AME5284 4A, 300KHz ~ 1.4MHz Synchronous Rectified

AME
AME5284
n General Description
The AME5284 is a Synchronous Rectified Step-Down
Converter with internal power MOSFETs. It achieves 4A
continous output current over a wide switching frequency
range with excellent load and line regulation.
Current mode operation provides fast transient response
and eases of loop stabilization. Internal soft-start minimizes the inrush supply current at startup. The circuit
protection includes cycle-by cycle current limiting, output short circuit frequency protection and thermal shutdown.
This device is available in SOP-8/PP package with exposed pad for low thermal resistance.
n Features
l 4A Output Current
l 70mΩ/70mΩ Internal Power MOSFET Switch
l Stable with Low ESR Output Ceramic Capacit
-ors
l Up to 95% Efficiency
l Less than 10µA Shutdown Current
l Wide Switching Frequency Range from
300KHz~1.4MHz
l Thermal Shutdown
l Cycle by cycle Over Current Protection and
Hiccup
l Output Adjustable from 0.8V to VIN
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
n Applications
l TV
l Distributed Power Systems
l Pre-Regulator for Linear Regulators
n Typical Application
L1
1.5µH
IN
5V
CIN
10µF
C2
Optional
IN
SW
EN
OFF ON
AME5284
C1
680pF
R3
5.1K
COMP
GND
FB
FREQ
R1
12K
OUT
1.2V 4A
COUT
22µF
R2
24K
RFREQ
30K
l Short Circuit Frequency Protection
l Green Products Meet RoHS Standards
Rev. A.02
1
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Functional Block Diagram
IN
CURRENT
SENSE
EN
ENABLE
CURRENT
LIMIT
UVLO
FREQ
OSC
SW
SLOPE
+
+
COMP
-
GND
+
0.8V
VREF
SOFT
START
EA
-
LOGIC
+
2
-
0.9V
OVP
SW
PWM
OTP
FB
DRIVER
IRCMP
+
PGND
Rev. A.02
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Pin Configuration
SOP-8/PP
Top View
8
7
6
AME5284-AZAADJ
1. COMP
2. GND
3. EN
4. IN
5. SW
6. SW
7. FREQ
* Die Attach:
8. FB
Conductive Epoxy
5
AME5284
1
2
3
4
Note: Connect exposed pad (heat sink on the back) to GND.
n Pin Descriptiion
Pin Number Pin Name
Rev. A.02
Pin Description
Compensation Node. COMP is used to compensate the regulation control
loop. Connect a series RC network from COMP to GND to compensate the
regulation control loop. In some cases, an additional capacitor from COMP
to GND is required.
1
COMP
2
GND
3
EN
Enable. Internal pull high with a resistor. Pull EN below 0.6V to shut down
the regulator.
4
IN
Power Input. IN supplies the power to the IC, as well as the step-down
converter switches. Bypass IN to GND with a suitable large capacitor to
eliminate noise on the input to the IC.
5, 6
SW
7
FREQ
8
FB
Ground. Connect the exposed pad to GND.
Power Switching Output. SW is the switching node that supplies power to
the output. Connect the output LC filter from SW to the output load. Note
that a capacitor is required from SW to BS to power the high-side switch.
Frequency Adjust Pin. Add a resistor from this pin to ground determines the
switching frequency.
Feedback Input. FB senses the output voltage to regulate that voltage.
Drive FB with a resistive voltage divider from the output voltage. The
feedback reference voltage is 0.8V.
3
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Ordering Information
AME5284 - x x x xxx
Output Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
A
(SOP-8/PP)
4
1.
2.
3.
4.
5.
6.
7.
8.
