AME5251 Dual 1A, 1.5MHz Synchronous Step-Down

AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n General Description
n Features
The AME5251 is a high efficiency monolithic synchronous dual buck regulator using a constant frequency, current mode architecture. Capable of delivering 1A output
cur-rent each channel over a wide input voltage range from
2.5V to 5.5V, the AME5251 is ideally suited for single LiIon battery powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. Under light load conditions, the AME5251
operates in a power saving mode that consumes just
around 20µA of supply current, maximizing battery life in
portable applications.
l High Efficiency: Up to 95%
l Very Low 20µA Quiescent Current
l
l
l
l
l
l
High Efficiency in Light Load Condition
2.5V to 5.5V Input Range
Adjustable Output From 0.6V to VIN
Adjustable Output Voltage
1A Output Current Per Channel
Low Dropout Operation: 100% Duty Cycle
l No Schottky Diode Required
l 1.5MHz Constant Frequency PWM Opera
tion
l Small DFN-12A Packages
l Green Products Meet RoHS Standard
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 AME5251 is available
in small DFN-12A packages.
n Applications
l
l
l
l
l
Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection.
Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
MPS Players
Portable Instruments
n Typical Application
COUT2
VOUT2
L2
ON
AME5251
VIN1
CIN2
R2
C1
R1
OFF
IN2
EN2
SW2
NC2
GND
FB2
FB1
GND
NC1
SW1
EN1
IN1
ON
VOUT1
OFF
R3
CIN1
C2
R4
VIN1
L1
COUT1
Rev.A.05
1
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Function Block Diagram
Constant
Off-time
Mode
Select
Slope
COMP
VIN
7 IN1
PWM
COMP
FB1 4
0.6V
0.6V
VREF
LOGIC
8 SW1
0.55V
UVDET
NMOS
COMP
Soft
Start
EN1 6
IRCOMP
OSC
9 GND
Constant
Off-time
Mode
Select
Slope
COMP
VIN
1 IN2
PWM
COMP
FB2 10
0.6V
0.6V
VREF
LOGIC
2 SW2
0.55V
UVDET
Soft
Start
EN2 12
OSC
NMOS
COMP
IRCOMP
3 GND
2
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Pin Configuration
DFN-12A
(3mmx3mmx0.75mm)
Top View
12
11
10
9
8
7
AME5251
1
2
3
4
5
6
AME5251-AVCxxxxxx
1. IN2
2. SW2
3. GND
4. FB1
5. NC1
6. EN1
7. IN1
8. SW1
9. GND
10. FB2
11. NC2
12. EN2
* Die Attach:
Conductive Epoxy
Note:
Connect exposed pad (heat sink on the back) to GND.
n Pin Description
Pin Name
NC
No connection. Not internally connected. Can left floating or connected to GND.
EN
Enable Control Input, active high.
IN
Input Supply Voltage Pin.
Bypass this pin with a capacitor as close to the device as possible.
SW
Switch Node Connection to Inductor.
GND
Ground. Tie directly to ground plane.
FB
Rev.A.05
Pin Description
Output voltage Feedback input.
3
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Ordering Information
AME5251 - x x x xxx xxx
Output Voltage 2
Output Voltage 1
Number of Pins
Package Type
Pin Configuration & Special Feature
Pin Configuration &
Special Feature
A
(DFN-12A)
4
1 IN2
2. SW2
3. GND
4. FB1
5. NC1
6. EN1
7. IN1
8. SW1
9. GND
10. FB2
11. NC2
12. EN2
Package
Type
V: DFN
Number of
Pins
C: 12
Output
Voltage1
ADJ: Adjustable
Output
Voltage2
ADJ: Adjustable
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Available Opetions
Part Number
Marking*
Output Voltage
AME5251-AVCADJADJ
A5251
CBLMXX
VOUT1=ADJ
VOUT2=ADJ
Package
Operating Ambient
Temperature Range
DFN-12A
-40oC to +85oC
Note:
1. The first 3 places represent product code. It is assigned by AME such as CBL .
2. A bar on top of first letter represents Green Part such as A5251.
3. The last 3 places MXX represent Marking Code. It contains M as date code in "month", XX as LN code and
that is for AME internal use only. Please refer to date code rule section for detail information.
4. Please consult AME sales office or authorized Rep./Distributor for the availability of output voltage and package
type.
n Absolute Maximum Ratings
Parameter
Input Supply Voltage
EN, VOUT Voltage
SW Voltage
ESD Classification
Symbol
Maximum
V IN
-0.3 to 6.5
V EN , VOUT
-0.3 to VIN
VSW
-0.3 to VIN
Unit
V
B*
Caution: Stress above the listed absolute maximum rating may cause permanent damage to the device.
* HBM B: 2000V~3999V
Rev.A.05
5
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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
θJC
8.5
Unit
o
DFN-12A
Internal Power Dissipation
Solder Iron (10Sec)**
Conductive Epoxy
C/W
θJA
65
PD
1.54
W
350
o
C
* Measure θJC on backside center of Exposed Pad.
