To change the output voltage of the EVMs, change the value of resistor R7 (RFB_TOP) and resistor R8 (RFB_BOT). Changing the value of R7 and R8 can change the output voltage above 0.6 V. The value of R7 and R8 for a specific output voltage can be calculated using Equation 1.
Equation 1.
Table 3-2 lists the R7 and R8 values for some common output voltages.
Table 2-2 Recommended Component ValuesSwitching Frequency (Hz) | OUTPUT VOLTAGE(1) (V) | R7(2) (kΩ) | R8 (kΩ) | COUT(3) (µF) | C8 (pF)(4) |
---|
TYP |
---|
800k | 1.05 | 7.5 | 10.0 | 68 | |
1.8 | 20 | 10.0 | 68 | 47 |
3.3 | 45.3 | 10.0 | 62 | 47 |
5 | 73.2 | 10.0 | 35 | 47 |
1.2M | 1.05 | 7.5 | 10.0 | 68 | |
1.8 | 20 | 10.0 | 68 | 47 |
3.3 | 45.3 | 10.0 | 62 | 47 |
5 | 73.2 | 10.0 | 35 | 150 |
(1) Please use the recommended COUT of the higher and closest output rail for unlisted output rails.
(2) R7 = 0 Ω for VOUT = 0.6 V.
(3) COUT is the sum of effective output capacitance. The effective
capacitance is defined as the actual capacitance under DC bias and temperature,
not the rated or nameplate values. All high value ceramic capacitors have a
large voltage coefficient in addition to normal tolerances and temperature
effects. A careful study of bias and temperature variation of any capacitor bank
must be made to verify that the minimum value of effective capacitance is
provided. Refer to the information of DC bias and temperature characteristics
from manufacturers of ceramic capacitors.