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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(guān)穩(wěn)壓器) |
| 中文描述： | 微功耗，降壓型開關(guān)穩(wěn)壓器（微功耗，可調(diào)/固定輸出，步升/步降開關(guān)穩(wěn)壓器） |
| 文件頁數(shù)： | 11/16頁 |
| 文件大小： | 370K |
| 代理商： | ADP1110 |
ADP1110
–11–
REV. 0
POSITIVE-TO-NEGATIVE CONVERSION
The ADP1110 can convert a positive input voltage to a negative
output voltage as shown in Figure 23. This circuit is essentially
identical to the step-down application of Figure 19, except that
the “output” side of the inductor is connected to power ground.
When the ADP1110’s internal power switch turns off, current
flowing in the inductor forces the output (–V
OUT
) to a negative
potential. The ADP1110 will continue to turn the switch on
until its FB pin is 220 mV above its GND pin, so the output
voltage is determined by the formula:
V
OUT
=
220
mV
1
+
R
1
R
2
ILIM
VIN
SW1
SW2
FB
GND
5
SET
7
AO
6
ADP1110
NC
NC
L1
C
L
R1
R2
D1
1N5818
OUTPUT
C
INPUT
R
LIM
INPUT
8
1
2
4
3
NEGATIVE
OUTPUT
Figure 23. A Positive-to-Negative Converter
The design criteria for the step-down application also apply to
the positive-to-negative converter. The output voltage should be
limited to |6.2 V| unless a diode is inserted in series with the
SW2 pin (see Figure 21.) Also, D1 must again be a Schottky
diode to prevent excessive power dissipation in the ADP1110.
NEGATIVE-TO-POSITIVE CONVERSION
The circuit of Figure 24 converts a negative input voltage to a
positive output voltage. Operation of this circuit configuration is
similar to the step-up topology of Figure 19, except the current
through feedback resistor R1 is level-shifted below ground by a
PNP transistor. The voltage across R1 is V
OUT
– V
BEQ1
. However,
diode D2 level-shifts the base of Q1 about 0.6 V below ground
thereby cancelling the V
BE
of Q1. The addition of D2 also reduces
the circuit’s output voltage sensitivity to temperature, which other-
wise would be dominated by the –2 mV V
BE
contribution of Q1.
The output voltage for this circuit is determined by the formula:
V
OUT
=
220
mV
R
1
R
2
Unlike the positive step-up converter, the negative-to-positive
converter’s output voltage can be either higher or lower than the
input voltage.
I
LIM
V
IN
SW1
SW2
4
FB
GND
5
SET
7
AO
6
ADP1110
NC
NC
L1
C
L
R2
D1
C
INPUT
R
LIM
8
1
2
3
POSITIVE
OUTPUT
10K
NEGATIVE
INPUT
Q1
2N3906
D2
1N4148
R1
Figure 24. A Negative-to-Positive Converter
LIMITING THE SWITCH CURRENT
The ADP1110’s R
LIM
pin permits the switch current to be
limited with a single resistor. This current limiting action occurs
on a pulse by pulse basis. This feature allows the input voltage
to vary over a wide range without saturating the inductor or
exceeding the maximum switch rating. For example, a particular
design may require peak switch current of 800 mA with a 2.0 V
input. If V
IN
rises to 4 V, however, the switch current will
exceed 1.6 A. The ADP1110 limits switch current to 1.5 A and
thereby protects the switch, but the output ripple will increase.
Selecting the proper resistor will limit the switch current to
800 mA, even if V
IN
increases. The relationship between R
LIM
and maximum switch current is shown in Figure 6.
The I
LIM
feature is also valuable for controlling inductor current
when the ADP1110 goes into continuous-conduction mode.
This occurs in the step-up mode when the following condition is
met:
V
OUT
+
V
D IODE
V
IN
–
V
SW
<
1
1–
DC
where DC is the ADP1110’s duty cycle. When this relationship
exists, the inductor current does not go all the way to zero
during the time that the switch is OFF. When the switch turns
on for the next cycle, the inductor current begins to ramp up
from the residual level. If the switch ON time remains constant,
the inductor current will increase to a high level (see Figure 25).
This increases output ripple and can require a larger inductor
and capacitor. By controlling switch current with the I
LIM
resistor, output ripple current can be maintained at the design
values. Figure 26 illustrates the action of the I
LIM
circuit.
10
0%
100
90
10μs
10mV
200mA/div.
Figure 25. I
LIM
Operation—I
L
Characteristic
10
0%
100
90
10μs
10mV
200mA/div.
Figure 26. I
LIM
Operation—I
L
Characteristic
相關(guān)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(guān)代理商/技術(shù)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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