AME5150 Evaluation Board User Guide
1. General Descriptions
The AME5150 is a fixed off time inverting 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: Up to -28V
● Duty ratio: Fixed 400ns TOFF PFM Control
● Oscillation frequency: Various Base on I/O Spec
● Current Limit and Enable Function
● Thermal Shutdown Function
● Input Under Voltage Lockout
● Small SOT-25 Package
3. Applications
● Electronic Information Organizers
● Palmtops
● Cellular and Portable Phones
● Portable Audio Systems
● Various Multi-function Power Supplies
4. Evaluation Board Schematic
(4.1) AME5150 Typical Schematic
D1
+Vout
R2
C5
C4
D2
ZD2
R8
C2
Vin
L1
C1
D3
C3
C9
D5
1
5
C6
SW
U1
AME5150
IN
EN
R6
IN
J1
4
-Vout
R7
EN
NFB
ZD1
C7
3
R4
C8
GND
GND
R1
2
R5
Figure 1
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Rev. A /01-2010
(4.2) AME5150 Typical Schematic for -25V Application
Figure 2
5. Bill of Materials
BOM for Item (4.2)
Component
Q’ty
C1
1
C3
Part No.
Manufacturer
Package
4.7uF/ 6.3V Ceramic Capacitor
1206B475K6R3C
WALSIN
1206
1
0.47uF/25V Ceramic Capacitor
0805B474K250C
WALSIN
0805
C7
1
15pF/ 50V
Ceramic Capacitor
0805B150K500C
WALSIN
0805
C8
1
4.7uF/50V
Ceramic Capacitor
1206B475K500C
WALSIN
1206
R4
1
470KΩ
Chip Resistor
RM10FTN4703
TA-I
0805
R5
1
24.9KΩ
Chip Resistor
RM10FTN2492
TA-I
0805
R6, R7
2
0Ω
Chip Resistor
RM10JTN0
TA-I
0805
L1
1
4.7uH
Inductor
SD52-4R7-R
COOPER
SD52
D3,D5
2
30V/0.2A
Schottky Diode
RB520S-30
ROHM
EMD2
U1
1
-
AME5150AEEVADJZ
AME
SOT-25
PCB
1
-
Blank PCB
TM091101 Rev. A
AME
6
-
Copper Pillar
-
-
-
J1
1
-
Pin Header
-
YD-TECH
1x40 12M/M
-
4
-
Plastic Screw
S-306
PINGOOD
-
-
4
-
Spacer Support
H-6
PINGOOD
-
Vin,+Vout,
-Vout,GND*3
Value
Description
PFM, Micro Power
Inverting Boost
2/5
Rev. A /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 AME5150. Logic high (VEN>1.5V) switches on
AME5150, 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 (R4 and R5 in Figure 2.)
from the output to the VNFB pin and is determined by:
⎞
⎛
R
VOUT = −⎜⎜ VNFB × (1 + 4 ) + R4 × I NFB ⎟⎟
R5
⎠
⎝
Where VNFB equals -1.23V and INFB equals 2uA for AME5150.
(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 + VDIODE − VIN
VOUT + VDIODE − 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
TOFF is the duration of switch off; for AME5150 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
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Rev. A /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 AME5150 application is 2.2uH ~ 10uH.
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 AME5150 working perfect to
achieve the best performance.
(7.5) PCB Layout Example
The PCB layout example is for standard Inverting converter application with AME5150 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 C8 signal path should be kept
extremely short.
(7.5.4) The feedback components R4, R5 and C7 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.
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Rev. A /01-2010
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 AME5150 to minimize noise
coupling due to trace inductance.
5/5
Rev. A /01-2010