LTC4367 datasheet(21/32 Pages) AD

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LTC7862

Rev 0

For more information www.analog.com

DRVCC Regulators

The LTC7862 features two separate low dropout linear

regulators (LDO) that can supply power at the DRVCC

pin. The internal VIN LDO uses an internal P-channel

pass device between the VIN and DRVCC pins. The inter-

nal EXTVCC LDO uses an internal P-channel pass device

between the EXTVCC and DRVCC pins.

The DRVCC supply is regulated to 6V or 9V, depending on

how the DRVUV pin is set. The internal VIN and EXTVCC

LDOs can supply a peak current of at least 50mA. The

DRVCC pin must be bypassed to ground with a minimum

of 4.7μF ceramic capacitor. Good bypassing is needed

to supply the high transient currents required by the

MOSFET gate drivers.

The DRVUV pin programs the DRVCC supply voltage and

also selects different DRVCC UVLO and EXTVCC switchover

threshold voltages. Tables 2a and 2b summarize the dif-

ferent DRVUV pin configurations along with the voltage

settings that go with each configuration. Tying the DRVUV

pin to INTVCC programs DRVCC to 9V. Tying the DRVUV

pin to GND programs DRVCC to 6V.

Table 2a.

DRVUV PIN

DRVCC VOLTAGE

GND

INTVCC

Table 2b.

DRVUV

DRVCC UVLO

RISING/FALLING

THRESHOLDS

EXTVCC SWITCHOVER

RISING/FALLING

THRESHOLD

GND

4.0V/3.8V

4.7V/4.45V

INTVCC

7.5V/6.7V

7.7V/7.45V

APPLICATIONS INFORMATION

High input voltage applications in which large MOSFETs

are being driven at high frequencies may cause the maxi-

mum junction temperature rating for the LTC7862 to be

exceeded. The DRVCC current, which is dominated by the

gate charge current, may be supplied by the VIN LDO, or

the EXTVCC LDO. When the voltage on the EXTVCC pin is

less than its switchover threshold (4.7V or 7.7V as deter-

mined by the DRVUV pin described above), the VIN LDO is

enabled. Power dissipation in this case is highest and is

equal to VIN • IDRVCC and is dissipated inside the IC. The

gate charge current is dependent on operating frequency.

When the voltage applied to EXTVCC rises above its

switchover threshold, the VIN LDO is turned off and the

EXTVCC LDO is enabled. The EXTVCC LDO remains on as

long as the voltage applied to EXTVCC remains above the

switchover threshold minus the comparator hysteresis.

The EXTVCC LDO attempts to regulate the DRVCC voltage

to the voltage as programmed by the DRVUV pin, so while

EXTVCC is less than this voltage, the LDO is in dropout

and the DRVCC voltage is approximately equal to EXTVCC.

When EXTVCC is greater than the programmed voltage,

up to an absolute maximum of 14V, DRVCC is regulated

to the programmed voltage.

Using the EXTVCC LDO allows the MOSFET driver and

control power to be derived from the LTC7862’s switch-

ing regulator output (4.7V/7.7V ≤ VOUT ≤ 14V). If more

current is required through the EXTVCC LDO than is speci-

fied, an external Schottky diode can be added between the

EXTVCC and DRVCC pins. In this case, do not apply more

than 10V to the EXTVCC pin and make sure that EXTVCC

≤ VIN.

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