COMP
GND
EN
IN
SW
SW
FREQ
FB
Package
Type
Z: SOP/PP
Number of
Pins
A: 8
Output Voltage
ADJ: Adjustable
Rev. A.02
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Absolute Maximum Ratings
Parameter
Maximum
Unit
Supply Voltage
-0.3V to +6V
V
Switch voltage
-0.7V to VIN+0.7V
V
EN, FB, COMP, FREQ to GND
-0.3V to VIN+0.3V
V
HBM
2
kV
MM
200
V
Symbol
Rating
Unit
Ambient Temperature Range
TA
-40 to +85
Junction Temperature Range
TJ
-40 to +125
Storage Temperature Range
TSTG
-65 to +150
ESD Classification
n Recommended Operating Conditions
Parameter
o
C
n Thermal Information
Parameter
Package
Die Attach
Thermal Resistance*
(Junction to Case)
Thermal Resistance
(Junction to Ambient)
Symbol Maximum
θJ C
Unit
15
o
SOP-8/PP
Internal Power Dissipation
Conductive Epoxy
θJA
75
PD
1.333
C/W
mW
Maximum Junction Temperature
150
o
C
Lead Temperature (soldering 10 sec)**
260
o
C
* Measure θJC on backside center of Exposed Pad.
** MIL-STD-202G 210F
Rev. A.02
5
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Electrical Specifications
VIN=5V, TA=25oC, unless otherwise noted.
Parameter
Symbol
Test Condition
Min
Input Voltage Range
3
Input UVLO
2
VEN=5V
Quiescent Current
(No Switching)
Shutdown Current
ISHDN
Feedback Voltage
VFB
0.784
Feedback Current
IFB
-50
VEN=0V
Typ
2.3
Units
5.5
V
2.6
V
450
µA
10
µA
0.8
0.816
V
50
nA
Load Regulation
0A<IOUT<4A
0.25
%
Line Regulation
3.3V<VIN<5.5V
0.25
%/V
EN Voltage High
EN Voltage Low
EN Leakage Current
Switching Frequency
Short-Circuit Frequency
1.5
VEN
IENLK
FSW
V
0.4
V
VEN=3V
4
µA
RFREQ=NC
300
KHz
RFREQ=120KΩ
600
KHz
RFREQ=47KΩ
1
MHz
RFREQ=30KΩ
1.4
MHz
0.25
FSW
8.5
A
-2
A
FSWSC
High-side Switch Current Limit
6
Low-side Switch Current Limit
Maximum Duty Cycle
100
Minimum On Time
%
100
ns
Error Amp Voltage Gain
AEA
600
V/V
Error Amp Tranconductance
GEA
390
µA/V
Switch Leakage Current
ISWLK
0.1
µA
VSW=0V, VEN=0V
High-side Switch On Resistance
RDSON,HI
70
mΩ
Low-side Switch On Resistance
RDSON,LO
70
mΩ
Thermal Shutdown Protection
6
Max
OTP
OTH
Rising
Hysteresis
170
o
C
20
o
C
Rev. A.02
AME
AME5284
n Detailed Description
Normal Operation
The AME5284 uses a user adjustable frequency, current mode step-down architecture with internal MOSFET
switch. During normal operation, the internal high-side
(PMOS) switch is turned on each cycle when the oscillator sets the SR latch, and turned off when the comparator resets the SR latch. The peak inductor current at
which comparator resets the SR latch is controlled by
the output of error amplifier EA. While the high-side switch
is off, the low-side switch turns on until either the lowside current limit reached or the beginning of the next
switching cycle.
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
Short Circuit Protection
When the output is shorted to ground, the frequency of
the oscillator is reduced to about 1/4 of the normal frequency to ensure that the inductor current has more time
to decay, thereby preventing runaway. Meanwhile,
AME5284 enters hiccup mode, the average short circuit
current is greatly reduced to alleviate the thermal issue
and to protect the regulator.
Dropout Operation
The output voltage is dropped from the input supply for
the voltage which across the high-side switch. 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 high-side switch to remain on for more
than one cycle until it reaches 100% duty cycle.
Soft-Start
The AME5284 employs internal soft-start circuitry to
reduce supply inrush current during startup conditions.
