Datasheet

 
 
SLVS485 − AUGUST 2003
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22
Ceramic Output Capacitor
SW
CDRH6D28-100
Si5475DC
MBRM120LT3
EN
GND
FB
VIN
ISENSE
5 V
C
I
10 µF
TPS64203
R1a
680 kΩ
R2
300 kΩ
Cff
82 pF
Co
22 µF X5R
6.3 V
3.3 V / 2 A
R1b
2.2 MΩ
R
(ISENSE)
= 33 mΩ
R
(GATE)
10 Ω
1
2
3
6
5
4
10 µH
Figure 27. Application Using a Ceramic Output Capacitor
The control scheme of the TPS6420x usually requires an output capacitor with some tens of milliohms of ESR
for stability, which is usually the case for tantalum capacitors. This application circuit above also works with
ceramic capacitors. Resistor R1b is used to add an additional control signal to the feedback loop, which is
coupled into the FB pin. The circuit works best with R1b = 2 …4 x R1a. If the resistance of R1b is too low
compared to R1a, the more load regulation the output voltage shows, but stability is best. The advantage of
this circuit is a very low output voltage ripple and small size. The gate resistor shown can be used in every
application. It minimizes switching noise of the converter and, therefore, increases stability and provides lower
output voltage ripple. However, it decreases efficiency slightly because the rise and fall time, and the associated
losses are larger.
(28)
R1 +
1
1
R1a
)
1
R1b
R1b +
1
1
R1
–
1
R1a
Use the following equation to calculate R1a if R1b = 4R1a
R1a +
5
4
R1
(29)