
VIN
(2)
VOUT
A drawback to this method is that it works well
only for mid-range frequencies (approximately 1 kHz to
LDO
500 kHz).
L
VIN
VIN
CIN
L
VAC
C
+
+
VDC
VOUT
COUT
GND
LDO
+
+
C
VDC
VOUT
VIN
CIN
LOAD
VOUT
GND
COUT
LOAD
VAC
Figure 2. Basic Method of Measuring PSRR of LDO
2
2. Measuring PSRR using summing amplifier
To improve the measurement of PSRR, a recommended method is described using a high-bandwidth
Figure 2. Basic
of Measuring
PSRR of LDO
图 Method
测量 and
的
PSRR的基本方法
amplifier as summing node to inject the2.signalsLDO
provides
the isolation between VAC and VDC. This
method
is tested
and
verified
using TPS72715
2.
PSRR
2.使用和放大器法测量
Measuring
PSRR
using summing
amplifier LDO and THS3120 high-speed amplifier from Texas
Instruments.
The
basic
set-up
is
shown
in Figure 3. The PSRR is measured with a no-load
condition
为了改进
PSRR 的测量方法，推荐的方法是，使用一个高带宽放大器作为总和节点来输入信号并提供
VACa和high-bandwidth
VDC 之间的隔离。
To improve
the measurement of PSRR, a recommended method is described using
and the resulting measured PSRR graph corresponds with the datasheet graph of PSRR.
amplifier as
summing
to inject
the signals and provides the isolation between3所示。
VAC PSRR
and VDC.
This
德州仪器使用
和 THS3120
高速放大器对这一方法进行了测试和验证。基本结构如图
在无负载的
TPS72715
LDOnode
Keep
in mind
the
following
while measuring
the PSRR
using
this method:
method
is
tested
and
verified
using
TPS72715
LDO
and
THS3120
high-speed
amplifier
from
Texas
条件下进行测量，而测量结果图与数据表中的 PSRR 结果图相一致。
Instruments.
The basic
set-up
is shown
in Figure
3. The
is measured
with athis
no-load
condition
a. The
input capacitor
of LDO
should
be removed
before
thePSRR
measurement
because
capacitor
当使用此方法测量
时，请记住以下几点：
PSRR
and the
resulting
measured
PSRR graph
could
cause
the
high-speed
amplifier
to gocorresponds
unstable. with the datasheet graph of PSRR.
在测量前，应去掉
的输入电容，因为它将引起高速放大器的不稳定。
LDO
Keep
in Vout
mind should
the
following
while measuring
the PSRR using
this(either
method:
b.a. Vin
and
be measured
with high-impedance
probes
scope or network analyzer)
当测量 Vin 和 Vout
时，应使用高阻抗探头（示波器或网络分析仪）迅速接触
或 Vout
引脚，以便使探头电感的影响降至最 低。
b. immediately
Vin
at
the
Vin
or
Vout
pins
to
minimize
the
set-up
inductance
effects.
a. The input capacitor of LDO should be removed before the measurement
because this capacitor
在这里测试探头不应具有过长的导线，否则将增大电感并影响测量结果。
c.c. There
testcause
set-upthe
should
not have
any long
since this will add inductance and impact the
could
high-speed
amplifier
to wires
go unstable.
当确定交流及直流输入的数值时，应考虑以下条件：
d. results.
b.
Vin and Vout should be measured with high-impedance probes (either scope or network analyzer)
d. While
selecting+ the
values
ofVABS
AC and
DC
thethe
following
immediately
at the
Vin 的
or
Vout
pins
to inputs,
minimize
set-up conditions
inductanceshould
effects.be considered:
（最大值）
（最大值）
VAC
VDC
< LDO
VAC
(max)
+
VDC
<
V
(max)
of
LDO
c.VDC
There
test
set-up
should
not
have
any
long
wires
since
this
will
add
inductance
and impact the
– VAC > LDO 的 VUVLO ABS
results.
