Bay Linear
Inspire the Linear Power
4.0A Low Dropout Voltage Regulator
Adjustable & Fix Output
B1587
Description
The Bay Linear B1587 is Monolithic low power 4.0A
Adjustable and fixed NPN voltage regulator that are easy to
use with minimum external components. It is suitable for
applications requiring a well-regulated positive output voltage
with low input-output differential voltage requirements and
output voltage 1.5V, 2.5V, 3.0V, 3.3V, or 5V.
The B1587 Outstanding features include full power usage up
to 4.0Amp of load current internal current limiting and thermal
shutdown. Other fixed versions are also available consult with
factory. The B1587 is offer in a new LPDD (Low Profile TO-
263) package from 4.47 mm (DD) thickness down to only 1.27
mm (LPDD) total thickness.
The B1587 is offered in a 3-pin TO-220, TO-263 & TO-252
packages compatible with other 3 terminal regulators. For 5A
Low dropout Regulator refer to the B1585 data sheet.
Features
•
•
•
•
•
•
Adjustable Output Down to 1.2V
Fixed Output Voltages 2.5V, 3.0V 3.3V,
and 5.0V
Output Current of 4.0A
Low Dropout Voltage 1.1V Typ.
Current & Thermal Limiting
Standard 3-Terminal Low Cost TO-220,
D
2
, D Packages
Similar to industry Standard
LT1085/LT1587/LT1585
•
Applications
•
•
•
•
•
•
3.3V to 2.5V for Pentium Processor
SMPS Post Regulator
High Efficiency “Green” Computer
Systems
High Efficiency Linear Power Supplies
5V to 3.XXV for Pentium Processor
Battery Charger
Pin Connection
Ordering Information
Devices
B1587T
B1587S
B1587D
B1587J
TO-263-3 (S)
(
Package
TO-220
TO-263
TO-252
LPDD
Temp.
0
°C
to 70
°C
0
°C
to 70
°C
0
°C
to 70
°C
0
°C
to 70
°C
TO-252 (D)
Bay Linear
1
2
3
1
2
3
ADJ/
GND
V
OU
V
IN
T
Top View
Front View
LPDD (J)
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
B1587
APPLICATION HINTS
The Bay Linear B1587 incorporates protection
against over-current faults, reversed load insertion,
over temperature operation, and positive and
negative transient voltage. However, the use of an
output capacitor is required in order to insure the
stability and the performances.
Stability
The output capacitor is part of the regulator’s
frequency compensation system. Either a 220µF
aluminum electrolytic capacitor or a 47µF solid
tantalum capacitor between the output terminal and
ground guarantees stable operation for all operating
conditions.
However, in order to minimize overshoot and
undershoot, and therefore optimize the design,
please refer to the section ‘Ripple Rejection’.
Ripple Rejection
Ripple rejection can be improved by adding a
capacitor between the ADJ pin and ground. When
ADJ pin bypassing is used, the value of the output
capacitor required increases to its maximum (220µF
for an aluminum electrolytic capacitor, or 47µF for
a solid tantalum capacitor). If the ADJ pin is not
bypass, the value of the output capacitor can be
lowered to 100µF for an electrolytic aluminum
capacitor or 15µF for a solid tantalum capacitor.
However the value of the ADJ-bypass capacitor
should be chosen with respect to the following
equation:
C = 1 / ( 6.28 * F
R
* R
1
)
Where C
= value of the capacitor in Farads
(select an equal or larger standard value),
F
R
= ripple frequency in Hz,
R
1
= value of resistor R
1
in Ohms.
If an ADJ-bypass capacitor is use, the amplitude of
the output ripple will be independent of the output
voltage. If an ADJ-bypass capacitor is not used, the
output ripple will be proportional to the ratio of the
output voltage to the reference voltage:
M = V
OUT
/ V
REF
Where M = multiplier for the ripple seen when
the ADJ pin is optimally bypassed.
V
REF
= Reference Voltage
Reducing parasitic resistance and inductance
One solution to minimize parasitic resistance and
inductance is to connect in parallel capacitors. This
arrangement will improve the transient response of
the power supply if your system requires rapidly
changing current load condition.
Thermal Consideration
Although the B1587 offers some limiting circuitry
for overload conditions, it is necessary not to exceed
the maximum junction temperature, and therefore to
be careful about thermal resistance. The heat flow
will follow the lowest resistance path, which is the
Junction-to-case thermal resistance. In order to
insure the best thermal flow of the component, a
proper mounting is required. Note that the case of
the device is electrically connected to the output. In
case the case has to be electrically isolated, a
thermally conductive spacer can be used. However
do not forget to consider its contribution to thermal
resistance.
Assuming:
V
IN
= 10V, V
OUT
= 5V, I
OUT
= 4A, T
A
= 90°C,
θ
CASE
=
1°C/W (no external heat sink, no wind)
Power dissipation under these conditions
P
D
= (V
IN
– V
OUT
) * I
OUT
= 15W
Junction Temperature
T
J
= T
A
+ P
D
* (θ
CASE
+
θ
JC
)
For the Control Section
T
J
= 90°C + 15W*(1°C/W + 0.6°C/W) = 114°C
114°C < T
JUNCTION MAX
for the control section.
For the Power Section
T
J
= 90°C + 15W*(1°C/W + 1.6°C/W) = 129°C
129°C < T
JUNCTION MAX
for the power transistor.
In both case reliable operation is insured by adequate
junction temperature.
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
B1587
Basic Adjustable Regulator
BAY
B1587
V
REF
I
ADJ
V
OU
T
V
OU
T
R
1
This current will go through the resistance R
2
to set
the overall output voltage. The current I
ADJ
is very
small and constant. Therefore its contribution to the
overall output voltage is very small and can generally
be ignored
Load Regulation
R
2
50µA
V
OUT
= V
REF
* ( 1 + R
2
/R
1
) + I
ADJ
* R
2
Fig.2 Basic Adjustable Regulator
Parasitic line resistance can degrade load regulation.
In order not to affect the behavior of the regulator, it
is best to connect directly the R
1
resistance from the
resistor divider to the case,
and not to the load. For the same reason, it is best to
connect the resistor R
2
to the Negative side of the
load.
Output Voltage Output Voltage
Output Voltage
Consider Figure 2. The resistance R
1
generates a
constant current flow, normally the specified load
current of 10mA
V
OUT
BAY
B1587
R
P
Parasitic Line
Resistance
Connect R
1
to
Case of Regulator
R
1
R
L
R
2
Connect R
2
to Load
Fig.3 Basic Adjustable Regulator
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
Embedded System
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