ISL6745ALEVAL3Z Intersil, ISL6745ALEVAL3Z Datasheet - Page 3

• Manufacturer Part Number: ISL6745ALEVAL3Z
• Description: EVAL BOARD 3 FOR ISL6745
• Manufacturer: Intersil

Specifications of ISL6745ALEVAL3Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The schematic diagram of the current reference circuit is
shown in Figure 6, where |VAC| is the rectified voltage after
the rectifier. The high performance Op-Amp EL5420 clamps
the current reference if the averaged input of U3A is beyond
the bias voltage.
The LED current reference can be changed through R
R
Figure 7 shows the LED current control circuit, where U4C
provides 10 times of gain to reduce the power loss in the
current sense resistor R
implemented with U3B eliminates any discrepancy between
the reference (I
constant set by C
the second order harmonics will not appear in the control
signal. A typical way is to set the time constant to 0.5 times
of the utility frequency.
29
VERR
FIGURE 5. AVERAGE VOLTAGE vs ANGLE OF A TRIAC
100
DNP
100k
C 5
R10
14.3k
for applications with different rated operating current.
IREF
90
80
70
60
50
40
30
20
10
|VAC|
R8
1%
0
1.5
EL5420
1%
1%
R9
100k
5V1
7
C19
2.2µF
2.0
R18
FIGURE 7. CURRENT CONTROL LOOP
C6
2.2µF
4
VX
DIMMER
U3B
FIGURE 6. REFERENCE CIRCUIT
3
2.5
BAT 54
REF
150k
R32
CR4
2
-
+
IREF
19
3.01M
) and the LED current (I
PHASE WIDTH OF TRIAC (MS)
6
5
3.0
1
and R
6.8µF
EL5420
C20
2
3
s
3.5
C21 DNP
. The integration circuit
-
+
33
U3A
11
4
R33
61.9k
4.0
should be large enough so that
C26
2.2µF
1%
1%
3
5V1
1
4.5
R34
196k
10.0k
8
R35
5V1
R27
10.0k
1%
11
R28
5.0
R29
U4C EL5420
10X
10.0k
1%
+
-
5.5
LED
10
9
59.0k
1%
ISEN
R31
10.0k
1%
). The time
6.0
5V1
Application Note 1487
C10
0.1µF
6.5
IREF
C25
1.2n
10
5V1
ILED
IREF
and
The bias circuit is shown in Figure 8 together with the
reference voltages for the control circuit. At the beginning,
the |V
about 12V, Q
through R
VDD is above its threshold. The output capacitor is charged
up once the converter begins to work. The VB2 presents an
alternative bias choice for the driver for high voltage
applications. If it is connected to the 3rd of the LED strings,
3 times of p-n junction voltage presents when LED strings
start conducting current. This will shut off the current path of
Q
normal operation conditions.
The following circuit in Figure 9 shows a soft-start circuit with
overvoltage protection and delayed start-up circuit. The VR
R
voltage applied to LED strings. For an overvoltage of any
reasons, the Q
discharged through R
over-shot current during start-up, a delayed start-up circuit
consisting of U4D and Q
voltage is beyond 3.6V, the Q
presented in the reference generation circuit. This greatly
reduces the over-shot of the LED strings during start-up.
The overall schematics of the driver and the associated
BOM are presented in the last pages of this application note.
The fixture of the PCB is a 2-layer board with dimensions
3.15 by 2.65 inches. Figures 10 and 11 show the top view
SS
39
0
12
13
, CR
FIGURE 9. CONFIGURATION OF ISL6754A, SOFT-START-UP
, R
3V6
1.0M
R6
1
VR1
5V1
+
-
11
U4D
Q0
4
AC
15
EL5420
3
1A
VX
| increases so that the voltage at the gate of Q
, and prevents the Q
set up the over voltage protection of the output
BSS138
4
14
Q5
. The ISL6745A starts to work as soon as the
R4
DNP
R16
BAT54C
0
AND OVERVOLTAGE PROTECTION
VX
6.8µF
C16
3
is turned on, and C
will be turned on, and the SS charges will be
CR3
47u
FIGURE 8. BIAS CIRCUIT
C7
µF
BSS138
Q3
OVP
R39
1.0k
C27
R15
51.1
47u
15
µF
. In order to suppress the LED
OUT
OUT
5
220n
VR2
C12
24V
SS
is necessary. Only after SS
VERR
C24
0.1µF
OUT
0
R22
1k
5
18V
from conducting current in
VR4
will be turned off, and V
30.1k
R26
1%
7
R19
2k
is charged up with |V
C28
1.2n
VR3
5.1V
R23
10.0k
1%
220p
C17
R11
100
1
2
3
4
5
470p
C15
10n
C18
CS
C0G
U1
SS
RTD
VERR
CS
CT
ISL6745A
5%
R25
14.0k
R24
10.0k
1%
1%
VDDP
OUTB
OUTA
VDD
GND
July 28, 2009
AN1487.0
10
9
8
7
6
0
x
|VAC|
VB2
3V6
VDD
VDD
5V1
is
is
AC
470n
C13
Gate
2
|
,