VDC – VAC > VUVLO of LDO
此外，若满足以下条件，将会得到最好结果：
A
d. Also,
While selecting
the values
ofobtained
AC
and DC
following conditions should be considered:
best+ Vdo
results
beVout
if: inputs, the
这里
是 LDO 的输出电压，
VDC–VACthe
> Vout
+ 0.5will
Vdo 是工作点的额定压降。
VAC (max) + +
VDC
(max) Vout
of LDO
VDC–VAC>Vout
Vdo<+V0.5
is the
voltage of the LDO and
Vdo
is the
ABS where
的 output
将会过小而无法在
e. 在非常高的频率下，放大器的响应将开始减弱应用于
LDO
VAC信号。在某些时候，被减弱的
VAC
LDO
specified
drop
out
voltage
at
the
operating
point.
VDC
–
VAC
>
V
of
LDO
UVLO
的输出端测到。
e. At veryAlso,
high frequencies,
the will
response
of the if:
amplifier will start to attenuate the VAC signal that is
the best results
be obtained
f. 随着负载电流的增加，LDO 的开环输出阻抗将会减小（因为 MOSFET 的输出阻抗与漏电流成反比），从而降低增益。增加
appliedVDC–VAC>Vout
to the LDO. At some
point,
the
attenuated
will bevoltage
too small
to measure
theisoutput
+ Vdo + 0.5 where Vout isVAC
the output
of the
LDO andonVdo
the
负载电流也会将输出极点推向更高的频率，从而增大了反馈回路的带宽。负载的增加带来的实际效果是，减小了更低频率的
of
the LDO.
specified drop out voltage at the operating point.
（由于增益的减小），而增大了更高频率的
。
PSRR
f. As
load
current
thethe
open-loop
output
of start
LDO to
decreases
a MOSFET
e.
At very
high increases,
frequencies,
responsePSRR
of theimpedance
amplifier will
attenuate(Since
the VAC
signal that is
output
impedance
is
inversely
proportional
to
the
drain
current),
thus
lowering
the
gain.
applied to the LDO. At some point, the attenuated VAC will be too small to measureIncreasing
on the output
the of
load
thecurrent
LDO. also pushes the output pole to higher frequencies, which increases the feedback
f. As load current increases, the open-loop output impedance of LDO decreases (Since a MOSFET
output impedance
gain. –Increasing
LDO PSRR Measurement
Simplifiedis inversely proportional to the drain current), thus lowering the
SLAA414
July 2009
the load current also pushes the output pole to higher frequencies, which
increases
the feedback
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测量简化说明
PSRR
2 2 LDOLDO
PSRR Measurement Simplified
www.BDTIC.com/TI
年 2009
ZHCA089
– 2009
7月
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– July
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Measuring PSRR Using Oscilloscope
Measuring
PSRR
Using
Oscilloscope
www.ti.com
Measuring
PSRR
Using
Oscilloscope
www.ti.com
www.ti.com
用示波器测量
www.ti.comPSRR
loop bandwidth. The net effect of increasing the load is therefore reduced PSRR at lower
loopfrequencies
bandwidth.
TheThe
net net
effect
of increasing
the the
load
is
therefore
reduced
PSRR
at lower
(because
of reduced
along
withload
increased
PSRR
at higher
frequencies.
loop
bandwidth.
effect
of gain)
increasing
is therefore
reduced
PSRR
at lower
frequencies
(because
of
reduced
gain)
along
with
increased
PSRR
at
higher
frequencies.
frequencies (because of reduced gain) along with increased PSRR at higher frequencies.
High�Impedance Adapters�(Model�#�41802A from Agilent)
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High�Impedance
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Figure 3.
of
Measuring PSRR of LDO
图Recommended
的Method
的推荐方法
3. 测量 LDOMethod
PSRR
Figure
3. Recommended
of Measuring
PSRR
of LDO
Figure
3. Recommended
Method
of Measuring
PSRR
of LDO
Figure
4
shows
the
PSRR
graph
measured
with
this
method.
图 4 显示的是使用这种方法测量 PSRR 的结果图。
Figure
4 shows
the the
PSRR
graph
measured
withwith
this this
method.
