ADPL74101 datasheet(34/49 Pages) AD

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Data Sheet

ADPL74101

analog.com

Rev. 0

34 of 49

Figure 40. Relationship Between INTVCC Voltage and Resistor Value at the DRVSET Pin

High-input-voltage applications in which large FETs are driven at high frequencies can exceed the maximum junction

temperature rating for the ADPL74101. The INTVCC current, which is dominated by the gate charge current, can be

supplied by either the VIN LDO regulator or the EXTVCC LDO regulator. When the voltage on the EXTVCC pin is less than

its switchover threshold (4.76V or 5.95V, as determined by the DRVUV pin), the VIN LDO regulator is enabled. In this

case, power dissipation for the IC is equal to VIN× INTVCC current (IINTVCC). The gate charge current is dependent on the

operating frequency, as discussed in the Efficiency Considerations section. To estimate the junction temperature, use

the equation detailed in Table 2. For example, the ADPL74101 INTVCC current is limited to less than 36mA from a 36V

supply when not using the EXTVCC supply at an ambient temperature of 70°C, as shown in Equation 20:

TJ = 70°C + (36mA)(36V)(43°C/W) = 125°C

(20)

To prevent the maximum junction temperature from exceeding, check the input supply current while operating in

continuous conduction mode (MODE = INTVCC) at maximum VIN.

When the voltage applied to EXTVCC exceeds its rising switchover threshold, the VIN LDO regulator turns off, and the

EXTVCCLDO regulator enables. The EXTVCC LDO regulator remains on as long as the voltage applied to EXTVCC remains

above its falling switchover threshold. The EXTVCC LDO regulator attempts to regulate the INTVCC voltage to the

voltage as programmed by the DRVSET pin. Therefore, while EXTVCC is less than 5V, the LDO regulator is in dropout,

and the INTVCC voltage is approximately equal to EXTVCC. When EXTVCC exceeds the programmed voltage (up to an

absolute maximum of 30V), INTVCC is regulated to the programmed voltage. Using the EXTVCC LDO regulator allows

the FET driver and control power to be derived from the switching regulator output of the ADPL74101 (4.7V ≤ VOUT ≤

30V) during normal operation, and from the VIN LDO regulator when the output is out of regulation (for example,

during startup or short-circuit). If more current is required through the EXTVCC LDO regulator than is specified, add

an external Schottky diode between the EXTVCCand INTVCC pins. In this case, do not apply more than 6V to the EXTVCC

pin.

Significant efficiency and thermal gains can be realized by powering INTVCC from an output, because the VIN current

resulting from the driver and control currents is scaled by a factor of VOUT/(VIN × efficiency). For 5V to 30V regulator

outputs, connect the EXTVCC pin to VOUT. Tying the EXTVCC pin to an 8.5V supply reduces the junction temperature as

shown in Equation 20 from 125°C to the results given by Equation 21, as follows:

TJ= 70°C + (36mA)(8.5V)(43°C/W) = 83°C

(21)

DRVSET PIN RESISTOR (kΩ)

5.5

5.4

5.3

5.2

5.1

5.0

4.6

4.4

4.2

4.7

4.8

4.9

4.5

4.3

4.1

4.0

110

120

100

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