Datasheet

 
 
SLVS485 − AUGUST 2003
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13
For a first approximation use:
L = 10 µH
V
(ripple)
= 150 mV (verify in the application)
Selecting the Inductor Value
The main parameters when choosing the inductor are current rating and inductance. The inductance mainly
determines the inductor current ripple. The TPS6420x operates with a wide range of inductor values. Values
between 4.7 µH and 47 µH work in most applications. Select an inductor with a current rating exceeding the
limit set by R
(ISENSE)
or r
DS(on).
The first step in inductor design is to determine the operating mode of the
TPS64200. The device can either work with minimum-on-time or minimum-off-time, depending on input voltage
and output voltage.
The device works with minimum-on-time if:
V
I
* V
O
* I
O
r
DS(on)
* R
RL
xI
O
w
t
off
,min
ǒ
V
O
) V
SCHOTTKY
) R
RL
I
O
Ǔ
t
on
,min
with R
RL
− inductor resistance
(8)
with L +
V Dt
DI
For minimum-on-time:
L +
ǒ
V
I
–V
O
–I
O
r
DS(on)
–R
RL
I
O
Ǔ
t
on
,min
DI
with: ∆I ≤ 0.3 × I
O
(9)
For minimum-off-time:
L +
ǒ
V
O
) V
SCHOTTKY
) R
RL
I
O
Ǔ
t
off
,min
DI
(10)
Table 1. List of Inductors Tested With the TPS6420x
MANUFACTURER TYPE INDUCTANCE DC RESISTANCE SATURATION CURRENT
TDK SLF7032T−100M1R4 10 µH ±20% 53 mΩ ±20% 1.4 A
TDK SLF6025−150MR88 15 µH ±20% 85 mΩ ±20% 0.88 A
Sumida CDRH6D28−5R0 5 µH 23 mΩ 2.4 A
Sumida CDRH103R−100 10 µH 45 mΩ 2.4 A
Sumida CDRH4D28−100 10 µH 95 mΩ 1.0 A
Sumida CDRH5D18−6R2 6.2 µH 71 mΩ 1.4 A
Coilcraft DO3316P−472 4.7 µH 18 mΩ 5.4 A
Coilcraft DT3316P−153 15 µH 60 mΩ 1.8 A
Coilcraft DT3316P−223 22 µH 84 mΩ 1.5 A
Wurth 744 052 006 6.2 µH 80 mΩ 1.45 A
Wurth 74451115 15 µH 90 mΩ 0.8 A