Preliminary
Checking Transient Response
Datasheet
LP3205
The regulator loop response can be checked by looking at the load transient response. Switching
regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT
immediately shifts by an amount equal to
∆ILOAD
(ESR), where ESR is the effective series
resistance of COUT.
∆ILOAD
also begins to charge or discharge COUT generating a feedback error
signal used by the regulator to return VOUT to its steady-state value. During this recovery time,
VOUT can be monitored for overshoot or ringing that would indicate a stability problem.
Layout Considerations
Follow the PCB layout guidelines for optimal performance of LP3205.
For the main current paths as indicated in bold lines, keep their traces short and wide.
Put the input capacitor as close as possible to the device pins (VIN and GND).
LX node is with high frequency voltage swing and should be kept small area. Keep analog
components away from LX node to prevent stray capacitive noise pick-up.
Connect feedback network behind the output capacitors. Keep the loop area small. Place the
feedback components near the LP3205.
Connect all analog grounds to a command node and then connect the command node to the
power ground behind the output capacitors.
LP3205 – Ver. 1.0 Datasheet
Feb.-2007
Page 9 of 10
POWER [ LOWPOWER SEMICONDUCTOR INC ]
