Datasheet

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OUT
SET
V
R 10 1 k
0.798
LMZ35003
www.ti.com SNVS988 –JULY 2013
ADJUSTING THE OUTPUT VOLTAGE
The LMZ35003 is designed to provide output voltages from 2.5V to 15V. The output voltage is determined by the
value of R
SET
, which must be connected between the VOUT node and the VADJ pin (Pin 36). For output voltages
greater than 5.0V, improved operating performance can be obtained by increasing the operating frequency. This
adjustment requires the addition of R
RT
between RT/CLK (Pin 31) and AGND (Pin 30). See the Switching
Frequency section for more details. Table 2 gives the standard external R
SET
resistor for a number of common
bus voltages and also includes the recommended R
RT
resistor for output voltages above 5.0V.
Table 2. Standard R
SET
Resistor Values for Common Output Voltages
OUTPUT VOLTAGE V
OUT
(V)
RESISTORS 2.5 3.3 5.0 8.0 12.0 15.0
R
SET
(kΩ) 21.5 31.6 52.3 90.9 140 178
R
RT
(kΩ) open open 1100 549 267 178
For other output voltages the value of R
SET
can be calculated using the following formula, or simply selected from
the range of values given in Table 3.
(1)
Table 3. Standard R
SET
and R
RT
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)
2.5 21.5 open 400 9.0 102 365 700
3.0 27.4 open 400 9.5 110 365 700
3.3 31.6 open 400 10.0 115 365 700
3.5 34.0 open 400 10.5 121 267 800
4.0 40.2 open 400 11.0 127 267 800
4.5 46.4 open 400 11.5 133 267 800
5.0 52.3 1100 500 12.0 140 267 800
5.5 48.7 1100 500 12.5 147 215 900
6.0 64.9 1100 500 13.0 154 215 900
6.5 71.5 1100 500 13.5 158 215 900
7.0 78.7 549 600 14.0 165 178 1000
7.5 84.5 549 600 14.5 174 178 1000
8.0 90.9 549 600 15.0 178 178 1000
8.5 97.6 365 700
Input Voltage
The LMZ35003 operates over the input voltage range of 7 V to 50 V. For reliable start-up and operation at light
loads, the minimum input voltage depends on the output voltage. For output voltages ≤ 12V, the minimum input
voltage is 7V or (VOUT + 3V), whichever is greater. For output voltages > 12V, the minimum input voltage is
(1.33 x VOUT).
The maximum input voltage is (15 x VOUT) or 50 V, whichever is less.
While the device can safely handle input surge voltages up to 65 V, sustained operation at input voltages above
50 V is not recommended.
See the Undervoltage Lockout (UVLO) Threshold section of this datasheet for more information.
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