CS5111 datasheet(8/16 Pages) ONSEMI

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CS5111

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Figure 11. Block Diagram of the 1.4 A Current Mode Control Switching Regulator Portion of the

CS5111 in a Boost Configuration

Overvoltage

Bandgap

Reference

IBIAS

RBIAS

64.9 k

Ω

Switcher

Error

Amplifier

VLIN

ENABLE

VREG

Oscillator

COSC

COMP

Logic

Current Sense Amplifier

Base Drive

–

Switcher Shutdown

1.25 V

Multiplexer

VIN

VOUT

COUT

VSW

GND

1.4 A

VFB1

VFB2

SELECT

–

Figure 12. Voltage and Current Waveforms

for Boost Topology in CS5111

IPeak

ISW

VSW

VSAT

VIN

VOUT

PROTECTION CIRCUITRY

If the input voltage at VREG is increased above the

overvoltage threshold, the drive to the linear and switcher

output transistors is shut off. Therefore, VLIN is disabled and

VSW can not be pulled low.

The current out of VLIN is sensed in order to limit

excessive power dissipation in the linear output transistor

over the output range of 0 V to regulation. Also, the current

into VSW is sensed in order to provide the current limit

function in the switcher output transistor.

If the die temperature is increased above 160

°C, either due

to excessive ambient temperature or excessive power

dissipation, the drive to the linear output transistor is

reduced proportionally with increasing die temperature.

Therefore, VLIN will decrease with increasing die

temperature above 160

°C. Since the switcher control

circuitry

powered

through

VLIN, the switcher

performance, including current limit, will be affected by the

decrease in VLIN.

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