поискавой системы для электроныых деталей |
|
LM3590 датащи(PDF) 7 Page - National Semiconductor (TI) |
|
|
LM3590 датащи(HTML) 7 Page - National Semiconductor (TI) |
7 / 9 page Application Information CIRCUIT DESCRIPTION The LM3590 is a constant current series White-LED Driver, providing up to 20mA from an input voltage between 7.5V to 12.6V. To set the LED drive current, the LM3590 uses a resistor connected to the I SET pin to set a reference current. This reference current is then multiplied and mirrored to the constant current output, I OUT. The LED brightness can be controlled by applying a PWM (Pulse Width Modulation) signal to the Enable pin (EN). (see PWM BRIGHTNESS CONTROL PROCEDURES section). ENABLE MODE The Enable pin (EN) disables the part and reduces the quiescent current to 0.1µA (typ.). The LM3590 has an active- high enable pin (LOW = shut down, HIGH = operating). The LM3590 EN pin can be driven with a low-voltage CMOS logic signal (1.5V logic, 1.8V logic, etc). There is an internal 500k Ω pull-down between the EN and GND pins of the LM3590. CAPACITOR SELECTION Although not required for normal operation, a capacitor can be added to the voltage input of the LM3590 to reduce line noise. A surface-mount multi-layer ceramic capacitor (MLCC) is recommended. MLCCs are small, inexpensive and have very low equivalent series resistance (ESR, ≤15mΩ typ.). MLCCs with a X5R or X7R temperature char- acteristic are preferred for use with the LM3590. Table 1. Ceramic Capacitor Manufacturers lists suggested capacitor suppliers for the typical application circuit. TABLE 1. Ceramic Capacitor Manufacturers Manufacturer Contact TDK www.component.tdk.com Murata www.murata.com Taiyo Yuden www.t-yuden.com LED SELECTION The LM3590 is designed to drive up to 3 LEDs with the combined forward voltages of the LEDs being no greater than 11.5V, when using a 12V input supply. The typical and maximum diode forward voltage depends highly on the manufacturer and their technology. Table 2. White LED Se- lection lists two suggested manufacturers. LED Forward cur- rent matching is guaranteed by design, due to the series LED configuration of the LM3590. TABLE 2. White LED Selection Manufacturer Contact Osram www.osram-os.com Nichia www.nichia.com LED HEADROOM VOLTAGE (V HR) A single current source is connected internally between V IN and I OUT. The voltage across the current source, (VIN − V IOUT), is referred to as headroom voltage (VHR). The cur- rent source requires a sufficient amount of headroom voltage to be present across it in order to regulate properly. Minimum required headroom voltage is proportional to the current flowing through the current source, as dictated by the equa- tion: V HR-MIN =kHR xIOUT The parameter k HR, typically 15mV/mA in the LM3590, is a proportionality constant that represents the ON-resistance of the internal current mirror transistors. For worst-case design calculations, using a k HR of 20mV/mA is recommended. (Worst-case recommendation accounts for parameter shifts from part-to-part variation and applies over the full operating temperature range). Figure 1 shows how output current of the LM3590 varies with respect to headroom voltage. On the flat part of the graph, the current is regulated properly as there is sufficient headroom voltage for regulation. On the sloping part of the graph the headroom voltage is too small, the current source is squeezed, and the current drive capa- bility is limited. Thus, operating the LM3590 with insufficient headroom voltage across the current source should be avoided. I SET PIN An external resistor, R SET, connected to the ISET pin sets the output current. The internal current mirror sets the series LED output current with a 100:1 ratio to the current through R SET. The current matching through each LED is guaranteed by the series LED drive topology. The following equation approximates the LED current: I OUT = 100 x (1.25V ÷ RSET) (Amps) PWM BRIGHTNESS CONTROL PROCEDURES The brightness of the LEDs can be linearly varied from zero up to the maximum programmed current level by applying a Pulse-Width-Modulated signal to the EN pin of the LM3590. The following procedures illustrate how to program the LED drive current and adjust the output current level using a PWM signal. 1. Determine the maximum desired I OUT current. Use the I OUT equation to calculate RSET 20081312 FIGURE 1. I OUT vs VHR V HR =VIN −VIOUT V IN = 12.0V www.national.com 7 |
Аналогичный номер детали - LM3590 |
|
Аналогичное описание - LM3590 |
|
|
ссылки URL |
Конфиденциальность |
ALLDATASHEETRU.COM |
Вашему бизинису помогли Аллдатащит? [ DONATE ] |
Что такое Аллдатащит | реклама | контакт | Конфиденциальность | обмен ссыками | поиск по производителю 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 |