AME5170 Evaluation Board User Guide
1. General Descriptions
The AME5170 is a fixed off time step-up DC/DC converter with integrated N-channel Power MOS. It’s
ideal for LCD panels requiring high efficiency with light load condition as well as LED application for
cellular phone back-lighting, PDAs and other hand-held devices.
2. Features
● Input voltage: 1.5V to 5.5V
● Output voltage: Vin to 28V
● Duty ratio: Fixed 400ns TOFF PFM control
● Oscillation frequency: Various base on I/O spec
● Current limit and Enable functions
● Thermal shutdown function
● Built-in internal SW N-channel power MOS
● Small SOT-25 Package
3. Applications
● LCD Bias Supplies
● White LED Back-Lighting
● Handheld Devices
● Digital Cameras
● Portable Applications
4. Evaluation Board Schematic
(4.1) AME5170 Typical Schematic
Figure 1
Rev. B /01-2010
(4.2) AME5170 Typical Schematic for 20V 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
1uF/25V
Ceramic Capacitor
0805B105K250C
WALSIN
0805
REN
1
100KΩ
Chip Resistor
RM10JTN104
TA-I
0805
R1
1
510KΩ
Chip Resistor
RM10FTN5103
TA-I
0805
R2
1
33KΩ
Chip Resistor
RM10FTN3302
TA-I
0805
R3
1
0Ω
Chip Resistor
RM10JTN0
TA-I
0805
L1
1
10uH
Inductor
SD52-10R0-R
COOPER
SD52
D1
1
30V/0.2A
Schottky Diode
RB520S-30
ROHM
EMD2
U1
1
-
AME5170AEEVADJZ
AME
SOT-25
PCB
1
-
Blank PCB
TM080104 Rev. D
AME
-
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
PFM, Micro Power
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 AME5170. Logic high (VEN>1.5V) switches on
AME5170, 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 AME5170.
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 − V SW
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
TOFF is the duration of switch off; for AME5170 TOFF is fixed 400ns
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
capacitance or using LC filter is able to achieve.
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 to select
because of 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. Low DCR inductor also
can increase average efficiency. Calculate the required inductance by the equation below.
The recommended value of inductor for AME5170 application is 2.2uH ~ 22uH.
L≥(
VOUT − VIN (min) + VDIODE
I CL (min)
) × TOFF
(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 AME5170 working perfect to
achieve the best performance.
(7.5) PCB Layout Example
The PCB layout example is for standard step-up converter application with AME5170 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 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 RB520S-30, with 30V reverse voltage, 0.2A forward current, and
around 0.4V forward voltage drop.
The freewheeling diode should be place close to the SW pin of the AME5170 to minimize noise
coupling due to trace inductance.
Rev. B /01-2010