High outp ut curr ent ( peak ) . . . . . . . . . . . . . . . . . 250mA
••
APPLICATIONS
Coaxial Cable Driver
••
Fast O p Amp Booster
••
Flash Converter Driver
••
Video Li ne Dr iv er
••
High Speed Sample and Hold
••
A TE Pi n Dri ver
••
Video Am pl ifier
••
Radar
••
Sonar
••
Boost OP Amp Output
••
Isolate Capacitance Load
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GENERAL DESCRIPTION
The LH0033 is a high speed, FET input, voltage
follower/buffer designed to provide high current drive (up to
100mA) at frequencies from DC to over 100MHz. The
LH0033 slews at 1500V/µs and exhibits excellent phase
linearity up to 20MHz.
LH0033 is intended to fulfill a wide range of buffer app lication s
such as high speed line drivers, video impedance
transformation, nuclear instrumentation amplifiers, op amp
isolation buffers for driving reactive loads and high im pe danc e
input buffers for high speed A to Ds and comparators. In
addition, the LH0033 can continuously drive 50Ω coaxial
cables or be used as a yoke driver for high resolution CRT
displays.
This device is constructed using specially selected junction
FETs and active laser trimming to achieve guaranteed
performance specifications. The LH0033 is specified for
operation from -55
from -25
TO-8 package.
ORDERING INFORMATION
PartPackageTemperature Range
LH0033GH12A (TO8 12 Lead )-55
LH0033CGH12A (TO8 12 Lead)-25
o
C to 85oC. The LH0033 is available in a 2.2W metal
Note 1: LH0033 is 100% production tested as specified at 25
o
C. Specifications at temperature extremes are verified by sample testing,
correlation or periodic characterization.
o
Note 2: Specification is at 25
will exceed the value at T
more under load conditions. Accordingly, V
C junction temperature due to requirements of high speed automatic testing. Actual values at operating temperature
= 25oC. When supply voltages are ±15V, no-load operating junction temperature may rise 40-60oC above ambient, and
J
may change one to several mV, and IB will change significantly during warm-up.
OS
Note 3: Limits are guaranteed by sample testing, periodic characterization or correlation.
Note 4: Mea sured in still air 7 minutes after appli catio n of power. Guaranteed throug h correlated autom at ic pulse testing .
Note 5: Guaranteed through correlated automatic pulse testing at T
APPLICATION INFORMATION:
Recommended Layout Pre caut ions
RF/video printed circuit board layout rules should be followed
when using the LH0033 since it will provide power gain to
frequencies over 100MHz. Ground planes are recommended
and power supplies should be decoupled at each device with
low inductance capacitors. In addition, ground p la ne sh ield ing
may be extended to the metal case of the device since it is
electrically isolated from internal circuitry. Alternatively the
case should be connected to the output to minimize input
capacitance.
LH0033 / LH0033C
where:
AV = No load voltage gain, typically 0.99
+
= Positive supply voltage
V
–
= Negative supply voltage
V
For the above example, ∆V
adjusted to zero as described in Figure 1. For AC coupled
applications, no additional offset occurs if the DC input is
properly biased as illustrated in the Typical Applications
section.
would be -35mV. This may be
O
Offset Voltage Adjust ment
The LH0033’s offset voltages have been actively trimmed by
laser to meet guaranteed specif ications when the off set p re set
pin is shorted to the off set adjust pin. If of fset n u ll is d esir able,
it is simply obtained by leaving the offset preset pin open and
connecting a trim pot of 200Ω for the LH0033 between the
offset adjust pin and V
–
, as illustrated in Figure 1.
Operation From Single Or Asymmetrical Power Supplies
LH0033 may be used in applications where symmetrical
supplies are unavailable or not desirable. A typical application
might be an interface to a MOS shift register where V
–
= -12V. In this case, an apparent output offset occurs
and V
+
= +5V
due to the device’s voltage gain of less than unity. This
additional output error may be pre dict ed by:
+−V−
(V
∆V
≅ (1−AV)
O
)
= 0.005 (V+ −V−)
2
FIGURE 1. Offset Zero Adju st
+15V
1
INPUT
OFFSET
PRESET
(OPEN)
OFFSET
ADJUST
200Ω
5
6
7
LH0033
9
12
10
11
OUTPUT
-15V
Short Circuit Protection
In o rder to o ptimize tra nsient re sponse and o utput swin g,
output current limit has been omitted from the LH0033.
Short circuit protection may be added by inserting
appropriate value resistors between V
–
V
and V
–
pins as il lustrated in Figure 2. Resistor values
C
+
and V
+
pins and
C
may be predi cted by:
+
−
V
R
LIM
≅
V
=
I
I
SC
SC
where:
≤ 100mA for LH0033
I
SC
The inclusion of limiting resistors in the collector s of the output
transistors reduces output voltage swing. Decoupling VC
–
and V
pins with capacitors to ground will retain full output
C
swing for transient pulses. Alternate active current limit
techniques that retain full DC output swing are shown in
FIGURE 2. Resistor Current Limiti ng Usi n g Resistor
Figure 3. In Figure 3, the current sources are saturated
during normal operation, thus apply full supply voltage to the
pins. Under fault conditions, the voltage decreases as
V
C
required by the overload.
For Figure 5:
V
0.6V
LIM
=
BE
=
I
SC
60mA
= 10Ω
R
Capacitive Loading
The LH0033 is designed to drive capacitive loads such as
coaxial cables in excess of several thousand picofarads
without susceptibility to oscillation. However, peak current
resulting from (C × d
) shoul d be limited below absolute
V/dt
maximum pe ak curr ent ratings for the devices.
Thus for the LH0 033:
∆V
IN
(
) × CL ≤ I
∆t
≤ ±250mA
OUT
In addition, power dissipation resulting from driving capacitive
loads plus standby power should be kept below total package
power rating:
pkg. ≥ P
P
D
PDpkg. ≥ (V+–V–) × IS + P
P
≅ (Vp-p)2 × f × C
AC
DC
+ P
AC
AC
L
where:
Vp-p = Peak-to-peak output voltage swing
f = Frequency
= Load Capacitanc e
C
L
Operation Within An Op Am p Loop
LH0033 may be used as a current booster or isolator buffer
within a closed loop with op amps such as LH0032, or
CLM4124. An isolation resistor of 47Ω should be used between
the op amp output and the input of LH0033. The wide bandwidth
and high slew rate of the L H0033 assur e that the loo p has the
characteristics of the op amp and that additional rolloff is not
required.
Hardware
In order to utilize the full drive capabilities of LH0033, it should
be mounted with a heat sink particulary for extended
temperature operation. The case is isolated from the circuit
and may be connect ed to the syst em chassis.
Design Precaution
Power supply bypassing is necessary to prevent oscillation.
Low inductance ceramic disc capacitors with the shortest
practical lead lengths must be connected from each supply
1
lead (within <
⁄4" to 1⁄2" of the device package) to a ground
plane. Capacitors should be one or two 0.1µF in parallel;
adding a 4.7µF solid tantalum capacitor will help t roublsome
instances.
FIGURE 3. Current Limiting Usin g Current Sour ces