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C3225X5R0J476M Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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C3225X5R0J476M Datasheet(HTML) 11 Page - Richtek Technology Corporation |
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11 / 15 page  RT7237B 11 DS7237B-01 September 2012 www.richtek.com © Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. OUT OUT L IN VV I = 1 fL V ⎡⎤ ⎡ ⎤ Δ× − ⎢⎥ ⎢ ⎥ × ⎣⎦ ⎣ ⎦ Under Voltage Protection Hiccup Mode For the RT7237BH, it provides Hiccup Mode Under Voltage Protection (UVP). When the VFB voltage drops below 0.4V, the UVP function will be triggered to shut down switching operation. If the UVP condition remains for a period, the RT7237BH will retry automatically. When the UVP condition is removed, the converter will resume operation. The UVP is disabled during soft-start period. 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 the highest efficiency operation. However, it requires a large inductor to achieve this goal. For the ripple current selection, the value of ΔIL= 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 : 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 NRS8040 8 x 8 x 4 OUT OUT L(MAX) IN(MAX) VV L = 1 fI V ⎡⎤ ⎡ ⎤ ×− ⎢⎥ ⎢ ⎥ ×Δ ⎣⎦ ⎣ ⎦ 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. Latch-Off Mode For the RT7237BL, it provides Latch-Off Mode Under Voltage Protection (UVP). When the FB voltage drops below half of the feedback reference voltage, VFB, UVP will be triggered and the RT7237BL will shut down in Latch- Off Mode. In shutdown condition, the RT7237BL can be reset by EN pin or power input VIN. Figure 5. Hiccup Mode Under Voltage Protection Figure 6. Latch-Off Mode Under Voltage Protection Over Temperature Protection The RT7237B features an Over Temperature Protection (OTP) circuitry to prevent from overheating due to excessive power dissipation. The OTP will shut down switching operation when junction temperature exceeds 150 °C. Once the junction temperature cools down by approximately 20 °C, the converter will resume operation. To maintain continuous operation, the maximum junction temperature should be lower than 125 °C. Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. Time (50ms/Div) Latch-Off Mode VOUT (2V/Div) IL (2A/Div) Time (50ms/Div) Hiccup Mode IL (2A/Div) VOUT (500mV/Div) |
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