US431L/431AL
2-1
Rev. 1.2
5/11/98
TYPICAL APPLICATION
TYPICAL APPLICATION
DESCRIPTION
DESCRIPTION
The US431L product is a 3 terminal adjustable shunt
regulator that can also be used as a precision voltage
reference. Its output voltage may be set to any value
between Vref(1.24V) and 6V with two external resistors
as shown in the typical application circuit. Other appli-
cations of this device include the use as a merged am-
plifier and reference in applications such as Linear regu-
lator or as the secondary side controller in low voltage
power supply applications. The US431L only requires
80uA maximum quiescent current before regulating,
making it ideal as a voltage reference for battery type
applications.
LOW -VOLTAGE ADJUSTABLE
PRECISION SHUNT REGULATOR
FEATURES
FEATURES
SOT23-5 package
0.5% Voltage Reference Initial Accuracy
(US431AL)
Low Operational Cathode Current
(80 uA max)
Unconditionally Stable with only 1uF
Adjustable Output from 1.24V to 6V
0.25
Typical Output Impedance
Pin to Pin Compatible with TLV431
APPLICATIONS
APPLICATIONS
Precision Voltage Reference
Linear Regulator Controller
Secondary Side Controller for the Low Voltage
Power Supply Applications
PRELIMINARY DATASHEET
PACKAGE ORDER INFORMATION
PACKAGE ORDER INFORMATION
Ta (C) 5 LEAD
3 PIN PLASTIC 8 PIN PLASTIC
SOT23-5
TO-92 SOIC
0 TO 70 US431LCL US431LCZ US431LCS
0 TO 70 US431ALCL US431ALCZ US431ALCS
431app1-1.0
R2
Co
R1
US431
V
R
B
IN
V
O
Typical application of the US431L as a shunt regulator / voltage reference.
Vo
Vref
R
R
=
+
1
1
2
US431L/431AL
2-2
Rev. 1.2
5/11/98
PARAMETER SYM
TEST CONDITION
MIN
TYP MAX
UNITS
Reference Voltage Vref
I
K
=10mA,V
KA
=Vref,Ta=25
C
1.228
1.240
1.252
V
US431L
I
K
=10mA,V
KA
=Vref
1.221
1.240
1.259
Reference Voltage Vref
I
K
=10mA,V
KA
=Vref,Ta=25
C
1.234
1.240
1.246
V
US431AL
I
K
=10mA,V
KA
=Vref
1.228
1.240
1.252
Vref deviation over full Vref(dev)
V
KA
=Vref, I
K
=10mA 4
12
mV
temperature range
Note 1
Ratio of Vref change to dVref/dV
KA
I
K
=10mA , dV
KA
=Vref to 6 V
-1.5
-2.7 mV/V
Cathode voltage change
Reference pin current
I
K
=10mA , R1=10k
, R2=open
0.15
0.5
uA
Iref deviation over full Iref(dev)
I
K
=10mA , R1=10k
, R2=open
0.05
0.3
uA
temperature range
Note 1
Minimum cathode current I
K
(min)
V
KA
=Vref
55
80
uA
Off state cathode current Ioff
V
KA
=6V , Vref=0V
0.001
0.1
uA
Dynamic impedance Zka
0
V
KA
=Vref, f<1 kHz,
0.25
0.4
I
K
=0.1 to 15 mA , Note 2
Unless otherwise specified ,these specifications apply over Ta=0 to 70
C, C
O
=1uF. Typical values refer to
Ta=25
C.Low duty cycle pulse testing are used which keeps junction and case temperatures equal to the
ambient temperature.
Note 2 :
Note 1 : The deviation parameters, Vref(dev) and Iref(dev) are
defined as the differences between the maximum and the minimum
values obtained over the rated temperature range. The average full
range temperature coeficient of the reference input voltage is de-
fined as :
ABSOLUTE MAXIMUM RATINGS
ABSOLUTE MAXIMUM RATINGS
Input Voltage (Vin) ............................................................. 7V
Continuous Cathode Current Range ......................................... -20 mA to +20 mA
Reference Current Range ...................................................... -0.05 mA to 3 mA
Storage Temperature Range ................................ -65
C TO 150
C
Operating Junction Temperature Range ...................... 0
C TO 150
C
PACKAGE INFORMATION
PACKAGE INFORMATION
5 PIN SOT 23 (L)
3 PIN PLASTIC TO-92 (Z) 8 PIN PLASTIC SOIC (S)
JA
= 450
C/W
JA
= 162C/W
JA
=160
C/W
ELECTRICAL SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
Vref
Vref dev
Vref
C
T
Vref
T
Vref can b
A
A
=
(
)
(
)
25
10
6
Where:
unit is ppm/ C
is the rated operating free air temperature
of the device.
e positive or negative depending on whether
minimum Vref or maximum Vref, respectively occurs at the
lower temperature.
