 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
CM9140-01QE Datasheet(PDF) 8 Page - California Micro Devices Corp |
|
||||||||||||||||||||||||||||||
CM9140-01QE Datasheet(HTML) 8 Page - California Micro Devices Corp |
|
|
8 / 12 page  © 2006 California Micro Devices Corp. All rights reserved. 8 490 N. McCarthy Blvd., Milpitas, CA 95035-5112 l Tel: 408.263.3214 l Fax: 408.263.7846 l www.cmd.com 04/26/06 CM9140 PRELIMINARY Many charge pumps are fixed 2x designs. The ideal 2x charge pump efficiency can be similarly expressed; In 1x mode, when the input voltage is above the output voltage, the ideal efficiency is simply VOUT/VIN. The typical conversion efficiency plots for these modes, with some losses, are shown in Figure 2. Figure 2. Ideal charge pump efficiency As can be seen, the CM9140, with 1x and 1.5x modes, has better efficiency in this application than a fixed 2x charge pump. At low battery voltages, the higher effi- ciency of the CM9140 charge pump’s 1,5x gain reduces the battery drain. At higher input voltages, typ- ically seen when the system is running off an AC adapter, the CM9140, operating the 1x mode, has bet- ter efficiency than single mode 1.5x or 2x charge pumps, lowering the power dissipation for cooler circuit operation and long life. While the charge pump efficiency is easily determined, the system efficiency is more difficult due to the current source outputs, which complicate measuring the output power. The forward voltage of the white LEDs will vary, and the constant current sources will adjust to maintain the current. When comparing systems, it is best to compare the input current for a specified LED drive current. The 1x mode has better efficiency than the 1.5x mode. Selecting LEDs with low forward voltage (VLED) increases the time spent in the 1x mode as the battery discharges, extending the operating time. Failed LED Detection If a LED is shorted, the CM9140 will continue to oper- ate and drive the remaining LEDs at the programmed current. If a LED opens, the other LEDs will still be reg- ulated at the programmed current. LED Current Set (ISET) An external resistor programs a reference current, set- ting the maximum driver current. This resistor must be tied to a good analog ground. If it is pulled to ground through a switch, for example, from the host controller output, the voltage drop across that switch should not exceed 10mV. The voltage at the ISET pin is provided by a .66V band- gap reference. The LED current is approximately 1000x the current set by the RSET resistor, according to the following formula: Logic Low is the voltage on device driving this pin to ground. If the resistor is tied to ground directly, Logic low = 0. For 20mA LED current, RSET≅33 k. When this pin is driven high or open, the device will enter a sleep mode with VOUT = 4.5V and, with no load, IQUIESCENT≅ 500μA. Analog Control of Display Intensity Typically, portable devices control the backlight display intensity in response to ambient light conditions, or lower the intensity after a short standby interval to con- verse battery charge. The luminous intensity of white LEDs is proportional to the amount of forward current through them, but the color wavelength emitted is also dependent upon the forward current. In applications where color shift is not critical, brightness can be con- trolled by adjusting the diode’s current. A typical white LED Intensity vs. forward current curve is shown in Figure 3. P OUT P IN ------------- 3.9V 2.0 V IN × ----------------------- ≈ 30 45 60 75 90 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) VLED=3.5V 2X 1X-1.5X dual mode 1.5X 1X R SET 0.66V LogicLow () – I LED ----------------------------------------------------- 1000 × = Application Information (cont’d) |
Similar Part No. - CM9140-01QE |
|
Similar Description - CM9140-01QE |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
