Texas Instruments TPS54380EVM-001, Руководство пользователя

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Modifications
1-4
1.3 Modifications
The TPS54380EVM–001 is designed to demonstrate the small size that can
be attained when designing with the TPS54380, so many of the features,
which allow for extensive modifications have been omitted from this EVM.
Changing the value of R2 can change the output voltage in the range of 0.9 V
to 3.3 V. The value of R2 for a specific output voltage can be calculated by
using Equation 1–1. Table 1–3 list the values for R2 for some common output
voltages.
Equation 1–1.
R2
+
10 k
W
0.891 V
V
O
*
0.891 V
Table 1–3. Output Voltage Programming
Output Voltage (V) R2 Value (k
Ω)
0.9 1000
1.2 28.7
1.5 14.7
1.8 9.76
2.5 5.49
3.3 3.74
The minimum output voltage is limited by the minimum controllable on time of
the device, 200 ns, and is dependent upon the duty cycle and operating
frequency. The approximate minimum output voltage can be calculated using
Equation 1–2.
Equation 1–2.
V
OUTMIN
= 200n sec
× ƒ
s
×
V
INMAX
The switching frequency may be trimmed to any value between 280 kHz and
700 kHz by changing the value of R4. Decreasing the switching frequency
results in increased output ripple unless the value of L1 is increased. A plot of
the value of RT versus the switching frequency is given in Figure 1–1.