B1581T-5.0 View Datasheet(PDF) - Bay Linear
Part Name
Description
MFG CO.
'B1581T-5.0' PDF : 6 Pages View PDF
APPLICATIONS NOTES
The B1581 is designed as a high performance and low cost
solution for application requiring a lower dropout than
traditional NPN regulators.
The B1581 uses a separate input voltage VCTRL (VCTRL ≥
VOUT+ 1.3V) to minimize the dropout voltage. This allows the
2.5V power for the load to come from a 3.3V system supply.
As added benefit this will reduce the heat dissipation, and
lower heat sink and cooling fan cost. A typical application
would use 5V for Vin and 3.3V for VCTRL from a motherboard
power supply to provide a nominal 2.5V output. Using the
sense pin allows to Kelvin measure the output, reducing
resistive-associated errors.
The B1581 can power the 2.5V core voltage for
microprocessors such as Pentium, P55C, AMD5k86 and
K6 and the IBM PowerPC 603EV and 604EV processors.
*The reduction of heat dissipation is a result of the increase of
the regulator efficiency (efficiency = VOUT / VIN).
B1581
Adjustable Regulator Design
1.25V reference voltage is being developed between the
SENSE pin and the ADJ pin of the AS1581. Adding two
external resistors (see fig 1.) will allow setting the output
voltage from 1.25V to 6V. R1 is chosen so that this
current is specified minimum load current of 10mA. R2 is
given by the formula: VOUT = VREF (1+ R2/R1) + IADJ (R2).
The current flowing from the ADJ pin is typically 50µA.
This ADJ pin contributes to the final VOUT but is usually
neglected. Connecting the sense pin to the top of the
resistor divider will improve load regulation.
Lowering Noise
Using the SENSE pin to Kelvin the load will increase
accuracy of the output voltage during load regulation. For
the fixed voltage devices, adding a capacitor at the GND
pin will improve transient response. This capacitor is
chosen in the range of 1µF to 0.1µF and will depend on
the amount of output capacitance in the system.
TYPICAL APPLICATION
3.3V
VIN
5V
VCTRL
Fig. 1 Adjustable Regulator
C1
330uF
VIN
5
3
BAY LINEAR
B1581
4
VCTRL
1
2
ADJ
C2
10uF
VOUT
SENSE
C3
.033uF
(1) VCTRL needed when VIN < 5V.
(2) VOUT = VREF (1 + R2/ R1) + I ADJ R2.
(3) VREF is measured across adjust to sense.
R1
124 Ω
R1
124 Ω
2.5V
VOUT
C4
2 X 330uF
Bay Linear, Inc 2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
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