User's Guide
SNVA127A – July 2006 – Revised April 2013
AN-1407 LM3502/03 Evaluation Board
1
General Description
The LM3502/03 evaluation board is a working demonstration of a step up DC-DC converter. The
LM3502/03 is a white LED driver for lighting applications. The LM3502/03 contains two LED strings
designed for dual displays with independence EN pins. The LM3502 LED current can be adjusted with a
PWM signal while the LM3503 LED current can be adjusted with a DC voltage or RC filtered pulse-widthmodulated (PWM) signal at the Cntrl pin. The LM3502/03 can drive up to 10 white LEDs. Both devices
feature internal over-voltage protection (OVP) and under-voltage protection (UVP). For evaluation
purpose, the evaluation board is assembled in DSBGA package for 25V version (LM3503ITL) and 44V
version (LM3502ITL). The LM3502/03 are also available in 16-WQFN package. For further information on
boost converter topology, device electrical characteristics, and component selection, see the LM3502
Step-Up Converter for White LED Applications Data Sheet (SNVS339) and the LM3503 Dual-Display
Constant Current LED Driver with Analog Brightness Control Data Sheet (SNVS329).
2
Operating Conditions
•
•
•
•
•
VIN range: 2.5V ≤ VIN ≤ 5.5V
OVP options: 16V, 25V, 35V & 44V
10 Bump DSBGA or 16 Pin WQFN package
Ambient temperature (TA) range: -40C to +85C
Junction temperature (TJ) range: -40C to +125C
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1
Typical Application
3
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Typical Application
L
22 μH
D
MAIN:
2 to 5
LEDs
Sw
CIN
+
VSUPPLY
VOUT1
VIN
4.7 μF
VOUT2
Cntrl
COUT
-
LM3502-44
En1
1 μF
Fb
En2
AGND
PGND
SUB:
2 to 5
LEDs
Logic
Voltage
Signal
Inputs
R1
Figure 1. Typical Application Circuit LM3502
2
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PWM Dimming
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L
22 μH
D
MAIN:
2 to 3
LEDs
Sw
VOUT1
VIN
+
CIN
-
VSUPPLY
4.7 μF
VOUT2
Cntrl
LM3503-25
En1
COUT
1 μF
Fb
En2
AGND
DC
Voltage
Signal
Input
PGND
SUB:
2 to 3
LEDs
Logic Signal
Inputs
R1
Figure 2. Typical Application Circuit for LM3503
4
PWM Dimming
If PWM dimming is desired to control the brightness of the LED string, care must be taken to balance the
tradeoffs between audible noise and brigthness control. For best PWM duty cycle vs current linearity, the
recommended PWM frequency should be between 200Hz to 500Hz for the LM3502.
Similarly if PWM dimming is desired to control the brightness, a RC filter is necessary at the control pin for
the LM3503 (Figure 3). To select the PWM frequency, use Equation 1 and Equation 2.
FPWM > 10 * FRC
(1)
1
FRC =
2*S*R*C
(2)
FPWM: PWM Singal Frequency
FRC: RC Filter Bandwidth Cutoff Frequency
R: Chosen Filter Resistor
C: Chosen Filter Capacitor
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LED Current Setting
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PWM Signal
Sw
VOUT1
VIN
X
R
Y
C
Cntrl
VOUT2
LM3503
En1
Fb
En2
AGND
PGND
R1
Figure 3. Typical Circuit for PWM Dimming (LM3503)
5
LED Current Setting
LEDcurrent is set using Equation 3 for LM3502/LM3503:
ILED =
VFb
(3)
R1
If analog control is used for brightness control in the LM3503, the relationship between VFB and VCNTRL can
be determined by using Equation 4:
VFB = (0.156) * (VCntrl)
(4)
For LM3502, the typical VFB is 0.25V to solve for ILED, or by rearranging ILED equation to solve for R1 .
4
AN-1407 LM3502/03 Evaluation Board
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Connection Diagram and Package Mark Information
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6
Connection Diagram and Package Mark Information
A2
A1
4
3
2
1
A3
B1
B3
C1
C3
D1
D3
5
16
6
15
7
14
8
13
9
10
11
12
D2
Figure 4. 10 Bump DSBGA Package
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Figure 5. 16-Thin WQFN (RGH0016A)
AN-1407 LM3502/03 Evaluation Board
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Connection Diagram and Package Mark Information
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Table 1. Pin Descriptions
6
Bump No
WQFN Pin No
Name
A1
9
Cntrl
Description
B1
7
Fb
C1
6
VOUT2
Drain Connections of the NMOS and PMOS Field Transistor (FET)
Switches. Connect 100nF at VOUT2 node if VOUT2 is not used
D1
4
VOUT1
Over-Voltage Protection (OVP) and source connection of the PMOS
FET switch
LED Current Control Connection
Feeback Voltage Connection ( 0.2V < VCNTRL < 3.5V )
D2
2 and 3
SW
D3
15 and 16
Pgnd
Drain Connection of Power NMOS Switch
Power Ground Connection
C3
14
Agnd
Analog Ground Connection
B3
13
VIN
Input Voltage Connection
A3
12
En1
NMOS FET Switch Control Connection
A2
10
En2
PMOS FET Switch Control Connection
1
NC
No connect
5
NC
No connect
8
NC
No connect
11
NC
No connect
DAP
DAP
Die Attache Pad (DAP), to be soldered to the printed circuit board's
ground plane for enhanced thermal dissipation
AN-1407 LM3502/03 Evaluation Board
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Printed Circuit Board (PCB) Layout
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Printed Circuit Board (PCB) Layout
Figure 6. Top Silk Screen
Figure 7. Bottom Silk Screen
Figure 8. Top Traces
Figure 9. Bottom Traces
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Printed Circuit Board (PCB) Layout
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Figure 10. Top Pads
Figure 11. Bottom Pads
Table 2. Bill of Materials (BOM) for LM3502ITL and LM3503ITL
Device
Description
Manufacture No
LM3502
44V version (Drive up to 10 LEDs)
Texas Instruments
LM3503
25V Version ( Drive up to 6 LEDs)
Texas Instruments
CIN
4.7µF, 16V (3216X7R1C475K)
TDK
COUT
1µF, 50V (3216X7R1H105K)
TDK
R1
CRCW060328R0F (28 ohms)
Vishay
DIODE
SS16
Vishay
WHITE LED
LTW67C
Osram
INDUCTOR
DO1608C-223C (22µH)
Coilcraft
Test pins: VOUT, SW, VIN, FB, CNTRL,
EN1, EN2 and GND
Turret 0.09 inches
8
AN-1407 LM3502/03 Evaluation Board
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SNVA127A – July 2006 – Revised April 2013
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