Automotive LED driver temperature compensation and Over temperature protection DownloadLink 5460

Temperature Compensation/Protection
1 Scope
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2 Table of Contents
1 Scope............................................................................................................................................1
2 Table of Contents .........................................................................................................................1
3 PTC compensation + NTC Overtemperature protection ................................................................2
3.1 Define PTC value ..................................................................................................................2
3.2 Define NTC value..................................................................................................................3
3.3 Conclusion.............................................................................................................................4
4 NTC based compensation example for amber LEDs .....................................................................5
4.1 Application Schematic review................................................................................................5
4.2 Calculation examples .............................................................................................................6
5 PTC based protection....................................................................................................................7
6 Compensation and Protection for the Buck-Boost Topology .........................................................8
6.1 Temperature protection ..........................................................................................................8
6.2 ‘Active’ Temperature compensation ......................................................................................8
7 Conclusions................................................................................................................................10
390111080333 Rev 001, DLM
Page 1 of 10
4-Sept-08
Temperature Compensation/Protection
3 PTC compensation + NTC Overtemperature protection
%
%
& '
(
%
•
•
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VREF
ROSC
IREF1
PTC
IREF2
MLX10803
Vbat
VS/
PWM
DRV
GND
RSENSE
NTC
R1
3.1 Define PTC value
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390111080333 Rev 001, DLM
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Page 2 of 10
4-Sept-08
1
Temperature Compensation/Protection
3.2 Define NTC value
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B ': '= C & ': '= A 4
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B '
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A 4*
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R_IREF1
4* PTC
R0 = 4* 3000
Temp Coeff = 3900
= 4 * PTC
ppm/C
'$
B'& -D
%
-4
$
>'
%
B '
'$
R_IREF2
= NTC + R3
NTC
150000
4500
Beta
10130124
2200688
597934
194091
72745
30676
14265
7202
3898
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
R = R0*(1+K*(T0-T))
-40
-20
0
20
40
60
80
100
120
9192
10128
11064
12000
12936
13872
14808
15744
16680
390111080333 Rev 001, DLM
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Page 3 of 10
4-Sept-08
Temperature Compensation/Protection
3.3 Conclusion
%
%
%
%
0 3
/ '
$
PTC Compens. + NTC protection
LED
Temp
-40C
-20C
0C
T0 =
20C
40C
60C
80C
100C
120
Min (R_IREF1, R_IREF2)
9192 ohm
10128 ohm
11064 ohm
ILED
reduction
-23%
-16%
-8%
12000
12936
13872
14808
7744
4440
0%
8%
16%
23%
-35%
-63%
VREF [V]
VREF [%]
0.80
VREF[V]
0.70
%Correction
0.60
0.50
ohm
ohm
ohm
ohm
ohm
ohm
0.40
0.30
0.20
0.10
0.00
-40
390111080333 Rev 001, DLM
-20
Page 4 of 10
0
20
40
60
80
30%
20%
10%
0%
-10%
-20%
-30%
-40%
-50%
-60%
-70%
Temp [C]
100 120
4-Sept-08
Temperature Compensation/Protection
4 NTC based compensation example for amber LEDs
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3
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1
=$ & ')
' :
%
#4 '
#0 3
%
$
9
B '
$
4.1 Application Schematic review
VREF
ROSC
IREF1
R3
NTC1
R1
•
•
>
IREF2
R2
VS/
PWM
DRV
GND
RSENSE
NTC2
>/
!
MLX10803
Vbat
$ > A>/A0 !
:8> 5 E 8
/ '=$
>
4
$ 4 3
-
- 3
%
> $ B '
%
>
> $
!
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%
$ (
$
390111080333 Rev 001, DLM
Page 5 of 10
'7 B '/
B '/
%
4-Sept-08
Temperature Compensation/Protection
4.2 Calculation examples
VREF[V]
IREF2[V]
2.00
100k NTC//(R3=330k3) Compensation +
200k NTC Protection
1.80
V(VREF)
1
•
•
•
•
1%/C Linear Fit
1.60
Min(VREF, IREF2)
> A 0 !.
>/ A 0 !.
> A
!.
B ' A
!.
"
A4/-
1.40
'
•
•
1.20
1.00
0.80
0.60
0.40
•
0.20
Temp [C]
0.00
-40
-20
0
20
40
60
80
100
D
> A FB '
#4 '
':
8> 5
1
B '/ A /F
!.
"
A4/&
=
0 '
120
VREF[V]
IREF2[V]
2.00
100k NTC//(R3=220k3) Compensation +
300k NTC Protection
1.80
V(VREF)
1
•
•
•
•
1%/C Linear Fit
1.60
#4+3
2-03
Min(VREF, IREF2)
> A 0 !.
>/ A 0 !.
> A // !.
B ' A
!.
"
A4/-
1.40
'
•
•
1.20
1.00
0.80
0.60
0.40
•
0.20
Temp [C]
0.00
-40
-20
0
20
40
60
80
100
# 3
24 3
D
> A /FB '
#4 '
'
1
B '/ A F
!.
"
A4/&
'
120
%
•
•
>
B '/
,
,
%
390111080333 Rev 001, DLM
$
Page 6 of 10
4-Sept-08
Temperature Compensation/Protection
5 PTC based protection
@
%
7
H
& ' !
B ' $
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4*
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7
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A - 8 :
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VREF
PTC
ROSC
IREF1
R3
NTC1
R1
390111080333 Rev 001, DLM
IREF2
MLX10803
Vbat
VS/
PWM
DRV
GND
RSENSE
R2
Page 7 of 10
4-Sept-08
Temperature Compensation/Protection
6 Compensation and Protection for the Buck-Boost Topology
6.1 Temperature protection
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%
%
-40
-20
0
20
40
60
80
100
120
690000
4500
46598572
10123166
2750497
892818
334627
141109
65621
33127
17929
1
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B '
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%
/ '
R0
Beta
#
* 3
B ' A // ! 2 4* !$
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ILED reduction
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
Ohm
-48%
-73%
4* ! 8
!
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J
'$ (
7
%
00!.
%
B '
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$
6.2 ‘Active’ Temperature compensation
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@> 5
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-
$
% @> 5$ "
(
%
9
%
$
390111080333 Rev 001, DLM
Page 8 of 10
4-Sept-08
Temperature Compensation/Protection
VREF
ROSC
IREF1
IREF2
R3
NTC1
R2
R1
MLX10803
Vbat
VS/
PWM
DRV
GND
RSENSE
NTC2
!
"
#
% >/$
5
>/ A
!.
9
8> 5 A $-8$
% > 7>
NTC on Voltage source
•
•
•
200%
%
180%
160%
B ' $
> A 4*
.
> A
!.
B ' A 4*
.
"
A -
140%
%
120%
3,'
100%
80%
/ '$
NTConly
NTC//R3
60%
1%/CLinear Fit
40%
20%
Temp (C)
•
•
0%
-40
-20
0
20
40
60
80
100
#0 3
2- 3
2/ '
#4 '
'
1
1
•
B '
1
•
•
B ',,> 1
1
>
A
%
$
!$
$
$
390111080333 Rev 001, DLM
Page 9 of 10
4-Sept-08
Temperature Compensation/Protection
7 Conclusions
9
!
7
7
%
!
"
!#"
$
390111080333 Rev 001, DLM
Page 10 of 10
4-Sept-08
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