TL1963A-XX Datasheet, PDF (16/26 Pages) Texas Instruments – 1.5-A LOW-NOISE FAST-TRANSIENT-RESPONSE LOW-DROPOUT REGULATOR

TL1963A-xx
SLVS719A – JUNE 2008 – REVISED AUGUST 2008 ........................................................................................................................................................ www.ti.com
IN
OUT
V_OUT
TL1963A
R₂
V_IN
ADJ
GND
R₁
) VOUT = 1.21 V 1 ⁺
R2
R1
+ (I_ADJ)(R2)
V_ADJ = 1.21 V
I_ADJ = 3 µA at 25°C
Output range = 1.21 V to 20 V
Figure 33. Adjustable Operation
The adjustable device is tested and specified with the ADJ pin tied to the OUT pin for an output voltage of
1.21 V. Specifications for output voltages greater than 1.21 V are proportional to the ratio of the desired output
voltage to 1.21 V: V_OUT/1.21 V. For example, load regulation for an output current change of 1 mA to 1.5 A is
–3 mV (typ) at V_OUT = 1.21 V. At V_OUT = 5 V, load regulation is:
(5 V/1.21 V)(–3 mV) = –12.4 mV
Output Capacitance and Transient Response
The TL1963A-xx regulators are designed to be stable with a wide range of output capacitors. The ESR of the
output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 10 µF with
an ESR of 3 Ω or less is recommended to prevent oscillations. Larger values of output capacitance can decrease
the peak deviations and provide improved transient response for larger load current changes. Bypass capacitors,
used to decouple individual components powered by the TL1963A-xx, increase the effective output capacitor
value.
Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior over temperature and applied voltage. The most common
dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high
capacitances in a small package, but exhibit strong voltage and temperature coefficients. When used with a 5-V
regulator, a 10-µF Y5V capacitor can exhibit an effective value as low as 1 µF to 2 µF over the operating
temperature range. The X5R and X7R dielectrics result in more stable characteristics and are more suitable for
use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less
expensive and is available in higher values.
Voltage and temperature coefficients are not the only sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor the stress can be
induced by vibrations in the system or thermal transients.
Overload Recovery
Like many IC power regulators, the TL1963A-xx has safe operating area protection. The safe area protection
decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe
operating region for all values of input-to-output voltage. The protection is designed to provide some output
current at all values of input-to-output voltage up to the device breakdown.
When power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to
start up into very heavy loads. During start up, as the input voltage is rising, the input-to-output voltage
differential is small, allowing the regulator to supply large output currents. With a high input voltage, a problem
can occur wherein removal of an output short does not allow the output voltage to recover. Other regulators also
exhibit this phenomenon, so it is not unique to the TL1963A-xx.
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