BD18340FV-M Datasheet, PDF (14/39 Pages) Rohm – Constant Current Controller for Automotive LED Lamps

BD18340FV-M BD18341FV-M
Datasheet
(1) CRT Ramp up Time tOFF and CRT Ramp down Time tON
CRT Ramp up Time tOFF and CRT Ramp down Time tON can be defined from the following equations.
Make sure that tON is set > PWM Minimum Pulse Width tMIN:10μs (Min).
∆
where:
ICRT is the CRT Terminal Charge Current
RCHA is the CRT Terminal Charge Resistor
RDISC1 is the DISC Terminal ON Resistor1
VCRT_CHA is the CRT Terminal Charge Voltage
VCRT_DIS1 is the CRT Terminal Discharge Voltage1
(2) PWM Dimming Frequency fPWM
PWM frequency is defined by tON and tOFF.
1
_
_
40μA(Typ)
30kΩ(Typ)
50Ω(Typ)
0.8V(Typ)
2.0V(Typ)
(3) ON Duty(DON)
Like the above, PWM ON duty is defined by tON and tOFF.
%
(Example) In case of RCRT=3.6kΩ, CCRT=0.1μF (Typ)
tOFF = RCHA × CCRT = 30kΩ × 0.1μF = 3.0ms
tON = - (RCRT + RDISC1) × CCRT × ln(VCRT_CHA / VCRT_DIS1)= - (3.6kΩ + 50Ω) × 0.1μF × ln(0.8V / 2.0V) = 0.334ms
fPWM = 1 / (tON + tOFF) = 1 / (3.0ms + 0.334ms) = 300Hz
DON = tON / (tON + tOFF) = 0.334ms / (3.0ms + 0.334ms) =10.0%
【PWM Dimming Operation using external signal】
In case external PWM input to CRT terminal,
Make sure that input pulse High voltage >2.2V and
pulse Low voltage<0.72V.
Also please open DISC terminal or connect to GND.
μ-Con
or
CRTIMER
VIN
EN
VREG
V REG
I CRT
CRT
Control
Logic
VREF
DISC
FB
BASE
ILED
GND
Figure 16. PWM Dimming Operation using external signal
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TSZ22111・14・001
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TSZ02201-0T1T0C700180-1-2
2016.04.21 Rev.002