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參數資料
| 型號： | LP2952A |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Adjustable Micropower Low-Dropout Voltage Regulators |
| 中文描述： | 可調微功率低壓差穩(wěn)壓器 |
| 文件頁數： | 15/22頁 |
| 文件大?。?/td> | 1050K |
| 代理商： | LP2952A |
Application Hints
(Continued)
DROPOUT VOLTAGE
The dropout voltage of the regulator is defined as the mini-
mum input-to-output voltage differential required for the out-
put voltage to stay within 100 mV of the output voltage
measured with a 1V differential. The dropout voltage is in-
dependent of the programmed output voltage.
DROPOUT DETECTION COMPARATOR
This comparator produces a logic “LOW” whenever the out-
put falls out of regulation by more than about 5%. This figure
results from the comparator’s built-in offset of 60 mV divided
by the 1.23V reference (refer to block diagrams on page 1).
The 5% low trip level remains constant regardless of the
programmed output voltage. An out-of-regulation condition
can result from low input voltage, current limiting, or thermal
limiting.
Figure 5
gives a timing diagram showing the relationship
between the output voltage, the ERROR output, and input
voltage as the input voltage is ramped up and down to a
regulator programmed for 5V output. The ERROR signal
becomes low at about 1.3V input. It goes high at about 5V
input, where the output equals 4.75V. Since the dropout
voltage is load dependent, the
input
voltage trip points will
vary with load current. The
output
voltage trip point does not
vary.
The comparator has an open-collector output which requires
an external pull-up resistor. This resistor may be connected
to the regulator output or some other supply voltage. Using
the regulator output prevents an invalid “HIGH” on the com-
parator output which occurs if it is pulled up to an external
voltage while the regulator input voltage is reduced below
1.3V. In selecting a value for the pull-up resistor, note that
while the output can sink 400 μA, this current adds to battery
drain. Suggested values range from 100 k
to 1 M
. This
resistor is not required if the output is unused.
When V
≤
1.3V, the error flag pin becomes a high imped-
ance, allowing the error flag voltage to rise to its pull-up
voltage. Using V
as the pull-up voltage (rather than an
external 5V source) will keep the error flag voltage below
1.2V (typical) 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.
OUTPUT ISOLATION
The regulator output can be left connected to an active
voltage source (such as a battery) with the regulator input
power shut off,
as long as the regulator ground pin is
connected to ground.
If the ground pin is left floating,
damage to the regulator can occur
if the output is pulled
up by an external voltage source.
REDUCING OUTPUT NOISE
In reference applications it may be advantageous to reduce
theAC noise present on the output. One method is to reduce
regulator bandwidth by increasing output capacitance. This
is relatively inefficient, since large increases in capacitance
are required to get significant improvement.
Noise can be reduced more effectively by a bypass capacitor
placed across R1 (refer to
Figure 4
). The formula for select-
ing the capacitor to be used is:
This gives a value of about 0.1 μF. When this is used, the
output capacitor must be 6.8 μF (or greater) to maintain
stability. The 0.1 μF capacitor reduces the high frequency
gain of the circuit to unity, lowering the output noise from 260
μV to 80 μV using a 10 Hz to 100 kHz bandwidth.Also, noise
is no longer proportional to the output voltage, so improve-
ments are more pronounced at high output voltages.
AUXILIARY COMPARATOR
(LP2953 only)
The LP2953 contains an auxiliary comparator whose invert-
ing input is connected to the 1.23V reference. The auxiliary
comparator has an open-collector output whose electrical
characteristics are similar to the dropout detection compara-
tor. The non-inverting input and output are brought out for
external connections.
01112709
* See Application Hints
** Drive with TTL-low to shut down
FIGURE 4. Adjustable Regulator
01112710
* In shutdown mode, ERROR will go high if it has been pulled up to an
external supply. To avoid this invalid response, pull up to regulator output.
** Exact value depends on dropout voltage. (See Application Hints)
FIGURE 5. ERROR Output Timing
L
www.national.com
15
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LP2952AI | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Adjustable Micropower Low-Dropout Voltage Regulators |
| LP2952AI-3.3 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Adjustable Micropower Low-Dropout Voltage Regulators |
| LP2952AIM | 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 回動電壓（最大值）:307 mV 輸出電流:1 A 負載調節(jié):0.3 % 輸出端數量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP2952AIM/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 回動電壓（最大值）:307 mV 輸出電流:1 A 負載調節(jié):0.3 % 輸出端數量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP2952AIM-3.3 | 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 回動電壓（最大值）:307 mV 輸出電流:1 A 負載調節(jié):0.3 % 輸出端數量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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