ZXSC400 Zetex Semiconductors plc., ZXSC400 Datasheet - Page 6

• Manufacturer Part Number: ZXSC400
• Description: Led Driver Boost Converter
• Manufacturer: Zetex Semiconductors plc.

Peak current definition
In general, the I
the switching transistor, Q1, is in full saturation with
maximum output power conditions, assuming
worse-case input voltage and transistor gain under all
operating temperature extremes.
Once I
determined by:
Sense Resistor
A low value sense resistor is required to set the peak
current. Power in this resistor is negligible due to the
low sense voltage threshold, V
the page there is a table of recommended sense
resistors.
Output power calculation
By making the above assumptions for inductance and
peak current the output power can be determined by:
where
and
and
and
and
Operating frequency can be derived by:
ZXSC400
Manufacture
Cyntec
IRC
T
PK
OFF
is decided the value of R
P
1.7 s (internally set by ZXSC400)
I
AV
OUT
PK
= efficiency e.g. 100% = 1
T
R
value must be chosen to ensure that
DIS
F
= I
SENSE
T
I
ON
PK
AV
2
Series
RL1220
LR1206
T
x V
(V
ON
LED
(T
(T
I
IN
I
PK
PK
V
ON
1
ON
V
x
SENSE
I
ISENSE
IN
T
PK
OFF
(Watts)
L
L
V )
IN
T
T
OFF
DIS
. At the bottom of
R
DC
)
0.010 - 1.0
)
0.022 - 10
SENSE
( ) Range
can be
6
Programming LED current
Once the required output power is determined, the LED
current can be programmed by adding a single resistor
in the LED chain. The resistor value is determined by
the following:
Where V
R LED selection table
Shutdown Control
The ZXSC400 offers a shutdown mode that consumes
a standby current of less than 5 A. When the voltage at
the S
the ZXSC400 is enabled and the driver is in normal
operation. When the voltage at the STDN pin is 0.7V or
lower, the ZXSC400 is disabled and the driver is in
shutdown mode. The SHDN input is a high impedance
current source of 1 A typ. The driving device can be an
open collector or an open drain or a logic output with a
“High“ voltage of 5V max. The device shutdown
current depends of the supply voltage, see typical
characteristics graph
0805
1206
Size
TDN
FB
pin between 1V and 8V (and also open circuit),
40mA
30mA
20mA
15mA
10mA
= 300mV
I
LED
Tolerance
I
LED
±5%
±5%
ISSUE 1 - JANUARY 2003
R
V
LED
FB
www.cyntec.com
7.5
R
10
15
20
30
www.irctt.com
LED
URL