Datasheet
Time(20ms/div)
V
IN
V
EN
V
OUT
TPS7A33
SBVS169C –DECEMBER 2011–REVISED FEBRUARY 2013
www.ti.com
ENABLE PIN OPERATION
The TPS7A33 provides a dual-polarity enable pin (EN) that turns on the regulator when |V
EN
| > 2.0 V, whether
the voltage is positive or negative, as shown in Figure 29.
This functionality allows for different system power management topologies; for example:
• Connecting the EN pin directly to a negative voltage, such as V
IN
, or
• Connecting the EN pin directly to a positive voltage, such as the output of digital logic circuitry.
Figure 29. Enable Pin Positive/Negative Threshold
CAPACITOR RECOMMENDATIONS
Low equivalent series resistance (ESR) capacitors should be used for the input, output, noise reduction, and
bypass capacitors. Ceramic capacitors with X7R and X5R dielectrics are preferred. These dielectrics offer more
stable characteristics. Ceramic X7R capacitors offer improved over-temperature performance, while ceramic X5R
capacitors are the most cost-effective and are available in higher values.
Note that high-ESR capacitors may degrade PSRR.
INPUT AND OUTPUT CAPACITOR REQUIREMENTS
The TPS7A33 family of negative, high-voltage linear regulators achieve stability with a minimum input and output
capacitance of 10 μF; however, it is highly recommended to use a 47-μF capacitor to maximize ac performance.
NOISE REDUCTION AND FEED-FORWARD CAPACITOR REQUIREMENTS
Although the noise-reduction (C
NR/SS
) and feed-forward (C
FF
) capacitors are not needed to achieve stability, it is
highly recommended to use a 0.01-μF feed-forward capacitor and a 1-μF noise-reduction capacitor to minimize
noise and maximize ac performance.
MAXIMUM AC PERFORMANCE
In order to maximize noise and PSRR performance, it is recommended to include 47-μF or higher input and
output capacitors, 1-μF noise-reduction capacitors, and 0.01-μF feed-forward capacitors, as shown in Figure 28.
The solution shown delivers minimum noise levels of 16 μV
RMS
and power-supply rejection levels above 55 dB
from 10 Hz to 1 MHz; see Figure 19.
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