AME5140 Evaluation Board User Guide
1. General Descriptions
The AME5140 is a non-synchronous step-up DC/DC converter with integrated N-channel Power MOS.
This device is a current-mode converter operating at fixed frequency of 1.6MHz. It’s available in
SOT-25, DFN-8C and MSOP-8 packages; it can support standard step-up application and provides a
backlight solution with minimal external components as well.
2. Features
● Input voltage: 2.7V to 5.5V
● Output voltage: Vin to 30V
● Oscillation frequency: 1.6MHz
● Switching current up t0 1.8A
● Current limit and Enable function
● Low Shutdown Current (<1uA)
● Uses Tiny Capacitors and Inductors
● Thermal shutdown function
3. Applications
● White LED Current Source
● PDA’s and Palm-Top Computers
● Portable Phones and Games
● Digital Cameras
● Local Boost Regulator
4. Evaluation Board Schematic
(4.1) AME5140 Typical Schematic
Figure 1
Rev. B /01-2010
(4.2) AME5140 Typical Schematic for 12V Application
Figure 2
5. Bill of Materials
BOM for Item (4.2)
Component Q’ty
Value
Description
Part No.
Manufacturer
Package
Cin1
1
4.7uF/6.3V
Ceramic Capacitor
1206B475K6R3C
WALSIN
1206
Cout1
1
4.7uF/16V
Ceramic Capacitor
1206B475K160C
WALSIN
1206
C1
1
22pF/16V
Ceramic Capacitor
0805B220K160C
WALSIN
0805
R1
1
120KΩ
Chip Resistor
RM10FTN1203
TA-I
0805
R2
1
13.7KΩ
Chip Resistor
RM10FTN1372
TA-I
0805
R3
1
0Ω
Chip Resistor
RM10JTN0
TA-I
0805
REN
1
100KΩ
Chip Resistor
RM10JTN104
TA-I
0805
L1
1
10uH
Inductor
SD52-10R0-R
COOPER
SD52
D1
1
30V/0.5A
Schottky Diode
RB550SS-30
ROHM
KMD2
U1
1
-
AME5140AEEVADJZ
AME
SOT-25
PCB
1
-
Blank PCB
TM080104 Rev.D
AME
-
4
4
-
Copper Pillar
-
-
EN
1
-
Switch
TS-006S-5-190g
HSUAN YI
-
-
4
-
Plastic Screw
S-306
PINGOOD
-
-
4
-
Spacer Support
H-6
PINGOOD
-
Vin,Vout
GND,GND
1.6MHz, 30V Boost
Converter
Rev. B /01-2010
6. Operating Instructions
(6.1) Connect Vin to the positive point of DC power supply and GND to supply ground.
(6.2) Connect Vout to the positive point of E-load and GND to supply ground or parallel an appropriate
resistor to pull up the loading.
(6.3) Importing a logic signal to EN pin will enable the AME5140. Logic high (VEN>2V) switches on
AME5140, logic low puts it into low current shutdown mode.
7. Application Information
(7.1) Setting Output Voltage & Current
(7.1.1) Output Voltage
The regulated output voltage is set by an external resistor divider (R1 and R2 in Figure 2.)
from the output to the VFB pin and is determined by:
VOUT = VFB × (1 +
R1
) ; Where VFB = 1.23V for AME5140.
R2
(7.1.2) Duty Cycle & Output Current
According to input and output voltage to calculate duty cycle and switching frequency.
Selecting feasible inductance can calculate output current by following equations.
D=
VOUT + V DIODE − V IN
VOUT + V DIODE − VSW
VSW = I CL (Typ ) × RDS ( ON )( Max )
I LOAD (max) = (1 − D ) × {I CL (min) −
D × (VIN − VSW )
}
2 fL
Where:
VIN is input voltage
VOUT is output voltage
VDIODE is the forward voltage of Schottky Diode
VSW is (“switch current limit” times “switch on-Resistance”); See the datasheet to have
L is the inductance
f is the switching frequency
ILOAD(max) means the maximum ability of output driving
Rev. B /01-2010
(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.
4.7uF 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
their wider voltage and temperature ranges.
22pF capacitor parallel with feedback resistor R1 is for compensation the output stability when
pulling up heavy loading. 10pF~100pF capacitance is common selection.
(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. Low DCR inductor also
can increase average efficiency. Calculate the required inductance by the equation below.
The recommended value of inductor for AME5140 application is 2.2uH ~ 10uH.
L≥
D × (VIN − VSW )
⎧
⎫
I
2 f × ⎨ I CL − LOAD ⎬
(1 − D) ⎭
⎩
(7.4) Board Layout Considerations
High frequency switching regulators require very careful layout of key components in order to get
stable operation and low noise. A good PCB layout could make AME5140 working perfect to
achieve the best performance.
(7.5) PCB Layout Example
The PCB layout example is for standard step-up converter application with AME5140 device. It
proves this EV board can achieve reliable performance. It follows the layout guidelines below.
(7.5.1) Use a ground plane under the switching regulator can effectively 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 Cout1 and Cout2 signal path should
be kept extremely short.
(7.5.4) The feedback components R1, R2, R3 and C1 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.
Rev. B /01-2010
EN
REN
IN
EN
GND
EN
Vin
GND
L1
Test Pin
4 Places
IN
IN
4 EN
Cin1
IN
5 IN
IN
U1
R1
FB
Vout
IN
FB
Vout
3 FB
GND
FB
R3_1
GND
GND
SW
2 GND
1 SW
Cin2
GND
GND
C2
GND
SW
Vout
Vout
R3_1
C1
R2
R3
Cout1
Cout2
GND
GND
Vout
Vout
IN
vout
D1
Screw & Spacer
4 Places
Figure 3
(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. Using schottky diodes as
freewheeling rectifiers reduces diode reverse recovery time and the voltage drop across the
diode is lower. For this design, choice RB550SS-30, with 30V reverse voltage, 0.5A forward
current, and around 0.5V forward voltage drop.
The freewheeling diode should be place close to the SW pin of the AME5140 to minimize noise
coupling due to trace inductance.
Rev. B /01-2010