AMS AMS2576 3.3v, 5v, 12vand adjustable version Datasheet

3A Step-Down Voltage Regulator
AMS2576
GENERAL DESCRIPTION
FEATURES
The AMS2576 Series are step-down switching
regulators with all required active functions. It is
capable of driving 3A load with excellent line and
load regulations. These devices are available in
fixed output voltages of 3.3V, 5V, 12V and an
adjustable output version.
‹
3.3V, 5V, 12Vand adjustable versions
‹
Wide input voltage range, up to 40V
‹
Internal oscillator of 52KHz fixed frequency
‹
Guaranteed 3A output current
‹
Wide adjust version output voltage range
from 1.23V to 37V ±4% max. at over line and
The AMS2576 series offers a high-efficiency
replacement for popular three-terminal linear
regulators. Also it requires a minimum number of
external components. It substantially not only
reduces the area of board size but also the size of
heat sink, and in some cases no heat sink is
required. The ±4% tolerance on output voltage
within specified input voltages and output load
conditions is guaranteed. Also, the oscillator
frequency accuracy is within ±10%. External
shutdown is included. Featuring 80µA (typical)
standby current. The output switch includes
cycle-by-cycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
load conditions
‹
Low standby current, typ. 80µA, at shutdown
mode
‹
Requires only 4 external components
‹
Thermal shutdown and current limit
protection
APPLICATIONS
This series are offered in 5-pin TO-263,
TO-220 package.
„
LCD Monitors.
„
ADD-ON Cards Switching Regulators
„
High Efficiency Step-Down Regulators
„
Efficient Pre-regulator for Linear Regulators
„
Positive to Negative converter (Buck-Boost)
Block Diagram
DC Input
Enable
Vin
Internal
Regulator
1
+
Enable
5
4
Feed
Back
Fixed Gain
Error amp. Comparator
R2
+
R1
1K
-
3Amp.
Driver Switch
+
-
2
1.23V
Band-Gap
Reference
52KHz
Oscillator
Reset
3
Current
Limited
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L1
+
Cout
D1
LOAD
Thermal
Shutdown
Output
AMS2576
Ordering Information
Operating Temp.
(Ambient)
Part No.
AMS2576T-XX
AMS2576T-ADJ
AMS2576S-ADJ
AMS2576S-XX
Package
TO-220-5L
-20 ~ +85℃
TO-263-5L
Note: Where XX denotes voltage option, Available are 12V, 5V and 3.3V. Leave blank for
adjustable version. Contact factory for additional voltage options.
Pin assignment
1. Input
2. Output
3. Ground
4. Feedback
5. Enable
TO-220
TO-263
Absolute Maximum Ratings
Input voltage
ENABLE Pin Input Voltage
Vin
+45
V
Vin (operate)
-0.3V ≤ V ≤ Vin
V
PD
Internal Limited
W
TJ
-40 ~ +150
℃
TSTG
-65 ~ +150
℃
10
S
Power Dissipation
Operating Junction Temperature Range
Storage Temperature Range
Lead Soldering Temperature (260℃)
TO-220-5L / TO-263-5L
Package
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AMS2576
Electrical Characteristics
Vin = 12V, IL= 500mA, Ta = 25oC unless otherwise specified.
