Hi Everyone,
I am working on a power supply design using the LTC3896 to create a negative PSU with an output range of -5V to -55V at 3A. My typical input voltage is 10-12V.
Design Approach:
To enable flexible Vout, I plan to implement an MCU-based voltage set point by introducing a variable resistor (Rc) alongside the standard VFB resistors (as shown in the schematic). The modified configuration allows MCU control of Rc to fine-tune Vout dynamically.
Testing Setup:
For testing, I am using the DC2447A Evaluation Board (Analog Devices). I modified it by introducing Rc and an external regulated power supply (0-2.4V), which acts as my VDAC output from my Atmel MCU.
The voltage equation follows:
Issues Faced:
-
Current Limitation & Crash:
-
When driving a load, the circuit crashes beyond 1A, requiring a reset.
-
Despite achieving a wide range of Vout values, I encounter issues when the electronic load starts.
-
-
Electronic Load Behavior (EL 9000T):Series EL 9000 T Conventional electronic loads 400W up to 600W | Programmable DC Electronic Loads (conventional and regenerative) | Products | EA Elektro-Automatik
-
Using the EL 9000T Electronic Load, I notice a switch from CV (Constant Voltage) to CC (Constant Current) mode unexpectedly when applying load.
-
-
Potential Voltage Instability at ExtVcc and Vfb:
-
I suspect that voltage instability at ExtVcc may be affecting the system performance.
-
The modified feedback resistor combinations allow for a broad Vout range, but certain parameters may be affecting IC operation, possibly turning off the chip or impacting FREG stability.
-
Request for Guidance:
I would appreciate any insights on:
-
Potential stability issues with ExtVcc and ways to mitigate them.
-
Any additional parameters that could be influencing the chip's operation or causing it to shut down.
-
Recommendations to prevent current crashes when exceeding 1A load.
-
Any best practices to ensure VFB resistor selection does not inadvertently impact IC performance.
Thanks in advance !
Sal
