ZXSC400EV2 User Guide issue 8

ZXSC400EV2
ZXSC400EV2 USER GUIDE
DESCRIPTION
The ZXSC400 is voltage mode boost converter in
SOT23-6 package. Its low feedback voltage allows the
current in a chain of LEDs to be set and accurately
monitored with a single resistor with minimal losses.
The ZXSC400EV2 is configured for 25W LED Driver
applications using the ZXSC400 boost converter.
FEATURES
•
Drives strings of 23 serially connected R,G & B
LEDs at 350mA
•
Typical efficiency of 85%
•
Over-voltage Protection
APPLICATIONS
•
LCD TV RGB Backlight
•
High Power LED driving
ORDERING INFORMATION
ORDER NUMBER
ZXSC400EV2
TYPICAL APPLICATION CIRCUIT
L1
VIN
D1
68uH/3.5A
R4
VCC
LED ANODE
10BQ100
1kohms
Please note evaluation boards
are subject to availability and
qualified leads.
Q1
U2
+
C1
ZXMN10A09K
D2
ZXT D6717E6
BZX84C47
+
100uF/25V
U1
ZXSC400
VCC
C2
C3
47uF/100V
100nF/100V
DRIVE
PWM
ST DN
GND
SENSE
D3
R1
VFB
BZX84C47
10m Ohm
C4
1uF/10V
R3
D4
R5
BZX84C7V5
10k
LED CATHODE
20k
R2
0.75 Ohm
ZXSC400EV2
ISSUE 8 - November 2005
1
ZXSC400EV2
REFERENCE DESIGN
ZXSC400EV2 is configured to the reference design below. The target application is a 25W LED Driver typically
White or RGB LED Driver for LCD TV backlighting.
The supply voltage is: VIN=24V and VCC=12V for the ZXSC400EV2.
For other reference designs or further applications information please refer to the ZXSC400 datasheet.
