AME5253A 1A, 1.5MHz Synchronous Step-Down

AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n General Description
The AME5253A is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. Capable of delivering 1A output
current over a wide input voltage range from 2.5V to 5.5V.
Supply current with no load is 400µA and drops to<1µA
in shutdown. The 2.5V to 5.5V input Voltage range makes
the AME5253A ideally suited for single Li-Ion batterypowered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems.
PWM pulse skipping mode operation provides very low
output ripple voltage for noise sensitive applications. At
very light load, the AME5253A will automatically skip
pulses in pulse skip mode operation to maintain output
regulation.
The internal synchronous switch increases efficiency
and eliminates the need for an external Schottky diode.
Low output voltages are easily supported with the 0.6V
feedback reference voltage. The AME5253A is available
in SOT-25 packages.
Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection.
n Applications
l
l
l
l
l
Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
MP3 Players
Portable Instruments
n Typical Application
VIN = 2.5V to 5.5V
VIN
IN
CIN
4.7µF
CER
2.2µH
AME5253A
EN
VOUT
SW
GND
CFWD
FB
R1
150K
R2
75K
1.8V
1000mA
COUT
10µF
CER
VOUT=VFB (R1+R2)/R2
Figure 1: 1.8V at 1000mA Step-Down Requlator
CFWD: 22pF~220pF
n Features
l
l
l
l
High Efficiency: Up to 95%
Shutdown Mode Draws < 1µA Supply Current
2.5V to 5.5V Input Range
Adjustable Output From 0.6V to VIN
l
l
l
l
l
l
1A Output Current
Low Dropout Operation: 100% Duty Cycle
No Schottky Diode Required
1.5MHz Constant Frequency PWM Operation
SOT-25 Packages
All AME’ s Lead Free Product Meet RoHS
Standard
Rev.A.03
1
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Function Block Diagram
Constant
Off-time
Mode
Select
Slope
COMP
VIN
IN
4
PWM
COMP
FB
5
0.6V
0.6V
VREF
SW
LOGIC
3
0.55V
UVDET
Soft
Start
EN
1
NMOS
COMP
IRCOMP
OSC
GND
2
Figure 2: Founction Block Diagram
2
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Pin Configuration
SOT-25
Top View
5
AME5253A-AEVADJ
1. EN
2. GND
3. SW
4. IN
5. FB
4
AME5253A
1
2
3
Die Attach:
Conductive Epoxy
n Pin Description
Pin Number
Pin Name
1
EN
2
GND
Ground. Tie directly to ground plane.
3
SW
Switch Node Connection to Inductor.
4
IN
Input Supply Voltage Pin.
Bypass this pin with a capacitor as close to the device as possible.
5
FB
Output voltage Feedback input.
Rev.A.03
Pin Description
No connection. Not internally connected. Can left floating or
connected to GND.
3
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Ordering Information
AME5253A - x x x xxx
Output Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
A
(SOT-25)
4
1. EN
2. GND
3. SW
4. IN
5. FB
Package Type Number of Pins
E: SOT-2X
V: 5
Output Voltage
ADJ: Adjustable
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Absolute Maximum Ratings
Parameter
Symbol
Maximum
V IN
-0.3 to 6.5
V EN , V OUT
-0.3 to V IN
V SW
-0.3 to V IN
Input Supply Voltage
EN, V OUT Voltage
SW Voltage
Unit
V
B*
ESD Classification
Caution: Stress above the listed absolute maximum rating may cause permanent damage to the device.
* HBM B: 2000V~3999V
n Recommended Operating Conditions
Parameter
Symbol
Rating
Unit
Supply Voltage Voltage
V IN
2.5 to 5.5
V
Ambient Temperature Range
TA
-40 to +85
o
C
Junction Temperature Range
TJ
-40 to +125
o
C
n Thermal Information
Parameter
Package
Die Attach
Thermal Resistance*
(Junction to Case)
Thermal Resistance
(Junction to Ambient)
Symbol
Maximum
θ JC
81
Unit
o
SOT-25
Conductive Epoxy
Internal Power Dissipation
Solder Iron (10Sec)**
θJA
260
PD
400
350
C/W
mW
o
C
* Measure θJC on center of molding compound if IC has no tab.
