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參數(shù)資料
| 型號： | ADP1110 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Micropower, Step-Up/Step-Down Switching Regulator(微功耗,可調(diào)/固定輸出,步升/步降開關穩(wěn)壓器) |
| 中文描述： | 微功耗，降壓型開關穩(wěn)壓器（微功耗，可調(diào)/固定輸出，步升/步降開關穩(wěn)壓器） |
| 文件頁數(shù)： | 10/16頁 |
| 文件大小： | 370K |
| 代理商： | ADP1110 |
ADP1110
–10–
REV. 0
turns “on” again, and the cycle repeats. The output voltage is
therefore set by the formula:
V
OUT
=
220
mV
1
+
R
1
R
2
The circuit of Figure 19 shows a direct current path from V
IN
to
V
OUT
, via the inductor and D1. Therefore, the boost converter
is not protected if the output is short circuited to ground.
CIRCUIT OPERATION, STEP-DOWN (BUCK) MODE
The ADP1110’s step-down mode is used to produce an output
voltage that is lower than the input voltage. For example, the
output of four NiCd cells (+4.8 V) can be converted to a +3 V
logic supply.
A typical configuration for step-down operation of the ADP1110 is
shown in Figure 20. In this case, the collector of the internal
power switch is connected to V
IN
and the emitter drives the
inductor. When the switch turns on, SW2 is pulled up towards
V
IN
. This forces a voltage across L1 equal to V
IN
– V
CE
– V
OUT
and causes current to flow in L1. This current reaches a final
value of:
I
PEAK
V
IN
V
CE
V
OUT
L
10
μ
s
where 10
μ
s is the ADP1110 switch’s “on” time.
V
IN
R
LIM
100
1
I
LIM
ADP1110
V
IN
SW1
SW2
GND
SET
AO
NC
NC
L1
C
1
R1
R2
D1
1N5818
V
OUT
C
2
2
FB
3
6
7
5
4
8
Figure 20. Step-Down Mode Operation
When the switch turns off, the magnetic field collapses. The
polarity across the inductor changes, and the switch side of the
inductor is driven below ground. Schottky diode D1 then turns
on, and current flows into the load. Notice that the Absolute
Maximum Rating for the ADP1110’s SW2 pin is 0.5 V below
ground. To avoid exceeding this limit, D1 must be a Schottky
diode. Using a silicon diode in this application will generate
forward voltages above 0.5 V that will cause potentially
damaging power dissipation within the ADP1110.
The output voltage of the buck regulator is fed back to the
ADP1110’s FB pin by resistors R1 and R2. When the voltage at
pin FB falls below 220 mV, the internal power switch turns
“on” again and the cycle repeats. The output voltage is set by
the formula:
V
OUT
=
220
mV
1
+
R
1
R
2
When operating the ADP1110 in step-down mode, the output
voltage is impressed across the internal power switch’s emitter-
base junction when the switch is off. To protect the switch, the
output voltage should be limited to 6.2 V or less. If a higher
output voltage is required, a Schottky diode should be placed in
series with SW2, as shown in Figure 21.
I
LIM
ADP1110
V
IN
SW1
SW2
FB
GND
5
SET
7
AO
6
NC
NC
L1
C
L
R1
R2
D1
1N5818
OUTPUT
C
INPUT
INPUT
8
1
2
3
4
R
LIM
Figure 21. Step-Down Mode, V
OUT
> 6.2 V
If the input voltage to the ADP1110 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, the peak current may exceed the switch maxi-
mum 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 ADP1110’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. This results in high power dissipation within the
ADP1110 when high peak current is required. To increase the
output current, an external PNP switch can be added (Figure
22). In this circuit, the ADP1110 provides base drive to Q1
through R3, while R4 ensures that Q1 turns off rapidly. Because
the ADP1110’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 ADP1110, this circuit also reduces the switch
voltage. When selecting an inductor value for the circuit of
Figure 22, 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
I
LIM
V
IN
SW1
SW2
4
FB
GND
5
SET
7
AO
6
ADP1110
NC
NC
L1
C
L
R1
R2
D1
1N5821
OUTPUT
C
INPUT
R
LIM
INPUT
8
1
2
3
R4
220
R3
330
MJE210
0.3
R5
Figure 22. High Current Step-Down Operation
相關PDF資料 |
PDF描述 |
|---|---|
| ADP1111AR-12 | Micropower, Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V |
| ADP1111 | PRECISION SEMICONDUCTOR PRESSURE SENSOR |
| ADP1111AR-33 | Micropower, Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V |
| ADP1111AR-5 | Micropower, Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V |
| ADP1111AR | Micropower, Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| ADP1110AN | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADP1110AN-12 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADP1110AN-3.3 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADP1110AN-33 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Micropower, Step-Up/Step-Down Switching Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V |
| ADP1110AN-5 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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