24-03-2012, 12:50 PM
DUAL FULL-BRIDGE DRIVER
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DESCRIPTION
The L298 is an integratedmonolithic circuit in a 15-
lead Multiwatt and PowerSO20 packages. It is a
high voltage, high current dual full-bridge driver designedto
acceptstandardTTLlogic levels anddrive
inductive loads such as relays, solenoids, DC and
steppingmotors. Two enableinputs are providedto
enableor disablethe deviceindependentlyof theinput
signals. The emitters of the lower transistors of
each bridge are connected togetherand the correspondingexternal
terminal can be used for the connectionofanexternalsensingresistor.
Anadditional
supply input is provided so that the logic works at a
lower voltage.
1.1.POWER OUTPUT STAGE
TheL298integratestwopoweroutputstages(A; B).
The power output stage is a bridge configuration
and its outputs can drive an inductive load in commonor
differenzialmode, dependingon thestate of
the inputs. The current that flows through the load
comes out fromthe bridge at the sense output : an
external resistor (RSA ;RSB.) allows to detect the intensity
of this current.
1.2. INPUT STAGE
Eachbridge is driven by meansof four gatesthe input
of which are In1 ; In2 ; EnA and In3 ; In4 ; EnB.
TheIn inputs set thebridgestatewhenThe En input
is high; a lowstate of theEninputinhibitsthe bridge.
All the inputs are TTL compatible.
2. SUGGESTIONS
A non inductive capacitor, usually of 100 nF, must
be foreseen between both Vs and Vss, to ground,
as near as possible toGNDpin. Whenthe large capacitor
of the power supply is too far from the IC, a
second smaller one must be foreseen near the
L298.
The sense resistor, not of a wire wound type, must
be groundednear the negativepole of Vs that must
be near the GND pin of the I.C.
3. APPLICATIONS
Fig 6 showsa bidirectionalDC motor controlSchematic
Diagramfor which only one bridge is needed.
The external bridge of diodesD1 to D4 is made by
four fast recovery elements (trr 3 200 nsec) that
must be chosen of a VF as low as possible at the
worst case of the load current.
The senseoutputvoltagecanbeused to controlthe
current amplitude by chopping the inputs, or to provide
overcurrent protectionby switching low theenable
input.
The brake function (Fast motor stop) requires that
the Absolute Maximum Rating of 2 Amps must
never be overcome.