Datasheet
( )
= W
æ ö
æ ö
-
ç ÷
ç ÷
è ø
è ø
SET
OUT
1.43
R k
V
1
0.8
LMZ31503
www.ti.com
SNVS992 –JULY 2013
APPLICATION INFORMATION
ADJUSTING THE OUTPUT VOLTAGE
The VADJ control sets the output voltage of the LMZ31503. The output voltage adjustment range is from 0.8V 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 43) and AGND (pin 45). The SENSE+ pin (pin 44) must be connected
to VOUT either at the load for improved regulation or at VOUT of the module. The R
RT
resistor must be
connected directly between the RT/CLK (pin 35) and AGND (pin 34).
Table 1 gives the standard external R
SET
resistor for a number of common bus voltages, along with the required
R
RT
resistor for that output voltage. For other output voltages, the value of the required resistor can either be
calculated using Equation 1, or selected from the values given in Table 2.
Table 1. Standard R
SET
Resistor Values for Common Output Voltages
RESISTORS OUTPUT VOLTAGE V
OUT
(V)
0.8 1.0 1.2 1.5 1.8 2.5 3.3 5.0
R
SET
(kΩ) open 5.76 2.87 1.62 1.13 0.665 0.453 0.267
R
RT
(kΩ) open open 324 324 324 324 158 105
(1)
Table 2. 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)
0.8 open open 330 3.2 0.475 191 580
0.9 11.3 open 330 3.3 0.453 158 630
1.0 5.76 open 330 3.4 0.442 158 630
1.1 3.83 open 330 3.5 0.422 158 630
1.2 2.87 324 480 3.6 0.402 158 630
1.3 2.26 324 480 3.7 0.392 158 630
1.4 1.91 324 480 3.8 0.374 137 680
1.5 1.62 324 480 3.9 0.365 137 680
1.6 1.43 324 480 4.0 0.357 137 680
1.7 1.27 324 480 4.1 0.348 137 680
1.8 1.13 324 480 4.2 0.332 118 730
1.9 1.02 324 480 4.3 0.324 118 730
2.0 0.953 324 480 4.4 0.316 118 730
2.1 0.866 324 480 4.5 0.309 118 730
2.2 0.806 324 480 4.6 0.301 118 730
2.3 0.750 324 480 4.7 0.294 118 730
2.4 0.715 324 480 4.8 0.287 105 780
2.5 0.665 324 480 4.9 0.280 105 780
2.6 0.634 237 530 5.0 0.267 105 780
2.7 0.604 237 530 5.1 0.267 105 780
2.8 0.562 237 530 5.2 0.261 105 780
2.9 0.536 237 530 5.3 0.255 105 780
3.0 0.511 191 580 5.4 0.249 105 780
3.1 0.499 191 580 5.5 0.243 105 780
Copyright © 2013, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: LMZ31503