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UP3861P Datasheet(PDF) 6 Page - uPI Group Inc. |
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UP3861P Datasheet(HTML) 6 Page - uPI Group Inc. |
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6 / 17 page  uP3861P 6 uP3861P-DS-F0002, Feb. 2018 www.upi-semi.com Functional Description Over Temperature protection (OTP) The OTP is triggered and shuts down the uP3861P if the junction temperature is higher than 150OC. The OTP is a non-latch type protection. The uP3861P automatically initiates another soft start cycle if the junction temperature drops below 110OC. Output Voltage Seting The output voltage can be programmed by resistive divider connected to the FB1/2 pin as shown in the typical application circuit: 1 R 2 R 1 R V 0 . 1 V 2 / 1 OUT + × = Over Current protection (OCP) The uP3861P monitors the voltage drop across the upper MOSFET for over-current protection (OCP). A resistor (R OCSET) connected between OCSET pin and the drain of the upper MOSFET programs the OCP threshold level as show in figure 3. An internal 200uA current source flows through the R OCSET1/2. Creating a voltage VOCSET1/2 at OCSET as: 2 / 1 OCSET IN 2 / 1 OCSET R uA 200 V I × − = The OCP comparator compares the VOCSET1/2 and VPHASE1/2 for over current protection when the upper MOSFET turn on if V PH1/2 is lower than VOCSET1/2, an OCP is traiggered The OCP threshold level is given by: ) ON ( DS 2 / 1 OCSET ) ON ( DS 2 / 1 OCSET 2 / 1 OCSET 2 / 1 OCP R R uA 200 R R I I × = × = An OCP will shut down the device and discharge the Css with a 30uA sinking current source. When the Css is discharged completely, another soft start cycle is initiated. If the over current condition is not removed during the soft start cycle, the uP3861P will shut down immediately when another OCP is triggered. However., the Vss keeps rising 30uA current source discharges the Css. If the over current condition is not removed, the re-soft-start cycle will repeat 3 times and then latch off uP3861P. To avoid false trigger of OCP, variations of all parameters in above equation should be well considered, including: 1.) The R DS(ON) of MOSFET varies with temperature and the gate to source voltage. Consider the highest operation temperature and lowest gate to source voltage. 2.) Consider the minimum I OCSET(~180uA) and minimum ROCSET. 3.) Consider the inductor ripple current. 4.) ROCSET is suggested to set above 1kΩ for the best stability. OCSET # PHASE # VIN OCP # comparator VOUT# 200uA COCSET ROCSET Figure 3. OCP Level Programming Under Voltage Protection (UVP) The FB1/2 voltage is monitored for under voltage protection after soft start end is asserted. If the FB1/2 voltage is lower than 0.5V (50% of 1V = 0.5V reference voltage), the UVP is triggered and shuts sown the uP3861P with about 3us time delay. The uP3861P turns off both upper and lower MOSFETs when UVP is triggered. The UVP is a latch-off type protection and can only be reset by POR of the device. Over Voltage Protection (OVP) The FB1/2 voltage is monitored for over voltage protection. If the FB1/2 voltage higher than 1.2V (120% of 1V =1.2V reference voltage), the OVP is triggered and shuts sown the uP3861P with about 10us time delay . The uP3861P turn off both upper and lower MOSFETs when OVP is triggered. The UVP is a latch-off type protection and can only be reset by POR of the device. Oscillation Frequency programming The uP3861P features adjustable switching frequency by a resistor connected to the RT pin. when the RT pin is floating. The uP3861P operates free-running 50KHz switch frequency. A resistor Rrt connected form RT pin to the ground programs the oscillation frequency as: ) k ( R 7550 50 ) kHz ( f RT OSC Ω + = |
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Similar Description - UP3861P |
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