7

Application Notes

Circuit Description: continued

This section outlines a procedure for designing a boost switch-

ing power supply operating in the discontinuous mode.

Step 1

Determine the output power required by the load.

(1)

Step 2

Figure 7: Voltage and current waveforms for boost topology in CS5111.

Step 3

Next select the output voltage feedback sense resistor

divider as follows (Figure 8).

.

(3a)

, (3b)

=

. (3c)

(3d)

)

(

0

t

0

t

0

t

Design Procedure for Boost Topology

Figure 6: Block diagram of the 1.4A current mode control switching regulator portion of the CS5111 in a boost configuration.

1.4A

COMP

SELECT

Over Voltage

Gnd

Bandgap

Reference

Oscillator

Switcher Shutdown

Switcher

Error

Amplifier

Current Sense Amplifier

ENABLE

Multiplexer

-

COMP

Base Drive

Logic

64.9kΩ

1.25V

{

Figure 8. Feedback sense

resistor divider connected

-1