CS52843 Просмотр технического описания (PDF) - Cherry semiconductor

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производитель

CS52843

Current Mode PWM Control Circuit

Cherry semiconductor 

Typical Performance Characteristics

900

800

RT =680Ω

700

600

500

RT =1.5kΩ

400

300

200

RT =10kΩ

100

.0005

.001

.002 .003 .005

.01

CT (µF)

.02 .03 .04 .05

Oscillator Frequency vs CT

100

90

80

70

60

50

40

30

20

10

100

200 300 400 500 700 1k

2k 3k 4k 5k 7k 10k

RT (Ω)

Oscillator Duty Cycle vs RT

Test Circuit Open Loop Laboratory Test Fixture

4.7kΩ

1kΩ

Error Amp

Adjust

4.7kΩ

RT

2N2222

100kΩ

COMP

5kΩ

Sense

Adjust

VFB

Sense

OSC

VREF

VCC

V O UT

Gnd

A

0.1µF

0.1µF

1kΩ

1W

VREF

VCC

V O UT

Gnd

CT

Circuit Description

VCC

ON/OFF Command

to reset of IC

VON =8.4V

VOFF = 7.6V

ICC

<15mA

<500µA

VON VOFF

VCC

Figure 1: Startup voltage for the CS52843.

Undervoltage Lockout

During Undervoltage Lockout (Figure 1), the output driv-

er is biased to sink minor amounts of current. The output

should be shunted to ground with a resistor to prevent

activating the power switch with extraneous leakage cur-

rents.

PWM Waveform

To generate the PWM waveform, the control voltage from

the error amplifier is compared to a current sense signal

which represents the peak output inductor current (Figure

2). An increase in VCC causes the inductor current slope to

increase, thus reducing the duty cycle. This is an inherent

feed-forward characteristic of current mode control, since

the control voltage does not have to change during

changes of input supply voltage.

4

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