Cirrus Logic CS1680 User Manual

Dimmable LED Driver IC

LED +

LED -

OUT

NTC

BST

BUCK

CS1680

VAC

BUCKGD

BSTOUT

CLAMP

BUCKZCD

BUCKSENSE

eOTP

CLAMP

NTC

BST

12VAC/VDC

rec t

BST

BUCK

CLAMP

VDD

GPIO

BST SENSE

BSTGD

rect

BUCK(Sense)

BST(Sense)

BST

GND

CTRL1

CTRL2

C1 C3

rect

BST

BUCK

for Low-voltage Lighting

CS1680

Features

• Best-in-class Transformer Compatibility

- Magnetic Transformers

- Electronic Transformers

• Best-in-class Dimmer Compatibility

- Leading-edge (TRIAC) Dimmers

- Trailing-edge Dimmers

• High Efficiency

- Up to 80% for CS1680-00 Applications

- Up to 83% for CS1680-02 Applications

• Flicker-free Dimming

• 5% Minimum Dimming Level

• Cascade Boost-buck Topology with Constant-current Output

- CS1680-00 Output Voltage 15V

- CS1680-02 Output Voltage 21V

• Fast Startup

• Tight LED Current Regulation: Better than ±10%

• >0.9 Power Factor on Magnetic Transformers

• Soft Start

• Protections:

- Output Open/Short

- Boost Overvoltage

- Overcurrent Detection

- External Overtemperature Using NTC

Overview

The CS1680 is a cascade boost-buck dimmable LED driver for the 12V halogen lamp-replacement market. The CS1680 uses a Cirrus Logic proprietary intelligent digital control that provides exceptional single-lamp and multi-lamp transformer compatibility for non-dimmer systems and dimmer systems paired with electronic and magnetic low-voltage transformers.

The CS1680 integrates a continuous conduction mode (CCM) boost converter that provides transformer compatibility and dimmer compatibility. An adaptive digital algorithm controls the boost stage and dimmer compatibility operation mode to enable flicker-free operation down to 5% output current with leading-edge and trailing-edge dimmers.

Applications

• MR16 Lamps

• All 12VAC/VDC Low-voltage Lighting Applications

Ordering Information

See page 15.

Cirrus Logic, Inc.

http://www.cirrus.com

OCT’14

DS1055F1

1. INTRODUCTION

POR

Voltage

Regulator

VDD

BUCKSENSE

BUCKZCD

BUCKGD

VAC

DAC

ZCD

GND

BSTOUT

OCP

CLAMP

ST(th)

STP(th)

BUCKOCP(th)

BUCKZCD(th)

BUCKPK(th)

ADC

ref

BSTGD

VDD

GPIO

STSENSE

DAC

Boost

Peak Ctrl

BOCP

BSTOCP(th)

BSTPK(th)

CONNECT

CONNECT (th)

VDD

Buck

Peak Ctrl

MUX

CTRL2

eOTP

CTRL1

20k

MUX

BST Blank

Buck Blank

VDD

Figure 1. CS1680 Block Diagram

CS1680

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

2 DS1055F1

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 is sensed through pin 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.

2. PIN DESCRIPTION

General Purpose Input/Output

Boost Gate Driver

Ground

Peak Current

xternal Overtemperature Protection

No Connect

GPIO

VDDIC Supply Voltage

BSTGD

GND

CTRL2

CLAMP

BUCKGD

BUCKSENSE

VAC

BSTOUT

CTRL1

eOTP

BSTSENSEBoost Stage Current Sense

16-lead TSSOP

BUCKZCD

No Connect

Voltage Clamp Current Source

Buck Gate Driver

Buck Stage Current Sense

Rectifier Voltage Sense

Boost Output Voltage Sense

Boost Stage Constant

Buck Stage Zero-current Detect

Figure 2. CS1680 Pin Assignments

CS1680

Pin Name

CTRL2

eOTP

BSTSENSE

GND

BSTGD

VDD

GPIO

BUCKZCD

CLAMP

BUCKGD

Pin # I/O

1IN

2IN

3IN

4PWR

5OUT

6PWR

7IN/OUT

8IN

9IN

10 IN

11 OUT

12 OUT

Description

Peak Current — Connect a resistor to this pin to set the comparator threshold to

reflect the desired boost peak current in Trailing Edge Electronic Transformer Mode (Mode 2).

External Overtemperature Protection — Connect an external NTC thermistor to this pin, allowing the internal A/D converter to sample the change to NTC resistance.

Boost Stage Current Sense — The current flowing in the boost stage FET is sensed across a resistor. The resulting voltage is applied to this pin and digitized for use by the boost stage computational logic to determine the FET duty cycle.

Ground — Common reference. Current return for both the input signal portion of the IC and the gate driver.

Boost Gate Driver — Gate drive for the boost stage power FET.

IC Supply Voltage —

operating current for the device, including the gate drive current to the power transistor

General Purpose Input/Output — Used to drive the FET gate for the startup circuit.

No Connect — Leave pin not connected.

Buck Stage Zero-current Detect — Buck stage inductor sensing input. The pin is

connected to the drain of the buck stage power FET with a capacitor.

No Connect — Leave pin not connected.

Voltage Clamp Current Source — Connect to a voltage clamp circuit on the output

of the boost stage.

Buck Gate Driver — Gate drive for the buck stage power FET.

Connect a storage capacitor to this pin to serve as a reservoir for

BUCKSENSE

VAC

BSTOUT

CTRL1

DS1055F1 3

13 IN

14 IN

15 IN

16 IN

Buck Stage Current Sense — The current flowing in the buck stage FET is sensed across a resistor. The resulting voltage is applied to this pin and digitized for use by the buck stage computational logic to determine the FET duty cycle.