Parameter
Conditions
Min
Typ
Max
Vin=12V, IL=0.5A (Figure 1)
0.98|Vo|
3.3
1.02|Vo|
0.5A ≤IL ≤3A, 6V ≤Vin ≤45V
0.96|Vo|
Unit
AMS2576-3.3V
Output Voltage (Note 1)
Output Voltage (Note 1)
Efficiency
1.04|Vo|
V
%
(Figure 1)
Vin=12V, IL=3A
--
75
--
Vin=12V, IL=0.5A(Figure 1)
0.98|Vo|
5.0
1.02|Vo|
0.5A ≤IL ≤3A, 8V ≤Vin ≤45V
0.96|Vo|
AMS2576-5V
Output Voltage (Note 1)
Output Voltage (Note 1)
Efficiency
1.04|Vo|
V
%
(Figure 1)
Vin=12V, IL=3A
--
77
--
Vin=25V, IL=0.5A (Figure 1)
0.98|Vo|
12
1.02|Vo|
0.5A ≤IL ≤3A, 15V ≤Vin ≤45V
0.96|Vo|
AMS2576-12V
Output Voltage (Note 1)
Output Voltage(Note 1)
Efficiency
1.04|Vo|
V
%
(Figure 1)
Vin=15V, IL=3A
--
88
--
0.98|Vo|
1.23
1.02|Vo|
AMS2576
Feedback Voltage
Vin=12V, Vout=5V,IL=0.5A
(Note 1)
(Figure 2)
Feedback Voltage
0.5A ≤IL ≤3A, 8V ≤Vin ≤45V,
(Note 1)
Vout=5V (Figure 2)
Efficiency
Vin=12V, Vout=5V, IL=3A
0.96|Vo|
--
1.04|Vo|
77
--
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V
%
AMS2576
All Output Voltage Version
(Vin=12V for 5V, 3.3V and Adjustable version, Vin=25V for 12V version, IL= 500mA)
Oscillator Frequency (Note 2)
47
52
58
kHz
Quiescent Current (Note 3)
--
5
10
mA
Standby Current
ENABLE =5V
--
80
250
uA
Saturation Voltage (Note 4)
ILOAD=3A
--
1.2
1.5
V
Feedback Bias Current
VOUT=5V (Adj. Version only)
--
10
100
nA
Duty Cycle (Note 5)
Operating (ON)
93
98
--
%
4.2
7.0
8.8
A
VOUT=0V
--
0.3
2
VOUT=-1V
--
7.5
30
2.2
1.4
--
VIL(VOUT=Normal Output Voltage)
--
1.2
1.0
IIH (ENABLE =5V)
--
12
30
IIH (ENABLE =0V)
--
0
10
Current Limit (Note 2)(Note 4)
Output Leakage Current (Note 3)
ENABLE Threshold Voltage
ENABLE Input Current
VIH(VOUT=0V)
mA
V
uA
Note 1: External components such as the catch diode, inductor, input and output capacitors can affect
switching regulator system performance. Refer to Application information for details.
Note 2: The oscillator frequency reduces to approximately 11KHz in the event of fault conditions, such
as output short or overload. And the regulated output voltage will drop approximately 40% from
the nominal output voltage. This self-protection feature lowers the average power dissipation by
lowering the minimum duty cycle from 5% down to approximately 2%.
Note 3: For these parameters, FB is removed from VOUT and connected to +12V to force the output
transistor OFF.
Note 4: VOUT pin sourcing current. No diode, inductor or capacitor connected to VOUT.
Note 5: FB is removed from VOUT and connected to 0V.
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be located close to the AMS2576 using short leads
Application Information
and short printed circuit traces as possible.
It is required that VIN must be bypassed with at
least a 100µF electrolytic capacitor for stability.
Also, it is strongly recommended the capacitor’s
leads must be dept short, and located near the
regulator as possible.
For low operating temperature range, for example,
below -25℃, the input capacitor value may need
to be larger. This is due to the reason that the
To satisfy the need to fast switching speed and
low forward voltage drop, Schottky diodes are
widely used to provide the best efficiency,
especially in low output voltage switching
regulators (less than 5V). Beside, Fast-Recovery,
high-efficiency, or ultra fast recovery diodes are
also suitable. But some types with an abrupt
turn-off characteristic may cause instability and
EMI problems. A fast recovery diode with soft
recovery characteristics is better choice.
capacitance value of electrolytic capacitors
decreases and the ESR increases with
lower temperatures and ago. Paralleling a
ceramic or solid tantalum capacitor will
increase the regulator stability at cold
temperatures.
