rt8060a Richtek Technology Corporation, rt8060a Datasheet - Page 7

• Manufacturer Part Number: rt8060a
• Description: 1.5mhz, 1a High Efficiency Step-down Converter
• Manufacturer: Richtek Technology Corporation

Applications Information
The basic RT8060A application circuit is shown in Typical
Application Circuit. External component selection is
determined by the maximum load current and begins with
the selection of the inductor value and operating frequency
followed by C
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current ΔI
with higher inductance.
Having a lower ripple current reduces the ESR losses in
the output capacitors and the output voltage ripple. Highest
efficiency operation is achieved at low frequency with small
ripple current. This, however, requires a large inductor.
A reasonable starting point for selecting the ripple current
is ΔI
highest V
below a specified maximum, the inductor value should be
chosen according to the following equation :
DS8060A-00 March 2011
ΔI
VLF5012ST-1R0N2R5
VLF5014ST-2R2M2R3
VLF3010A-1
VLF3012A
VLS2010E
VLS2012E
NR6045T1R0N
CB2016T2R2M
NR6020T2R2N
NR3015
LPS4018
D53LC
DB318C
WE-TPC Type M1
L
L
=
= 0.4(I
⎡
⎢
⎣
V
f L
OUT
×
IN
. To guarantee that the ripple current stays
P/N
MAX
IN
⎤
⎥
⎦
and C
x 1
). The largest ripple current occurs at the
L
increases with higher V
⎡
⎢
⎣
−
OUT
V
V
OUT
IN
.
⎤
⎥
⎦
Length
(mm)
Max.
2.1
2.1
2.2
3.9
3.8
4.8
5
5
3
3
6
6
3
5
IN
and decreases
Width
(mm)
Max.
4.8
4.8
2.8
2.8
2.1
2.1
1.8
3.9
3.8
4.8
6
6
3
5
Height
(mm)
Max.
Table
1.2
1.4
1.2
1.2
4.5
1.8
1.5
1.7
1.8
1.8
1
1
2
3
L
A smaller inductor changes its current more quickly for a
given voltage drive than a larger inductor, resulting in faster
transient response. A larger inductor will reduce output
ripple and current ripple, but at the expense of reduced
transient performance and a physically larger inductor
package size. For this reason, a larger capacitor, C1, will
be required for larger inductor sizes.
The input regulator has an instantaneous peak current
clamp to prevent the inductor from saturating during
transient load or start-up conditions. The clamp is
designed so that it does not interfere with normal operation
at high loads and reasonable inductor ripple. It is intended
to prevent inductor current runaway in case of a shorted
output.
The DC winding resistance and AC core losses of the
inductor will also affect efficiency, and therefore available
output power. These effects are difficult to characterize
and vary by application. Some inductors and capacitors
that may be suitable for this application are listed in Table
below :
=
⎡
⎢
⎣
Inductance
f
× Δ
V
(μH)
OUT
I
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
3.3
3.3
3.3
3.3
L(MAX)
L
1
1
⎤
⎥
⎦
x 1
⎡
⎢
⎢
⎣
(mΩ)
Max.
−
RDC
120
100
228
153
130
50
73
19
34
60
80
34
70
65
V
IN(MAX)
V
OUT
⎤
⎥
⎥
⎦
1.48
2.26
1.55
1.95
IDC
3.3
4.2
2.7
2.2
(A)
Max.
RT8060A
3
1
1
1
1
1
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