Dear team,
My customer is currently using TI part LM1085IS-ADJ/NOPB in one of their designs and are trying to route cause an issue.
They need help about the rise time for this device.
Their setup powers the part from 5V and it is configured for a 1V8 output – if we consider t0 to be application of steady 5V then at what time can the output be considered steady?
Do you have any graphs you can share with me?
Thanks in advance for your help.
Pol
Hello Pol,
"... if we consider t0 to be application of steady 5V then ..."
Vout rise time depends on : Vin rise time, the Cout value, and the Load current. The application of 'steady 5V' is a simplification, as to change the Vin voltage from 0V to 5V takes some finite amount of time (i.e rise time)
With no additional details available, I have created a generic test fixture and capture V(input), V(output), and I(input) for what I am calling 'fast', 'medium', and 'slow' Vin rise times.
Images follow:
Hi Jones,
The circuit associated with the TI part is as follows:
As you can see the LM1085IS-ADJ/NOPB is configured for a 1V8 output by setting R1=232ohms and R2=102ohms (both with tolerance 0.1%). The output capacitor is a 22uF tantalum capacitor, and the same for Cin.
This 1V8 is being monitored by another IC which then holds the CPLD in reset for a period.
For the output load, we can consider 2A.
Thanks for your help.
Pol
Hello Pol,
For the circuit described, it looks like Vout reaches final value in about 100 micro-sec.
