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C3225X5R1C22M Datasheet(PDF) 10 Page - Richtek Technology Corporation |
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C3225X5R1C22M Datasheet(HTML) 10 Page - Richtek Technology Corporation |
10 / 14 page RT8293B 10 DS8293B-03 March 2011 www.richtek.com Hiccup Mode For the RT8293BH, it provides Hiccup Mode Under Voltage Protection (UVP). When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP function will be triggered and the RT8293BH will shut down for a period of time and then recover automatically. The Hiccup Mode UVP can reduce input current in short-circuit conditions. Latch Off Mode For the RT8293BL, it provides Latch Off Mode Under Voltage Protection (UVP). When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP will be triggered and the RT8293BL will shut down in Latch Off Mode. In shutdown condition, the RT8293BL can be reset by EN pin or power input VIN. Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ∆IL increases with higher VIN and decreases with higher inductance. OUT OUT L IN VV I =1 f LV ∆ ×− × Figure 4. The Resistors can be Selected to Set IC Lockout Threshold Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. High frequency with small ripple current can achieve highest efficiency operation. However, it requires a large inductor to achieve this goal. For the ripple current selection, the value of ∆IL= 0.24(IMAX) will be a reasonable starting point. The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below the specified maximum, the inductor value should be chosen according to the following equation : OUT OUT L(MAX) IN(MAX) VV L =1 f IV ×− ×∆ The inductor's current rating (caused a 40 °C temperature rising from 25 °C ambient) should be greater than the maximum load current and its saturation current should be greater than the short circuit peak current limit. Please see Table 2 for the inductor selection reference. Table 2. Suggested Inductors for Typical Application Circuit Component Supplier Series Dimensions (mm) TDK VLF10045 10 x 9.7 x 4.5 TDK SLF12565 12.5 x 12.5 x 6.5 TAIYO YUDEN NR8040 8 x 8 x 4 OUT IN RMS OUT(MAX) IN OUT V V I = I1 VV − This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. For the input capacitor, two 10 µF low ESR ceramic capacitors are recommended. For the recommended capacitor, please refer to Table 3 for more detail. The selection of COUT is determined by the required ESR to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ∆VOUT , is determined by : CIN and COUT Selection The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : OUTL OUT 1 V I ESR 8fC ∆ ≤ ∆+ VIN EN GND BOOT FB SW 7 5 2 3 1 L R1 R2 VOUT VIN RT8293B SS 8 CSS COMP CC RC CP 6 4, 9 (Exposed Pad) CBOOT COUT CIN 100k 8V 12V REN2 REN1 10 µF |
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