Rectifier Voltage Sense — A current proportional to the rectified line voltage is fed into this pin. The current is measured with an A/D converter.

Boost Output Voltage Sense — A current proportional to the boost output is fed into this pin. The current is measured with an A/D converter.

Boost Stage Constant — Connect a resistor to this pin to set the constant ratio for the boost stage current calculations in Leading Edge Electronic Transformer Mode (Mode 3).

CS1680

3. CHARACTERISTICS AND SPECIFICATIONS

3.1 Electrical Characteristics

Typical characteristics conditions:

=25°C, VDD= 12V, GND = 0 V

- T

- All voltages are measured with respect to GND.

- Unless otherwise specified, all currents are positive when

flowing into the IC.

Parameter Condition Symbol Min Typ Max Unit

VDD Supply Voltage

Operating Range

Turn-on Threshold Voltage

Turn-off Threshold Voltage (UVLO)

GPIO Low

Zener Voltage

(Note 1)

(Note 2)

After Turn-on

VDD Increasing

VDD Decreasing

=20mA

VDD Supply Current

Startup Supply Current

Operating Supply Current

(Note 3)

VDD<V

= 0.25nF, fsw70 kHz

Reference

Reference Current I

Clamp Gate Drive

Output Source Resistance Z

Output Sink Resistance Z

Boost Output Mode1 Algorithm

Regulation Target

(Notes 1, 4) K

Boost Output Mode2 Mode Algorithm

Regulation Target

(Notes 1, 5) K

Boost Output Mode3 Algorithm

Regulation Range Low

(Notes 1, 6)

CS1680-00 CS1680-02

Regulation Range High

(Notes 1, 6) K

Accelerated Decrease On

CS1680-00 CS1680-02

Accelerated Increase On

(Notes 1, 7)

Accelerated Increase Off (Notes 1, 7)

Boost Pulse Width Modulator

Minimum On Time T1

Maximum On Time T1

Constant Off Time Mode1 T2

Minimum Off Time Mode2 & Mode3 T2

Maximum Off Time Mode2 & Mode 3 T2

Minimum Switching Frequency - 1.3 - kHz

Maximum Switching Frequency - 3.3 - MHz

Minimum/Maximum characteristics conditions:

- TJ= -40°C to +125 ° C, VDD= 11V to 17V, GND = 0 V

ST(th)

STP(th)

GPIO(low)

11 - 17 V

-8.5-V

-7.5-V

-50.0-%

18.5 - 19.8 V

--1.0mA

-11-mA

ref

CLAMP(Source)

CLAMP(Sink)

Mode1(target)

Mode2(target)

Mode3(low)

-64-A

- 290 - 

- 208 - 

-73.3-%

-78.4-%

Mode3(high)

DEC(on)

-82.0-%

CLAMP(on)

CLAMP(off)

BST(min)

BST(max)

BST(fixed)

BST(min)

BST(max)

-0.1-s

- 800 - s

-0.5-s

-0.2-s

-0.9-s

60.0

65.9

52.2

60.4

87.8

85.1

% %

4 DS1055F1

CS1680

Parameter Condition Symbol Min Typ Max Unit

Boost Gate Driver

Output Source Resistance Z

Output Sink Resistance Z

Rise Time

Fall Time

CL=0.25nF

BST(Source)

BST(Sink)

Boost Current Sense

Peak Control Threshold V

Leading-edge Blanking t

BSTPK(th)

BSTLEB

Delay to Output --100ns

Boost Protection

Overcurrent Protection (BOCP) V

Overvoltage Protection (BOP)

(Note 1) K

Clamp Turn-on Clamp Turn-off

BSTOCP(th)

BOP

CLAMP(on)

CLAMP(off)

Buck Zero-Current Detect

BUCKZCD Threshold V

BUCKZCD Blanking t

ZCD Sink Current

BUCKAUX Upper Voltage

(Note 8) I

BUCKZCD

=1mA

BUCKZCD(th)

BUCKZCD

Buck Current Sense

Peak Control Threshold V

Leading-edge Blanking t

BUCKPK(th)

BUCKLEB

Delay to Output --100ns

Buck Pulse Width Modulator

Minimum On Time T1

BUCK(min)

Maximum On Time

CS1680-00

BUCK(max)

CS1680-02

Minimum Switching Frequency - 625 - Hz

Maximum Switching Frequency - 200 - kHz

Buck Gate Driver

Output Source Resistance Z

Output Sink Resistance Z

Rise Time

Fall Time

CL=0.25nF

BUCK(Source)

BUCK(Sink)

Buck Protection

Overcurrent Protection (OCP) V

BUCKOCP(th)

External Overtemperature Protection (eOTP), Boost Stage Constant, Peak Current

Maximum Pull-up Current Source I

Conductance Accuracy

Conductance Offset

(Note 9) --±5

(Note 9) - ±250 - nS

Current Source Voltage Threshold V

CONNECT

CONNECT(th)

- 19.9 - 

- 10.5 - 

-11-ns

-6-ns

-0.33- V

- 100 - ns

-1.05- V

- 93.75 - 

87.8

85.1

 

- 200 - mV

- 250 - ns

-2 - - mA

-VDD+0.6 - V

-0.525- V

- 250 - ns

-0.55-s

12.8

25.6

s s

- 12.7 - 

-8.2-

-7.0-ns

-4.5-ns

-1.05- V

-80-A

-1.25- V

DS1055F1 5

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