elm915ba

ELM915BA 50V 1A switching LED driver
http://www.elm-tech.com
■General description
ELM915BA is capable of driving single or multiple series connected LEDs efficiently from a voltage source
higher than the LED voltage. ELM915BA is Buck and Buck-Boost controller with internal switching which can
stress 1A peak current stress. The controller operating wide input voltage range from 6V to 50V.
ELM915BA consists of an output switch and a high-side output current sensing circuit that uses an external
resistor to set the nominal average output current. Through applying an external control signal to the LD/PWM
pin, it can adjust the output current to above or below the set value. The LD/PWM pin will accept either a DC
voltage or a PWM waveform to provide a continuous or a gated output current. The LD/PWM also provide soft
start function to prevent inrush current.
The SOT-26 small package makes ELM915BA suitable for LED MR-16 bulb applications.
■Features
■Application
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•
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•
•
•
•
•
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•
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Linear or PWM dimming
Soft-start function
Cycle by cycle current limit
Constant off time control
Off time period programmable
Over temperature protection
Over voltage protection
Internal NMOS switch
NMOS with peak current
Low quiescent current
High efficiency
Wide input voltage range
Package
: 155±30°C
: 53V±5%
: 54V
: 1A
: <250μA
: Max.90%
: 6V to 50V
: SOT-26
MR16 and general lighting
Automotive lighting
Low voltage Industrial lighting
Battery charging
LED back lighting
Illuminated signs
■Maximum absolute ratings
Parameter
Input voltage
SW output peak current
Other I/O pin voltage
Junction temperature
Power dissipation
Operating ambient temperature
Storage temperature
Symbol
Vdd
Isw
Vio
Tj
Pd
Top
Tstg
Limit
60
1
7
+150
450
-40 to +85
-55 to +150
Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.
Unit
V
A
V
°C
mW
°C
°C
■Selection guide
ELM915BA-S
Symbol
a
b
c
Package
Product version
Taping direction
B: SOT-26
A
S: Refer to PKG file
ELM915BA - S
↑↑ ↑
ab c
* Taping direction is one way.
Rev.1.4
5-1
ELM915BA 50V 1A switching LED driver
http://www.elm-tech.com
■Pin configuration
SOT-26(TOP VIEW)
6
5
4
1
2
3
Pin No.
1
2
3
4
5
6
Pin name
CS
GND
RT
LD/PWM
VDD
SW
Pin description
Current sense
Ground
Constant off time setting
Linear dim/PWM dim
Power input
Internal switch drain
■Marking
SOT-26
a to e : Assembly lot No.
A to Z (I, O, X excepted) and 0 to 9
abcde
■Standard circuit
●
●
●
●
8 to 24Vac
C
●
●
▲
SBD
LED1
●
LED2
Dimming
L
●
LD/
PWM
VDD
SW
ELM915BA
RT
GND
CS
Rs
Rt
Rev.1.4
5-2
ELM915BA 50V 1A switching LED driver
http://www.elm-tech.com
■Block diagram
VDD
Regulator
5
5V
Toff time
modulation
5V
3 RT
Vd(mV)
LD/PWM 4
●
250
25
0.25 2.5
Vin
OTP/OVP
6 SW
250mV
+
S
R
●
Q
+
250mV
●
+
1
CS
2
GND
■Electrical characteristics
Vin=6.0V
Parameter
Input DC supply voltage range
LD/PWM Pull-up current
Symbol
Condition
Vin
Input voltage
Min.
6
Ild
Typ.
Top=25°C
Max. Unit
50
V
4.5
Shut-down mode
Iin_SD LD/PWM to GND, Vin=6V
supply current
VDD under voltage lockout
UVLO Vdd rising
threshold
UVLO hysteresis
ΔUVLO Vdd falling
LD/PWM low disable voltage
Vsd
LD/PWM voltage falling
LD/PWM linear dimming
Vld
voltage range
Current sense pull-in
Vcs-th Vin=6V, Top=25°C
threshold voltage
Constant off time(200kΩ)
Toff
Rt=200kΩ, Vin=6V, Vcs=0.4V
Toff
Rt=820kΩ, Vin=6V, Vcs=0.4V
Constant off time(820kΩ)
SW switch on resistor
Rsw(on) Vin=6V, Vcs=0V
Current sense blanking time
Tblank Vld/pwm=Vdd, Vcs=0.4V
OVP
Voltage overvoltage protection
Overheat protection temperature
OTP
μA
450
600
750
μA
4.86
5.40
5.94
V
180
300
0.25
238
250
2.5
9.0
50
125
53
155
mV
mV
2.50
V
262
mV
0.5
500
56
185
μs
μs
Ω
ns
V
°C
Rev.1.4
5-3
ELM915BA 50V 1A switching LED driver
http://www.elm-tech.com
■Application notes
1) Setting peak current with external resistor Rs
ELM915BA is open loop peak current mode driver with internal power switch; Which peak current setting by
external resistor Rs connected between CS and GND.
Ipk = 0.25/Rs (A)
2) Setting constant off time value (Toff)
The RT pin can set internal power switch of time with period. The time with period is constant when resistor
value between RT to GND is fixed. Following diagram is the reference data for setting the off-time.
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3) Dimming function
ELM915BA is capable of two types of dimming function-linear and PWM dimming. The linear dimming
function works by setting the LD/PWM voltage between 0.25V to 2.5V. ELM915BA shutdowns once the LD/
PWM voltage is bellow 0.25V.
LD/PWM(V)
LD/PWM-Luminance
120
5
Luminance (%)
100
PWM
80
60
0
40
T
20
0
0
0.5
1
1.5
2
2.5
3
LD/PWM (V)
Rev.1.4
5-4
ELM915BA 50V 1A switching LED driver
http://www.elm-tech.com
4) Buck topology application
●
●
●
Vin(dc)
▲
LED1
LED2
Dimming
L
●
LD/
PWM
SW
VDD
ELM915BA
RT
CS
GND
Rs
Rt
The above diagram is buck topology circuit. The input and output specifications as following.
Vin = 12Vdc. Vled = Vo = 3.5V
LED average current is 350mA, and the current ripple is ±20%. If constant off time is 1.2μs, then set Rt to
100kΩ.
Toff=1.2μs
420mA
±20%
350mA
280mA
D = Vled / Vin = 3.5 / 12 = 0.292,
ΔI = Vled / L × Toff ⇒ 140mA = 3.5 / L × 1.2μs,
Rs = 0.25 / Imax. = 0.25 / 420mA = 0.595 Ω
L = 3.5 × 1.2μs / 0.14 = 30μH
The duty will change when Vin voltage varies.
5) Buck-boost topology application
Vin
12Vdc
C1
10μF
25V
LED
LED
L
100μH
C2
10μF
25V
Dimming
Vld/PWM
LD VDD
PWM
SBD
SW
LED
LED
LED
LED
LEDx6
ELM915BA
RT
Rt
100kΩ
GND
CS
Rs
0.6Ω
Rev.1.4
5-5