Datasheet

LT4180
11
4180fb
For more information www.linear.com/4180
applicaTions inForMaTion
20µs/DIV
V
LOAD
11.9V
4180 F07b
I
DITHER
500mA/DIV
Figure 7b. Dither Current and V
OUT
with
10nF, 37k Compensation 1.5A Load
Figure 8a. 500mA to 1A Transient Response
Test with CHOLD4 = 25nF CHOLD4 Too Small
Figure 7c. Dither Current and V
OUT
with
3.3nF, 28k Compensation 1.5A Load
Figure 8b. 500mA to 1A Transient Response Test
with CHOLD4 = 47nF Nicely Damped Behavior
20µs/DIV
V
LOAD
11.9V
4180 F07c
I
DITHER
50mA/DIV
Set Final Value of CHOLD4
Set the minimum value for CHOLD4, by performing a
transient load test of 30% to 60% of the load and set the
value of CHOLD4 to where a nicely damped waveform is
observed. Refer to Figures 8a and 8b for an illustration.
10ms/DIV
V
LOAD
1V/DIV
4180 F08a
I
DITHER
500mA/DIV
V
LOAD
1V/DIV
4180 F08b
I
DITHER
500mA/DIV
After all the CHOLD values have been finalized, check for
proper voltage drop correction and converter behavior
(start-up, regulation, etc.), over the load and input volt-
age ranges.
Setting Output Voltage, Undervoltage and Overvoltage
Thresholds
The RUN pin has accurate rising and falling thresholds
which may be used to determine when Virtual Remote Sense
operation begins. Undervoltage threshold should never
be set lower than the minimum operating voltage of the
LT4180 (3.1V).
The overvoltage threshold should be set slightly greater
than the highest voltage which will be produced by the
power supply or regulator:
V
OUT(MAX)
= V
LOAD(MAX)
+ V
WIRE(MAX)
V
OUT(MAX)
should never exceed 1.5 • V
LOAD
Since the RUN and OV pins connect to MOSFET input
comparators, input bias currents are negligible and a com-
mon voltage divider can be used to set both thresholds
(Figure 9).