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參數(shù)資料
| 型號(hào)： | LP4951CM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類(lèi)： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | Adjustable Micropower Voltage Regulators |
| 中文描述： | FIXED/ADJUSTABLE POSITIVE LDO REGULATOR, 0.6 V DROPOUT, PDSO8 |
| 文件頁(yè)數(shù)： | 11/14頁(yè) |
| 文件大小： | 436K |
| 代理商： | LP4951CM |
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Application Hints
(Continued)
PROGRAMMING THE OUTPUT VOLTAGE (LP4951C)
The LP4951C may be pin-strapped for 5V using its internal
voltage divider by tying the pin 1 (output) to pin 2 (sense)
pins together, and also tying the pin 7 (feedback) and pin 6
(V
TAP
) pins together. Alternatively, it may be programmed for
any output voltage between its 1.235V reference and its 30V
maximum rating. As seen in
Figure 2
, an external pair of
resistors is required.
The complete equation for the output voltage is
where V
REF
is the nominal 1.235 reference voltage and I
FB
is
the feedback pin bias current, nominally 20 nA. The mini-
mum recommended load current of 1μAforces an upper limit
of 1.2 M
on the value of R
, if the regulator must work with
no load (a condition often found in CMOS in standby). I
will
produce a 2% typical error in V
which may be eliminated
at room temperature by trimming R
. For better accuracy,
choosing R
= 100k reduces this error to 0.17% while in-
creasing the resistor program current to 12μA. Since the
LP4951C typically draws 60μA at no load with Pin 2 open-
circuited, this is a small price to pay.
REDUCING OUTPUT NOISE
In reference applications it may be advantageous to reduce
the AC noise present at the output. One method is to reduce
the regulator bandwidth by increasing the size of the output
capacitor. This is the only way noise can be reduced on the
3 lead LP4950C but is relatively inefficient, as increasing the
capacitor from 1μF to 220μF only decreases the noise from
430μV to 160μV rms for a 100kHz bandwidth at 5V output.
Noise can be reduced fourfold by a bypass capacitor across
R
, since it reduces the high frequency gain from 4 to unity.
Pick
or about 0.01μF. When doing this, the output capacitor must
be increased to 3.3μF to maintain stability. These changes
reduce the output noise from 430μV to 100μV rms for a
100kHz bandwidth at 5V output. With the bypass capacitor
added, noise no longer scales with output voltage so that
improvements are more dramatic at higher output voltages.
20052820
*
When V
≤
1.3V, the error flag pin becomes a high impedance, and the
error flag voltage rises to its pull-up voltage. Using V
as the pull-up
voltage (see
Figure 2
), rather than an external 5V source, will keep the
error flag voltage under 1.2V (typ.) in this condition. The user may wish to
divide down the error flag voltage using equal-value resistors (10 k
suggested), to ensure a low-level logic signal during any fault condition,
while still allowing a valid high logic level during normal operation.
FIGURE 1. ERROR Output Timing
20052807
*
See Application Hints
**
Drive with TTL-high to shut down. Ground or leave open if shutdown
feature is not to be used.
Note:
Pins 2 and 6 are left open.
FIGURE 2. Adjustable Regulator (LP4951C)
L
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP4951CM/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類(lèi)型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP4951CMX | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類(lèi)型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP4951CMX/HAPB | 制造商:Texas Instruments 功能描述: |
| LP4951CMX/NAK2 | 制造商:Texas Instruments 功能描述: |
| LP4951CMX/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類(lèi)型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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