AME5253 1A, 1.5MHz Synchronous Step-Down Converter

AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n General Description
The AME5253 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,
the AME5253 is ideally suited for single Li-Ion battery
powered applications. 100% duty cycle provides low
dropout operation, extending battery life in portable systems. Under light load conditions, the AME5253 operates in a power saving mode that consumes just around
20µA of supply current, maximizing battery life in portable applications.
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 AME5253 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
VOUT
SW
AME5253
EN
GND
CFWD
R1
150K
FB
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
l
l
l
l
l
l
l
Rev.A.04
High Efficiency: Up to 95%
Very Low 20µA Quiescent Current
High efficiency in light load condition
2.5V to 5.5V Input Range
Adjustable Output From 0.6V to VIN
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
1
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Function Block Diagram
Constant
Off-time
Mode
Select
Slope
COMP
VIN
IN
3
PWM
COMP
FB
6
0.6V
0.6V
VREF
SW
LOGIC
4
0.55V
UVDET
Soft
Start
EN
2
NMOS
COMP
IRCOMP
OSC
GND
5
Figure 2. Founction Block Diagram
2
Rev. A.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Pin Configuration
SOT-25
Top View
5
AME5253-AEVADJ
1. EN
2. GND
3. SW
4. IN
5. FB
4
AME5253
1
2
3
Die Attach:
Conductive Epoxy
n Pin Description
Pin Number
Pin Name
Pin Description
1
EN
No connection. Not internally connected. Can left floating or connected
to GND.
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.04
3
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Ordering Information
AME5253 - x x x xxx
Output Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
Package Type
Number of Pins
1. EN
2. GND
3. SW
4. IN
5. FB
E: SOT-2X
V: 5
A
(SOT-25)
4
Output Voltage
ADJ: Adjustable
Rev. A.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Absolute Maximum Ratings
Parameter
Symbol
Maximum
VIN
-0.3 to 6.5
VEN, VOUT
-0.3 to VIN
VSW
-0.3 to VIN
Input Supply Voltage
EN, VOUT 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
VIN
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
θJ C
81
Unit
o
SOT-25
Internal Power Dissipation
Solder Iron (10Sec)**
Conductive Epoxy
θJA
260
PD
400
350
C/W
mW
o
C
* Measure θJC on backside center of Exposed Pad.
** MIL-STD-202G 210F
Rev.A.04
5
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
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
20
35
µA
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.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Detailed Description
Main Control Loop
AME5253 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.
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.
n Application Information
The basic AME5253 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.
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
V IN
VIN
−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.
Rev.A.04
7
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
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 +
1
8 fCOUT
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
Thermal Considerations
In most applications the AME5253 does not dissipate
much heat due to its high efficiency. But, in applications
where the AME5253 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 AME5253 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.
The output voltage is set by an external resistive divider
according to the following equation:
VOUT = V REF × 1 +
R1
R2
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 3.
0.6V ≤ V OUT ≤ 5.5V
R1
FB
AME5253
R2
GND
Figure 3. Setting the AME 5253 Output Voltage
8
Rev. A.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
VIN
2.5V to 5.5V
2.2µH
IN
SW
AME5253
EN
FB
GND
CIN
4.7µF
CER
VOUT
1.2V
V IN
2.7V to 5.5V
C OUT
10µF
CER
C FWD
IN
SW
AME5253
EN
FB
GND
CIN
4.7µF
CER
SW
EN
CIN
4.7µF
CER
FB
GND
IN
SW
FB
GND
V OUT
3.3V
C FWD
AME5253
CIN
4.7µF
CER
C OUT
10µF
CER
150K
33.3K
Figure 8: 3.3V Step-Down Regulator
C FWD: 22pF~220pF
VOUT
1.6V
C FWD
AME5253
150K
2.2µH
EN
Figure 5: 1.5V Step-Down Regulator
C FWD: 22pF~220pF
IN
FB
47.3K
V IN
3.6V to 5.5V
C OUT
10µF
CER
150K
2.2µH
C OUT
10µF
CER
Figure 7: 2.5V Step-Down Regulator
CFWD : 22pF~220pF
VOUT
1.5V
C FWD
V OUT
2.5V
CFWD
GND
CIN
4.7µF
CER
100 K
VIN
2.5V to 5.5V
SW
AME5253
Figure 4: 1.2V Step-Down Regulator
C FWD: 22pF~220pF
2.2µH
IN
EN
150K
150 K
VIN
3.3V to 5.5V
2.2µH
C OUT
10µF
CER
150K
90K
Figure 6: 1.6V Step-Down Regulator
C FWD: 22pF~220pF
Rev.A.04
9
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
PC Board Layout Checklist
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the
AME5253. 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.
