LM6321N National Semiconductor, LM6321N Datasheet - Page 7

• Manufacturer Part Number: LM6321N
• Description: IC BUFFER HIGH SPEED 8-DIP
• Manufacturer: National Semiconductor
• Series: VIP™r

Specifications of LM6321N

• Amplifier Type: Buffer
• Number Of Circuits: 1
• Slew Rate: 1200 V/µs
• -3db Bandwidth: 50MHz
• Current - Input Bias: 1µA
• Voltage - Input Offset: 15000µV
• Current - Supply: 15mA
• Current - Output / Channel: 300mA
• Voltage - Supply, Single/dual (±): 4.75 V ~ 32 V, ±2.38 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Output Type: -
• Gain Bandwidth Product: -
• Other names: *LM6321N; LM6321

Typical Performance Characteristics
Application Hints
POWER SUPPLY DECOUPLING
The method of supply bypassing is not critical for stability of
the LM6121 series buffers. However, their high current out-
put combined with high slew rate can result in significant
voltage transients on the power supply lines if much induc-
tance is present. For example, a slew rate of 900 V/µs into a
50Ω load produces a di/dt of 18 A/µs. Multiplying this by a
wiring inductance of 50 nH (which corresponds to approxi-
mately 1
minimize this problem use high quality decoupling very close
to the device. Suggested values are a 0.1 µF ceramic in
parallel with one or two 2.2 µF tantalums. A ground plane is
recommended.
LOAD IMPEDANCE
The LM6121 is stable to any load when driven by a 50Ω
source. As shown in the Overshoot vs Capacitive Load
graph, worst case is a purely capacitive load of about
1000 pF. Shunting the load capacitance with a resistor will
reduce overshoot.
SOURCE INDUCTANCE
Like any high frequency buffer, the LM6121 can oscillate at
high values of source inductance. The worst case condition
occurs at a purely capacitive load of 50 pF where up to
100 nH of source inductance can be tolerated. With a 50Ω
load, this goes up to 200 nH. This sensitivity may be reduced
at the expense of a slight reduction in bandwidth by adding a
resistor in series with the buffer input. A 100Ω resistor will
ensure stability with source inductances up to 400 nH with
any load.
OVERVOLTAGE PROTECTION
The LM6121 may be severely damaged or destroyed if the
Absolute Maximum Rating of 7V between input and output
pins is exceeded.
If the buffer’s input-to-output differential voltage is allowed to
exceed 7V, a base-emitter junction will be in reverse-
breakdown, and will be in series with a forward-biased base-
emitter junction. Referring to the LM6121 simplified sche-
matic, the transistors involved are Q1 and Q3 for positive
1
⁄
2
" of 22 gauge wire) result in a 0.9V transient. To
Forward Transmission
Gain (S12)
00922323
T
J
7
= 25˚C, unless otherwise specified (Continued)
inputs, and Q2 and Q4 for negative inputs. If any current is
allowed to flow through these junctions, localized heating of
the reverse-biased junction will occur, potentially causing
damage. The effect of the damage is typically increased
offset voltage, increased bias current, and/or degraded AC
performance. Furthermore, this will defeat the short-circuit
and over-temperature protection circuitry. Exceeding
input with a shorted output will destroy the device.
The device is best protected by the insertion of the parallel
combination of a 100 kΩ resistor (R1) and a small capacitor
(C1) in series with the buffer input, and a 100 kΩ resistor
(R2) from input to output of the buffer (see Figure 1). This
network normally has no effect on the buffer output. How-
ever, if the buffer’s current limit or shutdown is activated, and
the output has a ground-referred load of significantly less
than 100 kΩ, a large input-to-output voltage may be present.
R1 and R2 then form a voltage divider, keeping the input-
output differential below the 7V Maximum Rating for input
voltages up to 14V. This protection network should be suffi-
cient to protect the LM6121 from the output of nearly any op
amp which is operated on supply voltages of
HEATSINK REQUIREMENTS
A heatsink may be required with the LM6321 depending on
the maximum power dissipation and maximum ambient tem-
perature of the application. Under all possible operating
conditions, the junction temperature must be within the
range specified under Absolute Maximum Ratings.
To determine if a heatsink is required, the maximum power
dissipated by the buffer, P(max), must be calculated. The
formula for calculating the maximum allowable power dissi-
FIGURE 1. LM6121 with Overvoltage Protection
Current Limit
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±
00922324
15V or lower.
www.national.com
±
7V