ADP2450ASTZ-5-R7 datasheet(29/40 Pages) AD

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Data Sheet

ADP2450

Rev. B | Page 29 of 40

Buck Regulator Voltage Conversion Limitations

The minimum output voltage of a buck regulator for a given

input voltage and switching frequency is constrained by the

minimum on time. The minimum on time of the ADP2450

buck regulator is typically 50 ns. The minimum output voltage

at a given input voltage and frequency is calculated using the

following equation:

VOUT2_MIN = VIN × tMIN_ON × fSW − (RDSON_HS − RDSON_LS) ×

IOUT2_MIN × tMIN_ON × fSW − (RDSON_LS + RL) × IOUT2_MIN

(1)

where:

VOUT2_MIN is the minimum output voltage.

tMIN_ON is the minimum on time.

fSW is the switching frequency.

RDSON_HS is the high-side MOSFET on resistance.

RDSON_LS is the low-side MOSFET on resistance.

IOUT2_MIN is the minimum output current.

RL is the series resistance of the output inductor.

The maximum output voltage of a buck regulator for a given

input voltage and switching frequency is constrained by the

minimum off time. The minimum off time of the ADP2450

buck regulator is typically 150 ns.

The maximum output voltage, limited by the minimum off time

at a given input voltage and frequency, is calculated using the

following equation:

VOUT2_MAX =

VIN × (1 − tMIN_OFF × fSW) − (RDSON_HS − RDSON_LS) × IOUT2_MAX ×

(1 − tMIN_OFF × fSW) − (RDSON_LS + RL) × IOUT2_MAX

(2)

where:

VOUT2_MAX is the maximum output voltage.

tMIN_OFF is the minimum off time.

IOUT2_MAX is the maximum output current.

EXTERNAL MOSFET FOR ACTUATOR

The ADP2450 has an integrated actuator driver. When the

analog trip is triggered or the TRG pin is pulled up high, the

internal actuator driver outputs a 5 V driver signal on the

GATE pin and turns on the external MOSFET to trigger the

actuator. The instantaneous current when the actuator is

triggered is equal to VOUT1 divided by the resistance of the

actuator. The continuous drain current of the MOSFET must be

larger than the instantaneous current when the actuator is

triggered. In normal operation where the MOSFET is turned

off, VOUT1 the voltage added onto the drain and source nodes of

the MOSFET. It is recommended to select a MOSFET with a

VDSS that is twice as large as VOUT1 to provide enough margin.

The recommended MOSFETs listed in Table 12 can also be used

as the MOSFET for the actuator.

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