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RT6238AHGQUF Datasheet(PDF) 6 Page - Richtek Technology Corporation |
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RT6238AHGQUF Datasheet(HTML) 6 Page - Richtek Technology Corporation |
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6 / 23 page  RT6238A/B 6 DS6238A/B-08 July 2017 www.richtek.com © Copyright 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. will be triggered to shut down switching operation. If the UVP condition remains for a period, the RT6238 will retry automatically. When the UVP condition is removed, the converter will resume operation. The UVP is disabled during soft-start period. During hiccup mode, the shutdown time is determined by the capacitor at SS. A 2 μA current source discharges VSS from its starting voltage (normally VPVCC). The IC remains shut down until VSS reaches 0.2V, about 10ms for a 3.9nF capacitor. At that point the IC begins to charge the SS capacitor at 6 μA, and a normal start-up occurs. If the fault remains, UVP protection will be enabled when VSS reaches 2.2V (typical). The IC will then shut down and discharge the SS capacitor from the 2.2V level, taking about 4ms for a 3.9nF SS capacitor. Latch Mode For the RT6238AL/RT6238BL, it provides Latch-Off Mode Under Voltage Protection (UVP). When the FB voltage drops below 60% of the feedback reference voltage, the output voltage drops below the UVP trip threshold for longer than 270 μs (typical) then IC's UVP is triggered. UVP function will be triggered to shut down switching operation. In shutdown condition, the RT6238 can be reset by EN pin or power input VIN. Output Over-Voltage Protection If the output voltage VOUT rises above the regulation level and lower 1.2 times regulation level, the high-side switch naturally remains off and the synchronous rectifier turns on. For RT6238BL, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches the low side current limit. If the output voltage still remains high, then IC's switches remain that the synchronous rectifier turns on and high-side MOS keeps off to operate at typical 500kHz switching protection, again if inductor current reaches low side current limit, the synchronous rectifier will turn off until next protection clock. If the output voltage exceeds the OVP trip threshold (1.2 times regulation level) for longer than 10 μs (typical), then IC's output Over-Voltage Protection (OVP) is triggered. RT6238BL chip enters latch mode. For RT6238AL, if the output voltage VOUT rises above the regulation level and lower 1.2 times regulation level, the high-side switch naturally remains off and the synchronous rectifier turns on until the inductor current reaches zero current. If the output voltage remains high, then IC's switches remain off. If the output voltage exceeds the OVP trip threshold (1.2 times regulation level) for longer than 10 μs (typical), the IC's OVP is triggered. RT6238AL chip enters latch mode. For RT6238BH, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches the low side current limit. If the output voltage still remains high, the synchronous rectifier turns on and high-side MOSFET keeps off to operate at typical 500kHz switching protection, again if inductor current reaches low side current limit, the synchronous rectifier will turn off until next protection clock. RT6238BH is without OVP latch function and recover when OV condition release. For RT6238AH, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches zero current. If the output voltage still remains high, then IC's switches remain off. RT6238AH is without OVP latch function and recover when OV condition release. Latch-Off Mode The RT6238AL/BL uses latch-off mode OVP and UVP. When the protection function is triggered, the IC will shut down in Latch-Off Mode. The IC stops switching, leaving both switches open, and is latched off. To restart operation, toggle EN or power the IC off and then on again. Shut-Down, Start-Up and Enable (EN) The enable input (EN) has a shutdown level of 0.4V. When VEN is below this level the IC enters shutdown mode and supply current drops to less than 10 μA. When VEN exceeds its logic-high level of 1.2V the IC is fully operational. Between these 2 levels there are 2 thresholds (1V typical and 1.2V typical). Switching operation begins when VEN exceeds the upper threshold, and then switching operation stops when VEN decreases to the lower threshold. Since EN is a low voltage input, it must be connected to VIN (up to 18V) with a 100k Ω pull-up resistor for automatic start-up. |
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