SP7600EB Exar Corporation, SP7600EB Datasheet - Page 11

• Manufacturer Part Number: SP7600EB
• Description: EVAL BOARD FOR SP7600
• Manufacturer: Exar Corporation

Specifications of SP7600EB

• Current - Output / Channel: 2A
• Outputs And Type: 1, Non-Isolated
• Features: PWM Brightness control
• Voltage - Input: 4.5 ~ 29 V
• Utilized Ic / Part: SP7600
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Product: Display Modules
• Core Chip: SP7600
• No. Of Outputs: 1
• Output Current: 2A
• Output Voltage: 200mV
• Dimming Control Type: PWM
• Development Tool Type: Hardware - Eval/Demo Board
• Mcu Supported Families: SP7600
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 1016-1233

DESIGN EXAMPLE
Design a drive circuit for a 1.5A LED with a
12V input voltage. Nominal LED voltage is
3.6V.
A standard value of 0.12ohm 0805 is selected.
An inductor of 4.7uH, rated at 3A
I
A 10µF C
From Equ.4, the ripple current rating of C
a fraction of 1.5A. A 10uF/16V ceramic
capacitor easily meets this requirement and
offers low ESR and ESL.
LAYOUT CONSIDERATION
i) Place the bypass capacitors C4 and C5 as
close as possible to the 7600 IC. See figure 5
for details.
ii) Create a pad under the IC that connects the
power pad (pin 9) to the inductor. Duplicate
this pad through the pcb layers if present, and
on the bottom side of the PCB. Use multiple
vias to connect these layers to aid in heat
dissipation. Do not oversize this pad - since
the LX node is subjected to very high dv/dt
voltages,
between these islands and the surrounding
circuitry will tend to couple switching noise
iii) Connect the Schottky diode cathode as
close as possible to the LX node and inductor
input side. Connect the anode to a large
diameter trace or a copper area that connects
the input ground to the output ground.
iv) The output capacitor, if used, should be
placed close to the load. Use short wide
© 2009 Exar Corporation
SAT
Resistor RFB calculation
Inductor L1 calculation
Input capacitor
is selected.
L
1
=
IN
12
the
3
(C1) is needed (refer to table 1).
V
RFB
6 .
V
×
1
×
3 .
stray
=
(
12
MHz
1
0
V
5 .
2 .
V
A
−
×
3
capacitance
=
. 0
6 .
. 0
45
V
13
)
A
Ω
=
4
3 .
RMS
2
2
μ
A
H
A
and 3A
formed
2
2
IN
9
9
V
V
is
11/13
N
N
o
o
n
n
Voltage rating should be 30V. B340A rated at
30V/3A or equivalent can be used for its
ample current rating and low forward voltage.
Use standard resistor value for Rs of 470Ω.
copper regions to connect output capacitors to
load to minimize inductance and resistances.
v) Keep other sensitive circuits and traces
away from the LX node in particular and away
from the power supply completely if possible.
For more detail on the SP7600 layout see the
SP7600EB Evaluation Board Manual available
on our web site. Each layer is shown in detail
as well as a complete bill of materials.
-
-
Rs
S
S
Schottky current rating I
Rs calculation
y
y
=
n
n
. 0
c
c
35
.
.
B
V
B
Fig. 18: Circuit for design example
I
u
F
u
−
Fig. 19: SP7600 Eval Board
c
c
≥
1 (
k
k
5 .
Component Side Lay
1
H
H
×
−
. 1
i
i
3
g
12
g
05
33
3 .
h
h
V
V
μ
×
P
P
A
×
. 2
o
o
1
25
5 .
w
w
A
A
F
e
e
×
r
=
r
. 0
1
L
L
3 .
095
E
E
S
S
A
D
D
P
P
Ω
Rev. 2.0.0
D
D
)
7
7
=
r
r
6
6
i
i
424
v
v
0
0
e
e
0
0
r
r
Ω