** MIL-STD-202G 210F
6
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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
Symbol
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
For Adjustable OutputVoltage
0.588
0.612
V
Feedback Pin Bias Current
IFB
VFB=VIN
-50
50
nΑ
Quiescent Current
(For Adjustable Output Voltage)
IQ
IOUT=0mA, VFB=1V
20
40
µA
Shutdown Current
ISHDN
VEN =GND
0.1
1
µA
Switch Frequency
fOSC
1.5
1.8
MHz
1.2
0.6
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
V
0.4
1.8
V
0.1
V
o
160
Shutdown, temperature increasing
C
100
EN=0V, V IN =5.0V
VSW =0V or 5.0V
-1
V
%
1
µA
Note 1. Spec. for per channel
Rev.A.05
7
AME
AME5251
n Detailed Description
Main Control Loop
AME5251 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 abole 0V.
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
n Application Information
The basic AME5251 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 Selecton
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.
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.
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
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.
8
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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.
Thermal Considerations
In most applications the AME5251 does not dissipate
much heat due to its high efficiency. But, in applications
where the AME5251 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 AME5251 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.
Output Voltage Programming
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 1.
0.6V V OUT
5.5V
R1
FB
AME5251
R2
GND
Figure 1: Setting the AME5251 Output Voltage
Rev.A.05
9
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
VIN
2.5V to 5.5V
2.2µH
IN
SW
AME5251
EN
FB
GND
CIN
4.7µF
CER
2.2µH
VOUT 1.2V
IN
CFWD
AME5251
COUT
10µF
CER
150K
SW
GND
CIN
4.7µF
CER
150K
FB
EN
VOUT 2.5V
CFWD
COUT
10µF
CER
150K
47.3K
Figure 2: 1.2V Step-Down Regulator
Figure 5: 2.5V Step-Down Regulator
CFWD: 22pF~220pF
CFWD: 22pF~220pF
VIN
3.3 to 5.5V
2.2µH
IN
SW
AME5251
EN
FB
GND
CIN
4.7µF
CER
VOUT 1.5V
VIN
3.6 to 5.5V
CFWD
2.2µH
IN
SW
AME5251
EN
150K
CIN
4.7µF
CER
100K
FB
GND
VOUT 3.3V
CFWD
150K
33.3K
Figure 3: 1.5V Step-Down Regulator
Figure 6: 3.3V Step-Down Regulator
CFWD: 22pF~220pF
CFWD: 22pF~220pF
VIN
2.5 to 5.5V
2.2µH
IN
SW
AME5251
EN
CIN
4.7µF
CER
FB
GND
COUT
10µF
CER
VOUT 1.6V
CFWD
150K
COUT
10µF
CER
90K
Figure 4: 1.6V Step-Down Regulator
CFWD: 22pF~220pF
10
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
PCB Board Layout Check List
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the
AME5251. 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
AME5251
CIN
VOUT
SW
IN
EN
C1
R1
COUT
FB
VIN
CIN
L1
VOUT
SW
IN
AME5251
EN
OUT
COUT
NC
GND
Figure 7
Rev.A.05
R2
NC
GND
Figure 8
11
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Application Information
External components selection
Supplier
Inductance
(µ
µF)
Current Rating
(mA)
DCR
(mΩ
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
12
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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
Rev.A.05
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)
13
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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
+125
Output Voltage vs. Output Current
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
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
1.20
+20 +35 +50 +65 +80 +95 +110 +125
Temperature (oC)
14
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
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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
Rev.A.05
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
15
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Characterization Curve (Contd.)
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
16
Load Step
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
Rev. A.05
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
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
DFN-12A
(3mmx3mmx0.75mm)
P
PIN 1
W
AME
AME
Carrier Tape, Number of Components Per Reel and Reel Size
Rev.A.05
Package
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
DFN-12A
(3x3x0.75mm)
12.0±0.1 mm
4.0±0.1 mm
5000pcs
330±1 mm
17
AME
Dual 1A, 1.5MHz Synchronous
Step-Down Converter
AME5251
n Package Dimension
DFN-12A
(3mmx3mmx0.75mm)
e
D
L
k
E1
E
D1
PIN 1 IDENTIFICATION
b
TOP VIEW
P IN 1
BOTTOM VIEW
A1
A3
A
REAR VIEW
SYMBOLS
INCHES
MIN
MAX
MIN
MAX
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.203REF.
0.008REF.
D
2.924
3.076
0.115
0.121
E
2.924
3.076
0.115
0.121
D1
2.450
2.650
0.096
0.104
E1
1.500
1.700
0.059
0.067
k
b
e
L
18
MILLIMETERS
0.200MIN.
0.150
0.250
0.450TYP.
0.324
0.476
0.008MIN
0.006
0.010
0.018TYP.
0.013
0.019
Rev. A.05
www.ame.com.tw
E-Mail: [email protected]
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. , January 2014
Document: 1283-DS5251-A.05
Corporate Headquarter
AME, Inc.
8F, 12, WenHu St., Nei-Hu
Taipei 114, Taiwan.
Tel: 886 2 2627-8687
Fax: 886 2 2659-2989