Figure
4 shows
PSRR
graph
measured
method.
Figure 4. PSRR Measured With Recommended Method
Figure
4.
Measured
With
Recommended
图PSRR
使用推荐方法测量所得到的
Figure
4.
Measured
With
Recommended
Method
4. PSRR
PSRRMethod
The THS3120 is suitable for measuring PSRR up to VDC = 5V, Frequency = 10MHz and Iload =
The400mA.
THS3120
is suitable
for VDC
measuring
PSRR
up
to
= 5V,
Frequency
= 10MHz
andand
IloadI=
适用于测量最大值为
THS3120
= 5V, Frequency
= 10MHz
The
THS3120
is suitable
for measuring
PSRR
upVDC
to并且
VDC
= 5V,
Frequency
= 10MHz
load =
400mA.
的
。
Iload
= 400mA
PSRR
400mA.
Measuring PSRR Using Oscilloscope
Measuring
PSRR
Using
Oscilloscope
Measuring
PSRR
Using
Oscilloscope
用示波器测量
PSRR
If the user
does not have a network analyzer then there is a simpler but more cumbersome method which
If the
user
does
not
have
a network
analyzer
thenthen
there
istoameasure
but
more
cumbersome
method
which
uses
auser
signal
generator,
DC
source
and
oscilloscope
the but
PSRR.
An
AC signal
from
signal
If如果用户没有网络分析仪，那么一个更简单但更麻烦的方法是使用一个信号发生器、直流电源和示波器来测量
the
does
not
have
a network
analyzer
there
issimpler
a simpler
more
cumbersome
method
。 which
PSRR
uses
a
signal
generator,
DC
source
and
oscilloscope
to
measure
the
PSRR.
An
AC
signal
from
signal
generator
is
applied
along
with
DC
signal
at
the
input
of
the
LDO,
as
shown
in
either
of
the
afore
uses
a
signal
generator,
DC
source
and
oscilloscope
to
measure
the
PSRR.
An
AC
signal
from
signal
用信号发生器产生一个交流信号，与直流信号一起作为
的输入，这与前面所提到的方法是一样的，然后用一个
LDO
generator
is applied
along
with
DC
signal
input
of the
LDO,
in either
the
afore
mentioned
and
the
output
of at
thethe
LDO
isinput
measured
onasanshown
oscilloscope
atofdifferent
VAC
generator
ismethods,
applied
along
with
DC
signal
at
the
of the
LDO,
as
shown
in either
of the
afore
示波器以不同频率来测量
的输出。
由公式
计算得到，其中
是输入交流信号的幅度，而
LDO
PSRR
1
Ripple(input)
mentioned
methods,
and
the
output
of
the
LDO
is
measured
on
an
oscilloscope
at
different
VAC
is
the
amplitude
of the input
frequencies.
The PSRR
calculated
the Equation
1 where
Ripple
mentioned methods,
andisthe
output ofusing
the LDO
is measured
on an
oscilloscope
at
different
VAC
(input)
is
the
amplitude
of
the
input
frequencies.
PSRR
is
calculated
using
the
Equation
1
where
Ripple
重复以上测量过程，以产生
曲线图片段。
(input)
Ripple(output)
VAC
PSRR
AC
signalThe
and是输出信号的幅度。以不同频率的
Ripple
is
the
amplitude
of
output
signal.
This
is
then
repeated
at
different
frequencies
is
the
amplitude
of the
input
frequencies.
The
PSRR
is
calculated
using
the
Equation
1
where
Ripple
(output)
(input)
is
the
amplitude
of
output
signal.
This
is
then
repeated
at
different
frequencies
AC of
signal
and
Ripple
(output)
VAC
to generate
a (output)
piecemeal
of PSRR.
AC
signal
and Ripple
is thegraph
amplitude
of output signal. This is then repeated at different frequencies
这一方法可以与上一节所描述的结构一起使用。然而由于示波器的分辨率和灵敏度有限，这一方法仅仅对具有更低
of VAC
to generate
a piecemeal
graph
of PSRR.
of
VAC
to LDO
generate
a piecemeal
graph
of PSRR.
