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NCP3170BDR2G Datasheet(PDF) 10 Page - ON Semiconductor |
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NCP3170BDR2G Datasheet(HTML) 10 Page - ON Semiconductor |
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10 / 26 page  NCP3170 http://onsemi.com 10 DETAILED DESCRIPTION The NCP3170 is a current-mode, step down regulator with an integrated high-side PMOS switch and a low-side NMOS switch. It operates from a 4.5 V to 18 V input voltage range and supplies up to 3 A of load current. The duty ratio can be adjusted from 8% to 92% allowing a wide output voltage range. Features include enable control, Power-On Reset (POR), input under voltage lockout, fixed internal soft start, power good indication, over voltage protection, and thermal shutdown. Enable and Soft-Start An internal input voltage comparator not shown in Figure 28 will force the part to disable below the minimum input voltage of 4.13 V. The input under voltage disable feature is used to prevent improper operation of the converter due to insufficient voltages. The converter can be turned on by tying the enable pin high and the part will default to be input voltage enabled. The enable pin should never be left floating. Figure 28. Input Voltage Enable NCP3170 EN VIN AGND 4.5 V−18 V C1IN If an adjustable Under Voltage Lockout (UVLO) threshold is required, the EN pin can be used. The trip voltage of the EN pin comparator is 1.38 V typical. Upon application of an input voltage greater than 4.41 V, the VIN UVLO will release and the enable will be checked to determine if switching can commence. Once the 1.38 V trip voltage is crossed, the part will enable and the soft start sequence will initiate. If large resistor values are used, the EN pin should be bypassed with a 1 nF capacitor to prevent coupling problems from the switch node. Figure 29. Input Under Voltage Lockout Enable NCP3170 EN VIN AGND 4.5 V−18 V C1IN R1UV R2UV C1UV The enable pin can be used to delay a turn on by connecting a capacitor as shown in Figure 30. Figure 30. Delay Enable NCP3170 EN VIN AGND 4.5 V−18 V C1IN Rbias C1DLY If the designer would like to add hysteresis to the enable threshold it can be added by use of a bias resistor to the output. The hysteresis is created once soft start has initiated. With the output voltage rising, current flows into the enable node, raising the voltage. The thresholds for enable as well as hysteresis can be calculated using Equation 1. VINHYS + VINStart * ENTH ) R1UV (eq. 1) VOUT * ENTH R3UV * ENTH R2UV VINStart + ENTH 1 ) R1UV R2UV ) R3UV R2UV R3UV (eq. 2) where: ENTH = Enable Threshold VINSTART = Input Voltage Start Threshold R1UV = High Side Resistor R2UV = Low Side Resistor R3UV = Hysteresis Bias Resistor VOUT = Regulated Output Voltage Figure 31. Added Hysteresis to the Enable UVLO NCP3170 EN VIN AGND 4.5 V−18 V C1IN R1UV R2UV R3UV VOUT |
Similar Part No. - NCP3170BDR2G |
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Similar Description - NCP3170BDR2G |
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