Datasheet

C
1
+
(3 x 10
−7
) x (R
1
) R
2
)
(R
1
x R
2
)
V
OUT
+ V
REF
ǒ
1 )
R
1
R
2
Ǔ
R
1
+
ǒ
V
OUT
V
REF
* 1
Ǔ
R
2
V
IN
V
OUT
2.2 Fm
C
1
R
2
2.2 Fm
IN
EN
GND
OUT
FB
TPS78601
R
1
1.8V 14.0kW 30.1kW
57.9kW 30.1kW
33pF
15pF3.6V
OUTPUT
VOLTAGE
R
1
R
2
C
1
OUTPUTVOLTAGE
PROGRAMMINGGUIDE
TPS786xx
www.ti.com SLVS389L –SEPTEMBER 2002–REVISED OCTOBER 2010
PROGRAMMING THE TPS78601 The approximate value of this capacitor can be
ADJUSTABLE LDO REGULATOR calculated using Equation 3:
The output voltage of the TPS78601 adjustable
regulator is programmed using an external resistor
(3)
divider as shown in Figure 25. The output voltage is
The suggested value of this capacitor for several
calculated using Equation 1:
resistor ratios is shown in the table below. If this
capacitor is not used (such as in a unity-gain
configuration), then the minimum recommended
(1)
output capacitor is 2.2 mF instead of 1 mF.
where:
REGULATOR PROTECTION
• V
REF
= 1.2246 V typ (the internal reference
voltage)
The TPS786xx PMOS-pass transistor has a built-in
back diode that conducts reverse current when the
Resistors R
1
and R
2
should be chosen for
input voltage drops below the output voltage (for
approximately 40-mA divider current. Lower value
example, during power down). Current is conducted
resistors can be used for improved noise
from the output to the input and is not internally
performance, but the device wastes more power.
limited. If extended reverse voltage operation is
Higher values should be avoided, as leakage current
anticipated, external limiting might be appropriate.
at FB increases the output voltage error.
The TPS786xx features internal current limiting and
The recommended design procedure is to choose
thermal protection. During normal operation, the
R
2
= 30.1 kΩ to set the divider current at 40 mA,
TPS786xx limits output current to approximately
C
1
= 15 pF for stability, and then calculate R
1
using
2.8 A. When current limiting engages, the output
Equation 2:
voltage scales back linearly until the overcurrent
condition ends. While current limiting is designed to
prevent gross device failure, care should be taken not
(2)
to exceed the power dissipation ratings of the
In order to improve the stability of the adjustable
package. If the temperature of the device exceeds
version, it is suggested that a small compensation
approximately +165°C, thermal-protection circuitry
capacitor be placed between OUT and FB.
shuts it down. Once the device has cooled down to
below approximately +140°C, regulator operation
resumes.
Figure 25. TPS78601 Adjustable LDO Regulator Programming
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