zxld1362 Zetex Semiconductors plc., zxld1362 Datasheet - Page 20

• Manufacturer Part Number: zxld1362
• Description: 1a Led Driver With Internal Switch
• Manufacturer: Zetex Semiconductors plc.

Application notes
Setting nominal average output current with external resistor RS
The nominal average output current in the LED(s) is determined by the value of the external
current sense resistor (R
I
The table below gives values of nominal average output current for several preferred values of
current setting resistor (R
The above values assume that the ADJ pin is floating and at a nominal voltage of V
Note that R
maintain switch current below the specified maximum value.
It is possible to use different values of R
next section).
Output current adjustment by external DC control voltage
The ADJ pin can be driven by an external dc voltage (V
to a value above or below the nominal average value defined by R
The nominal average output current in this case is given by:
I
Note that 100% brightness setting corresponds to V
1.25V, R
The input impedance of the ADJ pin is 50k
voltages above V
Issue 1 - December 2007
© Zetex Semiconductors plc 2007
OUTnom
DC
OUTdc
R
GND
0.13
0.15
+
S
0.1
= (V
( )
S
= 0.1/R
must be increased in proportion to prevent I
ADJ
S
= 0.1
/1.25) x (100mV/R
Nominal average
output current (mA)
1000
760
667
S
REF
ADJ
[for R
is the minimum allowed value of sense resistor under these conditions to
+100mV.
S
S
S
) connected between V
) in the typical application circuit shown on page 1:
0.1 ]
ZXLD1362
GND
S
) [for 0.3< V
S
if the ADJ pin is driven from an external voltage. (See
±25% for voltages below V
ADJ
20
IN
<2.5V]
and I
ADJ
ADJ
OUTdc
SENSE
= V
), as shown, to adjust the output current
exceeding 1A maximum.
REF
and is given by:
. When driving the ADJ pin above
S
.
REF
and 14.2k
ZXLD1362
www.zetex.com
REF
±25% for
(=1.25V).