Texas Instruments TPS76933, Руководство пользователя

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Adjusting the TPS76x01/TPS77001 Output Voltage
3-2
3.1 Adjusting the TPS76x01/TPS77001 Output Voltage
All voltage regulators of the TPS76x01/TPS77001 families use the same inter-
nal bandgap voltage, see also Figure 1–1. In the adjustable version, the resis-
tors R1 and R2 are external resistors. Due to the virtual short circuit between
the input pins of an op amp, the voltage V
ref
applies to both the +input pin and
the –input pin.
Note:
All TPS76x01/TPS77001 devices except the TPS764xx use pin 4 as a feed-
back pin for the adjustable version. At the TPS764xx pin 4 acts as a bypass
pin for an external bypass capacitor. This capacitor is used to further reduce
output voltage noise. See the TPS764xx data sheet for details.
Figure 3–1. Programming the TPS76x01/TPS77001
_
+
_
+
R1
R2
V
ref
V
out
The equation for the output voltage is:
V
ref
V
out
+
R2
R1
)
R2
å
V
out
+
V
ref
R1
)
R2
R2
+
V
ref
ǒ
1
)
R1
R2
Ǔ
The resistor ratio is a function of
V
out
V
ref
*
1
+
R1
R2
Using Figure 3–2, it is possible to get a quick ratio for R1/R2 and their maxi-
mum value.