AME5142/5142A/5142B Evaluation Board User Guide

AME5142/5142A/5142B Evaluation Board User Guide
1. General Descriptions
The AME5142/AME5142A/AME5142B is a non-synchronous step-up DC/DC converter with integrated
N-channel Power MOS. The PWM operation is able to vary the duty ratio linearly from 0% up to 92%.
This device, available in a 6-pin SOT-26 package, provides a backlight solution with minimal external
components.
2. Features
● Input voltage: 2.7V to 5.5V
● Output voltage: Vcc to 26V
● Duty ratio: 0% to 92% PWM control
● Oscillation frequency: 1.2MHz
● Current limit and Enable function
● Thermal shutdown function
● Built-in internal SW N-channel MOS
● SOT-25 and SOT-26 Package
3. Applications
● LCD Bias
● Battery Backup
● Hand-held Computers
● Smart Phone
● Digital Cameras
● Digital Picture Frame
4. Evaluation Board Schematic
GND
GND
IN
(4.1) AME5142 Typical Schematic
Figure 1
Rev. B /01-2010
(4.2) AME5142 Typical Schematic for 12V Application
L1
5V
4.7uH
C1
4.7uF
12V
D1
RSX101VA-30
C6
10uF
C3
0.1uF
SW
IN
GND
EN
100KΩ
EN
GND
IN
C4
100pF
R1
C7
0.1uF
442KΩ
FB
AME5142
EN
R2
R3
5.6KΩ
Figure 2
GND
GND
IN
(4.3) AME5142 Typical Schematic for WLED Driver (6S1P) Application
Figure 3
Rev. B /01-2010
5. Bill of Materials
BOM for item (4.2)
Nomenclature Q’ty
Value
Description
Part No.
Manufacturer
Package
C1
1
4.7uF/ 6.3V
Ceramic Capacitor
C1608Y5V0J475ZT
TDK
1608
C3,C7
1
0.1uF/ 50V
Ceramic Capacitor
C1608X7R1H104KT
TDK
1608
C4
1
100pF/ 50V
Ceramic Capacitor
C1608C0G1H101JT
TDK
1608
C6
1
10uF/ 25V
Ceramic Capacitor
C3225X7R1E106KT
TDK
3225
R1
1
100KΩ
Chip Resistor
CR0805F100KP05
SYNTAX
0805
R2
1
442KΩ
Chip Resistor
CR0805F442KP05
SYNTAX
0805
R3
1
5.6KΩ
Chip Resistor
CR-05FL7---5K6
SYNTAX
0805
L1
1
4.7uH
Inductor
SD52-4R7-R
COOPER
SD52
D1
1
30V/1A
Schottky Rectifier
RSX101VA-30
ROHM
SMA
U1
1
-
AME5142AEEVADJZ
AME
SOT-25
PCB
1
-
Blank PCB
TM081001 Rev.B
AME
-
2
-
Terminal Blocks
EK381V-02P
DINKLE
-
EN
3
-
Pin Header
YD-TECH
1x40 12M/M
-
6
-
Test Pin
JT-1P-CIR
PINGOOD
-
-
4
-
Plastic Screw
S-306
PINGOOD
-
-
4
-
Spacer Support
H-6
PINGOOD
-
Value
Description
Part No.
Manufacturer
Package
Vin&GND,
Vout&GND
1.2MHz, 25V Boost
Converter
BOM for item (4.3)
Nomenclature Q’ty
C1
1
4.7uF/ 6.3V
Ceramic Capacitor
C1608Y5V0J475ZT
TDK
1608
C3,C7
1
0.1uF/ 50V
Ceramic Capacitor
C1608X7R1H104KT
TDK
1608
C6
1
1uF/ 16V
Ceramic Capacitor
C1608X5R1C105KT
TDK
1608
R1
1
100KΩ
Chip Resistor
CR0805F100KP05
SYNTAX
0805
R4
1
0Ω
Chip Resistor
RM-0
SYNTAX
0805
R5
1
7.5Ω
Chip Resistor
FCR05-F-T-0750
PDC
0805
L1
1
4.7uH
Inductor
SD52-4R7-R
COOPER
SD52
D1
1
30V/1A
Schottky Rectifier
RSX101VA-30
ROHM
SMA
D2~D7
6
-
White LED
LT8AW1-54-UEE3-TE
Ledtech
0603
U1
1
-
6S WLED Driver
AME5142AEEVADJZ
AME
SOT-25
PCB
1
-
Blank PCB
TM081001 Rev.B
AME
-
2
-
Terminal Blocks
EK381V-02P
DINKLE
-
Vin&GND,
Vout&GND
Rev. B /01-2010
Nomenclature Q’ty
EN
Value
Description
Part No.
Manufacturer
Package
YD-TECH
1x40 12M/M
3
Pin Header
6
Test Pin
JT-1P-CIR
PINGOOD
4
Plastic Screw
S-306
PINGOOD
4
Spacer Support
H-6
PINGOOD
6. Operating Instructions
(6.1) Connect VDD to the power source’s positive output.