Output Capacitor
An output capacitor is also required to filter
the output voltage and is needed for loop
stability. The capacitor should be located
Inductor Selection
The AMS2576 can be used for either continuous or
discontinuous modes of operation. Each mode
has distinctively different operating characteristics,
which can affect the regulator performance and
requirements.
With relatively heavy load currents, the circuit
operates in the continuous mode (inductor current
always flowing). But under light Load conditions,
the circuit will be force to the discontinuous mode
(inductor current falls to zero for a period of time).
For light loads (less than approximately 300mA) it
may be desirable to operate the regulator in the
discontinuous mode, primarily because of the
lower inductor values required for the
discontinuous mode.
Indictors are available in different styles such as
pot core, toroid, E-frame, bobbin core, et., as well
as different core materials such as ferrites and
powdered iron. The least expensive, the bobbin
core type, consists of wire wrapped on a ferrite
rod core. This type of construction makes for an
inexpensive inductor, but since the magnetic flux
is not completely contained within the core, it
generates more electromagnetic interference
(EMI). This EMI can cause problems in sensitive
circuits, or can give incorrect scope readings
because of induced voltage in the scope probe.
An inductor should not be operated beyond its
maximum rated current because it may saturate.
When an inductor begins to saturate, the
near the AMS2576 using short PC board traces.
Low ESR types capacitors are recommended for
low output ripple voltage and good stability.
Generally, low value or low voltage (less than12V)
electrolytic capacitors usually have higher ESR
numbers, For example, the lower capacitor
values (220µF - 1000µF) will yield typically 50mV
to 150mV of output ripple voltage, while
larger-value capacitors will reduce the ripple to
approximately 20mV to 50mV.
The amount of output ripple voltage is primarily a
function of the ESR (Equivalent Series
Resistance) of the output capacitor and the
amplitude of the inductor ripple current (△IIND)
Output Ripple Voltage = ( △ IIND) x (ESR of
COUT) Some capacitors called “high-frequency”,
“low-inductance”, or “low-ESR” are recommended
to use to further reduce the output ripple voltage
to 10mV or 20mV. However, very low ESR
capacitors, such as tantalum capacitors, should
be carefully evaluated.
Catch Diode
This diode is required to return path for the
inductor current when the switch is off. It should
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AMS2576
lead length and PCB traces is always the first
thought. Further more, an additional small LC
filter (30µH & 100µF) (as shown in Figure 3) will
possibly provide a 10X reduction in output ripple
voltage and transients.
inductance decreases rapidly and the inductor
begins to look mainly resistive (the DC resistance
of the winding). This will cause the switch current
to rise very rapidly. Different inductor types have
different saturation characteristics, and this
should be well considered when selecting as
inductor.
Heatsink and Thermal Consideration
Although the AMS2576 requires only a small
Feedback Connection
heatsink for most cases, the following thermal
consideration is important for all operation. With
the package thermal resistances Өja and Өjc ,
total power dissipation can be estimated as
follows:
For fixed output voltage version, the FB (feedback)
pin must be connected to VOUT. For the
adjustable version, it is important to place the
output voltage ratio resistors near AMS2576
as possible in order to minimize the noise
introduction.
PD= (Vin x Iq) + (Vout / Vin) (Iout x Vsat);
Enable Input
When no heatsink is used, the junction
temperature rise can be determined by the
following:
It is required that the ENABLE must not be left
open. For normal operation, connect this pin to
a ”LOW” voltage (typically, below 1.6V). On the
other hand, for standby mode, connect this pin
with a “HIGH” voltage.
This pin can be safely pulled up to +VIN without a
resistor in series with it.
∆TJ = PD x Өja
With the ambient temperature, the actual junction
temperature will be:
Grounding
Tj = ∆Tj + Ta
To maintain output voltage stability, the power
ground connections must be low-impedance. For
the 5-lead TO-220 and TO-263 style package,
both the tab and pin 3 are ground and rather
connection may be used.
If the actual operating junction temperature is out
of the safe operating junction temperature
(typically 125 ℃ ), then a heatsink is required.