** MIL-STD-202G 210F
Rev.A.03
5
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Electrical Specifications
VIN=3.6V, VOUT=2.5V, VFB=0.6V, L=2.2µH, CIN=4.7µF, COUT=10µF, TA=25oC, IMAX=1A unless otherwise specified.
Parameter
Test Condition
Min
Typ
Max
Units
Input voltage
VIN
2.5
5.5
V
Adjustable Output Range
Vout
VFB
VIN-0.2
V
Feedback Voltage
VFB
0.588
0.612
V
Feedback Pin Bias Current
IFB
VFB=VIN
50
nA
Quiescent Current
IQ
IOUT=0mA, VFB=1V
0.4
0.5
mA
Shutdown Current
ISHDN
VEN=GND
0.1
1
µA
Switch Frequency
fOSC
1.5
1.8
MHz
0.6
-50
1.2
High-side Switch On-Resistance
RDS,ON, LHI
ISW=200mA, VIN=3.6V
0.28
Ω
Low-side Switch On-Resistance
RDS,ON, LO
ISW=200mA, VIN=3.6V
0.25
Ω
Switch Current Limit
ISW,CL
VIN=2.5 to 5.5V
1.4
1.6
A
EN High (Enabled the Device)
VEN,HI
VIN=2.5 to 5.5V
1.5
EN Low (Shutdown the Device)
VEN,LO
VIN=2.5 to 5.5V
Input Undervoltage Lockout
VUVLO
rising edge
Input Undervoltage Lockout
Hysteresis
VUVLO,HYST
Thermal Shutdown Temperature
OTP
Maximum Duty Cycle
DMAX
SW Leakage Current
6
Symbol
V
0.4
Shutdown,
temperature increasing
1.8
V
0.1
V
o
160
100
EN=0V, VIN=5.0V
VSW=0V or 5.0V
-1
V
C
%
1
µA
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Detailed Description
Main Control Loop
AME5253A uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET)
switches are intermal. During normal operation, the internal top power MOSFET is turned on each cycle when
the oscillator sets the RS latch, and turned off when the
current comparator resets the RS latch. While the top
MOSFET is off, the bottom MOSFET is turned on until
either the inductor current starts to reverse as indicated
by the current reversal comparator IRCMP.
Pulse Skipping Mode Operation
At light loads, the inductor current may reach zero or
reverse on each pulse.The bottom MOSFET is turned off
by the current reversal comparator, IRCMP, and the switch
voltage will ring. This is discontinuous mode operation,
and is normal behavior for the switching regulator.
n Application Information
The basic AME5253A application circuit is shown in
Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and followed
by CIN and COUT.
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current DIL increases with higher VIN and decreases
with higher inductance.
∆I L =
1
( f )(L )
VOUT 1 −
VOUT
VIN
A reasonable starting point for setting ripple current is
∆IL=0.4(lmax). The DC current rating of the inductor
should be at least equal to the maximum load current
plus half the ripple current to prevent core saturation. For
better efficiency, choose a low DC-resistance inductor.
Short-Circuit Protection
When the output is shorted to ground, the frequency of
the oscillator is reduced to about 180KHz. This frequency
foldback ensures that the inductor current hsa more time
do decay, thereby preventing runaway. The oscillator’ s
frequency will progressively increase to 1.5MHz when VFB
or VOUT rises above 0V.
Dropout Operation
As the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases
toward the maximum on-time. Further reduction of the
supply voltage forces the main switch to remain on for
more than one cycle until it reaches 100% duty cycle.
The output voltage will then be determined by the input
voltage minus the voltage drop across the P-channel
MOSFET and the inductor.
