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Author Topic: TPS62220 dc-dc  (Read 1160 times)
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delamoure
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« on: May 24, 2012, 02:20:47 14:20 »

Hello All!
I have a problem with understanding Vi-min calculation for subject device, when operating in the Low Dropout Operation 100% Duty Cycle mode.
Why equation uses inductor ripple current?
I don't understand because P-channel switch is constantly on.
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fpgaguy
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« Reply #1 on: May 24, 2012, 09:56:04 21:56 »

Voltage drop on inductor is from two factors, its' intrinsic DC resistance (your referenced RL), and also from L di/dt

di/dt would come from changes in load, and L x di/dt would be the drop in voltage on the inductor from that change in the load.

I'll assume Vin doesn't change...




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FTL
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« Reply #2 on: June 09, 2012, 12:09:45 00:09 »

I think that the equation in question is referrring to the minimum input voltage where the regulator will maintain the specified output voltage. That has to include the inductor ripple voltage as the regulation will fail once the ripple causes the output voltage to drop below the set point. At any voltage lower than that it will be in 100% conduction mode where it will still provde an output voltage, but it will be unregulated as basically a fixed drop from the input voltage. The fixed drop will be the total drop across the n-channel switch and the inductor.
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