Cirrus Logic AN372 - Manual (Page 3)

AN372
AN372REV1 3
2 Introduction
This application note provides a guide to designing a Solid State Lighting (SSL) LED lamp circuit using Cirrus Logic's
CS1612/13. 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 CS1613 design. See the CS1610/11/12/13 TRIAC Dimmable LED Driver IC data sheet for more
details about the CS1612/13 IC.
2.1 Definition of Symbols
2.2 Definition of Acronyms
Symbol Description
F
sw Switching frequency
TT Switching period
T1 Buck FET Q4 ‘ON’ time
T2 Catch diode D3 conduction time
T3 Time when the FET and diode are ‘OFF’
 Duty ratio (T1/TT)
V
Reflected
Voltage across the N winding of inductor L4 during T2
V
CLAMP
Maximum voltage above boost output voltage (V
BST
)
V
DS
FET Q4 drain voltage
I
PK(FB) FET Q4 peak current
R
FBGAIN A resistor used to program the switching period TT
R
Sense Current sense resistor R21
I
PK(BST) Maximum boost inductor current
L Inductance as measured across the entire buck inductor L4 winding (N+1 turns)
L
BST
Boost inductance
V
BST
Boost output voltage
N Buck inductor normalized turns ratio
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
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.