Datasheet

Time(20ms/div)
V
IN
V
EN
V
OUT
TPS7A3001
OUT
FB
GND
C
10 F
IN
m
C
10nF
NR/SS
R
1
R
2
C
10nF
BYP
C
10 F
OUT
m
IN
EN
NR/SS
V
IN
V
OUT
V
OUT
V
REF
- 1 R =R
1 2
V
OUT
R +R
1 2
³ 5 Am,where
TPS7A30xx
SBVS125A –AUGUST 2010– REVISED MARCH 2011 www.ti.com
THEORY OF OPERATION
GENERAL DESCRIPTION
The TPS7A30xx belongs to a family of new
generation linear regulators that use an innovative
bipolar process to achieve ultralow-noise and very
high PSRR levels at a wide input voltage range.
These features, combined with a high thermal
performance MSOP-8 with PowerPAD package make
this device ideal for high-performance analog
applications.
ADJUSTABLE OPERATION
The TPS7A3001 has an output voltage range
of –1.174 to –33V. The nominal output voltage of the
device is set by two external resistors, as shown in
Figure 29.
Figure 30. Enable Pin Positive/Negative
Threshold
CAPACITOR RECOMMENDATIONS
Low 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
Figure 29. Adjustable Operation for Maximum AC
improved over-temperature performance, while
Performance
ceramic X5R capacitors are the most cost-effective
and are available in higher values.
R
1
and R
2
can be calculated for any output voltage
Note that high ESR capacitors may degrade PSRR.
range using the formula shown in Equation 1. To
ensure stability under no load conditions, this
INPUT AND OUTPUT CAPACITOR
resistive network must provide a current equal to or
REQUIREMENTS
greater than 5μA.
The TPS7A30xx family of negative, high-voltage
linear regulators achieve stability with a minimum
(1)
input and output capacitance of 2.2μF; however, it is
highly recommended to use a 10μF capacitor to
If greater voltage accuracy is required, take into
maximize ac performance.
account the output voltage offset contributions
because of the feedback pin current and use 0.1%
NOISE REDUCTION AND BYPASS
tolerance resistors.
CAPACITOR REQUIREMENTS
ENABLE PIN OPERATION
Although noise reduction and bypass capacitors
(C
NR/SS
and C
BYP
, respectively) are not needed to
The TPS7A30xx provides a dual polarity enable pin
achieve stability, it is highly recommended to use
(EN) that turns on the regulator when |V
EN
| > 2.0V,
0.01μF capacitors to minimize noise and maximize ac
whether the voltage is positive or negative, as shown
performance.
in Figure 30.
This functionality allows for different system power
MAXIMUM AC PERFORMANCE
management topologies:
In order to maximize noise and PSRR performance, it
• Connecting the EN pin directly to a negative
is recommended to include 10μF or higher input and
voltage, such as V
IN
, or
output capacitors, and 0.01μF noise reduction and
• Connecting the EN pin directly to a positive
bypass capacitors, as shown in Figure 29. The
voltage, such as the output of digital logic circuitry.
solution shown delivers minimum noise levels of
15.1μV
RMS
and power-supply rejection levels above
55dB from 10Hz to 700kHz; see Figure 18 and
Figure 19.
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