CS5111 데이터 시트보기 (PDF) - Cherry semiconductor

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CS5111

14.1A switching regulator with 5V,100mA linear regulator with watchdog,reset and enable

Cherry semiconductor 

Circuit Description: continued

VIN

VLIN

IBIAS

RBIAS

64.9kΩ

COSC

Oscillator

VREG

Over Voltage

COMP

COMP

Logic

Base Drive

VSW

1.4A

VOUT

COUT

Current Sense Amplifier

-

RS

Gnd

ENABLE

-

Switcher Shutdown

1.25V

Bandgap

Reference

Switcher

R1

VFB1

Error

Amplifier -

Multiplexer

VFB2

R2

R3

SELECT

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

Application Notes

Design Procedure for Boost Topology

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.

POUT = IOUTVOUT

(1)

Step 2

Choose COSC based on the target oscillator frequency with an

external resistor value, RBIAS = 64.9kΩ. (See Figure 1d).

VSW

VOUT

Step 3

Next select the output voltage feedback sense resistor

divider as follows (Figure 8).

For VFB1 active, choose a value for R1 and then solve for

REQ where:

REQ =

R1 .

VOUT

VFB1

-1

(3a)

For VFB2 active, find:

( ) VFB1 = VOUT

REQ

R1 + REQ

, (3b)

VOUT

{ VR2

REQ

R1

VFB1

R2

VFB2

R3

VIN

VSAT

0

ISW

IPeak

and then calculate R2 where:

Figure 8. Feedback sense

resistor divider connected

between VOUT and ground.

t

R2 =

VR2

IR2

=

VFB1 - VFB2

VFB1/REQ

. (3c)

Then find R3, where:

0

ID

IPeak

t

R3 = REQ - R2.

(3d)

0

t

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

7

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