值的
适用。由于大多数示波器可以测量到毫伏的范围，因此使用示波器可实际测量到的
的最大范围约
PSRRmethod
This
can
be used along with the set-ups described in the previous section. PSRR
But this
method is only
Thisgood
method
can
be
used
along
with
the
set-ups
described
in
the
previous
section.
But
this
method
is only
for LDOs
with
values
to resolution
and
sensitivity
of section.
oscilloscopes.
Since
most
This
method
can
belower
used PSRR
along with
thedue
set-ups
described
in the
previous
But this
method
is only
为 40dB–50dB
。
good
for
LDOs
with
lower
PSRR
values
due
to
resolution
and
sensitivity
of
oscilloscopes.
Since
most
oscilloscopes
can
measure
down
to
the
millivolt
range,
the
maximum
range
of
PSRR
that
could
good for LDOs with lower PSRR values due to resolution and sensitivity of oscilloscopes. Since most
oscilloscopes
can
measure
down
toanthe
millivolt
range,
the the
maximum
range
of PSRR
thatthat
could
realistically
be can
measured
using
oscilloscope
isrange,
about
40dB–50dB.
oscilloscopes
measure
down
to
the
millivolt
maximum
range
of PSRR
could
realistically
be
measured
using
an
oscilloscope
is
about
40dB–50dB.
realistically be measured using an oscilloscope is about 40dB–50dB.
SLAA414 – July 2009
年 7 Feedback
月
SLAA414
– July
2009
ZHCA089
2009
Submit
Documentation
SLAA414
––July
2009
Submit
Documentation
Feedback
提交文档反馈
Submit
Documentation
Feedback
LDO PSRR Measurement Simplified
测量简化说明
LDO PSRR
LDOLDO
PSRR
Measurement
Simplified
PSRR
Measurement
Simplified
www.BDTIC.com/TI
3
33 3
的PSRR测量
Measuring
PSRR Using Oscilloscope
LDO
www.ti.com
www.ti.com
Using the TPS78101EVM
from Texas Instruments, the
PSRR
is measured using signal
generator
在德州仪器的
进行测量。输入与输出波形如图
TPS78101 评估板上，使用信号发生器和示波器对
PSRR
5 所示。
oscilloscope. The input and output waveforms are as shown in Figure 5:
测试条件如下：
Test conditions
and
are:
a.
= 3V
a.Vout
Vout
=
3V
b.
150mA
b.Iload
Iload==150mA
时=
c.
VAC
1V (p-p)
c.1kHz
VAC
1V= (p-p)
at 1kHz
d.VDC
VDC
= 4.3V
d.
= 4.3V
dc dc
图and
的输入及输出波形
Figure 5. Input
Output Waveforms
Measuring PSRR Using Oscilloscope
5. 用示波器测量
PSRRfor
由图
中的波形可计算得到
PSRR：
And5the
PSRR is calculated
from
waveforms in Figure 5 is:
Ripple(input)
mV
984
mV
Ripple(input)==984
Ripple(output)
Ripple(output) ==194
194mV
mV
，这一结果与
/ Ripple(output)
= log10(0.984/0.194)
20 log10(0.984/0.194)
= 14.10dB
which
closely的数据表中规定的
matches the
PSRR= =2020
log10(Ripple(input)
PSRR
log10(Ripple(input)/
Ripple(output))
= )20
= 14.10dB
TPS78101
PSRR
specified in the datasheet of TPS78101.
相一致。
PSRR
This application report LDO
shows
various
methods to measure
the时需要考虑的不同方面。
PSRR of an LDO and
本应用报告给出了测量一个
的 PSRR
的多种方法并解释了测量
PSRR
different aspects which need to be considered while measuring PSRR.
44
LDO PSRR 测量简化说明
LDO PSRR Measurement Simplified
www.BDTIC.com/TI
also explains
ZHCA089
– 2009
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SLAA414
– July年2009
提交文档反馈
Submit Documentation Feedback
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5
ZHCA089
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