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参数资料
| 型号： | LM2781TPX/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHED CAPACITOR CONVERTER, 400 kHz SWITCHING FREQ-MAX, PBGA8 |
| 封装： | CSP-8 |
| 文件页数： | 6/7页 |
| 文件大小： | 162K |
| 代理商： | LM2781TPX/NOPB |
Operation Description (Continued)
OUTPUT RESISTANCE
Output resistance (R
OUT) models the internal non-idealities
of a charge pump that result in droop in the output voltage.
The effect of output resistance on output voltage is ex-
pressed in the following equation:
V
OUT =-[VIN -(|IOUT|xROUT )]
Output resistance is a function of the internal switch resis-
tance (R
SW)
, flying capacitance (C1), flying capacitor
equivalent series resistance (ESR
C1), output capacitor ESR
(ESR
Cout), and internal switching frequency (fSW). When the
LM2781 operates as a single charge pump (C2 removed),
the output resistance can be approximated by the following
equation:
1 Fly Cap: R
OUT1
~=2R
SW1+[1/(fSW*C1)]+4ESRC1+ESRCout
R
SW1 is the sum of the ON resistance of the four internal
MOSFET switches of Charge Pump 1.
With both C1 and C2 in place, the double pumping topology
of the LM2781 cuts the output resistance in half:
2 Fly Caps: R
OUT2
~= 0.5xR
OUT1
Recommendations for minimizing output resistance include
increasing flying capacitance and minimizing output and fly-
ing capacitor ESR.
CAPACITOR SELECTION
Surface-mount multi-layer ceramic capacitors are recom-
mended for use with the LM2781. These capacitors are
small, inexpensive and have very low equivalent series re-
sistance (ESR, < 15m
typ.). Tantalum capacitors, OS-CON
capacitors, and aluminum electrolytic capacitors generally
are not recommended for use with the LM2781 due to their
high ESR, as compared to ceramic capacitors.
For most applications, ceramic capacitors with X7R or X5R
temperature characteristic are preferred for use with the
LM2781. These capacitors have tight capacitance tolerance
(as good as ±10%), hold their value over temperature (X7R:
±15% over -55C to 125C; X5R: ±15% over -55C to 85C),
and typically have little voltage coefficient.
Capacitors with Y5V and/or Z5U temperature characteristic
are generally not recommended for use with the LM2781.
These types of capacitors typically have wide capacitance
tolerance (+80%, -20%), vary significantly over temperature
(Y5V: +22%, -82% over -30C to +85C range; Z5U: +22%,
-56% over +10C to +85C range), and have poor voltage
coefficients. Under some conditions, a nominal 1F Y5V or
Z5U capacitor could have a capacitance of only 0.1F. Such
deviation would severely affect performance of the LM2781
circuit.
LM2781
www.national.com
6
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2787 | 制造商:NSC 制造商全称: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: |
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| LM2787BP/NOPB | 功能描述:IC REG SWITCHD CAP INV ADJ 8USMD RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:1 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:3.3V 输入电压:4.5 V ~ 24 V PWM 型:- 频率 - 开关:- 电流 - 输出:125mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-6 包装:Digi-Reel® 供应商设备封装:SOT-6 其它名称:MAX1836EUT33#TG16DKR |
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