Datasheet

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SET
OUT
1.43
R k
V
1
0.6
LMZ31704
www.ti.com SLVSBV8A –JUNE 2013–REVISED AUGUST 2013
APPLICATION INFORMATION
Adjusting the Output Voltage
The VADJ control sets the output voltage of the LMZ31704. The output voltage adjustment range is from 0.6V to
5.5V. The adjustment method requires the addition of R
SET
, which sets the output voltage, the connection of
SENSE+ to VOUT, and in some cases R
RT
which sets the switching frequency. The R
SET
resistor must be
connected directly between the VADJ (pin 26) and AGND (pin 23). The SENSE+ pin (pin 27) must be connected
to VOUT either at the load for improved regulation or at VOUT of the device. The R
RT
resistor must be connected
directly between the RT/CLK (pin 22) and AGND (pin 23). Table 3 gives the standard external R
SET
resistor for a
number of common bus voltages, along with the recommended R
RT
resistor for that output voltage.
Table 3. Standard R
SET
Resistor Values for Common Output Voltages
RESISTORS OUTPUT VOLTAGE V
OUT
(V)
0.9 1.0 1.2 1.8 2.5 3.3 5.0
R
SET
(kΩ) 2.87 2.15 1.43 0.715 0.453 0.316 0.196
R
RT
(kΩ) 1000 1000 487 169 90.9 90.9 63.4
For other output voltages, the value of the required resistor can either be calculated using the following formula,
or simply selected from the range of values given in Table 4.
(1)
Table 4. Standard R
SET
Resistor Values
V
OUT
(V) R
SET
(kΩ) R
RT
(kΩ) f
SW
(kHz) V
OUT
(V) R
SET
(kΩ) R
RT
(kΩ) f
SW
(kHz)
0.6 open OPEN 200 3.1 0.348 90.9 750
0.7 8.66 OPEN 200 3.2 0.332 90.9 750
0.8 4.32 OPEN 200 3.3 0.316 90.9 750
0.9 2.87 1000 250 3.4 0.309 90.9 750
1.0 2.15 1000 250 3.5 0.294 90.9 750
1.1 1.74 1000 250 3.6 0.287 90.9 750
1.2 1.43 487 300 3.7 0.280 90.9 750
1.3 1.24 487 300 3.8 0.267 90.9 750
1.4 1.07 487 300 3.9 0.261 90.9 750
1.5 0.953 487 300 4.0 0.255 90.9 750
1.6 0.866 487 300 4.1 0.243 63.4 1000
1.7 0.787 487 300 4.2 0.237 63.4 1000
1.8 0.715 169 500 4.3 0.232 63.4 1000
1.9 0.665 169 500 4.4 0.226 63.4 1000
2.0 0.619 169 500 4.5 0.221 63.4 1000
2.1 0.576 169 500 4.6 0.215 63.4 1000
2.2 0.536 169 500 4.7 0.210 63.4 1000
2.3 0.511 169 500 4.8 0.205 63.4 1000
2.4 0.475 169 500 4.9 0.200 63.4 1000
2.5 0.453 90.9 750 5.0 0.196 63.4 1000
2.6 0.432 90.9 750 5.1 0.191 63.4 1000
2.7 0.412 90.9 750 5.2 0.187 63.4 1000
2.8 0.392 90.9 750 5.3 0.182 63.4 1000
2.9 0.374 90.9 750 5.4 0.178 63.4 1000
3.0 0.357 90.9 750 5.5 0.174 63.4 1000
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