TS1520CX5RF

TS1520 Step-Up DC-DC Converter, White LED Driver SOT-25 Pin Definition: 1. SW 2. Ground 3. Feedback 4. CTRL 5. Input General Description The TS1520 is a step-up DC-DC converter; operates as current source to drive up to 18 white LEDs in parallel/series configuration. Series connecting of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The light intensity of these LEDs is proportional to the current passing through them. The TS1520 switches at a fixed frequency of 700KHz, allowing the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space consideration applications for cellular phone backlighting or other hand held equipment. The TS1520 can drive up to 18 white LEDs form 4.5V supply. The wide input voltage range from 2.7V to7V is ideal for portable (5V) applications with higher conversion efficiency. To control LED brightness, the LED current can be pulsed by applying a PWM (pulse width modulated) signal with a frequency range of 100Hz to 50KHz to the CTRL pin. TS1520 has integrated Over Voltage Protection that prevents damage to the device in case of a high impedance output due to faulty LED or open circuit caused by abnormal conditions. Features ● ● ● ● ● ● Built-in Internal Switch 2.7V to 7V input range 1.8V generates full-scale LED current VCTRL < 0.4V chip is off Switching from 04V to 2.0V, PWM duty cycle controls the LED current Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible 4 CTRL 5 Input 3/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Application Information Operation The TS1520 uses a constant frequency, current mode control scheme to regulate the output LED current. Its operation can be understood by referring to the block diagram in Figure 3. At the start of each oscillator cycle, a voltage proportional to the switch current is added to a ramp output and the resulting sum is fed into the positive terminal of the PWM comparator. When this voltage exceeds the level of the comparator negative input, the peak current has been reached, and the SR latch is reset and turns off the power switch. The voltage at the negative input of the comparator comes from the output of the error amplifier. The error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. Inrush Current The maximum switch current is limited to about 900mA by the chip Typically, this large current will occur for about 40us during start up. A larger COUT will increase the duration of high current. However, when VIN is first connected, an even larger current can flow into COUT. This occurs when the SW pin is open circuit and the COUT voltage changes from 0V to VIN in a few microseconds. Because the duration of this large current is short, it will usually not cause problems. If this current is not desirable, an external soft-start circuit can be added to significantly reduce this inrush current. LED Current and Dimming Control The maximum LED current set initially can be reduced by pulse width modulating the CTRL voltage from 0.4V to 1.8V. A better approach is to adjust the feedback voltage for dimming control. Either a DC level signal or a filtered PWM signal can be used to control the LED current as illustrated in Figure 1 and Figure 2 respectively. Using the above different scheme, the LED current can be controlled from 0% to 100% to its maximum value. Figure 1. Dimming Control Using a DC Voltage Figure 2. Dimming Control Using a Filtered PWM Signal (1kHz, 2Vp-p, duty 20%~80%) Open Circuit Protection The TS1520 has an internal open-circuit protection circuit. When the LEDs are disconnected from the circuit or fail open, the TS1520 will shutdown automatically until input condition changes to bring it out of the shutdown mode. Inductor Selection A 47uH inductor is recommended for most applications to drive more than 10 LEDs in serials and 33Uh inductor is recommended for drive 30 LEDs in serials/parallel. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1MHz and low DCR (copper wire resistance). Diode Selection To maintain high efficiency, the average current rating of the Schottky diode should be large than the peak inductor current, IPK. Schottky diode with a low forward drop and fast switching speeds are ideal for increase efficiency in portable application. Choose a reverse breakdown of the Schottky diode large than the output voltage. 4/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Application Information (Continue) Capacitor Selection Choose low ESR capacitors for the output to minimize output voltage ripple. Multilayer capacitors are a good choice for this as well. A 47uF capacitor is sufficient for most applications. For additional bypassing, a 100nF ceramic capacitor can be used to shunt high frequency ripple on the input. The input bypass capacitor CIN, as shown in Figure 1, must be placed close to the IC. This will reduce copper trace resistance which affects input voltage ripple of the IC. For additional input voltage filtering, a 100nF bypass capacitor can be placed in parallel with CIN to shunt any high frequency noise to ground. The output capacitor, COUT, should also be placed close to the IC. Any copper trace connections for the COUT capacitor can increase the series resistance, which directly effect output voltage ripple. The feedback network, resister R2 should be kept close to the FB pin to minimize copper trace connections that can inject noise into the system. The ground connection for the feedback resistor network should connect directly to an analog ground plane. The analog ground plane should tie directly to the GND pin. If no analog ground plane is available, the ground connection for the feedback network should tie directly to the GND pin. Trace connections made to the inductor and Schottky diode should be minimized to reduce power dissipation and increase overall efficiency. Typical Performance Characteristics 5/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Typical Performance Characteristics (Continue) 6/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Typical Performance Characteristics (Continue) 7/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Typical Performance Characteristics (Continue) 8/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Typical Performance Characteristics (Continue) 9/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Typical Performance Characteristics (Continue) Figure 1. Saturation Voltage vs. Switch Current Figure 2. Switching Frequency vs. Temperature Figure 3. Leakage Current vs. Input Voltage Figure 4. Input Current vs. Input Voltage 10/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver SOT-25 Mechanical Drawing DIM A+A1 B C D E E H L Ө1 S1 SOT-25 DIMENSION MILLIMETERS INCHES MIN MAX MIN MAX. 0.09 1.25 0.0354 0.0492 0.30 0.50 0.0118 0.0197 0.09 0.25 0.0035 0.0098 2.70 3.10 0.1063 0.1220 1.40 1.80 0.0551 0.0709 1.90 BSC 0.0748 BSC 2.40 3.00 0.09449 0.1181 0.35 BSC 0.0138 BSC 0º 10º 0º 10º 0.95 BSC 0.0374 BSC 11/12 Version: B07 TS1520 Step-Up DC-DC Converter, White LED Driver Notice Specifications of the products displayed herein are subject to change without notice. TSC or anyone on its behalf, assumes no responsibility or liability for any errors or inaccuracies. Information contained herein is intended to provide a product description only. No license, express or implied, to any intellectual property rights is granted by this document. Except as provided in TSC’s terms and conditions of sale for such products, TSC assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of TSC products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. The products shown herein are not designed for use in medical, life-saving, or life-sustaining applications. Customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify TSC for any damages resulting from such improper use or sale. 12/12 Version: B07