Datasheet

LP38501-ADJ, LP38503-ADJ
www.ti.com SNVS522H –AUGUST 2007–REVISED APRIL 2013
Block Diagrams
Figure 13. LP38501-ADJ Block Diagram
Figure 14. LP38503-ADJ Block Diagram
APPLICATION INFORMATION
EXTERNAL CAPACITORS
The LP3850X requires that at least 10 µF (±20%) capacitors be used at the input and output pins located within
one cm of the IC. Larger capacitors may be used without limit on size for both C
IN
and C
OUT
. Capacitor
tolerances such as temperature variation and voltage loading effects must be considered when selecting
capacitors to ensure that they will provide the minimum required amount of capacitance under all operating
conditions for the application.
In general, ceramic capacitors are best for noise bypassing and transient response because of their ultra low
ESR. It must be noted that if ceramics are used, only the types with X5R or X7R dielectric ratings should be used
(never Z5U or Y5F). Capacitors which have the Z5U or Y5F characteristics will see a drop in capacitance of as
much as 50% if their temperature increases from 25°C to 85°C. In addition, the capacitance drops significantly
with applied voltage: a typical Z5U or Y5F capacitor can lose as much as 60% of it’s rated capacitance if only
half of the rated voltage is applied to it. For these reasons, only X5R and X7R ceramics should be used.
INPUT CAPACITOR
All linear regulators can be affected by the source impedance of the voltage which is connected to the input. If
the source impedance is too high, the reactive component of the source may affect the control loop’s phase
margin. To ensure proper loop operation, the ESR of the capacitor used for C
IN
must not exceed 0.5
Ohms. Any good quality ceramic capacitor will meet this requirement, as well as many good quality tantalums.
Aluminum electrolytic capacitors may also work, but can possibly have an ESR which increases significantly at
cold temperatures. If the ESR of the input capacitor may exceed 0.5 Ohms, it is recommended that a 2.2 µF
ceramic capacitor be used in parallel, as this will assure stable loop operation.
OUTPUT CAPACITOR
Any type of capacitor may be used for C
OUT
, with no limitations on minimum or maximum ESR, as long as the
minimum amount of capacitance is present. The amount of capacitance can be increased without limit.
Increasing the size of C
OUT
typically will give improved load transient response.
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