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IC
基本电气特性
Quiescent current
静态电流
Standby curr
ent
低功耗
电
流
Dropout voltage (LDO
特性
)
压
降的
输
入
电压
Efficiency
功率
Transient
response
顺势
特性
Line regulation
线
路
调
整器
Load
regulation
负载调
整率
Power supply rejection
电
源排除
/
抑制
Noise
Accuracy
精确性
IC
量测
I
C
（
LDO
）结构框图
Capacitor
电容
reference
参考（电压）
error
amplifier
误差信号放大器
Pass
element
无源元件（二极管）
dynamic load
动态负载
主要模块包括
;
Voltage
Reference
参考（电压）
Error
Amplifier
误差信号放大器
Feedback Network
反馈网络
Series-pass
Element
无源元件（二极管）
优点：简单、输出纹波电压低
、出色的
line
和负载稳压、对负载和
line
的变化响应迅速
、电
磁干扰
(EMI)
低
缺点：效率低
、如果需要冷却设备，则要求较大的空间
IC
基本电气特性－
Quiescent Current & Standby Current
Quiescent
Current(Ground current)
:
The difference between input and
output
。
Low
quiescent
current
is
necessary
to
maximize
the
efficiency.
低静态电流
是最
大限度地提高效率必要条件
。
Standby Current
:
The input current drawn by a regulator
when
the output voltage is disabled by
a shutdown
signal.
Quiescent Current and
Output Current
The value of quiescent current is
mostly determined
by
the
series
pass
element,
topologies,
ambient
temperature,
etc.
静态电流的值主要是一系列无源
元件，拓扑结
构，环境温度等
确定的
具体特性与
IC
结构、制程密切相关
IC
基本电气特性－
Dropout
V
oltage
（特有规格）
?
Low-Dropout
Linear Regulators
低压差线性稳压器
?
传统的三端稳压器如：
LM78xx
Vdrop
的典型值是
2V
，看到很多
7805
应用
时
都会背着一个散热器。
LM317
2V
LM1117
1.2V
。
?
调整管采用的结构
LM317
输出
Darlingtong
Vdrop=Vsat+2Vbe
1.6~2.5V
NPN
Vdrop=Vsat+Vbe
>0.9V
PNP
Vdrop=Vsat
0.15~0.4V
PMOS
Vdrop=Io X Ron
35~350mv
NMOS
Vdrop=Vsat+Vgs
1V
?
不同调整管结构的比较：
1
．
T
he
NMOS
pass
element
is
most
advantageous
due
to
its
low
on
resistance.
Unfortunately,
the gate drive difficulties make it less than
ideal in applicaitons and as
a result
there are few NMOS LDOs available.
传统上，
PNP
双极型晶体管应用到低压线性稳
压器，主要是因为它很容易实现了低压降电压。
2
．
T
raditionally, the PNP
bipolar transistor has been applied to low dropout
applications,
primarily
because
it
easily
enables
a
low
drop
out
voltage.
However,
it
has
a
high
quiescent
current
and
low
efficiency,
which
are
not
ideal
in
applications
where
maximizing efficiency
is a priority.
然而，它的高静态电流和低效率，这是不理想的应用最
大限度地提高了效率是一个优先事项。
3
．
P
MOS
devices
have
been
highly
developed
and
now
have
performance
levels
exceeding
most bipolar devices.
PMOS
上设
备已经高度发达，现在的性能水平超过最双极器
件。
?
Dropout
voltage
：
the
input-to-output
differential
voltage
at
which
the
circuit
ceases to regulate against further
reductions in input voltage; this point occurs
when the input voltage approaches the
output voltage.
压降：
对输入至输出差分电压在电
路不再规范对进一步削减输入电压
;
这一点时发生的输入电压接近输出电压。
Vds=Vo-Vin
IC
基本电气特性－
Efficiency
?
The efficiency
of a LDO regulator is limited by the quiescent
current and
input/output voltage as
follows:
效率是有限的
LD
O
稳压器的静态电流和输入
/
输出电压
如下：输
入电压降低
;
这一点时发生的
输入电压接近输出电压
。
Efficiency
?
I
o
V
o
?
I
o
?
I
q
?
V
i
?
100
V
i
_
m
in
?
V
o
?
V
drop
?
To have a high efficiency LDO
regulator, drop out voltage and quiescent
current must be minimized.
<
/p>
具有高效率的
LDO
稳压器，
电压和辍学静态电流必须减少到最低限度
IC
基本电气特性－
Load
Regulation
?
Load
Regulation:
A measure of the circuit’s
ability to maintain the specified
out
put voltage under
varying
load conditions.
衡量电路的能力，保持指定的输出电压在不同负载条件下。
?
?
Vo<
/p>
/
?
Io
?
The load regulation is
limited by the open loop current gain of the
system. As noted from the
above
equation, increasing dc open-loop current gain
improves load regulation.
负荷
调节是有限
的开环电流增益的系统。正如上述方程，增加直流开环电流增益改善负载调节
。
?
Line Regulation:
a measure
of the circuit’s ability to maintain the specified
output voltage with varying input
voltage.
衡量这条赛道的能
力，保持指定的输出电
环电流增益改善负载调节。
< br>?
Vo
/
?
Vi
?
?
其中，
Rds
为调整管
Q1
源漏等效电阻。
?
Increasing dc open loop current gain
improves the line regulation.
提高直流开环
电流增益提高了线路调整
Output
Voltage
With
Respect
to
Input
Voltage
Line Transient
Response
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