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參數資料
| 型號： | ah-27 |
| 廠商： | Micrel Semiconductor,Inc. |
| 元件分類： | 圓形連接器 |
| 英文描述： | Circular Connector; No. of Contacts:22; Series:MS27473; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:12; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:12-22 RoHS Compliant: No |
| 中文描述： | 減緩電壓調節(jié)導通的杰里克梅茨 |
| 文件頁數： | 1/3頁 |
| 文件大?。?/td> | 69K |
| 代理商： | AH-27 |
AH-27
Micrel
3-202
1997
Application Hint 27
Slowing Voltage Regulator Turn-On
by Jerry Kmetz
Slow Turn-On Circuits
The turn-on time interval of a voltage regulator is essentially
determined by the bandwidth of the regulator, its maximum
output current, and the load capacitance. To some extent the
rise time of the applied input voltage (which is normally quite
short, tens of milliseconds, or less) also affects the turn-on
time. However, the regulator output voltage typically steps
abruptly at turn-on. Increasing the turn-on interval via some
form of slew-limiting decreases the surge current seen by
both the regulator and the system. This application hint
addresses designing circuitry to change the step-function to
a smoother RC charge waveform.
Various performance features exist between the three cir-
cuits that are presented. These are (1) whether stability is
impacted, (2) whether start-up output is 0V, and (3) whether
the circuit quickly recovers from momentarily interrupted
input voltage or shorted output. The following table summa-
rizes the features of each circuit:
Circuit
Number Impacted Pedestal
Stability
Start-Up
V
IN
Interrupt
Recovery
V
OUT
Short
Recovery
1
yes
1.2V
no
no
2
no
1.8V
no
yes
3
no
0V
yes
no
Slow Turn-On Circuit Performance Features
1. The Simplest Approach
Figure 1 illustrates a typical LDO voltage regulator, the
MIC29153, with an additional capacitor (C
T
) in parallel with
the series leg (R1) of the feedback voltage divider. Since the
voltage (V
ADJ
) will be maintained at V
REF
by the regulator
loop, the output of this circuit will still rapidly step to V
REF
and
then rise slowly. Since V
REF
is usually only about 1.2V, this
eliminates a large part of the surge current.
As C
T
charges, the regulator output (V
OUT
) asymptotically
approaches the desired value. If a turn-on time of 300
milliseconds is desired then about three time constants
should be allowed for charge time:
then 3
τ
= 0.3s, or
τ
= 0.1s = R1
×
C
T
= 300k
×
0.33
μ
F.
Figure 2 shows the waveforms of the circuit of Figure 1. This
circuit has three shortcomings: (1) the approximately 1.2V
step at turn-on, (2) the addition of capacitor C
T
places a zero
in the closed-loop transfer function (which affects frequency
and transient responses and can potentially cause stability
problems) and (3) the recovery time associated with a mo-
mentarily short-circuited output may be unacceptably long.
This is because if the output is shorted C
T
is discharged only
by R2; if the short is removed before C
T
is fully discharged the
regulator output will not exhibit the desired turn-on behavior.
Typical LDO Regulator
V
REF
V
OUT
C
T
0.33μF
R1
300k
R2
100k
V
ADJ
OUT
IN
GND
C
IN
22μF
ADJ
MIC29153
V
IN
C
OUT
22μF
Figure 1. Simplest Slow Turn-On Circuit
Figure 2. Turn-On Behavior for Circuit of Figure 1
0
0
2
0.2
4
0.4
0.6
0.8
10
5
1.0
0
O
TIME (s)
相關PDF資料 |
PDF描述 |
|---|---|
| ah-29 | Circular Connector; No. of Contacts:22; Series:MS27473; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:12; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:12-22 RoHS Compliant: No |
| AH0014 | Sand Paper; Abrasive Grade:F SFN; Color:White; Pack Quantity:3; Roll Length:30ft; Width:4" |
| AH0014C | Sand Paper; Abrasive Grade:A MED; Color:Maroon; Pack Quantity:3; Roll Length:30ft; Width:4" |
| AH0014CD | DIP Socket; No. of Contacts:64; Pitch Spacing:0.07"; Row Spacing:0.8"; Terminal Type:PC Board; Leaded Process Compatible:Yes; Peak Reflow Compatible (260 C):No RoHS Compliant: Yes |
| AH0014D | DIP Socket; No. of Contacts:64; Pitch Spacing:0.07"; Row Spacing:0.8"; Terminal Type:Solder Tail; Leaded Process Compatible:Yes; Peak Reflow Compatible (260 C):No RoHS Compliant: Yes |
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