CS1680 datasheet(2/16 Pages) CIRRUS

2 / 16 page

CS1680

DS1055F1

1. INTRODUCTION

A typical schematic using the CS1680 for boost-buck

applications is shown on the previous page.

A startup circuit provides a low-impedance path to

improve electronic transformer compatibility. The GPIO

pin is used to disable the startup circuit when normal

operation is reached.

The CS1680 power supply is connected to an external

power supply network. A linear regulator at the output of

the boost converter provides steady-state operating

current to the IC. The rectified input voltage is sensed as

a current into pin VAC and is used to control the

adaptive

transformer

and

dimmer

compatibility

algorithm and extract the phase of the input voltage for

output dimming control.

During steady-state operation, the boost stage operates

in continuous conduction mode (CCM) to boost the

input voltage. This operation allows the boost stage to

provide transformer and dimmer compatibility, reduces

bulk capacitor ripple current, and provides a regulated

input voltage to the buck stage.

The output voltage of the CCM boost is sensed by the

current into the boost output voltage sense pin

(BSTOUT). The buck stage is implemented with

peak-current mode control. Voltage across an external

user-selected

resistor

sensed

through

BUCKSENSE to control the peak current through the

buck stage inductor. Leading-edge blanking on pin

BUCKSENSE prevents false triggering.

When an external negative temperature coefficient

(NTC) thermistor is connected to the eOTP pin, the

CS1680 monitors the system temperature, allowing the

controller to reduce the output current of the system. If

the temperature reaches a designated high set point,

the IC is shutdown and stops switching.

POR

Voltage

Regulator

VDD

BUCKSENSE

BUCKZCD

BUCKGD

VAC

DAC

ZCD

GND

BSTOUT

OCP

CLAMP

VST(th)

VSTP(th)

VBUCKOCP(th)

VBUCKZCD(th)

VBUCKPK(th)

ADC

Iref

BSTGD

VDD

GPIO

BSTSENSE

DAC

Boost

Peak Ctrl

BOCP

VBSTOCP(th)

VBSTPK(th)

ICONNECT

VCONNECT(th)

VDD

Buck

Peak Ctrl

MUX

CTRL2

eOTP

CTRL1

20k

MUX

BST Blank

Buck Blank

VDD

Figure 1. CS1680 Block Diagram

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