CS2841B datasheet(4/6 Pages) CHERRY

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VREF

VCC

1kΩ

0.1µF

VREF

VCC

VOUT

Gnd

VFB

Sense

OSC

COMP

5kΩ

100kΩ

4.7kΩ

1kΩ

Error Amp

Adjust

4.7kΩ

Sense

Adjust

2N2222

Gnd

Test Circuit

Undervoltage Lockout

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

er is biased to a high impedance state. The output should

be shunted to ground with a resistor to prevent output

leakage current from activating the power switch.

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.

When the power supply sees a sudden large output cur-

rent increase, the control voltage will increase allowing the

duty cycle to momentarily increase. Since the duty cycle

tends to exceed the maximum allowed to prevent trans-

VCC

VON = 8.0V

VOFF= 7.4V

ON/OFF Command

to reset of IC

<15mA

<1mA

7.4V 8.0V

ICC

VCC

Circuit Description

Typical Performance Characteristics:

.0005

.001

.002

.003

.005

.01

.02

.03

.04

800

900

CT (µF)

700

600

500

400

300

200

100

.05

RT =1.5kΩ

RT =680Ω

RT =10kΩ

100

200

700

10k

RT (Ω)

500

400

300

100

Oscillator Duty Cycle vs RT

Oscillator Frequency vs CT

Figure 1: Typical Undervoltage Characteristics

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