LM2685MTCX/NOPB【PDF 7/9 页】SWITCHED CAPACITOR REGULATOR, 180 kHz SW

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录39246

3页 4页 5页 6页 [7页]8页 9页

Detailed Device Description

(Continued)

CMOS switches which are in a sequence to invert the input

supply voltage. Figure 3 illustrates the voltage conversion

scheme. When S1 and S3 are closed, C1 charges to the

supply voltage V

05. During this time interval, switches S2

and S4 are open. In the second time interval, S1 and S3 are

open;at the same time, S2 and S4 are closed, C1 is charging

C2. After a number of cycles, the voltage cross C2 will be

pumped to V

05. Since the anode of C2 is connected to

ground, the output at the cathode of C2 equals (V

05) when

there is no load current. The output voltage drop when a load

is added is determined by the parasitic resistance (R

ds(on) of

the MOSFET switches and the ESR of the capacitors) and

the charge transfer loss between capacitors.

SHUTDOWN AND LOAD DISCONNECT

In addition to the nominal charge pump and regulator func-

tions, the LM2685 features shutdown and load disconnect

circuitry. CE (chip enable) and SDP (shutdown positive)

perform the same task with opposite input polarities. When

CE is low or SDP is high, all circuit blocks are disabled and

05 falls to ground potential. This is the same result as when

the die temperature exceeds 150C (typical), and the de-

vice’s internal thermal shutdown is triggered.

Forcing SDN (shutdown negative) high disables only the

inverting charge pump. The doubling charge pump and the

LDO regulator continue to operate, so the V

05 and the VPSW

remain at 5V.

The LM2685 incorporates two low impedance switches tied

to the V

05 and VNEG outputs, because some special appli-

cations require load disconnect and this is achievable via the

switches. Switch PSW connects V

05 to VPSW, and switch

NSW connects V

NEG to VNSW. In normal operation, these

switches are closed, allowing 5V loads to be tied to either

05 or VPSW and 5V loads to be tied to either VNEG or

NSW. Driving SDN high opens switch NSW only, while

forcing CE low or SDP high, opens both the PSW and NSW.

Application Information

CAPACITOR SELECTION

The output resistance and ripple voltage are dependent on

the capacitance and ESR values of the external capacitors.

VOLTAGE DOUBLER EXTERNAL CAPACITORS

The selection of capacitors are based on the specifications

of the dropout voltage (which equals I

OUT ROUT), the output

voltage ripple, and the converter efficiency.

where R

SW is the sum of the ON resistance of the internal

MOSFET switches as shown in Figure 2.

The peak-to-peak output voltage ripple is determined by the

oscillator frequency, the capacitance and ESR of the capaci-

tor C3.

High capacitance (2.2F to higher), low ESR capacitors can

reduce the output resistance and the voltage ripple.

where I

Q(V+) is the quiescent power loss of the IC device,

and I

LR is the conversion loss associated with the switch

on-resistance, the two external capacitors and their ESRs.

Low ESR capacitors (table to be referenced) are recom-

mended to maximize efficiency, reduce the output voltage

drop and voltage ripple.

+5 LDO REGULATOR EXTERNAL CAPACITORS

The voltage doubler output capacitor, C3, serves as the input

capacitor of the +5 LDO regulator. The output capacitor C4,

must meet the requirement for minimum amount of capaci-

tance and appropriate ESR (Equivalent Serving Resistance)

for proper operation. The ESR value must remain within the

regions of stability as shown in Figure 4, Figure 5 and Figure

6 to ensure output’s stability. A minimum capacitance of 1F

is required at the output. This can be increased without limit,

but a 4.7F tantalum capacitor is recommended for loads

ranging upto the maximum specification. With lighter loads

of less or equal to 10mA, ceramic capacitor of at least 1F

and ESR in the milliohms can be used. This has to be

connected to V

PSW pin instead of the V05 pin.

Any output capacitor used should have a good tolerance

over temperature for capacitance and ESR values. The

larger the capacitor, with ESR within the stable region, the

better the stability and noise performance.

10110005

FIGURE 3. Voltage Inverter Principle

10110025

FIGURE 4. ESR Curve for C

OUT = 2.2F

LM2685

www.national.com

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

我的联系方式

相关代理商/技术参数

LM2686MTC 制造商:Texas Instruments 功能描述:VOLT CONVERTER SMD 2686 TSSOP14

LM2686MTC/NOPB 功能描述:IC REG SWITCHED CAP DBL 14-TSSOP 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

LM2686MTCX/NOPB 功能描述:IC REG SWITCHED CAP DBL 14-TSSOP 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

LM2687LD 制造商:Texas Instruments 功能描述:

LM2687LD/NOPB 功能描述:IC REG SWITCHD CAP INV ADJ 8-LLP 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

LM2687LDX 功能描述:电荷泵 RoHS:否制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube

LM2687LDX/NOPB 功能描述:电荷泵 RoHS:否制造商:Maxim Integrated 功能:Inverting, Step Up 输出电压:- 1.5 V to - 5.5 V, 3 V to 11 V 输出电流:100 mA 电源电流:1 mA 最大工作温度:+ 70 C 封装 / 箱体:SOIC-8 Narrow 封装:Tube

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式