Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - gate drivers Non-inverting Low side SOIC 8

UCC27423-Q1

UCC27424-Q1

UCC27425-Q1

SGLS274F –SEPTEMBER 2008–REVISED SEPTEMBER 2012

www.ti.com

APPLICATION INFORMATION

General Information

High frequency power supplies often require high-speed, high-current drivers such as the UCC27423-

Q1/UCC27424-Q1. A leading application is the need to provide a high power buffer stage between the PWM

output of the control IC and the gates of the primary power MOSFET or IGBT switching devices. In other cases,

the driver IC is utilized to drive the power device gates through a drive transformer. Synchronous rectification

supplies also have the need to simultaneously drive multiple devices which can present an extremely large load

to the control circuitry.

Driver ICs are utilized when it is not feasible to have the primary PWM regulator IC directly drive the switching

devices for one or more reasons. The PWM IC may not have the brute drive capability required for the intended

switching MOSFET, limiting the switching performance in the application. In other cases there may be a desire to

minimize the effect of high frequency switching noise by placing the high current driver physically close to the

load. Also, newer ICs that target the highest operating frequencies may not incorporate onboard gate drivers at

all. Their PWM outputs are only intended to drive the high impedance input to a driver such as the UCC27423-

Q1/UCC27424-Q1. Finally, the control IC may be under thermal stress due to power dissipation, and an external

driver can help by moving the heat from the controller to an external package.

Input Stage

The input thresholds have a 3.3-V logic sensitivity over the full range of V

voltages; yet it is equally compatible

with 0 to V

signals. The inputs of UCC2742x-Q1 drivers are designed to withstand 500-mA reverse current

without either damage to the IC for logic upset. The input stage of each driver should be driven by a signal with a

short rise or fall time. This condition is satisfied in typical power supply applications, where the input signals are

provided by a PWM controller or logic gates with fast transition times (<200 ns). The input stages to the drivers

function as a digital gate, and they are not intended for applications where a slow changing input voltage is used

to generate a switching output when the logic threshold of the input section is reached. While this may not be

harmful to the driver, the output of the driver may switch repeatedly at a high frequency.

Users should not attempt to shape the input signals to the driver in an attempt to slow down (or delay) the signal

at the output. If limiting the rise or fall times to the power device is desired, limit the rise or fall times to the power

device, then an external resistance can be added between the output of the driver and the load device, which is

generally a power MOSFET gate. The external resistor may also help remove power dissipation from the device

package, as discussed in the section on Thermal Considerations.

Output Stage

Inverting outputs of the UCC2742x-Q1 are intended to drive external P-channel MOSFETs. Noninverting outputs

of the UCC2742x-Q1 are intended to drive external N-channel MOSFETs.

Each output stage is capable of supplying ±4-A peak current pulses and swings to both V

and GND. The

pullup/ pulldown circuits of the driver are constructed of bipolar and MOSFET transistors in parallel. The peak

output current rating is the combined current from the bipolar and MOSFET transistors. The output resistance is

the RDS(on) of the MOSFET transistor when the voltage on the driver output is less than the saturation voltage

of the bipolar transistor. Each output stage also provides a very low impedance to overshoot and undershoot due

to the body diode of the external MOSFET. This means that in many cases, external Schottky-clamp diodes are

not required.

The UCC2742x-Q1 family delivers the 4-A gate drive where it is most needed during the MOSFET switching

transition – at the Miller plateau region – providing improved efficiency gains. A unique bipolar and MOSFET

hybrid output stage in parallel also allows efficient current sourcing at low supply voltages.

Source/Sink Capabilities During Miller Plateau

Large power MOSFETs present a large load to the control circuitry. Proper drive is required for efficient, reliable

operation. The UCC2742x-Q1 drivers have been optimized to provide maximum drive to a power MOSFET

during the Miller plateau region of the switching transition. This interval occurs while the drain voltage is swinging

between the voltage levels dictated by the power topology, requiring the charging/discharging of the drain-gate

capacitance with current supplied or removed by the driver device. [1]