LTC6405
11
6405fb
pin Functions
VOCM (Pin 2/Pin 4): Output Common Mode Reference
Voltage. The voltage on VOCM sets the output common
mode voltage level (which is defined as the average of the
voltages on the +OUT and –OUT pins). The VOCM voltage
is internally set by a resistive divider between the supplies,
developing a default voltage potential of 2.5V with a 5V
supply. The VOCM pin can be over-driven by an external
voltage capable of driving the 19kΩ Thevenin equivalent
impedance presented by the pin. The VOCM pin should be
bypassedwithahighqualityceramicbypasscapacitorofat
least 0.01F, to minimize common mode noise from being
converted to differential noise by impedance mismatches
both externally and internally to the IC.
V+ (Pin 3/Pins 2, 10, 11):
V– (Pin 6/Pins 3, 9, 12):
Power Supply Pins. It is critical that close attention be
paid to supply bypassing. For single supply applications,
it is recommended that a high quality 0.1F surface mount
ceramicbypasscapacitorbeplacedbetweenV+andV–with
direct short connections. In addition, V– should be tied
directly to a low impedance ground plane with minimal
routing.Fordual(split)powersupplies,itisrecommended
that additional high quality, 0.1F ceramic capacitors are
used to bypass V+ to ground and V– to ground, again
with minimal routing. For driving large loads (<200Ω),
additional bypass capacitance may be needed for optimal
performance.Keepinmindthatsmallgeometry(e.g.,0603
orsmaller)surfacemountceramiccapacitorshaveamuch
higher self resonant frequency than do leaded capacitors,
and perform best in high speed applications.
+OUT, –OUT (Pins 4, 5/Pins 7, 14): Unfiltered Output
Pins. Besides driving the feedback network, each pin
can drive an additional 50Ω to ground with typical short
circuit current limiting of ±60mA. Each amplifier output
is designed to drive a load capacitance of 5pF. Larger
capacitive loads should be decoupled with at least 15Ω
resistors from each output.
VTIP (Pin 5) QFN Only: This pin can normally be left float-
ing. It determines which pair of input transistors (NPN or
PNP or both) is sensing the input signal. The VTIP pin is
set by an internal resistive divider between the supplies,
developing a default 2.8V voltage with a 5V supply. VTIP
has a Thevenin equivalent resistance of approximately
17k and can be over-driven by an external voltage. The
VTIP pin should be bypassed with a high quality ceramic
bypass capacitor of at least 0.01F. See the Applications
Information section for more details.
SHDN (Pin 7/Pin 1): When SHDN is floating or directly
tied to V+, the LTC6405 is in the normal (active) operating
mode.WhentheSHDNpinisconnectedtoV–,theLTC6405
enters into a low power shutdown state with Hi-Z outputs.
+IN,–IN(Pins8,1/Pins15,6):NoninvertingandInverting
Input Pins of the Amplifier, Respectively. For best perfor-
mance, it is highly recommended that stray capacitance
be kept to an absolute minimum by keeping printed circuit
connections as short as possible.
+OUTF, –OUTF (Pins 8, 13) QFN Only: Filtered Output
Pins. These pins have a series RC network (R = 50Ω,
C = 3.75pF) connected between the filtered and unfiltered
outputs. See the Applications Information section for
more details.
NC (Pin 16) QFN Only: No Connection. This pin is not
connected internally.
Exposed Pad (Pin 9/Pin 17): Tie the bottom pad to V–.
If split supplies are used, DO NOT tie the pad to ground.
(MSOP/QFN)