UCC1776_08 [TI]

Quad FET Driver;


型号：	UCC1776_08
厂家：	TEXAS INSTRUMENTS
描述：	Quad FET Driver
文件：	总7页 (文件大小：218K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

UCC1776

UCC2776

UCC3776

PRELIMINARY

Quad FET Driver

FEATURES

DESCRIPTION

The UCC3776 is a four output BCDMOS buffer/driver designed to drive highly

capacitive loads such as power MOSFET gates at high speeds. The device

can be configured as either an inverting or non-inverting driver via the POL

pin. The outputs are enabled by ENBL. When disabled, all outputs are active

low. The device incorporates thermal shutdown with hysteresis for stability.

The device also includes an undervoltage lockout circuit (UVLO) with hystere-

sis which disables the outputs when VDD is below a preset threshold. The

outputs are held low during undervoltage lockout, even in the absence of

VDD power to the device.This helps prevent MOSFET turn-on due to capaci-

tive current through the gate-drain capacitance of the power MOSFET in the

presence of high dV/dts. The logic input thresholds are compatible with

standard 5V HCMOS logic.

•

High Peak Output Current

Each Output – 1.5A Source,

2.0A Sink

•

Wide Operating Voltage

Range 4.5V to 18V

•

Thermal Shutdown

CMOS Compatible Inputs

Outputs Are Active Low

for Undervoltage Lockout

Condition

BLOCK DIAGRAM

UDG-95129-2

Note: Pin connections shown refer to 16-pin packages.

3/97

UCC1776

UCC2776

UCC3776

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage, VDD1, VDD2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20V

Maximum DC Voltage Difference, VDD1 vs.VDD2 . . . . . . . . . . . . . . . . . . . . . . .100mV

Logic Input, IN1, IN4, ENBL

Maximum forced voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .−0.3 to VDD1 + 0.3V

Logic Inputs, IN2, IN3, POL

Maximum forced voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .−0.3 to VDD2 + 0.3V

Latch-up Protection withstand Reverse Current

IREV, OUT1, OUT2, OUT3, OUT4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500mA

Power Outputs, OUT1, OUT2, OUT3, OUT4

Maximum pulsed current (10% duty max, 10µsec max pulse width) . . . . . . . . . .3A

Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .−65°C to +150°C

Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . .−55°C to +150°C

Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300°C

All currents are positive into, negative out of the specified terminal. Consult Packaging

Section of Databook for thermal limitations and considerations of packages.

CONNECTION DIAGRAMS

DIL-16 (Top View)

N or J, DP Packages

PLCC-28 (Top View)

Q Package

ELECTRICAL CHARACTERISTICS Unless otherwise stated these specifications apply for TA = −55°C to +125°C for

UCC1776;−40°C to +85°C for UCC2776;0°C to +70°C for UCC3776;VPOL = 5V, VENBL = 5V, 4.5V < VDD < 18V, TJ = TA.

PARAMETER

Input Section

TEST CONDITIONS

MIN

TYP

MAX

UNITS

VIH, Logic 1 Input Voltage

VIL, Logic 0 Input Voltage

IINn, Input Current

VINn = 5V

VINn = 0V

VENBL = 5V

VENBL = 0V

VPOL = 5V

VPOL = 0V

µA

–1

ENBL Input Current

POL Input Current

–1

−1

−30

UCC1776

UCC2776

UCC3776

ELECTRICAL CHARACTERISTICS (cont.) Unless otherwise stated these specifications apply for TA = −55°C to +125°C

for UCC1776;−40°C to +85°C for UCC2776;0°C to +70°C for UCC3776;VPOL = 5V, VENBL = 5V, 4.5V < VDD < 18V, TJ = TA.

PARAMETERTEST CONDITIONS

Output Section

MIN

TYP

MAX

UNITS

VOH, High Output Voltage

IOUTn = -10mA, VDD1 = VDD2 = 12V, VINn = 5V VDD− 1.0

IOUTn = 10mA, VDD1 = VDD2 = 12V, VINn = 0V

Ω

VOL, Low Output Voltage

Output Resistance

0.15

Output High Peak Current

VDD1 = VDD2 = 12V, OUTn = 5V, VINn = 5V,

TJ = 25°C (Note 1)

−1.5

Output Low Peak Current

VDD1 = VDD2 = 12V, OUTn = 5V, VINn = 0V,

TJ = 25°C (Note 1)

2.0

0.8

UVLO Output Pull-down Voltage

Switching Time Section

Output Rise Time

VDD1 = VDD2 = 3V, IOUTn = −10mA

1.5

COUTn = 1nF, VOUTn = 1V to 9V,

VDD1 = VDD2 = 12V

nsec

Output Fall Time

COUTn = 1nF, VOUTn = 9V to 1V,

VDD1 = VDD2 = 12V

nsec

IN−>OUT Delay Time (Rising Output) VINn = 2.5V, VOUTn = 0.1 • VDD,

VDD1 = VDD2 = 12, COUTn = 0nF

100

IN−>OUT Delay Time (Falling Output) VINn = 2.5V, VOUTn = 0.9 • VDD,

VDD1 = VDD2 = 12V, COUTn = 0nF

100

nsec

Power Supply Section

Power Supply Current

V(IN1−IN4) = 0V, VENBL = 0V,

VDD1 = VDD2 = 12V

UVLO Threshold

UVLO Hysteresis

4.5

0.5

Note 1: Guaranteed by design. Not 100% tested in production.

