Datasheet

LT1970
8
1970fc
PIN FUNCTIONS
V
EE
(Pins 1, 10, 11, 20, Package Base): Minus Supply
Voltage. V
EE
connects to the substrate of the integrated
circuit die, and therefore must always be the most negative
voltage applied to the part. Decouple V
EE
to ground with
a low ESR capacitor. V
EE
may be a negative voltage or it
may equal ground potential. Any or all of the V
EE
pins may
be used. Unused V
EE
pins must remain open.
V
–
(Pin 2): Output Stage Negative Supply. V
–
may equal
V
EE
or may be smaller in magnitude. Only output stage
current fl ows out of V
–
, all other current fl ows out of V
EE
.
V
–
may be used to drive the base/gate of an external power
device to boost the amplifi er’s output current to levels above
the rated 500mA of the on-chip output devices. Unless
used to drive boost transistors, V
–
should be decoupled
to ground with a low ESR capacitor.
OUT (Pin 3): Amplifi er Output. The OUT pin provides the
force function as part of a Kelvin sensed load connection.
OUT is normally connected directly to an external load cur-
rent sense resistor and the SENSE
+
pin. Amplifi er feedback
is directly connected to the load and the other end of the
current sense resistor. The load connection is also wired
directly to the SENSE
–
pin to monitor the load current.
The OUT pin is current limited to ±800mA typical. This
current limit protects the output transistor in the event
that connections to the external sense resistor are
opened or shorted which disables the precision current
limit function.
SENSE
+
(Pin 4): Positive Current Sense Pin. This lead is
normally connected to the driven end of the external sense
resistor. Sourcing current limit operation is activated when
the voltage V
SENSE
(V
SENSE
+ – V
SENSE
–) equals 1/10 of
the programming control voltage at VC
SRC
(Pin 13). Sink-
ing current limit operation is activated when the voltage
V
SENSE
equals –1/10 of the programming control voltage
at VC
SNK
(Pin 12).
FILTER (Pin 5): Current Sense Filter Pin. This pin is
normally not used and should be left open or shorted to
the SENSE
–
pin. The FILTER pin can be used to adapt the
response time of the current sense amplifi ers with a 1nF
to 100nF capacitor connected to the SENSE
–
input. An
internal 1k resistor sets the fi lter time constant.
SENSE
–
(Pin 6): Negative Current Sense Pin. This pin is
normally connected to the load end of the external sense
resistor.
Sourcing current limit operation is activated when
the voltage V
SENSE
(V
SENSE
+ – V
SENSE
–) equals 1/10 of
the programming control voltage at VC
SRC
(Pin 13). Sink-
ing current limit operation is activated when the voltage
V
SENSE
equals –1/10 of the programming control voltage
at VC
SNK
(Pin 12).
V
CC
(Pin 7): Positive Supply Voltage. All circuitry except
the output transistors draw power from V
CC
. Total sup-
ply voltage from V
CC
to V
EE
must be between 3.5V and
36V. V
CC
must always be greater than or equal to V
+
. V
CC
should always be decoupled to ground with a low ESR
capacitor.
–IN (Pin 8): Inverting Input of Amplifi er. –IN may be any
voltage from V
EE
– 0.3V to V
EE
+ 36V. –IN and +IN remain
high impedance at all times to prevent current fl ow into
the inputs when current limit mode is active. Care must
be taken to insure that –IN or +IN can never go to a volt-
age below V
EE
– 0.3V even during transient conditions or
damage to the circuit may result. A Schottky diode from
V
EE
to –IN can provide clamping if other elements in the
circuit can allow –IN to go below V
EE
.
+IN (Pin 9): Noninverting Input of Amplifi er. +IN may be any
voltage from V
EE
– 0.3V to V
EE
+ 36V. –IN and +IN remain
high impedance at all times to prevent current fl ow into
the inputs when current limit mode is active. Care must
be taken to insure that –IN or +IN can never go to a volt-
age below V
EE
– 0.3V even during transient conditions or
damage to the circuit may result. A Schottky diode from
V
EE
to +IN can provide clamping if other elements in the
circuit can allow +IN to go below V
EE
.