LTC7803 datasheet(20/36 Pages) AD

20 / 36 page

LTC7803

Rev 0

For more information www.analog.com

APPLICATIONS INFORMATION

INTVCC Regulators

The LTC7803 features two separate internal P-channel

low dropout linear regulators (LDO) that supply power

at the INTVCC pin from either the VIN supply pin or the

EXTVCC pin depending on the connection of the EXTVCC

pin. INTVCC powers the gate drivers and much of the

LTC7803’s internal circuitry. The VIN LDO and the EXTVCC

LDO regulate INTVCC to 5.15V. Each of these can supply

a peak current of at least 100mA and must be bypassed

to ground with a minimum of 2.2μF ceramic capacitor,

placed as close as possible to the pin. No matter what

type of bulk capacitor is used, an additional 1μF ceramic

capacitor placed directly adjacent to the INTVCC and GND

pins is highly recommended. Good bypassing is needed

to supply the high transient currents required by the

MOSFET gate drivers.

High input voltage applications in which large MOSFETs

are being driven at high frequencies may cause the maxi-

mum junction temperature rating for the LTC7803 to be

exceeded. The INTVCC current, which is dominated by

the gate charge current, may be supplied by either the

VIN LDO or the EXTVCC LDO. When the voltage on the

EXTVCC pin is less than 4.7V, the VIN LDO is enabled.

Power dissipation for the IC in this case is highest and is

equal to VIN • INTVCC. The gate charge current is depen-

dent on operating frequency as discussed in the Efficiency

Considerations section. The junction temperature can

be estimated by using the equations given in Note 2 of

the Electrical Characteristics. For example, the LTC7803

INTVCC current is limited to less than 20mA from a 40V

supply when not using the EXTVCC supply at a 70°C ambi-

ent temperature:

TJ = 70°C + (20mA)(40V)(68°C/W for QFN) = 125°C

In the MSOP package, the INTVCC current is limited to less

than 34mA from a 40V supply:

TJ = 70°C + (34mA)(40V)(40°C/W for MSOP) = 125°C

To prevent the maximum junction temperature from being

exceeded, the input supply current must be checked while

operating in forced continuous mode (MODE = INTVCC)

at maximum VIN.

Figure 6. Two Different Modes of Output Voltage Tracking

Figure 7. Using the TRACK/SS Pin for TrackingTracking

(6a) Coincident Tracking

(6b) Ratiometric Tracking

TIME

VX(MASTER)

VOUT(SLAVE)

7803 F06a

TIME

7803 F06b

VX(MASTER)

VOUT(SLAVE)

LTC7803

VOUT

VFB

TRACK/SS

7803 F07

RTRACKA

RTRACKB

LTC7803 Datasheet(PDF) 20 Page - Analog Devices

LTC7803 Datasheet(HTML) 20 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL