Datasheet

EN falling
Start Stop
EN rising
EN falling
p h
EN rising
V
V V
V
R6 
V
I 1 I
UVLO Top Res
V
istor
æ ö
´ -
ç ÷
ç ÷
è ø
=
æ ö
´ - +
ç ÷
ç ÷
è ø
SS SS
ref
T I
C14 
V
´
=
( )
out ref
ref
V V R10
R7 
V
- ´
=
www.ti.com Introduction
1.3 Modifications
These EVMs are designed to provide access to the features of the TPS54020. 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 R7 and R10. The lower divider resistor R10
should not be modified and should remain at 2.55 kΩ. To change the output voltage of the EVM, it is
necessary to change the value of resistor R7. Changing the value of R7 changes the output voltage
between 0.6 V and 5V. The value of R7 for a specific output voltage is calculated using Equation 1.
(1)
Table 3 lists the R7 values for some common output voltages. Note that V
IN
must then be within a range
so that the minimum on-time is greater than 150 ns. The values given in Table 3 show both the ideal
required values and the closest E96 standard values.
Table 3. Output Voltage Examples with R10 of 2.55 kΩ
Desired V
OUT
Ideal R7 Closest E96 Match Resulting V
OUT
1.8 5.100 kΩ 5.11 kΩ 1.802
2.5 8.075 kΩ 8.06 kΩ 2.496
3.3 11.475 kΩ 11.5 kΩ 3.306
5.0 18.700 kΩ 18.7 kΩ 5.000
1.3.2 Slow-Start Time
The slow-start time is adjusted by changing the value of C14. Use Equation 2 to calculate the required
value of C14 for a desired slow-start time.
(2)
Where:
T
SS
= desired slow start time
I
SS
= slow start charging current = 2.3-µA nominal
V
REF
= 0.6-V reference voltage
The EVM is set for a slow-start time of approximately 26 ms using C14 = 0.1 μF.
1.3.3 Adjustable UVLO
The undervoltage lockout (UVLO) is adjusted externally using R6 and R11. The EVM is set for a start
voltage of 7.5 V and a stop voltage of 7.1 V using R6 = 69.8 kΩ and R11 = 13.3 kΩ. Use Equation 3 and
Equation 4 to calculate required resistor values for different start and stop voltages.
spacer
(3)
spacer
3
SLVU777–September 2012 TPS54020EVM-082 Evaluation Module (PWR082)
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