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參數(shù)資料
| 型號： | ADP1108AN |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Circular Connector; No. of Contacts:19; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-19 |
| 中文描述： | 1.5 A SWITCHING REGULATOR, 25 kHz SWITCHING FREQ-MAX, PDIP8 |
| 封裝： | PLASTIC, DIP-8 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大小： | 234K |
| 代理商： | ADP1108AN |
ADP1108
–7–
REV. 0
where:
DC
= duty cycle (0.7 for the ADP1108)
V
SW
= voltage drop across the switch
V
D
= diode drop (0.5 V for a 1N5818)
I
OUT
= output current
V
OUT
= the output voltage
V
IN
= the minimum input voltage
As previously mentioned, the switch voltage is higher in step-
down mode than in step-up mode. V
SW
is a function of switch
current and is therefore a function of V
IN
, L, time and V
OUT
. For
most applications, a V
SW
value of 1.5 V is recommended.
T he inductor value can now be calculated:
L
=
V
IN
(
MIN
)
±
V
SW
±
V
OUT
I
PEAK
×
t
ON
(Equation 7)
where:
t
ON
= switch ON time (36
μ
s)
If the input voltage will vary (such as an application that must
operate from a 9 V, 12 V or 15 V source), an R
LIM
resistor
should be selected from Figure 4. T he R
LIM
resistor will keep
switch current constant as the input voltage rises. Note that
there are separate R
LIM
values for step-up and step-down modes
of operation.
For example, assume that +5 V at 250 mA is required from a +9 V
to +18 V source. Deriving the peak current from Equation 6
yields:
I
PEAK
=
2
×
250
mA
0.7
5
+
0.5
9
1.5
+
0.5
491
mA
T he peak current can than be inserted into Equation 7 to cal-
culate the inductor value:
L
=
9±1.5±5
491
mA
×
36
μ
s
=
183
μ
H
Since 183
μ
H is not a standard value, the next lower standard
value of 150
μ
H would be specified.
T o avoid exceeding the maximum switch current when the in-
put voltage is at +18 V, an R
LIM
resistor should be specified. Us-
ing Figure 4, a value of 160
will limit the switch current to
500 mA.
Inductor Selection—Positive-to-Negative Converter
T he configuration for a positive-to-negative converter using the
ADP1108 is shown in Figure 19. As with the step-up converter,
all of the output power for the inverting circuit must be supplied
by the inductor. T he required inductor power is derived from
the formula:
(
P
L
|
V
OUT
|
+
V
D
)
×
I
OUT
(
)
(Equation 8)
T he ADP1108 power switch does not saturate in positive-to-
negative mode. T he voltage drop across the switch can be mod-
eled as a 0.75 V base-emitter diode in series with a 0.65
resistor. When the switch turns on, inductor current will rise at
a rate determined by:
I
L
(
t
)
=
V
L
R
1
e
±
R
t
L
(Equation 9)
where:
R'
= 0.65
+ R
L
(DC)
V
L
= V
IN
– 0.75 V
For example, assume that a –5 V output at 100 mA is to be gen-
erated from a +4.5 V to +5.5 V source. T he power in the induc-
tor is calculated from Equation 8:
During each switching cycle, the inductor must supply the fol-
lowing energy:
P
L
f
OSC
19
kHz
Using a standard inductor value of 220
μ
H with 0.3
dc resis-
tance will produce a peak switch current of:
P
L
=
|±5
V
|
+
0.5
V
)
×
100
mA
(
)
=
550
mW
=
550
mW
=
28.9
μ
J
I
PEAK
=
4.5
V
±0.75
V
0.65
+
0.3
1
e
±0.95
×
36
μ
s
220
μ
H
=
568
mA
Once the peak current is known, the inductor energy can be cal-
culated from Equation 9:
E
L
=
1
2
T he inductor energy of 35.5
μ
J is greater than the P
L
/f
OSC
re-
quirement of 28.9
μ
J, so the 220
μ
H inductor will work in
this application.
T o avoid exceeding the maximum switch current when the in-
put voltage is at +5.5 V, an R
LIM
resistor should be specified.
Referring to Figure 4, a value of 150
V
is appropriate in this
application.
220
μ
H
×
568
mA
(
)
2
35.5
μ
J
Capacitor Selection
For optimum performance, the ADP1108’s output capacitor
must be carefully selected. Choosing an inappropriate capacitor
can result in low efficiency and/or high output ripple.
Ordinary aluminum electrolytic capacitors are inexpensive, but
often have poor Equivalent Series Resistance (ESR) and Equiva-
lent Series Inductance (ESL). Low ESR aluminum capacitors,
specifically designed for switch mode converter applications, are
also available, and these are a better choice than general purpose
devices. Even better performance can be achieved with tantalum
capacitors, although their cost is higher. Very low values of ESR
can be achieved by using OS-CON* capacitors (Sanyo Corpora-
tion, San Diego, CA). T hese devices are fairly small, available
with tape-and-reel packaging, and have very low ESR.
T he effects of capacitor selection on output ripple are demon-
strated in Figures 12, 13, and 14. T hese figures show the output
of the same ADP1108 converter, which was evaluated with
three different output capacitors. In each case, the peak switch
current is 500 mA and the capacitor value is 100
μ
F. Figure 12
shows a Panasonic HF-series* radial aluminum electrolytic.
When the switch turns off, the output voltage jumps by about
90 mV and then decays as the inductor discharges into the ca-
pacitor. T he rise in voltage indicates an ESR of about 0.18
V
. In
Figure 13, the aluminum electrolytic has been replaced by a
Sprague 593D-series* tantalum device. In this case the output
jumps about 35 mV, which indicates an ESR of 0.07
V
. Figure
14 shows an OS-CON SA series capacitor in the same circuit,
and ESR is only 0.02
V
.
*All trademarks are the property of their respective holders.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ADP1108AN-12 | Circular Connector; No. of Contacts:128; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:25-1 |
| ADP1108AN-33 | Circular Connector; No. of Contacts:128; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-1 |
| ADP1108AN-5 | Circular Connector; No. of Contacts:30; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-20 |
| ADP1108AR | Circular Connector; No. of Contacts:24; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-24 |
| ADP1108AR-12 | Circular Connector; No. of Contacts:128; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:25-35 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADP1108AN-12 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADP1108AN-3.3 | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Analog Devices 功能描述:IC MICROPROCESSOR DC/DC CONVERTER ((NS)) |
| ADP1108AN-33 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Micropower DC-DC Converter Adjustable and Fixed 3.3 V, 5 V, 12 V |
| ADP1108AN-5 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Micropower DC-DC Converter Adjustable and Fixed 3.3 V, 5 V, 12 V |
| ADP1108AR | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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