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參數(shù)資料
| 型號(hào)： | TB62731FUG |
| 廠商： | Toshiba Corporation |
| 元件分類： | LED驅(qū)動(dòng)器 |
| 英文描述： | Step-up DC-DC Converter for White LED Driver |
| 中文描述： | 升壓型DC - DC轉(zhuǎn)換器，用于白光LED驅(qū)動(dòng)器 |
| 文件頁數(shù)： | 10/20頁 |
| 文件大?。?/td> | 250K |
| 代理商： | TB62731FUG |
TB62731FUG
2006-06-14
10
Output Derating Function
Toshiba recommend derating the LED current depending on the increase in ambient temperature.
The TB62731FUG is designed to ensure safe and efficient driving of white LEDs used as backlight sources for color
LCDs. The IC incorporates a function that derates current according to the set temperature (the ambient
temperature when the IC is mounted), Ta.
The IC features an output current that varies according to the internally-detected temperature T
js
as follows:
when T
js
=
45 (
°
C), output current is 100%; when T
js
=
100 (
°
C), output current is 0%.
The derating start temperature T
s
(
°
C) is determined based on Ta (Ta
=
Ts when the IC is not operating) by
subtracting the self-generated temperature T
up
(
°
C) from T
js
=
45 (
°
C).
T
s
(
°
C)
=
45 (
°
C)
T
up
(
°
C) . . . formula 4
The derating characteristic is as shown in the graph below, Figure 5, which shows the relation between output
current change ratio and internally-detected temperature (IC temperature) T
js
.
The self-generated temperature T
up
(
°
C) is calculated as follows:
T
up
(
°
C)
=
(P loss (W)
P parts (W))
×
θ
ja
(
°
C/W) ) . . . formula 5
P loss: power loss
P parts: power loss of parts
θ
ja
: package saturation thermal resistance (
)
The parameters are described below:
DC resistance of inductor: RDC (
)
LED forward current: If LED (A)
LED forward voltage: Vf LED (V)
Schottky diode forward voltage: Vf schottky (V)
Setting resistance: R_sens
P loss (W)
～
P
o
(W)
÷
η
(%)
P
o
(W)
P
o
: output power
η
: power efficiency
P parts (W)
～
RDC
×
I
IN
+
Vf schottky
×
If LED
+
R_sens
×
If LED
×
If LED
θ
ja
(
°
C/W)
≤
260 (
°
C/W)
max when IC mounted on PCB
P
o
(W)
=
V
o
(V)
×
I
o
(A)
V
o
: Vf LED output voltage
I
o
: mean output current = set current
P
i
(W)
=
V
IN
(V)
×
I
IN
(A)
P
i
: input power
V
IN
: input voltage
I
IN
: mean input current
η
(%)
=
100
×
P
o
(W)
÷
P
i
(W)
Example of calculation: Where the measurement result for any lighting circuit shows the following values:
RDC
=
0.5 (
), P
o
=
320 (mW), I
IN
=
0.1 (mA), I
o
=
20 (mA), R_sens
=
1.8 (
), Vf schottky
=
0.3 (V), and
η
=
70
(%)
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