Texas Instruments TPS769 Series, Руководство пользователя, Страница: 9 / 25

Output Voltages Greater Than V
REF
1-3 Introduction
1.2 Output Voltages Greater Than V
REF
For applications requiring an output voltage greater than the internal reference
voltage (V
FB
) of 1.224 V, a standard linear regulator circuit with an external
voltage divider is all that is necessary. The lower section of Figure 1 shows a
generic linear regulator circuit with an input capacitor (C1), output capacitor
(C3), external voltage divider (R3/R4), and the enable circuit with either a
pullup resistor (R1) or pulldown resistor (R2) as required. None of the backside
components are required for this application. If a delayed enabled is desired,
the R1 and R2/C2 component pads can be used for an RC circuit. When using
the TPS76918EVM–127 or the TPS76933EVM–127, the external divider is
not required and R3 is a 0-
Ω
resistor used to connect the sense terminal to V
O
.
When using the TPS76901EVM–127 (adjustable output voltage), it is recom-
mended that the divider current (I
REF
) be set to 7
µ
A. Choosing R4 to be
169 k
Ω
and calculating R3 for V
O
accomplishes this.
R3
+
ǒ
V
O
V
FB
*
1
Ǔ
R4
(1)
Where:
V
FB
= 1.224 V
R4 = 169 k
Ω
Then
R3
+
ǒ
138.07 V
O
Ǔ
*
169 k
Ω
Lower value resistors can be used but are not as power efficient. Higher value
resistors should be avoided due to leakage currents at FB increasing the out-
put voltage error. Table 1–1 shows various voltage options and the suggested
resistor values.
Table 1–1. Resistor Values
OUTPUT VOLTAGE
(V)
DIVIDER RESISTANCE
(k
Ω
)
(V)
R3 R4
2.5 174 169
3.3 287 169
3.6 324 169
4.0 383 169
5.0 523 169