Datasheet

Modifications
1-7
Introduction
1.4 Modifications
The TPS54x80EVM-228 evaluation module is designed to demonstrate the
small size using ceramic capacitors that can be attained when designing with
the TPS54x80. Meanwhile, the solution is not limited only to these particular
output voltages and switching frequency. The following paragraphs describe
what kind of modifications can be done to meet different application
requirements.
1.4.1 Output Voltage
The 1.8-V core and 3.3-V I/O output voltage is selected for this EVM. The
output voltage of the TPS54x80 and TPS54X10 regulators can be adjusted to
any value down to 0.9 V by changing resistor R20 (for the TPS54x80) or R19
(for the TPS54x10). The location of these resistors in the schematic is shown
in Figure 4-1. The value of these resistors for a specific output voltage can be
calculated by using equation 4. Table 1-4 lists the value of resistor R19 (or
R20) for some common bus voltages.
R
19, 20
+ 10 kW
0.891 V
V
O
* 0.891 V
Table 1-4.Output Voltage Programming
Output Voltage, (V) R19 or R20, (kΩ)
0.9 1000
1.2 28.7
1.5 14.7
1.8 9.76
2.5 5.49
3.3 3.74
1.4.2 Switching Frequency
The switching frequency of TPS54x80 and TPS54x10 regulators may be
trimmed to any value between 280 kHz and 700 kHz by changing the value of
resistors R9 (for TPS54x80) or R8 (for TPS54x10). The location of these
resistors in the schematic is shown in Figure 4-1. Increasing the switching
frequency reduces the output ripple. It is not recommended to decrease the
switching frequency for the selected output filter in this EVM below 600 kHz.
The nominal switching frequencies in SLVP228 EVM are set about 20% apart
for each channel to synchronize the I/O regulator to the higher switching
frequency of the core regulator. If there is no need to synchronize channels,
and synchronization circuit parts are left open, then it is recommended to use
71.5 kΩ value resistor for R8, the same value as R9. A plot of the value of
resistors R8 (or R9) versus the switching frequency is given in Figure 1-2.
(4)