VIN
L1
IN
SW
C FWD
AME5253
EN
CIN
FB
GND
C OUT
R2
R1
CFWD : 22pF~220 pF
10
VOUT
Figure 9: AME5253 Adjustable Voltage
Regulator Layout Diagram
Rev. A.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
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.04
11
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Characterization Curve
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
Efficiency(%)
Efficiency(%)
90
VIN = 2.7V
90
80
70
60
80
70
60
50
50
VOUT = 2.5V
40
0.1
VIN = 3.6V
1
COUT = 10µF L = 2.2µH
10
100
VOUT = 2.5V
40
0.1
1000
1
COUT = 10µF L = 2.2µH
10
100
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
Efficiency(%)
VIN = 2.7V
Efficiency(%)
80
70
60
50
VOUT = 1.5V
40
0.1
1
10
100
VIN = 3.6V
80
70
60
50
COUT = 10µF L = 2.2µH
VOUT = 1.5V
40
0.1
1000
Output Current(mA)
1
COUT = 10µF L = 2.2µH
10
100
Efficiency vs. Output Current
100
100
VIN = 2.5V
Efficiency(%)
Efficiency(%)
VIN = 5.5V
90
90
80
70
60
80
70
60
50
50
VOUT = 1.2V
12
1000
Output Current(mA)
Efficiency vs. Output Current
40
0.1
1000
Output Current(mA)
Output Current(mA)
1
VOUT = 1.2V
COUT = 10µF L = 2.2µH
10
100
Output Current(mA)
1000
40
0.1
1
COUT = 10µF L = 2.2µH
10
100
1000
Output Current(mA)
Rev. A.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Characterization Curve (Contd.)
Reference Voltage vs. Temperature
Frequency vs. Temperature
1.70
0.620
1.65
1.60
0.610
Frequency(MHz)
Reference Voltage(V)
0.615
0.605
0.600
0.595
0.590
0.585
-25
0
+25
+50
+75
+100
1.50
1.45
1.40
1.35
1.30
1.25
1.20
VIN = 3.6V
VIN = 3.6V
1.15
1.10
+125
-50
+50
+75
+100
Output Voltage vs. Output Current
1.90
1.89
1.60
1.88
1.55
1.87
1.50
1.45
1.40
1.35
1.30
1.25
1.20
+125
VOUT = 1.8V
VIN = 3.6V
1.86
1.85
1.84
1.83
1.82
1.81
1.80
1.79
1.15
1.78
1.10
2.5
3.0
3.5
4.0
VIN(V)
4.5
5.0
5.5
1.77
100
Current Limit(A)
-10
+5
300
400
500
600
700
800
900
1000
Current Limit vs. Temperature
VIN = 3.3V
VOUT = 1.2V
-25
200
Output Current(mA)
Current Limit vs. Temperature
Current Limit(A)
+25
Frequency vs. Supply Voltage
1.65
+20 +35 +50 +65 +80 +95 +110 +125
Temperature (oC)
Rev.A.04
0
Temperature (oC)
1.70
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
-25
Temperature (oC)
Output Voltage(V)
Frequency(MHz)
0.580
-50
1.55
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
AME5253
n Characterization Curve (Contd.)
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
o
Temperature ( C)
VIN = 3.6V
VOUT = 1.8V
IOUT = 50mA
1) VSW= 5V/div
2) VOUT = 100mV/div
3) IL = 200mA/div
Power Off from EN
14
Load Step
VIN = 3.6V
VOUT = 1.8V
IOUT = 1A
VIN = 3.6V
VOUT = 1.8V
IOUT = 0A~1A~0A
1) EN = 2V/div
2) VOUT = 2V/div
3) IL = 500mA/div
1) VOUT= 100mV/div
2) IOUT = 500mA/div
Rev. A.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Characterization Curve (Contd.)
Load Step
Load Step
VIN = 3.6V
VOUT = 1.8V
IOUT = 50mA~1A~50mA
VIN = 3.6V
VOUT = 1.8V
IOUT = 100mA~1A~100mA
1) VOUT= 100mV/div
2) IOUT = 500mA/div
1) VOUT= 100mV/div
2) IOUT = 500mA/div
Load Step
Rev.A.04
Power On from EN
VIN = 3.6V
VOUT = 1.8V
IOUT = 200mA~1A~200mA
VOUT = 1.2V
IOUT = 1A
1) VOUT= 100mV/div
2) IOUT = 500mA/div
1) EN= 2V/div
2) VOUT = 500mV/div
3) IL = 1A/div
15
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Date Code Rule
Month Code
1: January 7: July
2: February 8: August
3: March
9: September
4: April
A: October
5: May
B: November
6: June
C: December
Marking
A
M
X
X
Year
xxx0
M
X
X
xxx1
A
M
X
X
xxx2
A
A
M
X
X
xxx3
A
A
A
M
X
X
xxx4
A
A
A
M
X
X
xxx5
A
A
A
M
X
X
xxx6
A
A
A
M
X
X
xxx7
A
A
A
M
X
X
xxx8
A
A
A
M
X
X
xxx9
A
A
A
A
A
A
A
A
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.04
AME
1A, 1.5MHz Synchronous
Step-Down Converter
AME5253
n Package Dimension
SOT-25
Top View
Side View
D
E
H
L
PIN 1
S1
e
A1
A
Front View
b
2.40 BSC
1.00 BSC
0.70 BSC
0.95 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.
0.95 BSC
1.90 BSC
Rev.A.04
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-DS5253-A.04
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