September
2005
ET- AMS1084M-XX
DESCRIPTION
Inv
№
400
LOW DROPOUT POSITIVE VOLTAGE REGULATOR
The AMS1084M series of positive adjustable and fixed regulators are designed to provide 5A with high efficiency. All internal
circuitry is designed to operate down to 1.3V input to output differential. On-chip trimming adjusts the reference voltage to
1%.
APPLICATIONS
•
•
•
High Efficiency Linear Regulators
Post Regulators for Switching Supplies
Adjustable Power Supply
FEATURES
•
•
•
•
•
•
Adjustable or Fixed Output
Output Current of 5A
Low Dropout, 1.5V max at 5A Output Current
0.04% Line Regulation
0.2 % Load Regulation
100% Thermal Limit Burn-In
Fast Transient Response
•
TYPICAL APPLICATION DATA
4.8V
4.95V
AMS1084M-3.3
AMS1085
AMS1084M
PIN DESCRIPTION
Page 1 of 3
BEIJING ESTEK ELECTRONICS CO.,LTD
ET- AMS1084M-XX
ABSOLUTE MAXIMUM RATINGS
SYMBOL
PARAMETER
V
CC
Power Dissipation
V
IN
Input Voltage
Operation Junction Temperature Range
T
J
Control Section
Power Transistor
T
STG
Storage Temperature Range
T
LEAD
Lead Temperature (Soldering 10 sec)
VALUE
Internally Limited
15
0 to 125
0 to 150
-65 to +150
300
UNIT
W
V
0
0
0
C
C
C
ELECTRICAL CHARACTERISTICS
I
LOAD
= 0mA and T
J
= +25
0
C (unless otherwise noted)
PARAMETER
Reference Voltage Note 1
DEVICE
AMS1084M
TEST CONDITIONS
V
IN
=5V, I
LOAD
= 10mA
V
IN
– V
OUT
= 1.5V to 10V,
I
LOAD
= 10mA to 5A
V
IN
– V
OUT
= 1.5V,
Variator from nominal V
OUT
V
IN
– V
OUT
= 1.5V to 10V
I
LOAD
= 0mA to 5A,
Variator from nominal V
OUT
I
LOAD
= 10mA,
V
IN
– V
OUT
= 1.5V to 10V
V
IN
– V
OUT
= 1.5V
I
LOAD
= 10mA to 5A
V
IN
=5V, V
ADJ
= 0V
V
IN
– V
OUT
= 1.5V
I
LOAD
= 10mA to 5A
V
IN
– V
OUT
= 1.5V to 10V
I
LOAD
= 10mA
V
IN
– V
OUT
= 1.5V
V
IN
– V
OUT
= 3V
I
LOAD
= 5A
I
LOAD
= 5A
V
IN
– V
OUT
= 1.5V,
I
LOAD
= 10mA
MIN.
1.238
*
1.225
-1
*
*
*
*
*
*
*
*
*
*
-2
-
-
-
-
-
5
60
-
-
TYP.
1.250
1.250
-
-
0.04
0.2
3
7
40
6.5
72
1.3
0.005
MAX.
1.262
1.275
+1
%
+2
0.20
%
0.40
7
10
90
-
-
1.5
-
mA
mA
µA
A
dB
V
%/
0
C
V
UNIT
Output Voltage Note 1
All fixed
versions
Line Regulation Note 1
Load Regulation Note 1
Minimum Load Current
Ground Pin Current
Adjust Pin Current
Current Limit
Ripple Rejection Note 2
Dropout Voltage Note 1,3
Temperature Coefficient
All
All
AMS1084M
All fixed
versions
AMS1084M
All
All
All
All
The
*
denotes the specifications which apply over the full temperature range (see previous table,
T
J
)
NOTES:
1:
Low duty pulse testing with Kelvin connections required.
2:
120Hz input ripple (C
ADJ
for ADJ = 25µF, C
OUT
= 25µF)
3:
∆
V
OUT
,
∆
V
REF =
1%
APPLICATION INFORMATION
The AMS1084M series of adjustable and fixed regulators are easy to use and have all the protection features expected in
high performance voltage regulators: short circuit protection and thermal shut-down.
