TABLE 1. Components for Typical 2.5V, 300kHz Application Circuits

Input Voltage

4.75V to 24V

4.5V to 6V

Output Current

4A

10A

Application

Notebook

Desktop

Q1 and Q2

Fairchild FDS6680; Siliconix

Si4410DY; or International Rectifier

IRF7805

Fairchild FDB7030L; or Motorola

MTB75N03HDL

Inductor L1

Sumida CDRH127-7R6: 7.6 µH, 5.9A

Pulse PE-53681: 2.5 µH, 11.4A

Input Capacitors

2 x 22µF, 35V Sprague 593D or TPS

2 x 220 µF, 10V Sanyo OS-CON SA

Output Capacitors

2 x 220µF, 10V Sprague 593D or TPS

3 x 330 µF, 6.3V Sanyo OS-CON SA

Rectifier D1

Motorola MBRS140T3

Motorola MBRS340T3

Sensing Resistor R3

15 m

Ω IRC

3x20m

Ω IRC

Compensation components C8 and

R8

R8 = 3.3 K

Ω,C8 = 1nF

R8 = 4K

Ω,C8 = 1nF

When the input voltage is low (less than 5V), the bootstrap

function cannot deliver enough gate voltage to fully drive the

high-side MOSFET on, which increases Rdson, and conse-

quently reduces efficiency. An external charge-pump doubler

can be added to double the CBOOT pin voltage (see

Figure

3). It can also be added to the VIN pin to increase the gate

drive voltage at both high-side and low-side MOSFETs.

DS100937-4

FIGURE 2. The Typical 2.5V Application Circuit

www.national.com

10