SP7600EB Exar Corporation, SP7600EB Datasheet - Page 9

• 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

M
SEQUENCING
The SP7600 has a unique modulator design
which improves the device’s ability to operate
at very high duty cycle. While seamless in
operation as the duty cycle is increasing (input
voltage
decreased (input voltage rising), the user will
observe the switching frequency increasing in
distinct fractions of the switching frequency. If
the device is operating at 100% duty cycle, a
unique advantage of using a p-channel pass
device,
increased, the frequency will start at 300kHz,
then 600kHz, and then finally 1.2MHz. The
frequency will tend to increase to the next
higher fraction once the duty cycle reaches 75
to 65 percent. This is the normal operation of
the device and should be expected. There is
no impact on the LED current accuracy. If
PWM dimming is being used as the input
voltage
frequency increasing when the duty cycle is <
90%. When power is initially applied the
device will begin operating as if the input
voltage is increasing and may start operation
at one of the fractional operating frequencies.
Many users will prefer to have the device start
operating at the nominal operating frequency,
thus it is recommended that Vin be applied
after FB is set at the high state (>1.2V). The
regulator is now in standby and once Vin has
reached steady-state then FB is transitioned
from a high to a low state. The regulator then
starts operating at nominal frequency.
© 2009 Exar Corporation
ODULATOR OPERATION AND POWER
Fig. 17: LED Duty Cycle vs (1-D) DIM pin Duty Cycle
Vin=12V, 2 Luxeon K2 in Parallel with 2A total
falling),
and
is
increased,
then
when
the
one
the
input
duty
will
voltage
2
2
see
cycle
A
A
2
2
9
9
the
V
V
is
is
N
N
9/13
o
o
n
n
Another benefit of using power sequencing for
power up is that it ensures all internal circuitry
is alive and fully operational before the device
is required to regulate the current through the
LEDs. Since the regulator was “Off” before
power was applied, it is unlikely the LED is
under any type of thermal stress. EXAR does
not
applications where dimming of the LED is
achieved by PWM’ing the actual input power as
is
applications.
B
CAPACITOR
In
aforementioned dimming signal to the LED,
the output filter capacitor that is normally
used with a buck converter has to be removed
from the circuit. Thus the LED current ripple
equals the inductor current ripple. As a rule of
thumb current ripple should be limited to 30%
of ILED. Allowing for a higher current ripple,
up
manufacturer ripple guidelines, will reduce
inductance and possibly inductor size.
O
Resistor
Overcurrent
following equation for calculating the Rs value.
Where Iocp is the programmed overcurrent
and is generally set 50% above nominal
output current, and Rds(on) = 95mohms.
Maximum value of Rs that can be used for
programming OCP is 3k.
I
Select the inductor L1 for inductance, Irms
and Isat. Calculate inductance from
Where Vin is converter input voltage and Vo is
converter output voltage. Since voltage across
Rset is small, Vo approximately equals Vf (for
-
Equ.2:
-
NDUCTOR SELECTION
S
S
UCK OPERATION WITHOUT OUTPUT
VERCURRENT PROGRAMMING
y
y
n
n
order
to
common
recommend
c
c
.
.
Rs
B
B
30%,
Rs
Equ.3:
=
u
u
c
c
. 0
to
k
k
Protection
35
can
H
H
V
while
in
be
L
i
i
−
g
g
=
using
1 (
h
h
be
Vo
5 .
Vin
automotive
P
able
P
×
staying
×
o
o
. 1
×
(
used
w
w
33
Vin
(OCP).
05
f
the
e
e
μ
×
×
to
r
r
A
−
Δ
I
Vo
L
L
OCP
I
to
L
E
E
within
SP7600
S
)
S
apply
D
D
×
P
P
Use
Rev. 2.0.0
Rds
dimming
program
D
D
7
7
r
r
6
6
(
i
i
on
v
v
0
0
LED
the
the
e
e
))
0
0
in
r
r