- 您現(xiàn)在的位置：買(mǎi)賣(mài)IC網(wǎng) > PDF目錄374018 > ADP1108 (Analog Devices, Inc.) Circular Connector; No. of Contacts:19; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:25-19 PDF資料下載
參數(shù)資料
| 型號(hào)： | ADP1108 |
| 廠(chǎng)商： | Analog Devices, Inc. |
| 元件分類(lèi)： | 圓形連接器 |
| 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:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:25-19 |
| 中文描述： | 微功率DC - DC轉(zhuǎn)換可調(diào)和固定3.3伏，5伏，12伏 |
| 文件頁(yè)數(shù)： | 9/12頁(yè) |
| 文件大小： | 234K |
| 代理商： | ADP1108 |
ADP1108
–9–
REV. 0
When the switch turns on, SW2 is pulled up toward V
IN
. T his
forces a voltage across L1 equal to (V
IN
2
V
CE
)
2
V
OUT
, and causes
current to flow in L1. T his current reaches a final value of:
I
PEAK
V
IN
±
V
CE
±
V
OUT
L
×
36
μ
s
where 36
μ
s is the ADP1108 switch’s “on” time.
5
1
8
4
2
I
LIM
V
IN
SW1
FB
SW2
GND
ADP1108
L1
D1
1N5818
V
OUT
C2
R
LIM
100
R1
R2
V
IN
3
C1
Figure 16. Step-Down Mode Operation
When the switch turns off, the magnetic field collapses. T he po-
larity across the inductor changes and the switch side of the in-
ductor is driven below ground. Schottky diode D1 then turns on
and current flows into the load. Notice that the Absolute Maxi-
mum Rating for the ADP1108’s SW2 pin is 0.5 V below ground.
T o avoid exceeding this limit, D1 must be a Schottky diode. If a
silicon diode is used for D1, Pin SW2 can go to
2
0.8 V, which
will cause potentially damaging power dissipation within the
ADP1108.
T he output voltage of the buck regulator is fed back to the
ADP1108’s FB pin by resistors R1 and R2. When the voltage at
Pin FB falls below 1.245 V, the internal power switch turns
“on” again and the cycle repeats. T he output voltage is set by
the formula:
V
OUT
=
1.245
V
×
1
+
R
1
R
2
When operating the ADP1108 in step-down mode, the output
voltage is impressed across the internal power switch’s emitter-
base junction while the switch is off. T o protect the switch, the
output voltage should be limited to 6.2 V or less. If a higher out-
put voltage is required, a Schottky diode should be placed in se-
ries with SW2, as shown in Figure 17.
5
1
8
4
2
I
LIM
V
IN
SW1
FB
SW2
GND
ADP1108
L1
D1
1N5818
V
OUT
C2
R
LIM
100
R1
R2
V
IN
3
C1
D2
Figure 17. Step-Down Model, V
OUT
> 6.2 V
If the input voltage to the ADP1108 varies over a wide range, a
current limiting resistor at Pin 1 may be required. If a particular
circuit requires high peak inductor current with minimum input
supply voltage, then the peak current may exceed the switch
maximum rating and/or saturate the inductor when the supply
voltage is at the maximum value. See the Limiting the Switch
Current section of this data sheet for specific recommendations.
Increasing Output Current in the Step-Down Regulator
Unlike the boost configuration, the ADP1108’s internal power
switch is not saturated when operating in step-down mode. A
conservative value for the voltage across the switch in step-down
mode is 1.5 V. T his results in high power dissipation within the
ADP1108 when high peak current is required. T o increase the
output current, an external PNP switch can be added (Figure
18). In this circuit, the ADP1108 provides base drive to Q1
through R3 while R4 ensures that Q1 turns off rapidly. T he
ADP1108’s internal current limiting function will not work in
this circuit, R5 is provided for this purpose. With the value
shown, R5 limits current to 2 A. In addition to reducing power
dissipation on the ADP1108, this circuit also reduces the switch
voltage. When selecting an inductor value for the circuit of Fig-
ure 18, the switch voltage can be calculated from the formula:
V
SW
=
V
R
5
+
V
Q
1(
SAT
)
0.6
V
+
0.4
V
1
V
L1*
100
m
H
5V
200mA AT 6.5V
500mA AT 8V
R4
100
R5
0.22
Q1
ZETEX
ZTX749
*L1 = COILTRONICS CTX100-4
R2
100
5
8
2
I
LIM
V
IN
SW1
SW2
4
GND
ADP1108-5
D1
1N5818
C2
V
IN
6.5V TO 20V
3
C1
R3
220
1
SENSE
Figure 18. High Current Step-Down Operation
Positive-to-Negative Conversion
T he ADP1108 can convert a positive input voltage to a negative
output voltage, as shown in Figure 19. T his circuit is essentially
identical to the step-down application of Figure 16, except that
the “output” side of the inductor is connected to power ground.
When the ADP1108’s internal power switch turns off, current
flowing in the inductor forces the output (
2
V
OUT
) to a negative
potential. T he ADP1108 will continue to turn the switch on un-
til its FB pin is 1.245 V above its GND pin, so the output volt-
age is determined by the formula:
V
OUT
=
1.245
V
×
1
+
R
1
R
2
5
1
8
4
2
I
LIM
V
IN
SW1
FB
SW2
GND
ADP1108
L1
D1
1N5818
–V
OUT
C2
R3
R1
R2
V
IN
3
C
L
Figure 19. A Positive-to-Negative Converter
T he design criteria for the step-down application also apply to
the positive-to-negative converter. T he output voltage should be
limited to |6.2 V|, unless a diode is inserted in series with the
SW2 pin (see Figure 17). Also, D1 must again be a Schottky di-
ode to prevent excessive power dissipation in the ADP1108.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ADP1108AN | 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 |
| 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 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADP1108AN | 制造商:Rochester Electronics LLC 功能描述:MICROPOWER DC-DC CONVERTER "ADJ" - Bulk |
| 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(chēng):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(chēng):Analog Devices 功能描述:Micropower DC-DC Converter Adjustable and Fixed 3.3 V, 5 V, 12 V |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。