Texas Instruments TPS54521EVM-607, Руководство пользователя

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1.3 Modifications
These evaluation modules are designed to provide access to the features of the TPS54521. Some modifications
can be made to this module.
1.3.1 Output Voltage Set Point
The output voltage is set by the resistor divider network of R8 and R9. R9 is fixed at 10 kΩ. To change the output
voltage of the EVM, it is necessary to change the value of resistor R8. Changing the value of R8 can change the
output voltage above 0.8 V. The value of R8 for a specific output voltage can be calculated using
Equation 1 .
( )
OUT
10 kΩ V - 0.8 V
R8 =
0.8 V (1)
Table 1-3 lists the R8 values for some common output voltages. Note that V
IN
must be in a range so that the
minimum on-time is greater than 135 ns, and the maximum duty cycle is less than 95%. In addition, different
output voltages may require different frequency compensation, which will require changes to the values of R4,
C4, C6, and C11. The values given in
Table 1-3 are standard values, not the exact value calculated using
Equation 1 .
Table 1-3. Output Voltages Available
OUTPUT
VOLTAGE (V)
R
8
VALUE (kΩ)
1.8 12.4
2.5 21.5
3.3 31.6
5 52.3
1.3.2 Slow-Start Time
The slow-start time can be adjusted by changing the value of C7. Use Equation 2 to calculate the required value
of C7 for a desired slow-start time.
Tss(ms) Iss( A)
C7(nF) =
Vref(V)
´ m
(2)
The EVM is set for a slow start time of 3.5 msec using C7 = 0.01 μF.
1.3.3 Track In
The TPS54521 can track an external voltage during start up. The J5 connector is provided to allow connection
to that external voltage. Ratio-metric or simultaneous tracking can be implemented using resistor divider R5 and
R6. See the
TPS54521 4.5-V to 17-V Input, 5-A Synchronous Step-Down Converter Data Sheet for details.
1.3.4 Adjustable UVLO
The under voltage lock out (UVLO) can be adjusted externally using R1 and R2. The EVM is set for a start
voltage of 6.806 V and a stop voltage of 4.824 V using R1 = 511 kΩ and R2 = 100 kΩ. Use
Equation 3 and
Equation 4 to calculate required resistor values for different start and stop voltages.
1
æ ö
-
ç ÷
è ø
æ ö
- +
ç ÷
è ø
ENFALLING
START STOP
ENRISING
ENFALLING
p h
ENRISING
V
V V
V
R1 =
V
I I
V
(3)
( )
´
- + +
ENFALLING
STOP ENFALLING p h
R1 V
R2 =
V V R1 I I
(4)
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4 TPS54521 Step-Down Converter Evaluation Module User's Guide SLVU379A – AUGUST 2010 – REVISED AUGUST 2021
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