Zxsc310 – Diodes ZXSC310 User Manual
Page 10
Peak current definition
The peak current rating is a design parameter whose
value is dependent upon the overall application. For
the high brightness reference designs, a peak current
of 190mA was chosen to ensure that the converter
could provide the required output power to the LED.
In general, the I
PK
value must be chosen to ensure that
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
PK
is decided the value of R
SENSE
can be
determined by:
A selection guide of sense resistor and inductor values
for given input voltages, output currents and number
of LED connected in series is provided in the table
below.
S E M I C O N D U C T O R S
ZXSC310
ISSUE 3 - SEPTEMBER 2007
10
R
V
I
SENSE
ISENSE
PK
=
Input Voltage
(V)
LED current
(mA)
No. of LED’s
R
SENSE
(m )
Inductor
( H)
Efficiency
(%)
3.3V
10
3
510
68
80
3.3V
10
4
330
68
81
3.3V
10
6
150
68
79
3.3V
20
3
220
68
84
3.3V
20
4
150
68
93
3.3V
20
6
77
68
79
3.3V
30
3
170
68
84
3.3V
30
4
100
68
84
3.3V
30
6
47
68
77
5V
10
3
750
68
83
5V
10
4
510
68
84
5V
10
6
330
68
79
5V
20
3
440
68
85
5V
20
4
250
68
85
5V
20
6
150
68
82
5V
30
3
330
68
86
5V
30
4
170
68
85
5V
30
6
100
68
83