Over Temperature Protection
The In most applications the AME5284 does not dissipate much heat due to high efficiency. But, in applications where the AME5284 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 170oC, the internal high-side power switch will be turned off and the SW
switch will become high impedance.
Rev. A.02
7
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Application Information
Inductor Selection
For most applications, the value of the inductor will fall
in the range of 2.2µH to 4.7µH. Its value is chosen based
on the desired ripple current. Large value inductors lower
ripple current and small value inductors result in higher
ripple currents. Higher VIN or VOUT also increase the ripple
current ∆IL:
1
V
VOUT 1 − OUT
∆I L =
f ×L
VIN
A reasonable inductor current ripple is usually set as
1/3 to 1/5 of maximum out current. 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 DCR inductor.
Capacitor Selection
In continuous mode, the source current of the top
MOSFET is a square wave of duty cycle VOUT/VIN. To
prevent large voltage transients, a low ESR input capacitor sized for maximum RMS current must be used. The
maximum RMS capacitor current is given by:
CIN requires IRMS
≅ I OMAX
VOUT (V IN − VOUT )
VIN
For a fixed output voltage, the output ripple is highest
at maximum input voltage since ∆IL increases with input
voltage.
When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage characteristics of all the ceramics for given value and size.
Output Voltage Programming
The output voltage of the AME5284 is set by a resistive
divider according to the following formula:
V OUT = 0 .8 × 1 +
R1
Volt .
R2
Some standard value of R1, R2 for most commonly used
output voltage values are listed in Table 1.
VOUT(V)
R1(KΩ )
R2(KΩ )
1.1
7.5
20
1.2
10
20
1.5
17.4
20
1.8
30
24
2.5
51
24
3.3
75
24
This formula has a maximum at VIN=2VOUT, where
IRMS=IOUT/2. For simplification, use an input capacitor with
a RMS current rating greater than half of the maximum
load current.
The selection of COUT is driven by the required effective
series resistance (ESR). Typically, once the ESR requirement for COUT has been met, the RMS current rating
generally far exceeds the IRIPPLE(P-P) requirement. The
output ripple ∆VOUT is determined by:
∆VOUT ≅ ∆I L ESR +
8
1
8 fCOUT
Rev. A.02
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
where GEA is the error amplifier transconductance
Loop Compensation
The AME5284 employs peak current mode control for
easy use and fast transient response. Peak current mode
control eliminates the double pole effect of the output LC filter. It greatly simplifies the compensation loop design.
With peak current mode control, the buck power stage
can be simplified to be a one-pole and one-zero system
in frequency domain. The pole can be calculated by:
f P1 =
1
2π × C OUT × R L
The zero is a ESR zero due to output capacitor and its
ESR. It can be calculated by:
f Z1 =
1
2π × C OUT × ESRCOUT
The compensation design is to shape the converter close
loop transfer function to get desired gain and phase. For
most cases, a series capacitor and resistor network connected to the COMP pin sets the pole-zero and is adequate for a stable high-bandwidth control loop.
In the AME5284, FB pin and COMP pin are the inverting
input and the output of internal transconductance error
amplifier (EA). A series RC and CC compensation network connected to COMP pin provides one pole and one
zero:
for RC<<AEA/GEA
1
2π × CC × RC +
fZ2 =
Rev. A.02
1
2 π × C C × RC
AEA
G EA
RC is the compensation resistor
CC is the compensation capacitor
The desired crossover frequency fC of the system is defined to be the frequency where the control loop has unity
gain. It is also called the bandwidth of the converter. In
general, a higher bandwidth means faster response to
load transient. However, the bandwidth should not be too
high because of system stability concern. When designing the compensation loop, converter stability under
all line and load condition must be considered. Usually,
it is recommended to set the bandwidth to be less than
1/10 of switching frequency. Using selected crossover
frequency, fC, to calculate RC:
RC = f C ×
Where COUT is the output capacitor, RL is load resistance; ESRCOUT is the equivalent series resistance of
output capacitor.
f P2 =
AEA is the error amplifier voltage gain
≈
GEA
2π × CC × AEA
VOUT 2π × COUT
×
VFB GEA × GCS
where GCS is the current sense circuit transconductance.
