+

LG

HG

BOOT

+

VIN

D1

CBOOT

LM2743

LM78L05

5V

VO

VCC

+

BOOT

HG

LG

VIN

VO

VCC

+

LM2743

D1

CBOOT

15

LM2743

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SNVS276I – APRIL 2004 – REVISED FEBRUARY 2019

Product Folder Links: LM2743

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Copyright © 2004–2019, Texas Instruments Incorporated

Feature Description (continued)

Figure 25. Basic Charge Pump (Bootstrap)

Note that the LM2743 can be paired with a low cost linear regulator like the LM78L05 to run from a single input

rail between 6.0 and 14 V. The 5-V output of the linear regulator powers both the VCC and the bootstrap circuit,

providing efficient drive for logic level MOSFETs. An example of this circuit is shown in Figure 26.

Figure 26. LM78L05 Feeding Basic Charge Pump

Figure 27 shows a second possibility for bootstrapping the MOSFET drives using a doubler. This circuit provides

an equal voltage drive of VCC - 3VD + VIN to both the high-side and low-side MOSFET drives. This method should

only be used in circuits that use 3.3 V for both VCC and VIN. Even with VIN = VCC = 3.0 V (10% lower tolerance on

3.3 V) and VD = 0.5 V both high-side and low-side gates will have at least 4.5 V of drive. The power dissipation of

the gate drive circuitry is directly proportional to gate drive voltage, hence the thermal limits of the LM2743 IC will

quickly be reached if this circuit is used with VCC or VIN voltages over 5V.