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SGM3141B Datasheet(PDF) 9 Page - SG Micro Corp |
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SGM3141B Datasheet(HTML) 9 Page - SG Micro Corp |
9 / 14 page 700mA Buck/Boost Charge Pump LED Driver 9 SGM3141B SG Micro Corp www.sg-micro.com APPLICATION INFORMATION Over-Temperature Protection When the temperature of SGM3141B rises above 145 ℃, the over-temperature protection circuitry turns off the output switches to prevent damage to the device. If the temperature drops back down below 130 ℃, the part automatically recovers and executes a soft-start cycle. Over-Voltage Protection The SGM3141B has over-voltage protection. If the output voltage rises above the 5.5V threshold, the over-voltage protection shuts off all of the output switches to prevent the output voltage from rising further. When the output decreases below 5.2V, the device resumes normal operation. Over-Current Protection The over-current protection circuitry monitors the average current out of the VOUT = 47mV (Torch Mode) pin. If the average output current exceeds approximately 1A, then the over-current protection circuitry shuts off the output switches to protect the chip. Component Selection The SGM3141B charge pump circuit requires 3 capacitors: 4.7μF input, 1μF output and 1μF flying capacitors are typically recommended. For the input capacitor, a larger value of 10μF will help reduce input voltage ripple for applications sensitive to ripple on the battery voltage. All the capacitors should be surface mount ceramic for low lead inductance necessary at the 2.2MHz switching frequency of the SGM3141B and to obtain low ESR, which improves bypassing on the input and output and improves output voltage drive by reducing output resistance. Ceramic capacitors with X5R or X7R temperature grade are recommended for most applications. The input and output capacitors should be located as close to the VIN and VOUT pins as possible to obtain best bypassing, and the returns should be connected directly to the PGND pin or to the thermal pad ground located under the SGM3141B. The flying capacitor should be located as close to the C1 and C2 pins as possible. To obtain lower output ripple, the COUT value can be increased from 1μF to 2.2μF or 4.7μF with a corresponding decrease in output ripple. For output currents of 500mA to 700mA, the recommended CF flying capacitor value of 1μF should be used. Output currents in Flash of 100mA to 400mA can use a 0.47μF CF but a minimum 1μF COUT is still needed. Resistor Selection The sense resistor RSENSE is determined by the value needed in the Torch mode for the desired output current by the equation: RSENSE = VFB/IOUT where VFB = 47mV (Torch Mode) Once the RSENSE resistor has been selected for Torch mode, the VFB voltage can be selected for Flash mode using the following equation: VFB = IOUT × RSENSE (Flash Mode) where IOUT is for Flash Mode. Next, the RSET resistor can be selected for Flash mode using the following equation: RSET = (1.26V/VFB) × 10.2kΩ (Flash Mode) For an example of 190mA Torch mode and 600mA Flash mode, the values of RSENSE = 0.25Ω, VFB = 150mV (Flash Mode), and RSET = 86.6kΩ are calculated. The power obtained in the Flash mode would be: PFLASH = VFB × IOUT = 150mV × 600mA = 90mW The typical 0603 surface mount resistor is rated 1/10 Watt continuous power and 1/5 Watt pulsed power, more than enough for this application. For other applications, the PFLASH power can be calculated and resistor size selected. The RSENSE resistor is recommended to be size 0603 for most applications. The range of typical resistor values and sizes are shown here in Table 1. |
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