Thedynamic
VKA
IK
When the d
V
I
R
R
impedance when VKA = Vref is defined as :
Zka0
evice is operating with two external
resistors (see Figure 2), the total dynamic impedance
of the circuit is given by:
Zka
Zka0
=
=
=
+
1
1
2
3
2
1
4
5
TOP VIEW
Anode
Ref
NC
NC
Cathode
1
2
3
BOTTOM VIEW
Ref
Anode
Cathode
4
3
2
1
5
6
7
8
TOP VIEW
NC
NC
Anode
Anode
NC
NC
Ref
Cathode
US431L/431AL
2-3
Rev. 1.2
5/11/98
Pin Descriptions
Pin Descriptions
BLOCK DIAGRAM
BLOCK DIAGRAM
Figure 1 - Simplified block diagram of the US431L
431blk1-1.0
+
Cathode
1.24V
Anode
Ref
SOT 23
TO 92
8 PIN
SOIC
PIN#
PIN#
PIN# PIN SYMBOL
4
1 8
Ref
3
3 1
Cathode
5
2 3,6
Anode
1,2 NA 2,4,5,7 NC
Pin Description
A resistor divider from this pin to the Cathode pin and
ground sets the output voltage.
The output of the shunt regulator .A minimum of 1uF
capacitor must be connected from this pin to Anode pin
to insure unconditional stability.
Ground pin. This pin must be connected to the lowest
potential in the system & all other pins must be at higher
potential with respect to this pin.
These pins are not connected internally.
US431L/431AL
2-4
Rev. 1.2
5/11/98
APPLICATION INFORMATION
APPLICATION INFORMATION
Vo
V
Vref
R
R
Iref
R
KA
=
=
+
+
1
1
2
1
The maximum value for the biasing resistor is calcu-
lated using the following equations :
Assuming R1=2k
as before,
The maximum power dissipation of the resistor is
calculated under the maximum supply voltage as
follows :
Thermal Design
The US431L is offered in the plastic TO-92 (Z) or the
surface mount SOT23-5 (L) packages. The TO-92 pack-
age has the maximum power dissipation capability of
775mW at Ta=25
C with the derating factor of -6.2mW/
C.The SOT23-5 package has the maximum power dis-
sipation capability of 150mW at Ta =25
C with the
derating factor of -1.2mW/
C.
Table below summarizes the maximum power dissipa-
tion capability of each package versus ambient tempera-
ture.
Ambient Temperature (Ta) -
C
Pkg 25 40 50 60 70
TO 92 775mW 682mW 620mW 558mW 496mW
SOT23-5 150mW 132mW 120mW 108mW 96mW
Output Voltage Setting
The US431L can be programmed to any voltages in the
range of 1.24 to 6V with the addition of R1 and R2 exter-
nal resistors according to the following formula:
The US431L keeps a constant voltage of 1.240V be-
tween the Ref pin and ground pin. By placing a resistor
R2 across these two pins a constant current flows
through R2, adding to the Iref current and into the R1
resistor producing a voltage equal to the (1.240/R2)*R1
+ Iref * R1 which will be added to the 1.240V to set the
output voltage as shown in the above equation. Since
the Input bias current of the Ref pin is 0.5 uA max , it
adds a very small error to the output voltage and for most
applications can be ignored . For example, in a typical
5V to 3.3V application where R2=1.21k
and R1=2k
the error due to the Iadj is only 1mV which is about
0.03% of the nominal set point.
Figure 2 - Typical application of the US431L for program-
ming the output voltage.
Biasing Resistor (R
B
) Selection
The biasing resistor R
B
is selected such that it does
not limit the input current under the minimum input
supply and maximum load and biasing current.
An example is given below on how to properly select
the biasing resistor.
Assuming :
V
MIN
= 4.5 V
V
MAX
= 6 V
V
KA
= 3.3 V
I
L
= 10 mA
R
V
Where :
B
MIN
MAX
=
- V
I
+ I
I
= I
+ I
V
= Minimum supply voltage
I
= Maximum load current
I
= Maximum bias current
I
= Maximum value for the minimum
cathode current spec
I = Current through R1
KA
B
L
B
K
R
MIN
L
B
K
R
MAX
MAX
MAX
MIN
MAX
MAX
MIN
I =
3.3 - 1.24
2
mA
I
= 0.08 + 1.03 = 1.11 mA
.5 - 3.3
1.11+ 10
R = 100
R
B
B
MAX
=
=
=
103
4
108
.
R
Selecting
B
MAX
431app2-1.0
V
R2
Co
R1
R
US431
I
R
K
I
L
V
KA
= V
O
B
IN
L
(
)
P
V
Where :
P
R MAX
MAX
R MAX
B
B
(
)
(
)
=
=
- V
R
V
= Maximum supply voltage
Maximum R power dissipation
KA
B
MAX
B
2
(
)
P
R MAX
B
(
)
=
- 3.3
mW
6
100
73
2
=
US431L/431AL
2-5
Rev. 1.2
5/11/98
In our previous example, the maximum power dissipa-
tion of the device is calculated under no load and maxi-
mum input supply condition.
The maximum power is calculated using the following
equation :
As shown in the power dissipation table, both packages
can handle this power dissipation.
Stability
The US431L has many different regions of stability do-
main as a function of the cathode current which are typi-
cal characteristics of the 3 terminal shunt regulators.
However in general the device will be unconditionaly
stable for any cathode current if the capacitor, C
O
=
1 uF or bigger is connected from Cathode to Anode
pins. If the cathode current is always kept higher than
500uA under minimum line and maximum load condi-
tions , the C
O
can be cut to 0.01uF and the system will
be stable.
P
V
V
Where :
P
P
MAX
KA
MAX
MAX
MAX
=
=
=
=
- V
R
Maximum power dissipation of the 431L
For our example :
- 3.3
100
mW
KA
B
3 3
6
89
.
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