Cirrus Logic AN379 - Manual (Page 4)

AN379
4 AN379REV2
2.2 Definition of Symbols
Symbol Description
F
BSTSW
, F
BUCKSW
Switching frequency for boost stage and buck stage
TT
BST
, TT
BUCK
Switching period for boost stage and buck stage
T1
BST
, T1
BUCK
Power FET turn-on time for boost stage and buck stage
T2
BST
, T2
BUCK
Rectifier diode conduction time for boost stage and buck stage
T3
BST
, T3
BUCK
Time when the FET and diode are ‘OFF’ for boost stage and buck stage
GAIN
TT
Gain factor for buck stage
I
BSTPK
, I
BUCKPK
Peak current in power FET for boost stage and buck stage
I
RMS
RMS current
I
INPK
Peak line current
I
OUT Nominal LED string DC current
I
fb
Dimmer current at full brightness. Line current required to guarantee I
OUT
under worst case conditions
R
BST(Sense) Boost stage current sense resistor
R
BUCK(Sense) Buck stage current sense resistor
R
CTRL1 Resistor used to set the constant ratio for the boost stage current calculations in Mode3.
R
CTRL2
Resistor used to set the comparator threshold to reflect the desired boost peak current in
Mode2.
R
NTC
Negative temperature coefficient resistance
V
INPK
Peak line voltage
V
rect
Primary input voltage
V
OUT
Output DC voltage and the LED string supply voltage
V
IN
AC RMS line voltage
P
Target
Target Power
P
OUT
Load power which is equal to the power to the LED string
P
IN
Input power
 Power stage efficiency
 Duty ratio (T1/TT)
L
BST
, L
BUCK Inductor in boost stage and buck stage