LP2981-N_16 Datasheet, PDF (16/30 Pages) Texas Instruments – Micropower 100-mA Ultralow Dropout Regulator

LP2981-N
SNOS773N – MARCH 2000 – REVISED APRIL 2016
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LP2981-N is a linear voltage regulator operating from 2.1 V to 16 V on the input and regulates voltages
between 2.5 V to 5 V with 0.75% accuracy and 100-mA maximum output current. Efficiency is defined by the
ratio of output voltage to input voltage because the LP2981-N is a linear voltage regulator. To achieve high
efficiency, the dropout voltage (V_IN – V_OUT) must be as small as possible, thus requiring a very-low-dropout LDO.
Successfully implementing an LDO in an application depends on the application requirements. If the
requirements are simply input voltage and output voltage, compliance specifications (such as internal power
dissipation or stability) must be verified to ensure a solid design. If timing, start-up, noise, power supply rejection
ratio (PSRR), or any other transient specification is required, then the design becomes more challenging.
8.2 Typical Application
VIN
CIN
IN
GND
OUT
COUT
VOUT
ON/OFF
ON/OFF
NC
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*ON/OFF input must be actively terminated. Tie to V_IN if this function is not to be used.
**Minimum output capacitance is shown to insure stability over full load current range. More capacitance provides
superior dynamic performance and additional stability margin (see Capacitor Characteristics).
***Do not make connections to this pin.
Figure 33. LP2981-N Typical Application
8.2.1 Design Requirements
PARAMETER
Input voltage
Output voltage
Output current
RMS noise, 300 Hz to 50 kHz
PSRR at 1 kHz
DESIGN REQUIREMENT
5 V ±10%, provided by the DC-DC converter switching at 1 MHz
3.3 V ±5%
100 mA (maximum), 1 mA (minimum)
< 1 mV_RMS
> 40 dB
8.2.2 Detailed Design Procedure
8.2.2.1 External Capacitors
Like any low-dropout regulator, the external capacitors used with the LP2981-N must be carefully selected to
assure regulator loop stability.
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