an1490

Application Note 1490
ISL97801BOOSTEVALZ HPLED Driver Boost
Configured Evaluation Board
Introduction
The schematic of the ISL97801BOOST EVALZ Demo
Board is shown in Figure 1. This board is suitable for
evaluation of the ISL97801 in a boost mode LED driving
scheme. On the demo board, there are two resistors (R2
and R4). They are used to bypass the optional MOSFETs
Q1 and Q2, which can be omitted in low cost
applications. MOSFET Q1 is used as a fault protection
switch to disconnect the input supply if a fault occurs for
more than 50ms. It is also used to provide load-dump
protection in automotive applications. For applications
not requiring load dump or fault protection, it can bypass
Q1 with R2 (0Ω).
Q2 is used as an optional PWM dimming and load
isolation switch. When using PWM dimming control, the
LED bias current will vary with the PWM duty-cycle due to
the discharge of the output capacitor by the LED’s during
the PWM off time. Without Q2, (due to the discharge of
the output capacitor), the linear accuracy of the average
output current in the LED’s can not be controlled. With
Q2, the discharge of the capacitor is eliminated, leading
to better linearity of the LED current. For applications not
requiring high linear accuracy, MOSFET Q2 can be
bypassed with Resistor (0Ω).
Using the Board
Connect the load to the output marked “2 Power Post”.
The load of series LEDs must be connected between the
LED+ and LED- pins. The ISL97801 is a current mode
output converter, and the output voltage is the product of
the programmed output current and the load impedance.
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If the output circuit is opened, the output voltage can
rise, and the part will enter overvoltage protection and
the device will be shutdown.
Set-up the required output current. The output load
current is determined with the voltage on the Level pin in
this demo board, and the current sense resistor R9.
(Vlevel pin biased can be omitted with internal fixed
voltage 0.4V if the mode pin is grounded in the actual
application).
Apply a DC power voltage source on VBAT and PGND
pins. For ISL97801, the allowed input voltage range is
from 5V to 18V. Due to the boost function, the input DC
voltage must be lower than the output voltage. The
ISL97801 includes a circuit to generate a 5V voltage
which is used to drive the chip, and offer a reference
voltage for the system control (VDC). If the applied DC
power voltage is lower than 5V, the VDC voltage will
track with the applied DC power voltage. It is
recommended to apply DC power voltage of over 5V for
optimum demo board performance.
Apply VLEVEL voltage. The LED bias current is
determined by the LEVEL pin voltage (0V to 3V range)
and the sense resistor R9. The board is set-up with a
0.5Ω R9 resistor with 1V VLEVEL. The output current will
be ~350mA to 400mA depending on the tolerance of the
resistor.
Apply EN/PWM signal. Apply EN/PWM pin a DC signal for
enable signal. If PMW dimming is needed, apply a PWM
signal at EN/PWM pin.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2009. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Application Note 1490
ISL97801BOOSTEVALZ Boost Configured Evaluation Board Schematic
R2 0Ω
Q1
SI4482
J1
VBAT
L1
10µH
C1
47nF/25V
PGND
R1
100
C2
22µF/25V
J5
SS25
D1
C8
C9
C10
C11
C5
4.7µF/50V 4.7µF/50V 4.7µF/50V 4.7µF/50V 0.1µF/50V
J2
J8
C4
ISL97801
12 SWSI
R5
10
OVP 3
C14
SWDI 4
SWD2 5
R10
0
J3
LEVEL
J9
0.1µF/16V
6
7
TEMP 8
LEVEL
FB 9
TMAX 10
11 SWSI
R3
OPEN
VDD 1
LED+
LED-
VHI 2
BOOST/BUCK
13 EN/PWM
20 VIN
14 MODE
EN/PWM
J4
19 FAULT
18 GND
17 NC
16 VBAT
15 ENL
U1
0.1µF/6.3V
SGND
PGND
R7
0
6
5
2
1
4
3
R4
OPEN
FDC3512
R8
OPEN
R9
0.5
R6
OPEN
FIGURE 1. ISL97801BOOSTEVALZ BOOST CONFIGURED EVALUATION BOARD SCHEMATIC
ISL97801BOOSTEVALZ Board Layout
FIGURE 2. TOP VIEW
2
FIGURE 3. BOTTOM VIEW
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Application Note 1490
TABLE 1. BILL OF MATERIALS
PART
DESIGNATOR
FOOTPRINT
0.1µF/16V
C14
603
0.1µF/50V
C5
603
0.5
R9
603
0
R10
603
0
R7
603
0
R4 (Open)
1206
0
R2
1206
Open
R6
603
4.7µF/50V
C8, C9, C10, C11
1812
10
R5
603
10µF/6.3V
C4
603
10µH
L1
DS3316
22µF/25V
C2
1210
47nF/25V
C1
603
100
R1
603
FDC3512
Q2
SOT23-6
ISL97801
U1
LPP-20
SI4482
Q1 (open)
SO-8
SS25
D1
DO-214
VBAT
J1
POWERPOST
open
R3
603
open
R8
603
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the
reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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