Texas Instruments TPS76933, User Manual

Page: 25 / 37

Adjusting the TPS76x01/TPS77001 Output Voltage
3-5 Circuit Design
For 3 V, one gets:
I) R1
R2
+
1.546689 II) R1
)
R2
+
428.571 k
W
å
I
Ȁ
) R1
+
1.546689 R2
I
Ȁ
) in II) :
å
1.546689 R2
)
R2
+
428.571 k
W
å
R2
+
428.571 k
W
2.546689
+
168.286 k
W
Make R2 = 169 k
Ω
and calculate R1:
Derived from equation I), one gets for R1:
R1
+
1.546689 169 k
W +
261.39 k
W
The next value in the E96 series shown in Table 3–2 is 261 k
Ω
.
The error for using these resistors is:
261 k
W
169 k
W +
1.544379
å
Error
+
ǒ
1 – 1.544379
1.546689
Ǔ
100%
+
0.149371%
A free-ware program called WinResis available on the Internet can help you
find the correct resistor values.
Table 3–2. E96 Resistor Series
E96 series
100 147 215 316 464 681
102 150 221 324 475 698
105 154 226 332 487 715
107 158 232 340 499 732
110 162 237 348 511 750
113 165 243 357 523 768
115 169 249 365 536 787
118 174 255 374 549 806
121 178 261 383 562 825
124 182 267 392 576 845
127 187 274 402 590 866
130 191 280 412 604 887
133 196 287 422 619 909
137 200 294 432 634 931
140 205 301 442 649 953
143 210 309 453 665 976