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I am planning to use TPS65070 to power up OMAP L138. as per there recommendation I have configured DCDC1 to 3.3v output. If I go through the datasheet it list two possible current paramtere
1. Minimum Output current which is 600 mA
This is must drain current to have good load regulation.
2. Forward current limit of 2.2A (maximum)
Can anyone explain what this means?
If my understanding is correct then Forward current limit should be the maximum current which I can drain continuously from TPS65070.
Please share your views and if possible some documents on this. I hope TI will provide explanation on this.
The maximum output current you can supply from the DCDC1 converter is 600 mA for the TPS65070. You are guaranteed at least 600mA max under normal operating conditions, which is why it is shown as the “minimum” on p.5 in the datasheet. You can use less than 600 mA if needed.
The forward current limit is not the same as maximum output current. The current out of the L1 pin will ramp up and down at the switching frequency, and the average of this ramp waveform is the DC output current. The peak current (top of the ramp) will be about twice the output current; so the forward current limit is the limit for this peak. If you would like, you can calculate the peak inductor current (ILmax) for your circuit using equations 4 and 5 on pg.63 of the TPS65070 datasheet.
The OMAP-L138 reference schematic on p.72 can serve as a guide for your design. If you would like more information on buck converter operation, the SLVA057 application note is a good resource.
In reply to Bryan McLaughlin:
We need to draw 2A+ current from DCDC1. Well I am trying to figure out ways to deal with this situation and it seems TPS65070 is not well suited for our application.
Thanks for application note, I was searching for something like that.
In reply to Pankaj katiyar:
Could you describe your application? I might be able to help find a solution.
Also, welcome to the E2E Forums!
As per recommendation we are using TPS65070 to power up OMAP-L138. TPS is configured as shown below
DCDC1 (3.3 V) : for 3G card, ADC, FPGA etc
DCDC2 (1.8 V) : mDDR, OMAP, and other digital section
DCDC3 (1.2 V): OMAP
Our application is using 3G card, in which we need to support 1.8A of peak current during transmission. If I am connecting the power of 3G to DCDC1 then this converter needs to support this current surge. This is surge will be there for 600 uSec.
Now, I am trying to figure out whether TPS could be used to power up 3G or not because of power surge.
The TPS65070 should be able to meet your power needs for the OMAP very well. But if your system has several other loads (ADC, FPGA, 3G radio) besides the OMAP processor, then separate DC/DC converters might be a better option. Supplying dynamic loads like the 3G radio from the 3V3 OMAP supply might cause disturbances in the rail that the OMAP cannot tolerate.
There can be advantages to using multiple DC/DC converters. With separate converters, thermal dissipation can be spread across the board instead of being localized in one place. Using separate converters also allows more flexibility in PCB layout, since your inductors and caps won't have to be crowded into one section of the PCB.
The Power Management Quick Search tool can help point you in the right direction for a DC/DC converter or LDO that will work for your application.
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