The compensation capacitor CC and resistor RC together
make zero. This zero is put somewhere close to the
pole fP1 of selected frequency. CC is selected by:
CC =
COUT × RL
RC
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to (∆ILOAD¡ÑESR), where ESR is the effective series resistance of COUT. ∆ILOAD also begins to charge or
discharge COUT, which generates a feedback error signal.
The regulator loop then acts to return VOUT to its steadystate value. During this recovery time VOUT can be monitored for overshoot or ringing that would indicate a stability problem.
9
AME
AME5284
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
Efficiency Considerations
Although all dissipative elements in the circuit produce
losses, one major source usually account for most of the
losses in AME5284 circuits: I2R losses. The I2R loss
dominates the efficiency loss at medium to high load
currents.
The I2R losses are calculated from the resistances of
the internal switches, RSW, and external inductor RL. In
continuous mode, the average output current flowing
through inductor L is "chopped" between the main switch
and the synchronous switch. Thus the series resistance
looking into the SW pin is a function of both top and
bottom MOSFET RDS(ON) and the duty cycle (D) as follows:
RSW = (RDS(ON)TOP)(D) + (RDS(ON)BOTTOM)(1-D)
The RDS(ON) for both the top and bottom MOSFETs can
be obtained from Electrical Characteristics table. Thus,
to obtained I2R losses, simply add RSW to RL and multiply the result by the square of the average output current.
Other losses including CIN and COUT ESR dissipative
losses and inductor core losses generally account for
less than 2% total additional loss.
Thermal Considerations
In most application the AME5284 does not dissipate
much heat due to its high efficiency. But, in applications
where the AME5284 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 170oC, both power
switches will be turned off and the SW switch will become high impedance.
10
Rev. A.02
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Typical Operating Circuit
VIN
3V to 5V
1
3
CIN
10µF
Chip Enable
4
C2
C1
Optional
R3
SW
IN
VOUT
EN
R1
AME5284
COMP
FB
FREQ
2
L
5,6
GND
GND
COUT
8
7
RFREQ
9 (Exposed pad)
R2
V OUT(V)
CIN (µF)
R1(K Ω R2(KΩ R3(KΩ C1pF
L(µH)
COUTµF
3.3
10
75
24
25
680
2.2
22
2.5
10
51
24
20
680
2.2
22
1.8
10
30
24
15
680
1.5
22
1.5
10
21
24
13
680
1.5
22
1.2
10
12
24
11
680
1.5
22
1.1
10
6
24
8.2
680
1.5
22
Table 1. Recommended Components Selectin for fsw = 1.4MHz
The ground area must provide adequate heat
dissipating area to the thermal pad andusing
multiple vias to help thermal dissipation.
R3
Connect the
FB pin directly
to feedback
R2 resistors.
C1
8
COMP 1
GND
FB
7 FREQ
2
GND
EN
3
6
SW
VIN
4
5
SW
R1
V OUT
GND
R FREQ
SW
V IN
SW pad should be
connected together to
Inductor by wide and short
trace, keep sensitive
components away from
this trace.
L1
C IN must be placed
between V IN and
GND as close as
CIN
possible
Place the input and output
capacitors as close to the
IC as possible
C OUT
V OUT
Figure 3. AME5284 Regulators Layout Diagram
Rev. A.02
11
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Characterization Curve
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
VOUT=3.3V
80
Efficiency (%)
Efficiency (%)
80
70
60
50
40
30
VIN =5V
RFREQ= 30K
20
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
30
0
4.0
VIN =5V
RFREQ= 30K
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Output Current (A)
Efficiency vs. Output Current
Efficiency vs. Output Current
4. 0
100
90
V OUT=3.3V
80
Efficiency (%)
80
Efficiency (%)
40
Output Current (A)
90
70
60
50
40
30
VIN =5V
RFREQ =NC
20
V OUT=1V
70
60
50
40
30
VIN =5V
R FREQ=NC
20
10
10
0
0.5
1.0
1. 5
2. 0
2. 5
3.0
Output Current (A)
12
50
10
100
0
60
20
10
0
VOUT=1V
70
3.5
4.0
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Output Current (A)
Rev. A.02
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Characterization Curve (Contd.)