Rev.A.03
CIN and COUT Selection
The input capacitance, CIN is needed to filter the trapezoidal current at the source of the top MOSFET. To
prevent large voltage transients, a low ESR input
capacitorsized for the maximum RMS current must be
used. The maximum RMS capacitor current is given by:
I RMS = I OUT ( MAX )
VOUT
VIN
V IN
−1
VOUT
This formula has a maximum at VIN=2VOUT, where
IRMS=IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that the capacitor
manufacturer ripple current ratings are often based on 2000
hours of life. This makes it advisable to further derate the
capacitor, or choose a capacitor rated at a higher temperature than required.
7
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
The selection of COUT is determined by the effective series
resistance(ESR) that is required to minimize voltage ripple
and load step transients. The output ripple, VOUT, is determined by:
∆VOUT ≅ ∆I L ESR +
Where VREF equals to 0.6V typical. The resistive divider allows the FB pin to sense a fraction of the output
voltage as shown in Figure 4.
0.6V ≤ VOUT ≤ 5.5V
1
8 fCOUT
R1
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Output Voltage Programming
The output voltage is set by an external resistive divider
according to the following equation :
VOUT = V REF × 1 +
R1
R2
FB
AME5253 A
R2
GND
Figure 3: Setting the AME5253A Output Voltage
Thermal Considerations
In most applications the AME5253A does not dissipate
much heat due to its high efficiency. But, in applications
where the AME5253A is running at high ambient temperature with low supply voltage and high duty cycles,
such as in dropout, the heat dissipated may exceed the
maximum junction temperature of the part. If the junction
temperature reaches approximately 160OC, both power
switches will be turned off and the SW node will become
high impedance. To avoid the AME5253A from exceeding the maximum junction temperature, the user will need
to do some thermal analysis. The goal of the thermal
analysis is to determine whether the power dissipated
exceeds the maximum junction temperature of the part.
The temperature rise is given by:
TR = (PD )(θ JA )
Where PD is the power dissipated by the regulator and
θJA is the thermal resistance from the junction of the die
to the ambient temperature.
8
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
VIN
2.5V to 5.5V
2.2µH
VIN
2.7V to 5.5V
VOUT
1.2V
SW
IN
AME5253 A
EN
FB
GND
CIN
4.7µF
CER
COUT
10µF
CER
AME5253 A
EN
150K
2.2µH
CIN
4.7µF
CER
EN
FB
GND
CIN
4.7µF
CER
COUT
10µF
CER
EN
FB
GND
CIN
4.7µF
CER
VOUT
3.3V
SW
AME5253 A
150K
Figure 5: 1.5V Step-Down Regulator
CFWD: 22pF~220pF
CFWD
COUT
10µF
CER
150K
33.3K
Figure 8: 3.3V Step-Down Regulator
CFWD: 22pF~220pF
VOUT
1.6V
SW
IN
AME5253 A
EN
FB
GND
CIN
4.7µF
CER
COUT
10µF
CER
150K
2.2µH
IN
CFWD
2.2µH
CFWD
47.3K
VIN
3.6V to 5.0V
VOUT
1.5V
100K
VIN
2.5V to 5.5V
VOUT
2.5V
Figure 7: 2.5V Step-Down Regulator
CFWD: 22pF~220pF
SW
AME5253 A
FB
GND
Figure 4: 1.2V Step-Down Regulator
CFWD: 22pF~220pF
IN
SW
IN
CFWD
150K
VIN
3.3V to 5.5V
2.2µH
CFWD
COUT
10µF
CER
150K
90K
Figure 6: 1.6V Step-Down Regulator
CFWD: 22pF~220pF
Rev.A.03
9
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
PC Board Layout Checklist
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the
AME5253A. These items are also illustrated graphically in Figures 9. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide.
2. Does the VFB pin connect directly to the feedback resistors? The resistive divider R2/R1 must be connected between
the (+) plate of COUT and ground.
