Texas Instruments ATL431, User Manual

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= + ´ + ´
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A
KA REF REF A
B
R
V 1 V I R
R
-
=
CC KA
KA
SUP
V V
I
R
REF
CATHODE
ANODE
R
B
V
CC
R
SUP
R
A
V
KA
(
R
A
V
REF
0.1%
R
B
0.1%
ATL431
= 1 +
V
REF
)
C
L
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EVM Theory and Operation
3 EVM Theory and Operation
The following single channel schematic is representative of the ATL431EVM with each passive bank
selection.
Figure 3. Base Shunt Regulator Schematic
The ATL431EVM is designed to allow users to setup configuration in Figure 3 with multiple options for
each passive component and open footprints to test multiple use cases. Table 2 shows a mapping of EVM
components to the base components shown in Table 2 .
Table 2. EVM Component Mapping
Base Component EVM Components
R
SUP
R1 - R5
R
A
R6 - R10
R
B
R11 and R12
C
L
C1 - C12
As shown in Figure 2 , the EVM is designed to allow users to visually map out each jumper connection to
its respective passive component by the labeling of the component value next to it.
3.1 Setting the Cathode Current (I
KA
)
R
SUP
should be set in conjunction with V
CC
and the desired cathode voltage (V
KA
) to provide enough
current for operation. The ATL431 needs > 35 µA in order to operate in the proper gain region for accurate
regulation. Use
Equation 1 to determine the cathode current.
(1)
As shown in Figure 2 , this portion is in the top left hand corner and is indicated as "Ik Selection" on the
PCB. Each jumper is denoted with its respective resistor value.
When setting I
KA
with R1 - R5, be sure to not exceed the absolute maximum rating of 100 mA for the
cathode current.
3.2 Setting the Cathode Voltage (V
KA
)
Once a desirable cathode current is determined. R
A
and R
B
must be selected to determine the Cathode
Voltage. Use Equation 2 to determine the cathode voltage. As I
REF
is 150 nA maximum, the I
REF
× R
A
portion of the equation is almost negligible.
(2)
As shown in Figure 2 , this portion is in the bottom left hand corner and is indicated as "Gain (R1)
Selection" on the PCB. Each jumper is denoted with its respective cathode voltage value. Please take in
to account that these values are only valid with R
B
= 10 k Ω (or jumper connection to R11). If R
B
is
disconnected or tied to a user setting, use Equation 2 to determine the cathode voltage values.
5 SLVUAE7 – April 2015 ATL431 Adjustable Shunt Regulator EVM
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