(6.2) Connect GND to supply ground.
(6.3) Applying a logic signal to EN pin will enable the AME5142/AME5142A/AME5142B. Logic high
(VEN>1.5V) turns on AME5142/AME5142A/AME5142B, logic low puts it into low current
shutdown mode.
7. Application Information
(7.1) Setting Output Current
The regulated output current is set with an external resistor divider (R5 in Figure 1.) from the
output to the VFB pin and is determined by:
I OUT =
VFB
R5
To prevent stray capacitance and noises, locate resistors R5 close to AME5142/AME5142A
/AME5142B.
The external resistor sets the output current table as below:
IOUT
R5
20mA
7.5Ω
40mA
3.75Ω
60mA
2.5Ω
80mA
1.875Ω
(7.2) Capacitor Selection
4.7uF input capacitor can reduce input ripple. For better voltage stability, to increase the input
capacitor value or using LC filter is feasible.
1uF output capacitor is sufficient to reduce output voltage ripple. For better voltage filtering,
ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of
Rev. B /01-2010
their wider voltage and temperature ranges.
(7.3) Inductor Value Calculation
A larger value of inductor will reduce the peak inductor current, resulting in smaller input ripple
current, higher efficiency and reducing stress on the internal MOSFET. Calculate the required
inductance value by the equation:
(7.3.1) Calculating Duty cycle
The Duty cycle can’t over the maximum duty of specification.
D=
VOUT + VDIODE − VIN
VOUT + VDIODE − VSW
(7.3.2) Calculating Inductor
The recommended value of inductor for AME5142/AME5142A/AME5142B/5142A
application is 2.2uH ~ 10uH.
L≥
D × (V IN − VSW )
I
2 f sw × ( I CL − Load )
(1 − D )
Where:
VDIODE is the forward voltage of schottky
VSW is (“switch current” x “switch on-Resistance”)
L is the inductance.
fsw is the switching frequency.
ILoad is the LED current.
(7.4) Board Layout Considerations
High frequency switching regulators require very careful layout of components in order to get
stable operation and low noise. A good PCB layout could make AME5142/AME5142A/AME5142B
work its best performance.
(7.5) PCB Layout Example
This PCB layout example uses the AME5142/AME5142A/AME5142B for 6 LEDs in one string
application. The placement is suitable and smooth, and follows the layout guide lines.
Rev. B /01-2010
(7.5.1) Use a ground plane under the switching regulator to minimize inter-plane coupling.
(7.5.2) Using 20mil wide track for GND (as wide as possible), and all GND nodes are as close
as possible.
(7.5.3) The SW node, schottky diode D1 and output capacitor C6, C7 and C8 signal path should
be kept extremely short.
(7.5.4) The feedback components R2, R3 and C4 must be kept close to the FB pin of U1 to
prevent noise injection on the FB pin trace and keeping far away from SW node.
Test Pin
GND
EN
IN
Net1
GND
Net1
EN
LED
R1
EN
Vo
EN
IN
1210
OVP
D23
0805
FB
D29
D35
Vout
Vo
D13
GND
D36
D31
GND
D36
D37
D37
D31
D25
R9
GND
D30
R10
GND
D25
R8
R7
R6
R5
GND
D19
D19
D13
R4
D30
D37
R4
FB
R4
D24
D18
D31
GND
R3 C5
D24
D35
D29
GND
D12
D6
D18
D25
GND
D12
D19
R4
D13
FB
0805
D7
FB
D1
D6
FB
D23
D36
FB
D34
D34
D35
D17
D17
D11
D5
Vo
D30
Vo
D24
SW
D33
D33
D34
D28
D28
D29
D11
D22
D23
GND
D32
D33
D27
D27
D28
D16
D22
D10
D22
D26
D27
D21
Vo
D21
D16
D18
SW
D15
D10
D17
C8
D16
Vo
D5
C6
GND
D21
R2 C4
D12
SW
Vo
D6
GND
GND
D11
D5
GND
1210
D15
D4
GND
D20
D14
D15
Vo
D32
Vo
IN
C3
D10
GND
U1
0603
1210
GND
D9
D4
IN
IN
D3
D4
0603
IN
C1
D9
D3
Vin
C7
C2
IN
D9
Vo
D26
D32
D8
D3
Vo
D20
D26
D2
D14
D20
D8
D14
D8
D2
Test Pin
6 places
1210
GND
L1
Vo
Vo
D2
GND
GND
Screw
Spacer
4 places
Figure 4
(7.6) Freewheeling Diode Selection
The freewheeling diode conduction time is longer than the N-channel Power MOS off time.
Therefore, the diode parameters improve the overall efficiency. Use of schottky diodes as
freewheeling rectifiers reduces diode reverse recovery time and the voltage drop across the diode
is lower. For this design, RSX101VA-30 is chosen, with 30V reverse voltage, 1A forward current,
and around 0.5V forward voltage drop.
The freewheeling diode should be place close to the SW pin of the AME5142/AME5142A/
AME5142B to minimize ring due to trace inductance.
Rev. B /01-2010