3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal
power MOSFETs.
4. Keep the switching node, SW, away from the sensitive VFB node.
5. Keep the (-) plates of CIN and COUT as close as possible.
L1
VIN
IN
CFWD
AME5253 A
CIN
R2
GND
-
R1
CFWD: 22pF~220pF
10
+
COUT
FB
EN
+
-
VOUT
SW
Figure 9: AME5253A Adjustable Voltage
Regulator Layout Diagram
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Application Information
External components selection
Supplier
Inductance
(µ H)
Current Rating
(mA)
DCR
(m Ω )
Dimensions
(mm)
Series
TAIYO YUDEN
2.2
1480
60
3.00 x 3.00 x 1.50
NR 3015
GOTREND
2.2
1500
58
3.85 x 3.85 x 1.80
GTSD32
Sumida
2.2
1500
75
4.50 x 3.20 x 1.55
CDRH2D14
Sumida
4.7
1000
135
4.50 x 3.20 x 1.55
CDRH2D14
TAIYO YUDEN
4.7
1020
120
3.00 x 3.00 x 1.50
NR 3015
GOTREND
4.7
1100
146
3.85 x 3.85 x 1.80
GTSD32
Table 1. Recommended Inductors
Table 2. Recommended Capacitors for CIN and COUT
Rev.A.03
11
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Characterization Curve
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
80
VIN = 3.6V
80
70
Efficiency(%)
Efficiency(%)
90
VIN = 2.7V
60
50
40
30
20
70
60
50
40
30
20
10
VOUT = 2.5V
0
1
10
10
COUT = 10µF L = 2.2µH
100
VOUT = 2.5V
0
1
1000
Output Current(mA)
100
90
90
70
Efficiency(%)
Efficiency(%)
80
VIN = 2.7V
60
50
40
30
10
VOUT = 1.5V
0
60
50
40
30
1
10
10
COUT = 10µF L = 2.2µH
100
0
1
1000
Output Current(mA)
100
90
90
80
10
COUT = 10µF L = 2.2µH
100
Output Current(mA)
1000
80
Efficiency(%)
VIN = 2.5V
70
VOUT = 1.5V
Efficiency vs. Output Current
Efficiency vs. Output Current
100
Efficiency(%)
VIN = 3.6V
70
20
20
60
50
40
30
V IN = 5.5V
70
60
50
40
30
20
20
10
VOUT = 1.2V
1
10
100
V OUT = 1.2V
10
COUT = 10µF L = 2.2µH
Output Current(mA)
12
1000
Efficiency vs. Output Current
Efficiency vs. Output Current
0
100
Output Current(mA)
100
80
10
COUT = 10µF L = 2.2µH
1000
0
1
10
COUT = 10µF L = 2.2µH
100
1000
Output Current(mA)
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Characterization Curve
Reference Voltage vs. Temperature
Frequency vs. Temperature
0. 620
1.90
1.80
1.75
0. 610
1.70
1.65
Frequency(MHz)
Reference Voltage(V)
1.85
0. 615
0. 605
0. 600
0. 595
0. 590
1.55
1.50
1.45
1.40
1.35
1.30
VIN = 3.6V
1.25
1.20
VIN = 3.6V
0. 585
1.60
1.15
0. 580
-50
-25
0
+25
+50
O
+75
+100
1.10
+125
-50
-25
+0
Temperature( C)
1.90
1.65
1.89
1.60
1.88
1.55
1.87
1.50
1.45
1.40
1.35
1.30
1.25
VIN(V)
5. 0
1.82
1.81
1.80
1.77
0
5. 5
Current Limit(A)
Current Limit(A)
-10
+5
+20 +35 +50 +65 +80 +95 +110 +125
Temperature (oC)
Rev.A.03
200
300
400
500
600
700
800
900
1000
Current Limit vs. Temperature
VIN = 3.3V
VOUT = 1.2V
-25
100
Output Current(mA)
Current Limit vs. Temperature
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
-40
VOUT = 1.8V
VIN = 3.6V
1.83
1.78
