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GRM32ER71C226M Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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GRM32ER71C226M Datasheet(HTML) 9 Page - Richtek Technology Corporation |
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9 / 14 page  RT8283B 9 DS8283B-01 March 2011 www.richtek.com Application Information The RT8283B is a synchronous high voltage buck converter that can support an input voltage range from 4.5V to 23V and the output current can be up to 3A. Output Voltage Setting The resistive voltage divider allows the FB pin to sense the output voltage as shown in Figure 1. Figure 1. Output Voltage Setting The output voltage is set by an external resistive voltage divider according to the following equation : ⎛⎞ + ⎜⎟ ⎝⎠ OUT FB R1 V = V 1 R2 Where VFB is the feedback reference voltage (0.8V typ.). External Bootstrap Diode Connect a 100nF low ESR ceramic capacitor between the BOOT pin and SW pin. This capacitor provides the gate driver voltage for the high side MOSFET. It is recommended to add an external bootstrap diode between an external 5V and BOOT pin for efficiency improvement when input voltage is lower than 5.5V or duty cycle is higher than 65% .The bootstrap diode can be a low cost one such as IN4148 or BAT54. The external 5V can be a 5V fixed input from system or a 5V output of the RT8283B. Note that the external boot voltage must be lower than 5.5V. Figure 2. External Bootstrap Diode RT8283B GND FB R1 R2 VOUT SW BOOT 5V RT8283B 100nF Soft-Start The RT8283B contains an external soft-start clamp that gradually raises the output voltage. The soft-start timing can be programmed by the external capacitor between SS pin and GND. The chip provides a 6 μA charge current for the external capacitor. If 0.1 μF capacitor is used to set the soft-start, it's period will be 13.5ms (typ.). Chip Enable Operation The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shutdown the device. During shutdown mode, the RT8283B quiescent current will drop below 3 μA. Driving the EN pin high (>2.7V, < 5.5V) will turn on the device again. For external timing control (e.g.RC), the EN pin can also be externally pulled high by adding a REN* resistor and CEN* capacitor from the VIN pin (see Figure 5). An external MOSFET can be added to implement digital control on the EN pin when no system voltage above 2.5V is available, as shown in Figure 3. In this case, a 100k Ω pull-up resistor, REN, is connected between VIN and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. Figure 3. Enable Control Circuit for Logic Control with Low Voltage To prevent enabling circuit when VIN is smaller than the VOUT target value, a resistive voltage divider can be placed between the input voltage and ground and connected to the EN pin to adjust IC lockout threshold, as shown in Figure 4. For example, if an 8V output voltage is regulated from a 12V input voltage, the resistor REN2 can be selected to set input lockout threshold larger than 8V. VIN EN GND BOOT FB SW 7 5 2 3 1 L R1 R2 VOUT Chip Enable VIN RT8283B SS 8 CSS COMP CC RC CP 6 4, Exposed Pad(9) CBOOT COUT CIN REN Q1 100k |
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