BD9206EFV Datasheet, PDF (9/13 Pages) Rohm – Simple Structure Constant Current Backlight Driver for LCD panels (Non-step type)

BD9206EFV
Technical Note
●The calculation of electric power consumption for IC and the deciding method of external resistance value
Electric power consumption of IC is decided with formula below.
P(N)=ICC*VCC+[(Vo-RL*ILED)-(Vf+⊿Vf+⊿VfT)*M]*N*ILED ・・・・①
ICC
：
IC Consumed electric
current
VCC ^： Input voltage
Vf ^： LED Vf voltage
： _{（normal temperature typ）}
⊿Vf ^： LED Vf Variation
⊿VfT ^： LED Vf Temperature
Vo
RL
VF
： variation
＊M
M ： Stage number around
： ^{LED 1 line}
N _： LED line number
＊N
ILED LED Constant current
value
ILED
Vo
Voltage OF LED anode
side
RL
external resistance
(external loss)
Fig..9
Please insert the heat-radiation resistor RL in order to decrease the heat radiation at the IC.
If the value of RL is made to be larger, then the heat radiation of the IC is decreased, but if the terminal voltage VLED of the
LED driver is less than 0.6V, then the constant current operation becomes impossible, therefore please set the RL in such a way
that the following expression is met:
VLED=Vo-（Vf+⊿Vf+⊿VfT）*M-RL*ILED>0.6V
Please set the ILED and RL in such a way that the relational expressions ① & ② are met.
Moreover, the permissible loss of the package is as shown in the following graph.
HTSSOP-B20 Pd
4 .0
3 .5
3.20
3 .0
2 .5
2.30
2 .0
1 .5
1.00
1 .0
0 .5
0 .0
0
25
③
②
①
50
75
100
125
150
Tem_周per_囲atur_温e ar_度oun_Td_aT₍a_℃（℃₎）
①^{①（1}_H：^la_e1^y_a^e層_t^r _d^b_i^a基_s^s_s^e_i板^p_p^l_a^a_t^t　^e_io　_n 　　
(c表op層per放fo熱il o銅n s箔urf：ace：
0^Om^mmm²2^）
②2layer base―plate
（Heat dissipation
c②op：p2e層r fo基il o板n I　ns　id　e　
a_(表nd_裏ou_層tsid_放e l_熱aye_éŠr：_箔：
4₄9₉0₀0₀m_mm_m2)₂₎
③4layer base―plate
（^③H^：e⁴at^層dis^基sip^板at^　io^　n ^　　
c(全opp層er放foi熱l on銅w箔ho：le
l₄ay₉e₀r：_0m49_m0₂0mm2）
Fig..10
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9/12
2009.07 - Rev.A