Electronic Components Datasheet Search |
|
LM27951SDX Datasheet(PDF) 7 Page - Texas Instruments |
|
LM27951SDX Datasheet(HTML) 7 Page - Texas Instruments |
7 / 20 page VIN C2+ C2- CIN 3.3 µF 1 µF C1+ C1- 1 µF ISET RSET LM27951 D1 VOUT 3.3 µF EN Voltage Reference 1x/1.5x Charge Pump Current Control Gain Select OSC D4 D2 D3 PWM Regulated Current Sources GND D4 D3 D2 D1 COUT 7 LM27951 www.ti.com SNVS416C – NOVEMBER 2005 – REVISED FEBRUARY 2016 Product Folder Links: LM27951 Submit Documentation Feedback Copyright © 2005–2016, Texas Instruments Incorporated 7 Detailed Description 7.1 Overview The LM27951 is an adaptive 1.5×/1× CMOS charge pump, optimized for driving white LEDs used in small-format display backlighting. It provides four constant current outputs capable of sourcing up to 30 mA through each LED. The well-matched current sources ensure the current through all the LEDs are virtually identical, providing a uniform brightness across the entire display. Each current source is internally connected to the charge pump output, VOUT. LED drive current is programmed by connecting a resistor, RSET, to the current set pin, ISET. LED brightness is adjusted by applying a pulse width modulated (PWM) signal to the dedicated PWM input pin. 7.2 Functional Block Diagram 7.3 Feature Description 7.3.1 Charge Pump The input to the 1.5×/1× charge pump is connected to the VIN pin, and the loosely regulated output of the charge pump is connected to the VOUT pin. The recommended input voltage range of the LM27951 is 3 V to 5.5 V. The loosely regulated charge pump of the device has both open loop and closed loop modes of operation. When the device is in open loop, the voltage at VOUT is equal to the gain times the voltage at the input. When the device is in closed loop, the voltage at VOUT is loosely regulated to 4.5 V (typical). The charge pump gain transitions are actively selected to maintain regulation based on LED forward voltage and load requirements. This allows the charge pump to stay in the most efficient gain (1×) over as much of the input voltage range as possible, reducing the power consumed from the battery. 7.3.2 Soft Start The LM27951 contains internal soft-start circuitry to limit input inrush currents when the part is enabled. Soft start is implemented internally with a controlled turnon of the internal voltage reference. Due to the soft-start circuitry, startup time of the LM27951 is approximately 330 µs (typical). 7.3.3 Thermal Protection Internal thermal protection circuitry disables the LM27951 when the junction temperature exceeds 150°C (typical). This feature protects the device from being damaged by high die temperatures that might otherwise result from excessive power dissipation. The device recovers and operate normally when the junction temperature falls below 140°C (typical). It is important that the board layout provide good thermal conduction to keep the junction temperature within the specified operating ratings. |
Similar Part No. - LM27951SDX |
|
Similar Description - LM27951SDX |
|
|
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 |