R1240K003A-TR Просмотр технического описания (PDF) - RICOH Co.,Ltd.

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производитель

R1240K003A-TR

1.2A 30V Input PWM Step-down DC/DC Converter

RICOH Co.,Ltd. 

R1240x

NO.EA-190-170609

OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS

The following equations explain the relationship between output current and peripheral components.

Ripple Current P-P value is described as IRP, ON resistance of switch is described as RONP, forward drop

voltage is described as VF, and DC resistance of inductor is described as RL.

First, when the switch is turned on, the following equation is satisfied.

VIN = VOUT + (RONH + RL) × IOUT + L × IRP / ton ································································· Equation 1

Second, when the switch is turned off, the diode is turned on, the following equation is satisfied.

L × IRP / toff = VF + VOUT + RL × IOUT ·············································································· Equation 2

Put Equation 2 into Equation 1 to solve the ON duty of the switch (DON = ton / (toff + ton)):

DON = (VOUT + VF + RL × IOUT) / (VIN + VF − RONH × IOUT) ····················································· Equation 3

Ripple Current is described as follows:

IRP = (VIN − VOUT − RONH × IOUT − RL × IOUT) × DON / fosc / L ················································ Equation 4

Peak current that flows through L and the switch is described as follows:

ILmax = IOUT + IRP / 2 ································································································ Equation 5

Notes: Please consider ILmax when setting conditions of input and output, as well as selecting the external

components. The above calculation formulas are based on the ideal operation of the ICs in continuous mode.

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