Tool/software:
I want to replace the LT3045 with the TPS7A94. The LT3045 also uses a resistor between the SET pin and GND to set the VOUT. A DAC output can also be connected to the LT3045 SET pin, so that DAC VOUT = LDO VOUT. I need 0 - 3 V output and about 840 mA current.
Please tell me if I can connect a DAC output to the TPS7A94 NRSS input so that DAC VOUT = TPS7A94 VOUT. Do you have an example circuit? What should I be careful about?
Hi Mango,
I don't believe we have a proven design of this technique. I'm not too concerned with how it works when the DAC is constant or device is already on, but I'm concerned how it will interfere with startup (soft start/fast charge, etc) or how driving a modulated voltage on that pin will affect the rest of the device.
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We actually have Tracking LDOs with a specific pin designed to accomplish this. Vout = VADJ. This link should be pre filtered to show only our tracking LDO selection:
Linear & low-dropout (LDO) regulators product selection | TI.com
While none of our tracking LDOs reach 840mA, we have a proven reference design and collateral about putting them in parallel (n LDOs can collectively drive any arbitrary output voltage):
Scalable, High-Current, Low-Noise Parallel LDO Reference Design
Various Applications for Voltage-Tracking LDO
Parallel LDO Architecture Design Using Ballast Resistors
PARALLEL-LDO-CALC Calculation tool | TI.com
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We also have a proven design for margining output voltage with a DAC, but your DAC output may have to be shifted:
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Best,
Gregory Thompson
Hi Mango,
Thanks for reaching out and sharing this information with us.
Same as the LT3045, you can use a DAC to control VOUT.
Voltage margining is something very common to do for LDOs using a DAC, and we show this in TPS7A57 datasheet (Sections 8.1.16 and 8.1.17):
In addition to the collateral that Greg has already shared, here is some more related to margining using a DAC:
Voltage Regulator Margining with Precision DACs | TI.com Video
Voltage Margining and Scaling Circuit with Voltage Output Smart DAC
Although this is shown using a more traditional architecture of a Feedback Network, the concept is the same and the same principles can be implemented as well.
Best,
E.A.
