Texas Instruments TPS54110EVM-044, Руководство пользователя, Страница: 11 / 28

Modifications
1-4
1.3 Modifications
The TPS54110EVM−044 is designed to demonstrate the small size that can
be attained when designing with the TPS54110; therefore, many of the
features, which allow for extensive modifications, have been omitted from this
EVM. For reference designators, see the schematic in Figure 4−1.
1.3.1 Output Voltage Set Point
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. Note that 3.3-V output is not available with V
I
less than 4 V.
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 ( )
1.2 28.7 k
1.5 14.7 k
1.8 9.76 k
2.5 5.49 k
3.3 3.74 k
The minimum output voltage is limited by the minimum controllable on time of
the device, 200 ns, and depends on the duty cycle and operating frequency.
The approximate minimum output voltage can be calculated using
Equation 1−2:
Equation 1−2.
V
O(min)
= 200 nsec
× ƒ
s
×
V
I(max)
1.3.2 Switching Frequency
The switching frequency is set to 700 kHz with R4. The switching frequency
of this EVM should not be adjusted. Any lowering of the switching frequency
results in increased output ripple current in the inductor L1 unless the value
of L1 is increased.
1.3.3 Input Filter
An onboard electrolytic input capacitor may be added at C1.