LTC4449 datasheet(9/14 Pages) AD

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LTC7067

Rev. 0

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OPERATION

Overview

The LTC7067 has two ground-referenced, low voltage dig-

ital signal inputs to drive two N-channel high-side power

MOSFETs. The output G2 is driven high or low, swinging

between G2VCC and G2RTN, depending on the G2IN pin.

Similarly, the output G1 is swinging between G1VCC and

G1RTN. Each channel is controlled by its input pins (G1IN

and G2IN), allowing independent flexibility to control on

and off state of the output.

Both the G1 and G2 drivers are high-side gate drivers.

LTC7067 features robust drive with excellent noise

and transient immunity, including large negative ground

difference tolerance (−10V) on switch node (G1RTN,

G2RTN). The two drivers are symmetric and indepen-

dent of each other, allowing G1 and G2 complementary

or non-complementary switching.

VCC Supply

VCC is the power supply for the LTC7067’s internal cir-

cuitry. An internal 4.5V supply is generated from the

VCC supply to bias all the internal circuits referred to

SGND. The VCC pin may be tied to the G2VCC pin if SGND

and G2RTN are at the same potential. VCC is independent

of VIN.

Input Stage (G1IN, G2IN)

The LTC7067 employs two logic inputs with fixed tran-

sition thresholds. When the voltage on G1IN is greater

than the threshold VIH(G1IN), G1 is pulled up to G1VCC,

turning the external MOSFET on. This MOSFET will stay

on until G1IN falls below VIL(G1IN). Similarly, when G2IN

is greater than VIH(G2IN), G2 is pulled up to G2VCC, turning

the external MOSFET on. G2 will stay high until G2IN falls

below the threshold VIL(G2IN).

The hysteresis between the corresponding VIH and VIL

voltage levels eliminates false triggering due to the noise

during switch transitions. However, care should be taken to

keep noise from coupling into the input pins (G1IN, G2IN),

particularly in high frequency, high voltage applications.

When G1IN/G2IN pin is floating, there is an internal 1000k

pull-down resistor from the G1IN/G2IN pin to SGND, keep-

ing the G1/G2 default state low if the input is not driven.

Both G1IN and G2IN pin can be used by the controller IC

to perform the Discontinuous Conduction Mode (DCM)

in switching regulator applications.

Output Stage

A simplified version of the LTC7067’s output stage is

shown in Figure 1. Both G1 and G2 designs are sym-

metrical and have floating gate-driver outputs. The

pull-up device is a P-channel MOSFET with a typical

1.5Ω RDS(ON) and the pull-down device is a N-channel

MOSFET with a typical 0.8Ω RDS(ON). The wide driver

supply voltage ranging from 4V to 14V enables driving

different power MOSFETs, such as logic level or high

threshold MOSFETs. However, LTC7067 is optimized for

high threshold MOSFETs (e.g., G1VCC – G1RTN = 10V

and G2VCC – G2RTN = 10V). The driver output pull-up

and pull-down resistance may increase with lower driver

supply voltage.

Figure 1. Simplified Output Stage

1.5

0.8

1.5

CGD

CGS

CGD

CGS

LTC7067

G1VCC

G1RTN

G2VCC

G2RTN

VIN

FLOATING

GROUND

VIN

FLOATING

GROUND

7067 F01

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