Datasheet

t
DELAY
=
V
TH(DELAY)
I
DELAY
C
DELAY
X
LP3997
www.ti.com SNVS272B –MAY 2004–REVISED MAY 2013
Applications Information
External Capacitors
In common with most regulators, the LP3997 requires the inclusion of external capacitors.
V
IN
An input capacitor is required for stability. It is recommended that a minimum of 1.0µF capacitor is connected
between the LP3997 input pin and ground (this capacitance value may be increased without limit).
This capacitor must be located a distance of not more than 1cm from the input pin and returned to a clean
analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.
Important: To ensure stable operation it is essential that good PCB design practices are employed to minimize
ground impedance and keep input inductance low. If these conditions cannot be met, or if long wire leads are
used to connect the battery or other power source to the LP3997, then it is recommended to increase the input
capacitor to at least 2.2µF. Also, tantalum capacitors can suffer catastrophic failures due to surge current when
connected to a low-impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is
used at the input, it must be ensured by the manufacturer to have a surge current rating sufficient for the
application.
There are no requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance and
temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will remain ≊
1.0µF over the entire operating temperature range.
V
OUT
V
OUT
is the output voltage of the regulator. Connect capacitance (minimum 1.0µF) to ground from this pin. To
ensure stability the capacitor must meet the minimum value for capacitance and have an ESR in the range 5mΩ
to 500mΩ. Ceramic X7R types are recommended. If an output capacitor larger than 4.7µF is fitted then checks
on in-rush current, transient performance and stability, should be made.
SENSE
SENSE is used to sense the output voltage. Connect sense to V
OUT
SHUTDOWN
SD controls the turning on and off of the LP3997. V
OUT
is ensured to be on when the voltage on the SD pin is
greater than 0.95V. V
OUT
is ensured to be off when the voltage on the SD pin is less than 0.4V.
ERROR
ERROR is an open drain output which is set low when V
OUT
is more than 5% below its nominal value. An
external pull up resistor is required on this pin. When a capacitor is connected from DELAY to GROUND, the
error signal is delayed (see DELAY section). This delayed error signal can be used as the power-on reset signal
for the application system. The ERROR pin is disconnected when not used.
DELAY
A capacitor from DELAY to GROUND sets the time delay for ERROR changing from low to high state. The delay
time is set by the following formula.
V
TH(DELAY)
is nominally 1.2V.
The DELAY pin should be open circuit if not used.
Copyright © 2004–2013, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LP3997