Cirrus Logic AN364 - Manual (Page 3)

AN364
AN364REV3 3
2 Introduction
This application note is a guide to designing a Solid State Lighting (SSL) LED lamp circuit using Cirrus Logic's
CS1610/11. The first half of the document presents a step-by-step design procedure for calculating the required
components for each stage of the system. The second half of the document supports the design effort by showing
an example of a CS1611 design. The CS1611 example will be based on the Cirrus Logic CRD1611-8W reference
design. See the CS1610/11/12/13 TRIAC Dimmable LED Driver IC data sheet for more details about the CS1610/11
IC. See the CRD1610-8W 8 Watt Reference Design and CRD1611-8W 8 Watt Reference Design data sheets for
more details regarding the reference design.
2.1 Definition of Symbols
2.2 Definition of Acronyms
Symbol Description
F
sw Switching frequency
TT Switching period
T1 Primary FET ‘ON’ time
T2 Secondary rectifier diode conduction time
T3 Time when the FET and diode are OFF
D Duty ratio (T1/TT)
V
Reflected
Voltage across secondary winding reflected onto primary
V
CLAMP
Primary clamping voltage above boost output voltage (V
BST
)
I
PK(FB) Peak current in primary-side FET
R
FBGAIN
A resistor used to program the switching period TT
R
Sense
Primary current sense resistor
I
PK(BST) Maximum boost inductor current
L
P Flyback transformer primary inductance
L
BST Boost inductance
V
BST Boost output voltage
N Flyback transformer turns ratio N
P
/N
S
V
OUT Secondary output voltage DC = the LED string supply voltage
P
OUT Load power = Power to the LED string
 Power stage efficiency
Acronym Description
PFC Power Factor Correction
OVP Overvoltage Protection
eOTP External Overtemperature Protection
OCP Overcurrent Protection
iOTP Internal Overtemperature Protection
OLP Open Loop Protection
LED Light Emitting Diode
TXF Transformer
TRIAC
TRIode for Alternating Current, which is an electronic component that can conduct current in
either direction when it is triggered. It is formally called a bidirectional triode thyristor.
SSL
Solid State Lighting. Refers to a type of lighting that uses semiconductor LEDs as a source of
illumination rather than electrical filaments, plasma, or gas.