Datasheet

OUT
V
8
V 0.6V
k
R
10 W ´ 0.6
=
-
´Tss(ms) Iss(μA)
C8(nF)=
Vref(V)
ENFALLING
START STOP
ENRISING
ENFALLING
p h
ENRISING
V
V - V
V
R1=
V
I 1- +I
V
æ ö
ç ÷
è ø
æ ö
ç ÷
è ø
ENFALLING
STOP ENFALLING p h
R1×V
R2=
V - V +R1(I +I )
www.ti.com Introduction
1.3 Modifications
These evaluation modules are designed to provide access to the features of the TPS54821. Some
modifications can be made to this module.
1.3.1 Output Voltage Setpoint
The output voltage is set by the resistor divider network of R7 and R8. R7 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 0.6 V. The value of R8 for a specific output voltage can be
calculated using Equation 1.
(1)
Table 3 lists the R8 values for some common output voltages. Note that V
IN
must be in a range so that the
on-time is greater than the minimum controllable on-time (94 ns typical, 145 ns maximum), and the
maximum duty cycle is less than 95%. The values given in Table 3 are standard values, not the exact
value calculated using Equation 1.
Table 3. Output Voltages Available
Output Voltage R8 Value
(V) (kΩ)
1.8 4.99
2.5 3.16
3.3 2.21
5 1.37
1.3.2 Slow-Start Time
The slow-start time can be adjusted by changing the value of C8. Use Equation 2 to calculate the required
value of C8 for a desired slow-start time
(2)
The EVM is set for a slow-start time of 5.7 ms using C8 = 0.022 µF.
1.3.3 Track In
The TPS54821 can track an external voltage during start-up. The J3 connector is provided to allow
connection to that external voltage. Ratiometric or simultaneous tracking can be implemented using
resistor divider R5 and R6. See the TPS54821 data sheet (SLVSA70) for details.
1.3.4 Adjustable UVLO
The undervoltage lockout (UVLO) can be adjusted externally using R1 and R2. The EVM is set for a start
voltage of 6.528 V and a stop voltage of 6.193 V using R1 = 35.7 kΩ and R2 = 8.06 kΩ. Use Equation 3
and Equation 4 to calculate required resistor values for different start and stop voltages.
(3)
(4)
3
SLVU479– October 2011 TPS54821EVM-049, 8-A, SWIFT™ Regulator— Evaluation Module
Submit Documentation Feedback
Copyright © 2011, Texas Instruments Incorporated