Bay Linear, Inc
2418 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556 www.baylinear.com
B4150
PRODUCT DESCRIPTION
The B4150 is precision fixed output voltage regulator.
Unlike bipolar regulators, the B4150 supply current
does not increase with load current. In addition, V
out
remains stable and within regulator at very low load
currents (an important consideration in RTC and
CMOS RAM battery back-up application).
Figure 1 shows a typical application circuit. The
regulator is enabled any time the shutdown input is at
or above V
IH.
And shutdown (disabled) when SHDN is
at or below V
IL
. SHDN maybe controlled by a CMOS
logic gate, or I/O port of a micro controller. If the
SHDN input is not. Required, it should be connected
directly to the supply. While in shutdown, supply
current decreases to 0.05µA (typical) and V
out
falls to
zero volts.
Bypass Input
A 470pF capacitor connected from the bypass input to
ground reduces noise present on the internal reference,
which in turn significantly reduces output noise. If
output noise is not a concern, this input maybe left
unconnected. Larger capacitor values maybe used, but
it results in a longer time period to rated output
voltage power is initially applied.
Output Capacitor
A 1µF (min) capacitor from V
out
to ground is required.
Then output capacitor should have an effective series
resistance of 5Ω or less. A 1µA capacitor should be
connected from V
in
to GND if there is more than 10
inches of wire between the regulator and the AC filter
capacitor, or if a battery is used as the power source.
Aluminum electrolytic or tantalum capacitor types can
be used. (since many aluminum electrolytic capacitors
freeze at approximately- 30°C, solid tantalums are
recommended for applications operating below –25
°C.) When operating from sources other than
batteries, supply-noise rejection and transient response
can be improved by increasing the value of the input
and output capacitors and employing passive filtering
techniques.
Thermal Considerations
Thermal Shutdown
Integrated thermal protection circuitry shuts the
regulator off when die temperature exceeds 160°C.
The regulator remaining off until the die temperature
drops to approximately 150 °C.
Power Dissipation
The amount of power the regulator dissipates is
primarily a function of input and output voltage, and
output current. The following equation is used to
calculate worst case power dissipation:
P
D
=(V
INMAX-VOUTMIN)ILOADMAX
Where:
P
D
= worst case actual power dissipation
V
INMAX
= Maximum voltage on V
IN
V
OUTMIN
=Minimum regulator output voltage
I
LOADMAX
= maximum output (LOAD) Current
The maximum allowable power dissipation is function
of the maximum ambient temperature (T
AMAX
). The
maximum allowable die temperature (125°C) and the
thermal resistance from junction-to-air (θ
JA
). The 5-
pin SOT-23A package has a θ
JA
of approximately
220°C/Watt when mounted on a single layer FR4
dielectric copper clad PC board.
P
DMAX
=(T
JMAX-TAMAX
)/ θ
JA
Where all terms are previously defined
This can be caused in conjunction with other equation
to ensure regulator thermal operation is within limit.
For example:
Given:
V
INMAX
=3.0V+10%
V
OUTMIN
=2.7V-2.5%
I
LOADMAX
=40 mA
T
JMAX
=125°C
T
AMAX
=55°C
Find:
1. Actual power dissipation
2. Maximum allowable dissipation
Actual power dissipation:
P
D
=(V
INMAX-VOUTMIN)ILOADMAX
=[(3.0 x 1.1)-(2.7 x 0.975)]40 x 10
-3
=26.7mW
Maximum allowable power dissipation:
P
DMAX
=(T
JMAX-TAMAX
)
=(125-55)/220
=318Mw
These equations can be used to calculate maximum
current and/or input voltage limits.