LT1366/LT1367
LT1368/LT1369
Typical applicaTions
High Side Current Source
high input voltage, circuit operation is limited by the
LT1366’sabsolutemaximumratingsandtheoutputpower
requirements.
The wide compliance current source shown in Figure 7
takes advantage of the LT1366’s ability to measure small
signals near the positive supply rail. The LT1366 adjusts
Q1’s gate voltage to force the voltage across the sense
The circuit delivers 1A at 200mV of sense voltage. With a
5V input supply, the power dissipation is 5W. For opera-
tion at 70°C ambient temperature, the MOSFET’s heat sink
must have a thermal resistance of:
resistor (R ) to equal the voltage from the supply to
SENSE
the potentiometer’s wiper. A rail-to-rail op amp is needed
because the voltage across the sense resistor must drop
to zero when the divided reference voltage is set to zero.
Q2 acts as a constant current sink to minimize error in the
reference voltage when the supply voltage varies.
θ
HS
= θ
– θ
JA(SYSTEM) JC(FET)
= (125°C – 70°C)/5W – 1.25°C/W
= 11°C/W –1.25°C/W
= 9.75°C/W
The circuit can operate over a wide supply range
which is easily achievable with a small heat sink. Input
voltages greater than 5V require the use of a larger heat
sink or a reduction of the output current.
(5V < V < 30V). At low input voltage, circuit operation
CC
is limited by the MOSFET’s gate drive requirements. At
V
CC
R
SENSE
0.2Ω
Thecircuit’ssupplyregulationisabout0.03%/V.Theoutput
impedance is equal to the MOSFET’s output impedance
multipliedbytheopamp’sopen-loopgain.Degradationsin
current-sourcecomplianceoccurwhenthevoltageacross
the MOSFET’s on-resistance and the sense resistor drops
below the voltage required to maintain the desired output
current. This condition occurs when:
1k
0.0033µF
100Ω
LT1004-1.2
–
Q1
MTP23P06
1/2 LT1366
R
P
+
10k
I
LOAD
[V – V ] < [I
• (R
+ R )]
CC
OUT
LOAD
SENSE ON
40k
5V < V < 30V
CC
0A < I
< 1A AT V = 5V
LOAD
CC
Single Supply, 1kHz, 4th Order Butterworth Filter
0mA < I
< 160mA AT V = 30V
CC
LOAD
Q2
2N4340
An LT1367 is used in Figure 8 to form a 4th order But-
terworth filter. The filter is a simplified state variable ar-
chitecture consisting of two cascaded 2nd order sections.
Each section uses the 360 degree phase shift around
LT1366 F07
Figure 7. High Side Current Source
C1
10,000pF
C2
10,000pF
R1*
29.5k
10,000pF
R2*
8.6k
V
–
IN
10,000pF
A1
–
1/4 LT1367
11.8k*
A2
+
–
1/4 LT1367
21.5k*
11.8k*
A3
+
–
1/4 LT1367
A4
+
V
OUT
1/4 LT1367
29.5k*
+
10k
3.3V
10k
1µF
*1% RESISTORS
LT1366 F08
Figure 8. 4-Pole 1kHz, 3.3V Single Supply, State Variable Filter Using the LT1367
1366fb
ꢀꢄ
Linear [ Linear ]
