Datasheet

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APPLICATION INFORMATION
DEVICE OPERATION
OUTPUT NOISE
ENABLE
POWER-SUPPLY REJECTION
ADJUSTABLE VOLTAGE APPLICATIONS CURRENT LIMIT
THERMAL PROTECTION
OUT
FB
GND
EN
IN
R1
1
2
3
4
5
R2
V = 1.186–
OUT
1+
R1
R2
R1+R2 ≈ 100kΩ
CAPACITOR SELECTION FOR STABILITY
TPS72301
TPS72325
SLVS346B – SEPTEMBER 2003 – REVISED JULY 2007
used for stable operation. Both the capacitor value
and ESR affect stability, output noise, PSRR, and
transient response. For typical applications, a 2.2 μ F
The TPS723xx is a low-dropout negative linear
ceramic output capacitor located close to the
voltage regulator with a rated current of 200mA. It is
regulator is sufficient.
offered in trimmed output voltages between –1.5V
and –5.2V and as an adjustable regulator from –1.2V
to –10V. It features very low noise and high
power-supply rejection ratio (PSRR), making it ideal Without external bypassing, output noise of the
for high-sensitivity analog and RF applications. A TPS723xx from 10Hz to 100kHz is 200 μ V
RMS
typical.
shutdown mode is available, reducing ground current The dominant contributor to output noise is the
to 2 μ A maximum over temperature and process. The internal bandgap reference. Adding an external
TPS723xx is offered in a small SOT23 package and 0.01 μ F capacitor to ground reduces noise to
is specified over a –40 ° C to +125 ° C junction 60 μ V
RMS
. Best noise performance is achieved using
temperature range. appropriate low ESR capacitors for bypassing noise
at the NR and OUT pins. See Figure 21 in the
Typical Characteristics section.
The enable pin is active above +1.5V and below
–1.5V, allowing it to be controlled by a standard TTL
signal or by connection to V
I
if not used. When The TPS723xx offers a very high PSRR for
driven to GND most internal circuitry is turned off, applications with noisy input sources or highly
putting the TPS723xx into shutdown mode, drawing sensitive output supply lines. For best PSRR, use
2 μ A maximum ground current. high-quality input and output capacitors.
The TPS72301 allows designers to specify any The TPS723xx has internal circuitry that monitors
output voltage from –10V to –1.2V. As shown in the and limits output current to protect the regulator from
application circuit in Figure 27 , an external resistor damage under all load conditions. When output
divider is used to scale the output voltage (V
OUT
) to current reaches the output current limit (550mA
the reference voltage. For best accuracy, use typical), protection circuitry turns on, reducing output
precision resistors for R1 and R2. Use the equations voltage to ensure that current does not increase. See
in Figure 27 to determine the values for the resistor Figure 9 in the Typical Characteristics section.
divider.
Do not drive the output more than 0.3V above the
input. Doing so will bias the body diode in the pass
FET, allowing current to flow from the output to the
input. This current is not limited by the device. If this
condition is expected, care should be taken to
externally limit the reverse current.
As protection from damage due to excessive junction
temperatures, the TPS723xx has internal protection
circuitry. When junction temperature reaches
approximately +165 ° C, the output device is turned
off. After the device has cooled by about 20 ° C, the
output device is enabled, allowing normal operation.
Figure 27. TPS72301 Adjustable LDO Regulator
Programming
For reliable operation, design is for worst-case
junction temperature of ≤ +125 ° C taking into account
worst-case ambient temperature and load conditions.
Appropriate input and output capacitors should be
used for the intended application. The TPS723xx
only requires a 2.2 μ F ceramic output capacitor to be
10
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