Pin compatible with older three terminal adjustable regulators, these devices offer the advantage of a lower dropout voltage,
more precise reference tolerance and improved reference stability with temperature.
STABILITY
The circuit design used in the AMS1084M series requires the use of an output capacitor as part of the device frequency
compensation.
The addition of 150µF aluminum electrolytic or a 22µF solid tantalum on the output will ensure stability for all operating
conditions.
When the adjustment terminal is bypassed with a capacitor to improve the ripple rejection, the requirement for an output
capacitor increases. The value of 22µF tantalum or 150µF aluminum covers all cases of bypassing the adjustment terminal.
Without bypassing the adjustment terminal smaller capacitors can be used with equally good results.
Page 2 of 3
BEIJING ESTEK ELECTRONICS CO.,LTD
ET- AMS1084M-XX
To ensure good transient response with heavy load current changes capacitor values on the order of 100µF are
used in the output of many regulators. To further improve stability and transient response of these devices larger
values of output capacitor can be used.
PROTECTION DIODES
Unlike older regulators, the AMS1084M family does not need any protection diodes
between the adjustment pin and the output and from the output to the input to
prevent over-stressing the die.
Internal resistors are limiting the internal current paths on the AMS1084M
adjustment pin, therefore even with capacitors on the adjustment pin no protection
diode is needed to ensure device safety under short-circuit conditions.
Diodes between the input and output are not usually needed.
Microsecond surge currents of 50A to 100A can be handled by the internal diode between the input and output pins of the
device. In normal operations it is difficult to get those values of surge currents even with the use of large output
capacitances. If high value output capacitors are used, such as 1000µF to 5000µF and the input pin is instantaneously
shorted to ground, damage can occur. A diode from output to input is recommended, when a crowbar circuit at the input of
the AMS1084M is used. Normal power supply cycling or even plugging and unplugging in the system will not generate
current large enough to do any damage.
The adjustment pin can be driven on a transient basis ±25V, with respect to the output without any device degradation. As
with any IC regulator, none the protection circuitry will be functional and the internal transistors will break down if the
maximum input to output voltage differential is exceeded.
AMS1084M
RIPPLE REJECTION
The ripple rejection values are measured with the adjustment pin bypassed. The impedance of the adjust pin capacitor at the
ripple frequency should be less than the value of R1 (normally 100Ω to 120Ω) for a proper bypassing and ripple rejection
approaching the values shown. The size of the required adjust pin capacitor is a function of the input ripple frequency. If
R1=100Ω at 120Hz the adjust pin capacitor should be 25µF. At 10kHz only 0.22µF is needed.
The ripple rejection will be a function of output voltage, in circuits without an adjust pin bypass capacitor. The output ripple
will increase directly as a ratio of the output voltage to the reference voltage (V
OUT
/ V
REF
).
OUTPUT VOLTAGE
AMS1084M
The AMS1084M series develops a 1.25V reference voltage between the output and
the adjust terminal. Placing a resistor between these two terminals causes a
constant current to flow through R1 and down through R2 to set the overall output
voltage.
This current is normally the specified minimum load current of 10mA. Because I
ADJ
is very small and constant it represents a small error and it can usually be ignored.
LOAD REGULATION
AMS1084M
True remote load sensing it is not possible to provide, because the AMS1084M is a
three terminal device. The resistance of the wire connecting the regulator to the
load will limit the load regulation.
The data sheet specification for load regulation is measured at the bottom of the
package. Negative side sensing is a true Kelvin connection, with the bottom of the
output divider returned to the negative side of the load.
The best load regulation is obtained when the top of the resistor divider R1 is
connected directly to the case not to the load. If R1 were connected to the load, the
effective resistance between the regulator and the load would be:
Connected as shown Fig.3, R
Ρ
is not multiplied by the divider ratio. Using 16-gauge wire the parasitic line resistance is about
0.004Ω per foot, translating to 4mV/ft at 1A load current. It is important to keep the positive lead between regulator and load
as short as possible and use large wire or PC board traces.
Page 3 of 3
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