Schematic Diagram
L1
VIN
R4
VCC
D1
68uH/3.5A
LED ANODE
10BQ100
1kohms
Q1
ZXMN10A09K
U2
+
C1
D2
ZXT D6717E6
BZX84C47
+
100uF/25V
U1
ZXSC400
VCC
DRIVE
ST DN
SENSE
C2
C3
47uF/100V
100nF/100V
PWM
GND
D3
R1
VFB
BZX84C47
10m Ohm
C4
1uF/10V
R3
D4
R5
BZX84C7V5
LED CATHODE
20k
10k
R2
0.75 Ohm
Materials List
Ref
Value
Package
Part Number
Manufacturer
Notes
U1
U2
Q1
D1
D2
D3
D4
L1
R1
ZXSC400E6
ZXTD6717E6
ZXMN10A09K
10BQ100
BZX84C47
BZX84C47
BZX84C7V5
DO5022P-683
10mΩ
SOT23-6
SOT23-6
DPAK
SMB
SOT23
SOT23
SOT23
N/A
1206
Zetex
Zetex
Zetex
IR
Philips
Philips
Philips
Coilcraft
Generic
Boost converter
MOSFET gate driver
N-Channel MOSFET 100V
100V/1A Schottky diode
47V Zener diode
47V Zener diode
7V5 Zener diode
68uH/3.5A SMT Inductor
1206 5% tolerance
R2
0.75Ω
1206
Generic
1205 1% tolerance
R3
20kΩ
0805
Generic
0805 5% tolerance
R4
1kΩ
0805
Generic
0805 5% tolerance
Generic
0805 5% tolerance
C1
C2
C3
10kΩ
100µF/25V
47µF/100V
100nF/100V
0805
E
H13
1206
Panasonic
Panasonic
Generic
C4
1µF/10V
0805
SMT Electrolytic capacitor
SMT Electrolytic capacitor
100nF/100V/1206/Y5V
Ceramic capacitor
1µF/10V/0805/Y5V Ceramic
capacitor
R5
N/A
N/A
N/A
100V/1A
47V
47V
7V5
68uH/3.5A
EEVFK1E101P
EEVFK2A470Q
Generic
ZXSC400EV2
ISSUE 8 - November 2005
2
ZXSC400EV2
ZXSC400EV2 OPERATION
Connection diagram
25W LED DRIVER BOARD
ZXSC400EV2
L1
ZDB246R2
VIN
LED ANODE
D1
U2
VCC
C2
+
+
R3
R4
Q1
R5
LK1
PWM
D3
U1
C4 D4
GND
C1
R1
R2
D2
C3
LED CATHODE
Copyright Zetex plc 2005
ZXSC400EV2 Set-up and Test
1. Connect VIN and GND to positive and zero volts of PSU1 supply respectively.
2. Connect VCC and GND to positive and zero volts of PSU2 supply respectively.
3. Connect LED chain to LED ANODE and LED CATHODE outputs on ZXSC400EV2
4. Set the PSU1 to 24V and PSU2 to 12V.
5. Turn on PSU1 and PSU2.
6. The LED chain should illuminate and be regulated at 350mA - THIS IS A FUNCTIONAL EVAL BOARD.
ZXSC400EV2
ISSUE 8 - November 2005
3
ZXSC400EV2
LED Dimming using the PWM Input.
By injecting a PWM signal on the PWM input and varying the duty cycle, LED current and hence LED brightness
can be adjusted.
To implement this method of brightness control on the ZXLD1100EV2:
1. Connect a 10kΩ resistor between the drive pin of the ZXSC400 and GND (see diagram below).
2. Apply PWM signal with amplitude of between 0.7V and Vcc at a frequency of 100Hz to 1kHz (to
eliminate LED flicker). The LED current and hence LED brightness is linearly proportional to the duty
cycle ratio, so for brightness control adjust duty cycle ratio as necessary. For example, a 10% duty cycle
equates to 10% of full LED brightness.
L1
VIN
VCC
D1
68uH/3.5A
R4
LED ANODE
10BQ100
1kohms
Q1
ZXMN10A09K
U2
+
C1
D2
ZXT D6717E6
BZX84C47
+
100uF/25V
U1
ZXSC400
VCC
DRIVE
ST DN
SENSE
C2
C3
47uF/100V
100nF/100V
PWM
GND
D3
R1
VFB
BZX84C47
10m Ohm
C4
1uF/10V
R3
D4
BZX84C7V5
R5
LED CATHODE
20k
10k
R2
0.75 Ohm
Note: It may be necessary to reduce to value of the output capacitor, C2, to optimize for a 1kHz PWM dimming
signal. We recommend a value of 10µF/100V for the best compromise between PWM switching and LED current
ripple at full power.
ZXSC400EV2
ISSUE 8 - November 2005
4
ZXSC400EV2
Layout considerations
PCB tracks should be kept as short as possible to minimise ground bounce, and the ground pin of the device
should be soldered directly to the ground plane. It is particularly important to mount the coil and the input/output
capacitors close to the device to minimise parasitic resistance and inductance, which will degrade efficiency. The
FB pin is a high impedance input, so PCB track lengths to this should also be kept as short as possible to reduce
noise pickup. Excess capacitance from the FB pin to ground should be avoided.
Below is the recommended layout of the ZXSC400EV2.
25W LED DRIVER BOARD
ZXSC400EV2
L1
ZDB246R2
VIN
LED ANODE
LK1
C2
+
R3
+
PWM
D3
U1
C4 D4
GND
D1
U2
VCC
R4
Q1
R5
C1
R1
D2
R2
C3
LED CATHODE
Copyright Zetex plc 2005
Top Silk
Top Copper
Bottom Copper
Drill File
ZXSC400EV2
ISSUE 8 - November 2005
5
ZXSC400EV2
© Zetex Semiconductors plc 2005
Europe
Zetex GmbH
Streitfeldstraße 19
D-81673 München
Germany
Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
email: [email protected]
The Americas
Zetex Inc
700 Veterans Memorial Hwy
Hauppauge, NY 11788
USA
Telephone: (1) 631 360 2222
Fax: (1) 631 360 8222
email: [email protected]
Asia
Zetex (Asia) Ltd
3701-04 Metroplaza Tower 1
Hing Fong Road, Kwai Fong
Hong Kong
Telephone: (852) 26100 611
Fax: (852) 24250 494
email: [email protected]
Corporate Headquarters
Zetex Semiconductors plc
Zetex Technology Park,
Chadderton, OL9 9LL
United Kingdom
Telephone (44) 161 622 4444
Fax: (44) 161 622 4446
email: [email protected]
These offices are supported by agents and distributors in major countries world-wide.
This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or
reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services
concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or
service.
For the latest product information, log on to www.zetex.com
ZXSC400EV2
ISSUE 8 - November 2005
6