Datasheet

VCC
R
OH
R
OL
Gate
Voltage
Boost
Narrow Pulse at
each Turn On
Anti Shoot-
Through
Circuitry
Input Signal
R
NMOS
, Pull Up
OUTL
OUTH
UCC27511
UCC27512
SLUSAW9E FEBRUARY 2012REVISED DECEMBER 2013
www.ti.com
Enable Function
As mentioned earlier, an enable/disable function is easily implemented in UCC27511 and UCC27512 using the
unused input pin. When IN+ is pulled down to GND or IN- is pulled down to VDD, the output is disabled. Thus
IN+ pin can be used like an enable pin that is based on active-high logic, while IN- can be used like an enable
pin that is based on active-low logic.
Output Stage
The output stage of the UCC27511 and UCC27512 devices are illustrated in Figure 23. OUTH and OUTL are
internally connected and pinned out as OUT pin in the UCC27512 . The UCC27511 and UCC27512 devices
feature a unique architecture on the output stage which delivers the highest peak-source current when it is most
needed during the Miller plateau region of the power switch turnon transition (when the power switch
drain/collector voltage experiences dV/dt). The device output stage features a hybrid pullup structure using a
parallel arrangement of N-Channel and P-Channel MOSFET devices. By turning on the N-Channel MOSFET
during a narrow instant when the output changes state from low to high, the gate-driver device is able to deliver a
brief boost in the peak-sourcing current enabling fast turn on.
Figure 23. UCC2751X Gate Driver Output Structure
The R
OH
parameter (see ELECTRICAL CHARACTERISTICS) is a DC measurement and it is representative of
the on-resistance of the P-Channel device only, since the N-Channel device is turned on only during output
change of state from low to high. Thus the effective resistance of the hybrid pullup stage is much lower than what
is represented by R
OH
parameter. The pulldown structure is composed of a N-Channel MOSFET only. The R
OL
parameter (see ELECTRICAL CHARACTERISTICS), which is also a DC measurement, is representative of true
impedance of the pull-down stage in the device. In UCC27511 and UCC27512, the effective resistance of the
hybrid pullup structure is approximately 2.7 x R
OL
.
The UCC27511 and UCC27512 are capable of delivering 4-A source, 8-A sink (asymmetrical drive) at VDD = 12
V. Strong sink capability in asymmetrical drive results in a very low pulldown impedance in the driver output
stage which boosts immunity against parasitic, Miller turnon (C x dV/dt turn on) effect, especially where low gate-
charge MOSFETs or emerging wide band-gap GaN-power switches are used.
An example of a situation where Miller turnon is a concern is synchronous rectification (SR). In SR application,
the dV/dt occurs on MOSFET drain when the MOSFET is already held in off state by the gate driver. The current
discharging the C
GD
Miller capacitance during this dV/dt is shunted by the pulldown stage of the driver. If the
pulldown impedance is not low enough then a voltage spike can result in the V
GS
of the MOSFET, which can
result in spurious turnon. This phenomenon is illustrated in Figure 24. UCC27511 and UCC27512 offers a best-
in-class, 0.375-Ω (typ) pulldown impedance boosting immunity against Miller turnon.
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