Load Step
Load Step
µSec/Div)
Time (100µ
µSec/Div)
Time (100µ
VIN = 5V
VOUT = 3.3V
IOUT = 1mA to 4A
R
= 30K
VIN = 5V
VOUT = 1V
IOUT = 1mA to 4A
R
= 30K
1) VOUT = 100mV/Div
2) IL = 2A/Div
1) VOUT = 50mV/Div
2) IL = 2A/Div
FREQ
Power ON from EN
Power ON form VIN
Time (2.0ms/Div)
Time (5.0ms/Div)
VIN = 5V
VOUT = 3.3V
R
= NC
FREQ
1) VEN = 2V/Div
2) VOUT = 2V/Div
3) IL = 4A/Div
Rev. A.02
FREQ
VIN = 5V
VOUT = 3.3V
R
= NC
FREQ
1) VIN = 2V/Div
2) VOUT = 2V/Div
3) IL = 4A/Div
13
AME
AME5284
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
n Characterization Curve (Contd.)
Power Off from EN
Power Off from VIN
Time (5.0ms/Div)
Time (5.0ms/Div)
VIN = 5V
VOUT = 3.3V
= NC
R
VIN = 5V
VOUT = 3.3V
R
= NC
1) VEN = 2V/Div
2) VOUT = 2V/Div
3) IL = 4A/Div
1) VIN = 2V/Div
2) VOUT = 2V/Div
3) IL = 4A/Div
FREQ
FREQ
Short Circuit Test
Quiescent Current vs. Input Voltage
µA)
Quiescent Current (µ
490
480
470
460
450
440
430
420
410
VOUT=3.3V
RFREQ =NC
400
390
380
3.5
Time (100ms/Div)
4.0
4.5
5.0
Input Voltage (V)
VIN = 5V
VOUT = 3.3V
R
= NC
FREQ
1) VIN = 5V/Div
2) VOUT = 2V/Div
3) IL = 4A/Div
14
Rev. A.02
AME
4A, 300KHz ~ 1.4MHz Synchronous
Rectified Step-Down Converter
AME5284
n Tape and Reel Dimension
SOP-8/PP
P
PIN 1
W
AME
AME
Carrier Tape, Number of Components Per Reel and Reel Size
Pa c ka ge
C arrier W id th (W )
P itc h (P)
Pa rt P er Fu ll Re e l
R ee l Size
SO P- 8/PP
1 2.0 ±0 .1 m m
4.0±0 .1 m m
2 50 0p cs
33 0 ±1 m m
n Package Dimension
SOP-8/PP
TOP VIEW
SIDE VIEW
D1
θ
SYMBOLS
E1
E2
E
L1
C
PIN 1
D
e
Rev. A.02
A1
FRONT VIEW
A
A2
b
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
1.350
1.750
0.053
0.069
A1
0.000
0.250
0.000
0.010
A2
1.250
1.650
0.049
0.065
C
0.100
0.250
0.004
0.010
E
3.750
4.150
0.148
0.163
E1
5.700
6.300
0.224
0.248
L1
0.300
1.270
0.012
0.050
b
0.310
0.510
0.012
0.020
D
4.720
5.120
0.186
0.202
1.270 BSC
e
0.050 BSC
θ
0
E2
1.940
2.600
0.076
0.102
D1
1.940
3.500
0.076
0.138
o
8
o
0
o
8o
15
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. , July 2013
Document: A005-DS5284-A.02
Corporate Headquarter
AME, Inc.
8F, 12, WenHu St., Nei-Hu
Taipei 114, Taiwan .
Tel: 886 2 2627-8687
Fax: 886 2 2659-2989