4. 5
+125
1.84
1.79
4. 0
+100
1.85
1.15
3. 5
+75
1.86
1.20
3. 0
+50
Output Voltage vs. Output Current
Output Voltage(V)
Frequency(MHz)
Frequency vs. Supply Voltage
1.70
1.10
2. 5
+25
Temperature(OC)
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
-40
VIN = 3.6V
VOUT = 1.2V
-25
-10
+5
+20
+35 +50
+65 +80
Temperature (oC)
+95 +110 +125
13
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Characterization Curve
Current Limit(A)
Current Limit vs. Temperature
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
-40
Light Load Mode output voltage ripple
VIN = 5.0V
VOUT = 1.2V
-25
-10
+5
+20
+35 +50 +65 +80 +95 +110 +125
Temperature (oC)
VIN = 3.6V
VOUT = 1.2V
IOUT = 50mA
1) VSW= 2V/div
2) VOUT = 10mV/div
3) IL = 500mA/div
Heavy Load Mode Output Voltage Ripple
14
Load Step
VIN = 3.6V
VOUT = 1.2V
IOUT = 1A
VIN = 3.6V
VOUT = 1.8V
IOUT = 0A~1A~0A
1) VSW= 2V/div
2) VOUT = 10mV/div
3) IL = 500mA/div
1) VOUT= 100mV/div
2) IOUT = 500mA/div
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Characterization Curve
Load Step
VIN = 3.6V
VOUT = 1.8V
IOUT = 50mA~1A~50mA
VIN = 3.6V
VOUT = 1.8V
IOUT = 200mA~1A~200mA
1) VOUT= 100mV/div
2) IOUT = 500mA/div
1) VOUT= 100mV/div
2) IOUT = 500mA/div
Power On from EN
VOUT = 1.2V
IOUT = 1A
1) EN= 2V/div
2) VOUT = 500mV/div
3) IL = 1A/div
Rev.A.03
Load Step
Power Off from EN
VIN = 3.6V
VOUT = 1.8V
IOUT = 1A
1) EN = 2V/div
2) VOUT = 2V/div
3) IL = 500mA/div
15
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Tape and Reel Dimension
SOT-25
P0
W
AME
AME
PIN 1
P
Carrier Tape, Number of Components Per Reel and Reel Size
16
Package
Carrier Width (W)
Pitch (P)
Pitch (P0)
Part Per Full Reel
Reel Size
SOT-25
8.0±0.1 mm
4.0±0.1 mm
4.0±0.1 mm
3000pcs
180±1 mm
Rev. A.03
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253A
n Package Dimension
SOT-25
Top View
Side View
D
E
H
L
PIN 1
S1
e
b
A1
A
Front View
n Lead Pattern
SOT-25
2.40 BSC
1.00 BSC
0.70 BSC
0.95 BSC
0.95 BSC
1.90 BSC
Note:
1. Lead pattern unit description:
BSC: Basic. Represents theoretical exact dimension or dimension target.
2. Dimensions in Millimeters.
3. General tolerance +0.05mm unless otherwise specified.
Rev.A.03
17
www.ame.com.tw
E-Mail: sales@ame.com.tw
Life Support Policy:
These products of AME, Inc. are not authorized for use as critical components in life-support
devices or systems, without the express written approval of the president
of AME, Inc.
AME, Inc. reserves the right to make changes in the circuitry and specifications of its devices and
advises its customers to obtain the latest version of relevant information.
 AME, Inc. , August 2014
Document: 1283-DS5253A-A.03
Corporate Headquarter
AME, Inc.
2F, 302 Rui-Guang Road, Nei-Hu District
Taipei 114, Taiwan.
Tel: 886 2 2627-8687
Fax: 886 2 2659-2989