AN1108 Advanced Linear Devices, AN1108 Datasheet - Page 7

• Manufacturer Part Number: AN1108
• Description: Application Note For Electrically Programmable Analog Device Applications
• Manufacturer: Advanced Linear Devices

APPLICATION NOTE AN1108
Mached EPAD Pair With A Single Supply
Matched EPAD Pair With Dual Supplies
For low tempco set Ids
For V+ = +5V & V- = -5V, R
For low tempco set Ids 68 A
For V+ = +5V, R
GN1
GN1
Ids
V-
Ids
V-
DN1
DN1
V+
Figure 4
Figure 5
S12
V-
S12
R
R
2
47K
Ids x 2
V+
1/2 ALD1108E
68 A
DN2
R
DN2
R
Ids
47K
1/2 ALD1108E
Ids
GN2
GN2
V
V
O
O
Advanced Linear Devices
EPAD VOLTAGE OUTPUT WITH BUFFER
A simple voltage follower is shown in Figure 6. The voltage
follower isolates the output and prevents it from loading the
EPAD bias resistor and causing loading effects. Again, for
low tempco, set R such that the current I is 68 A.
BASIC CURRENT SOURCE
A basic current source with output I
Value of resistor R is selected such that current through R is
approximately 68 A for low temperature effects. Resistor
Rset is biased with the same voltage registered across the
EPAD. This voltage is set by bias resistor value R and the
EPAD programmed threshold voltage. The tempco of out-
put current I
This tempco can be minimized by selection of an appropri-
ate resistor type. In this circuit, the output current can be
set by programming the EPAD threshold voltage.
In order to set the output current I
set up to monitor I
while a voltage source forces a voltage on Vbias. Once a
desired current level is attained, then that voltage which pro-
duces this desired current, Vbias, can be noted. The EPAD
Vt can now be programmed to Vbias, using the same sup-
ply voltage and resistor R. This entire process can be fully
automated with the appropriate equipment, setup and cus-
tomized control software.
EPAD Output With Buffer Amplifier
O
is directly proportional to the tempco of Rset.
For low tempco set Ids 68 A
For V+ = +5V, R
GN1
O
through ALD1106 N-Channel MOSFET
V+
I
R
DN1
S12
1/4 ALD1108E
Figure 6
47K
O
-
+
,
O
a current meter can be
V+
is shown in Figure 7.
ALD1702
V
O
7