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| 型号： | OP184FSZ-REEL7 |
| 厂商： | Analog Devices Inc |
| 文件页数： | 11/24页 |
| 文件大小： | 0K |
| 描述： | IC OPAMP GP R-R 4.25MHZ LN 8SOIC |
| 设计资源： | Variable Gain Noninverting Amplifier Using AD5292 and OP184 (CN0112) Variable Gain Inverting Amplifier Using AD5292 and OP184 (CN0113) Programmable High Voltage Source with Boosted Output Current Using AD5292, OP184, and MOSFETs (CN0115) Low-Noise Microwave fractional-N PLL using active loop filter and RF prescaler (CN0174) |
| 标准包装： | 1,000 |
| 放大器类型： | 通用 |
| 电路数： | 1 |
| 输出类型： | 满摆幅 |
| 转换速率： | 4 V/µs |
| 增益带宽积： | 4.25MHz |
| 电流 - 输入偏压： | 80nA |
| 电压 - 输入偏移： | 175µV |
| 电流 - 电源： | 2.25mA |
| 电流 - 输出 / 通道： | 10mA |
| 电压 - 电源，单路/双路(±)： | 3 V ~ 36 V，±1.5 V ~ 18 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SO |
| 包装： | 带卷 (TR) |
| 其它名称： | OP184FSZ-REEL7-ND OP184FSZ-REEL7TR |
OP184/OP284/OP484
Rev. J | Page 19 of 24
LOW DROPOUT REGULATOR WITH CURRENT
LIMITING
Many circuits require stable, regulated voltages relatively close
in potential to an unregulated input source. This low dropout
type of regulator is readily implemented with a rail-to-rail output
op amp, such as the OP284, because the wide output swing allows
easy drive to a low saturation voltage pass device. Furthermore,
it is particularly useful when the op amp also employs a rail-to-
rail input feature because this factor allows it to perform high-
side current sensing for positive rail current limiting. Typical
examples are voltages developed from 3 V to 9 V range system
sources or anywhere that low dropout performance is required
for power efficiency. This 4.5 V example works from 5 V nominal
sources with worst-case levels down to 4.6 V or less. Figure 58
shows such a regulator set up, using an OP284 plus a low RDS(ON),
P-channel MOSFET pass device. Part of the low dropout perform-
ance of this circuit is provided by Q1, which has a rating of 0.11
Ω with a gate drive voltage of only 2.7 V. This relatively low gate
drive threshold allows operation of the regulator on supplies as
low as 3 V without compromising overall performance.
The main voltage control loop operation of the circuit is
provided by U1B, half of the OP284. This voltage control
amplifier amplifies the 2.5 V reference voltage produced by
Three Terminal U2, a REF192. The regulated output voltage,
VOUT, is then
+
=
3
1
R
R2
V
2
OUT
For this example, because VOUT of 4.5 V with VOUT2 = 2.5 V requires
a U1B gain of 1.8 times, R3 and R2 are chosen for a ratio of 1.2:1 or
10.0 kΩ:8.06 kΩ (using closest 1% values). Note that for the lowest
VOUT dc error, R2||R3 should be maintained equal to R1 (as in
this example), and the R2 to R3 resistors should be stable, close
tolerance metal film types. The table in Figure 58 summarizes
R1 to R3 values for some popular voltages. However, note that,
in general, the output can be anywhere between VOUT2 and the
12 V maximum rating of Q1.
While the low voltage saturation characteristic of Q1 is a key part
of the low dropout, another component is a low current sense com-
parison threshold with good dc accuracy. Here, this is provided by
Current Sense Amplifier U1A, which is provided by a 20 mV
reference from the 1.235 V, AD589 Reference Diode D2, and the
R7 to R8 divider. When the product of the output current and the
RS value match this voltage threshold, the current control loop is
activated, and U1A drives the Q1 gate through D1. This causes the
overall circuit operation to enter current mode control with a
current limit, ILIMIT, defined as
( )
+
=
R8
R
R7
R
V
I
S
D2
R
LIMIT
7
3
2
1
8
4
U1A
OP284
U1B
OP284
D2
AD589
D1
1N4148
Q1
SI9433DY
6
5
7
D3
1N4148
2
6
4
3
U2
REF192
R3
10k
VC
VIN COMMON
+VS
VS > VOUT + 0.1V
C4
0.1F
C5
0.01F
C2
1F
C1
0.01F
C6
10F
VOUT COMMON
VOUT =
4.5V @ 350mA
(SEE TABLE)
C2
0.1F
OPTIONAL
ON/OFF CONTROL INPUT
CMOS HI (OR OPEN) = ON
LO = OFF
VOUT
R1k
R2k R3k
OUTPUT TABLE
5.0V
4.99
10.0
4.5V
4.53
8.08
10.0
3.3V
2.43
3.24
10.0
3.0V
1.69
2.00
10.0
R5
22.1k
R4
2.21k
R6
4.99k
R9
27.4k
R11
1k
R10
1k
R1
4.53k
VOUT2
2.5V
R7
4.99k
R8
301k
R2
8.06k
RS
0.05
00293-
058
Figure 58. Low Dropout Regulator with Current Limiting\
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