When using a heatsink, the junction temperature
rise will be reduced by the following:
Thermal Characteristics
∆Tj= PD x (Өjc + Ө interface + Ө heatsink );
The output ripple voltage is due mainly to the
inductor sawtooth ripple current multiplied by the
ESR of the output capacitor. The output ripple
voltage of a switching power supply will contain a
sawtooth ripple voltage at the switcher frequency,
typically about 1% of the output voltages, and
may also contain short voltage spokes of the
sawtooth waveform.
Also one can see from the above, it is important
to choose an heatsink with adequate size and
thermal resistance, such that to maintain the
regulator’s junction temperature below the
maximum operating temperature.
Due to the fast switching action, and the parasitic
inductance of the output filter capacitor, there is
voltage spikes presenting at the peaks of the
sawtooth waveform. Cautions must be taken for
stray capacitance. Wiring inductance, and even
the scope probes used for transients evaluation.
To minimize these voltage spikes, shortening the
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AMS2576
Application Circuit
Vin
1
AMS2576
Fixed
Voltage
3
Cin
L1
Output
2
Vout
100µH
5
Enbale
Gnd
+
100µF
MBR340
Cout
1000µF
LOAD
Unregulated
DC Input
+
FeedBack
4
Figure 1 Fixed Voltage version
Vin
1
AMS2576
Adjustable
Voltage
3
Cin
L1
Output
2
Vout
Vout
100µH
5
Enbale
Gnd
100µF
+
MBR340
Cout
R2
LOAD
Unregulated
DC Input
+
FeedBack
4
1000µF
R1
Vout=1.23×(1+R2/R1)
Figure 2: Adjustable Voltage Version
Vin
1
AMS2576
Adjustable
Voltage
3
Unregulated
DC Input
+
Cin
2
FeedBack
L1
Output
Vout
Vout
Enbale
+
MBR340
Cout
Output
R2
C1
1000µF
R1
Figure 3: LC filter for Low Output Ripple
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20µH
100µH
5
Gnd
100µF
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100µF
AMS2576
Package
Description
TO-220-5L Mechanical Drawing
TO-220 DIMENSION
DIM
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
10.00
10.50
0.394
0.413
B
3.240
4.440
0.128
0.175
C
2.440
2.940
0.096
0.116
D
0.260
1.020
0.010
0.040
E
1.570
1.830
0.062
0.072
F
13.31
14.13
0.524
0.556
G
4.475
5.225
0.176
0.206
H
1.170
1.370
0.046
0.054
I
27.60
29.44
1.087
1.159
J
2.175
2.925
0.086
0.115
K
0.297
0.477
0.012
0.019
L
8.280
8.800
0.326
0.346
M
6.010
6.510
0.237
0.256
N
14.29
15.31
0.563
0.603
TO-263-5L Mechanical Drawing
TO-263 DIMENSION
A
MILLIMETERS
MIN
MAX
10.220
10.260
INCHES
MIN
MAX
0.402
0.404
B
14.600
15.870
0.575
0.625
C
0.750
0.770
0.030
0.030
D
1.573
1.827
0.062
0.072
E
4.560
4.570
0.179
0.180
F
1.240
1.270
0.049
0.050
G
2.280
2.790
0.090
0.110
H
0.280
0.320
0.011
0.013
I
8.240
8.280
0.324
0.326
J
1.540
1.800
0.060
0.071
DIM
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AMS2576
Disclaimer:
•
AMS reserves the right to make changes to the information herein for the improvement of the design and performance
without further notice! Customers should obtain the latest relevant information before placing orders and should verify
that such information is complete and current.
•
All semiconductor products malfunction or fail with some probability under special conditions. When using AMS products
in system design or complete machine manufacturing, it is the responsibility of the buyer to comply with the safety
standards strictly and take essential measures to avoid situations in which a malfunction or failure of such AMS products
could cause loss of body injury or damage to property.
•
AMS will supply the best possible product for customers!
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