TLD1125EL_15 Datasheet, PDF (14/36 Pages) Marl International Limited – Basic LED Driver

TLD1125EL
PWMI Pin
6.2
Internal PWM Unit
Connecting a resistor and a capacitor in parallel on the PWMI pin enables the internal pulse width modulation unit.
The following figure shows the charging and discharging defined by the RC-network according to Figure 10 and
the internal PWM unit.
V_PWMI
V_PWMI(H)
Outputs OFF
Internal PWM
V_PWMI(L)
Outputs ON
OUT-
ON
OUT - OFF
OUT-
ON
OUT - OFF
OUT-
ON
OUT - OFF
OUT-
ON
t
OUT - OFF
Figure 9 PWMI operating voltages
The PWM Duty cycle (DC) and the PWM frequency can be adjusted using the formulas below. Please use only
typical values of V_PWMI(L), V_PWMI(H) and I_PWMI(on) for the calculation of t_PWMI(on) and t_PWMI(off) (as described in
Pos. 6.3.15 to Pos. 6.3.18).
t_PWMI(on)
=
–R_PWMI
⋅
C_PWMI
⋅
L
N
⎛
⎜
⎝
-^VV----^PP---^WW-----^MM----^I-_I-⁽-₍-^HL----₎₎---_––----_II---_PP---_WW-----_MM----_II--₍₍--_oo---_nn--₎-⁾--_â‹-^â‹--_R-^R----_PP---_WW-----_MM-----_{II⎠⎟⎞}
(2)
t_PWMI(off)
=
R_PWMI
⋅
C_PWMI
⋅
L
N
⎛
⎜
⎝
V_{-V----P-P--WW-----MM----I-I-(-(-H-L---))⎠⎟⎞}
(3)
f_PWMI
=
----------------------------1-----------------------------
t_PWMI(on) + t_PWMI(off)
(4)
DC = t_PWMI(on) ⋅ f_PWMI
(5)
Out of this equations the required C_PWMI and R_PWMI can be calculated:
–I_PWMI(on) ⋅ t_PWMI(off) ⋅
t_{----P---W----M----I--(--o--n---)}
⎛
⎜
-^V----^P---^W-----^M-----^I--⁽-^L----⁾_⎟⎞
t_PWMI(off)
–
1
⎝ V_PWMI(H)⎠
C_PWMI
=
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
t_{----P---W----M----I--(--o--n---)}
(6)
LN
⎛
⎜
-^V----^P---^W-----^M-----^I--⁽-^L----⁾_⎟⎞
⋅
⎝ ^V_PWMI(H)⎠
V_PWMI(L)
⋅
⎛
⎜
-^V----^P---^W-----^M-----^I--⁽--^L---⁾_⎟⎞
⎝ ^V_PWMI(H)⎠
t_PWMI(off)
–
V_PWMI(H)
R_PWMI = -------------------^t---^P---^W----^M-----^I--⁽--^o--^f--^f--⁾-------------------
C_P
W
M
I
⋅
⎛
LN⎜
⎝
V_{-----P---W-----M----I--(--H----)⎟⎞}
V_PWMI(L)⎠
Data Sheet
14
(7)
Rev. 1.0, 2013-08-08