PIN DESCRIPTIONS

ENBL: Logic level input to enable the drivers.When ENBL OUT1 - OUT4: Outputs to each driver (1-4). The outputs

is low, the drivers outputs will be at GND potential, regard- are totem pole DMOS circuits. In the absence of VDD on

less of the status of POL. The input threshold is designed the device, the outputs will stay off, even with a capacitive

to be 5 volt CMOS compatible, independent of the VDD displacement current into the output node.

voltage used on the device. There is a slight hysteresis in

POL: Polarity selection for the drivers. A logic 0 selects

the input circuit to help reduce sensitivity to noise on the

inverting operation. A logic 1 selects non-inverting opera-

input signal or input ground.

tion. The input threshold is designed to be 5 volt CMOS

GND: Ground for the device, the supply return for the compatible, independent of the VDD voltage used on the

VDDs.There are four GND pads on the device.

device. There is a slight hysteresis in the input circuit to

help reduce sensitivity to noise.

IN1 - IN4: Inputs to each driver (1-4).The input threshold

is designed to be 5 volt CMOS compatible, independent VDD1: Supply Voltage for drivers 1 and 4. Tied internally

of the VDD voltage used on the device. There is a slight to VDD2.

hysteresis in the input circuit to help reduce sensitivity

to noise.

VDD2: Supply Voltage for drivers 2 and 3. Tied internally

to VDD1.

APPLICATION INFORMATION

Figure 1 depicts a block diagram of the UCC3776 Quad tion flexibility, while power packaging and high speed

FET Driver. Four high current, high speed gate drivers drive circuitry allow for driving high power MOSFET

with CMOS compatible input stages are provided. gates in high speed applications.

Polarity select and enable inputs provide circuit integra-

UCC1776

UCC2776

UCC3776

APPLICATION INFORMATION (cont.)

UDG-96006

Figure 1.Typical FET Driver Application

Input Stage

tify speed performance. While these specifications are

important, they do not provide all the required informa-

tion. The UCC3776 specifies rise and fall times of 25ns

and 10ns respectively into a load of 1nF. This specifica-

tion can be used to calculate the average slew rate capa-

bility of the driver stage over the output voltage range.

Each of the four UCC3776 FET driver circuits provides

an independent, CMOS compatible input stage. The

allowable input voltage range extends from ground to

VDD, allowing for easy interface to a wide variety of

PWM and power supply support circuitry. The POL and

ENBL inputs are tied to all four drivers, and all drivers

must be configured as either inverting or noninverting,

and all must be either enabled or not enabled.

However, the gate of a power MOSFET cannot be mod-

eled accurately with a simple capacitor. The voltage/cur-

rent requirements of the gate vary widely over several

distinct phases of FET turn-on and turn-off. The most

accurate way to calculate the switching times of power

MOSFETs is to determine the total gate charge require-

ment (Qg), which is usually specified by the MOSFET

manufacturer, and determine the peak current capability

of the MOSFET gate driver. Ideally the driver’s peak cur-

rent can be delivered while the MOSFET gate is transi-

tioning through its plateau or “Miller” level, when current

demands are highest.

To prevent oscillations in noisy PWM environments, any

unused drivers should have their input stages tied to

either VDD or ground. Unlike other CMOS FET drivers,

quiescent power current is not significantly affected by

the polarity of the driver input signal.

Output Stage/Gate Driver Considerations

Many power FET driver data sheets rely solely on rise

and fall time specifications into a capacitive load to quan-

UCC1776

UCC2776

UCC3776

APPLICATION INFORMATION (cont.)

The UCC3776 specifies peak source and sink currents gate drive energy (WGD) is computed as:

for a driver output voltage of 5V. This output voltage

WGD = 2 • 0.5 • CG • V²=

• V = QG • V

approximately coincides with the average gate plateau

voltage of a power MOSFET. Outside of the plateau

region the gate drive waveform is primarily limited by the

slew rate capability of the driver.Through proper analysis

of the MOSFET’s gate drive requirements and the speci-

fications for the UCC3776, an accurate model of AC per-

formance can be created. For a detailed description of

MOSFET AC gate drive requirements please see

Unitrode Application Notes U-118 and U-137. Although

the Unitrode power drivers referenced in these applica-

tion notes are bipolar devices, the information relating to

MOSFET gate drive characteristics is applicable.

