LP38511_14 Datasheet, PDF (9/19 Pages) Texas Instruments – 800 mA Fast-Transient Response Low-Dropout Linear Voltage Regulator with Error Flag

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LP38511
BLOCK DIAGRAM
SNOSAU6D – NOVEMBER 2007 – REVISED MARCH 2009
IN
Thermal
Limit
EN
Current
Limit
V_REF
OUT
ERROR
LP38511
V_REF
GND
APPLICATION INFORMATION
EXTERNAL CAPACITORS
Like any low-dropout regulator, external capacitors are required to assure stability. These capacitors must be
correctly selected for proper performance.
Input Capacitor
A ceramic input capacitor of at least 10 µF is required. For general usage across all load currents and operating
conditions, a 10 µF ceramic input capacitor will provide satisfactory performance.
Output Capacitor
A ceramic capacitor with a minimum value of 10 µF is required at the output pin for loop stability. It must be
located less than 1 cm from the device and connected directly to the output and ground pin using traces which
have no other currents flowing through them. As long as the minimum of 10 µF ceramic is met, there is no
limitation on any additional capacitance.
X7R and X5R dielectric ceramic capacitors are strongly recommended, as they typically maintain a capacitance
range within ±20% of nominal over full operating ratings of temperature and voltage. Of course, they are typically
larger and more costly than Z5U/Y5U types for a given voltage and capacitance.
Z5U and Y5V dielectric ceramics are not recommended as the capacitance will drops severely with applied
voltage. A typical Z5U or Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage
applied to it. The Z5U and Y5V also exhibit a severe temperature effect, losing more than 50% of nominal
capacitance at high and low limits of the temperature range.
REVERSE VOLTAGE
A reverse voltage condition will exist when the voltage at the output pin is higher than the voltage at the input pin.
Typically this will happen when V_IN is abruptly taken low and C_OUT continues to hold a sufficient charge such that
the input to output voltage becomes reversed. A less common condition is when an alternate voltage source is
connected to the output.
There are two possible paths for current to flow from the output pin back to the input during a reverse voltage
condition.
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