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參數(shù)資料
| 型號： | LM2781TPX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Ultra-Low Ripple Switched Capacitor Voltage Inverter |
| 中文描述： | SWITCHED CAPACITOR CONVERTER, 400 kHz SWITCHING FREQ-MAX, PBGA8 |
| 封裝： | CSP-8 |
| 文件頁數(shù)： | 5/7頁 |
| 文件大?。?/td> | 162K |
| 代理商： | LM2781TPX |
Block Diagram
20044710
Operation Description
The LM2781 is a switched capacitor voltage inverter that
produces a negative output voltage from a positive input
voltage. To minimize output voltage ripple, the LM2781 con-
tains two charge pump inverters that operate 180 out of
phase. These two charge pumps can be seen in the block
diagram above.
A basic switched capacitor inverter is a two-phase charge
pump circuit that transfers charge from the input to the
output using a flying capacitor. Charge Pump 1 in the block
diagram will be used to illustrate the operation of a single
charge pump. Disregard Charge Pump 2 in the diagram for
now. In phase 1 (
φ
1), the CLK1A signal of Charge Pump 1 is
high, and MOSFET switches S1A and S1B are ON. For
Charge Pump 1, this is the charge phase, as the flying
capacitor C1 is charged to the input voltage. In the second
phase (
φ
2), the positive-charged plate of C1 is connected to
GND through switch S1C, and the negative-charged plate is
connected to the output through switch S1D. This results in
the output voltage being approximately equal in magnitude
to the input voltage, but opposite in sign (V
OUT
~= - V
IN
). In
this pump phase, charge stored on the flying capacitor sup-
plies the current to the load and transfers charge to the
output capacitor.
This basic inverter has ripple in the output voltage. During
the charge phase, the load current is supplied by the charge
on the output capacitor. As charge is pulled off C
, the
voltage across the capacitor drops, and the magnitude of the
output voltage ( |V
OUT
| ) falls. During the pump phase, the
flying capacitor transfers charge to the C
, elevating both
the voltage across the C
OUT
and the magnitude of the output
voltage.
The LM2781 contains two charge pump inverters running
180 out of phase. Notice in the block diagram that the clock
connections on Charge Pump 2 are opposite of the clock
connections to Charge Pump 1. Thus, when Charge Pump 1
is in the charge phase, Charge Pump 2 is in the pump phase,
and vice-versa. With this double-pump technology, there is
always a flying capacitor connected to the output. This re-
sults in significantly lower output voltage ripple than that of a
single-pump inverter.
OUTPUT VOLTAGE RIPPLE
Several factors influence the magnitude of voltage ripple on
the output of the LM2781. Primary influences are output
capacitance, flying capacitance, load current, input voltage,
and output capacitor ESR.
The magnitude of the output voltage ripple is difficult to
predict with equations when the LM2781 is double pumping.
Refer to the Typical Performance Characteristic curves for
this information. In general, ripple decreases with increased
output capacitance, decreased load current, a lower input
voltage, a smaller flying capacitance and/or a smaller output
capacitor ESR.
When only one charge pump is active (C2 removed), the
output ripple is more predictable, and can be estimated with
the following equation:
V
RIPPLE
= [(0.5xI
OUT
) / (f
SW
xC
OUT
) ] + (2xI
OUT
xESR
Cout
)
L
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| LM2781TPX/NOPB | 功能描述:IC REG SWITCHD CAP INV ADJ 8USMD RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:1 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:3.3V 輸入電壓:4.5 V ~ 24 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:125mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-6 包裝:Digi-Reel® 供應商設備封裝:SOT-6 其它名稱:MAX1836EUT33#TG16DKR |
| LM2787 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Low Noise Regulated Switched Capacitor Voltage |
| LM2787AUP E WAF | 制造商:Texas Instruments 功能描述: |
| LM2787AUPN E WAF | 制造商:Texas Instruments 功能描述: |
| LM2787BP | 制造商:Texas Instruments 功能描述:INVERTER REG SW CAP REG SMD 2787 |
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