Where QG is the MOSFET’s total gate charge, and V is

the gate voltage. The factor of two results from the fact

that the gate drive circuit must charge and discharge the

gate every electrical cycle. Each time the gate is charged

or discharged, the gate drive dissipates an amount of

energy equal to the energy supplied to the gate. Power

lost due to driving the gate is:

WGD

Q • V

PLGD =

= QG • V • F

Where F is the operating frequency of the MOSFET.This

is a worst case assumption since the power loss is

shared by the output driver and the gate resistor. If a rel-

atively large value series gate resistor is used, the power

loss in the gate driver is reduced. The penalty for this is

slower switching speed, and therefore more loss in the

MOSFET. For high power MOSFETs this power loss can

be significant.

Power Supply Decoupling/Grounding

The high peak currents required to charge high capaci-

tance MOSFET gates make proper power supply decou-

pling and grounding essential. The UCC3776 provides

two power supply inputs (VDD1 and VDD2) to allow for

optimum internal circuit layout and minimum resistive

voltage drop with high peak current loads. VDD1 pro-

vides the drive current for outputs 1 and 4, while VDD2

provides drive current for outputs 2 and 3. Both of these

pins must be externally connected to the source power

supply, and the DC potential difference between these

two points should be limited to 100mV. Under no circum-

stances should an output driver be used with only one

supply input connected.

To illustrate a typical example of driver loss, consider a

MOSFET with 70nC of gate charge and a 15V gate volt-

age.The power loss at 200kHz is:

PLGD = 70nC • 15V • 200kHz = 210mW

This analysis applies to one of the four drivers on the

UCC3776. Four drivers operating under the same condi-

tions results in a total power loss of 840mW. At higher

frequencies the dissipation will be proportionally greater.

This example demonstrates the need for power packag-

ing which is available on the UCC3776, and not available

on many other FET drivers.

To guarantee a low impedance current path over a wide

frequency range, each supply input should be separately

bypassed to ground with both a high value tantalum or

electrolytic capacitor in parallel with a 0.1µF ceramic

capacitor. The exact value of the tantalum or electrolytic

capacitor will depend on the charge requirements of the

MOSFET gate. For most applications a value between

1µF and 10µF should suffice. Connections for ground

leads should be kept as short as possible. The driver

chip and support electronics should be located over a

large copper ground plane if layout conditions allow it.

After device power dissipation has been estimated, prop-

er heat sinking must be provided to ensure that the

device junction temperature does not exceed the speci-

fied maximum. Refer to the packaging section of the

databook for package thermal impedance information.

Application Circuits

Power Dissipation/Thermal Considerations

Figure 1 depicts a typical gate drive application circuit.

Four independent, noninverting low side FET drivers are

shown. Although series gate drive resistors are not

required because all FET drivers have a finite peak current

capability, it is good practice to include some series resis-

tance to limit peak current and to prevent oscillations due

to parasitic inductance and capacitance.The parallel diode

and resistor allow for a faster gate turn off than turn on.

This characteristic is often desirable for bridge driver appli-

cations to prevent MOSFET cross conduction in the power

stage.

Being a CMOS device, the standby power dissipation of

the UCC3776 is quite low. For a 15V supply, the maxi-

mum quiescent current of 2mA results in a maximum

power loss of only 30mW. However, driving high frequen-

cy MOSFETs at high peak currents results in additional

power dissipation. This is because each time the MOS-

FET gate is charged or discharged, the energy transfer is

only 50% efficient. The same amount of energy that is

transferred to the gate is lost in the drive stage.

In order to determine the average output stage loss, the

UCC1776

UCC2776

UCC3776

APPLICATION INFORMATION (cont.)

Figure 2 shows an applications circuit with paralleled out- a single MOSFET, then four separate gate drive resistor

put drivers. If it is required to drive high gate charge

MOSFETs, the UCC3776 output drivers can be combined

for higher peak current capability. It is good practice to pro-

vide separate gate resistor networks to each individual

MOSFET as shown. This will ensure that each driver cir-

cuit will not see excessive current during the high gate

charge portion of the switching waveform. This practice

also tends to isolate driver circuits to reduce the possibility

of ringing and crosstalk. If all four drivers are used to drive

networks should be used.

Figure 3 shows a transformer coupled full bridge power

stage. The UCC3776 is ideally suited for interfacing

between low power PWM outputs and high power output

stages. Although the UC3879 phase shift controller is

shown in this example, the UCC3776 can be used in

many PWM controller applications where high power FET

drivers are required.

UDG-96007

Figure 2. Parallel Output Drivers

UDG-96008-1

Figure 3. Full Bridge Driver Application

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UCC1776_08 [TI]

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