LT1801/LT1802
20
18012fc
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2002
LT 0309 REV C • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LT1399 Triple 300MHz Current Feedback Amplifi er 0.1dB Gain Flatness to 150MHz, Shutdown
LT1498/LT1499 Dual/Quad 10MHz, 6V/μs Rail-to-Rail Input and Output C-Load
™
Op Amps High DC Accuracy, 475μV V
OS(MAX)
, 4μV/°C Max Drift
LT1630/LT1631 Dual/Quad 30MHz, 10V/μs Rail-to-Rail Input and Output Op Amps High DC Accuracy, 525μV V
OS(MAX)
, 70mA Output
Current, Max Supply Current 4.4mA per Amplifi er
LT1800 80MHz, 25V/μs Low Power Rail-to-Rail Input/Output Precision Op Amp Single Version of LT1801/LT1802
LT1806/LT1807 Single/Dual 325MHz, 140V/μs Rail-to-Rail Input and Output Op Amps High DC Accuracy, 550μV V
OS(MAX)
, Low Noise 3.5nV/√Hz,
Low Distortion –80dB at 5MHz, Power-Down (LT1806)
LT1809/LT1810 Single/Dual 180MHz Rail-to-Rail Input/Output Op Amps 350V/μs Slew Rate, Low Distortion –90dBc at 5MHz,
Power-Down (LT1809)
C-Load is a trademark of Linear Technology Corporation
Low Power High Voltage Amplifi er
Certain materials used in optical applications have charac-
teristics that change due to the presence and strength of a
DC electric fi eld. The voltage applied across these materials
should be precisely controlled to maintain desired proper-
ties, sometimes as high as 100’s of volts. The materials
are not conductive and represent a capacitive load.
The circuit of Figure 6 shows the LT1801 used in an ampli-
fi er capable of a 250V output swing and providing precise
DC output voltage. When no signal is present, the op
+
–
1/2 LT1801
5V
10k
10k
Q3
Q1
4.99k 1k
1k
–130V
18012 F06
4.99k
Q5
Q7
Q2
Q4
Q6
Q8
R1
2k
R2
2k
R5
2k
R4
2k
R7
2k
R6
2k
R3
200k
0.1μF
C1
39pF
C2
8pF
150V
V
OUT
V
IN
MATERIAL UNDER
ELECTRIC FIELD
100pF
130V
5V
5V
A
V
= V
OUT
/V
IN
=
–100
±130V SUPPLY I
Q
= 130μA
OUTPUT SWING = ±128.8V
OUTPUT OFFSET ≅ 20mV
OUTPUT SHORT-CIRCUIT CURRENT ≅ 3mA
10% TO 90% RISE TIME ≅ 8μs, 200V OUTPUT STEP
SMALL-SIGNAL BANDWIDTH ≅ 150kHz
Q1, Q2, Q7, Q8: ON SEMI MPSA42
Q3, Q4, Q5, Q6: ON SEMI MPSA92
Figure 6. Low Power, High Voltage Amplifi er
Figure 7. Large-Signal Time Domain
Response of the Amplifi er
V
IN
2V/DIV
V
OUT
50V/DIV
10μs/DIV 18012 F07
amp output sits at about mid-supply. Transistors Q1 and
Q3 create bias voltages for Q2 and Q4, which are forced
into a low quiescent current by degeneration resistors
R4 and R5. When a transient signal arrives at V
IN
, the op
amp output moves and causes the current in Q2 or Q4
to change depending on the signal polarity. The current,
limited by the clipping of the LT1801 output and the 3kΩ
of total emitter degeneration, is mirrored to the output
devices to drive the capacitive load. The LT1801 output
then returns to near mid-supply, providing the precise DC
output voltage to the load. The attention to limit the current
of the output devices minimizes power dissipation thus
allowing for dense layout, and inherits better reliability.
Figure 7 shows the time domain response of the amplifi er
providing a 200V output swing into a 100pF load.
