ELM915BA
54V 1A switching LED driver
■General
description
ELM915BA is constant current LED driver with fixed off time, which consists of internal switching that
can drive 1A peak current and capable of driving single or multiple LEDs in series connection efficiently.
ELM915BA consists of switch NMOS transistor (Max.1A current) can operate from 6V to 54V. The low-side
current detection circuit which is able to set the average current of output by output NMOS switch and external
resistors is also included in ELM915BA. ELM915BA can be used as buck type and buck-boost type as well.
Through input of external control signal to LD/PWM pin, ELM915BA is capable of adjusting the value of
output current. The LD/PWM is able to control the continuous output current which is from DC level input and
the digital one which is from PWM input. The LD/PWM is also equipped with soft start function to prevent
inrush current.
The SOT-26 small package makes ELM915BA suitable for LED MR-16 bulb applications.
■Features
•
•
•
•
•
•
•
•
•
•
Linear or PWM dimming
Soft-start function
Cycle by cycle current limit
Constant off time control
Off time period programmable
Thermal shutdown protection
Internal NMOS switch
High efficiency
Wide input voltage range
Package
■Application
•
•
•
•
•
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: 54V, 1A
: Max.90%
: 6V to 54V
: SOT-26
MR16 and general lighting
Automotive lighting
Low voltage Industrial lighting
Battery charging
LED back lighting
Illuminated signs
■Maximum absolute ratings
Parameter
Power supply voltage
SW output peak current
I/O pin voltage
Power dissipation
Operating ambient temperature
Storage temperature
Symbol
Vdd
Isw
Vio
Pd
Top
Tstg
Limit
60
1
GND-0.3 to Vdd+0.3
450
-40 to +125
-55 to +150
Unit
V
A
V
mW
°C
°C
Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.
■Selection guide
Symbol
a
b
c
ELM915BA-S
Package
Product version
Taping direction
B: SOT-26
A
S: Refer to PKG file
ELM915BA - S
↑↑ ↑
ab c
* Taping direction is one way.
6-1
Rev.1.1
ELM915BA
54V 1A switching LED driver
■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
abcde
a to e : Assembly lot No.
A to Z (I, O, X excepted) and 0 to 9
■Standard circuit
●
●
●
●
●
●
●
8 to 24Vac
C
▲
SBD
LED1
LED2
Dimming
●
L
LD/
PWM
VDD
SW
ELM915BA
RT
GND
CS
Rt
Rs
6-2
Rev.1.1
ELM915BA
54V 1A switching LED driver
■Block diagram
VDD
5
5V
Vd(mV)
Regulator
5V
Toff time
modulation
250
25
3
RT
LD/PWM
4
●
0.25
2.5
Vin
OTP/OVP
250mV
-
+
S
6
SW
Q
R
●
-
+
●
250mV
-
+
1
CS
2
GND
■Electrical characteristics
Vin=6V
Parameter
Input DC supply voltage range
Shut-down mode
supply current
VDD under voltage lockout
threshold
UVLO hysteresis
LD/PWM low disable voltage
LD/PWM linear dimming
voltage range
Current sense pull-in
threshold voltage
Constant off time(100kΩ)
Constant off time(500kΩ)
SW switch resistance
Current sense blanking time
Symbol
Condition
Vdd
DC supply voltage
Iin_
SD
LD/PWM to GND, Vin=6V
Min.
6
Typ.
600
5.4
180
0.25
Vin=6V, Top=25°C
Rt=100kΩ, Vin=6V, Vcs=0.4V
Rt=500kΩ, Vin=6V, Vcs=0.4V
Vin=6V, Vcs=0V
Vld/pwm=Vdd, Vcs=0.4V
238
250
0.7
3.5
0.5
300
300
2.50
262
Top=25°C
Max. Unit
54
V
μA
V
mV
mV
V
mV
μs
μs
Ω
ns
UVLO Vdd rising
ΔUVLO Vdd falling
Vsd
LD/PWM voltage falling
Vld
Vcs-th
Toff
Toff
Rsw(on)
Tblank
6-3
Rev.1.1
ELM915BA
54V 1A switching LED driver
■Application notes
1) Setting peak current with external resistor Rs
ELM915BA uses open loop peak current mode driver with internal power switch; peak current is determined
by the value of Rs which is connected between CS and GND.
Ipk = 0.25/Rs (A)
2) Setting constant off time period Toff
RT is used to set the fixed off time of internal NMOS switch . The fixed off time is determined by the value of
the resistor which is connected to RT and GND. The connection between Rt and ToffIt is shown as following
chart. When RT is set to be 100kΩ, Toff becomes 700ns.
Toff-Rt characteristic
1000
Rt (k½)
100
10
0.1
1
10
Toff (½S)
3) Dimming function
ELM915BA provides two types of dimming function: linear dimming and PWM one. Linear dimming activates
when DC voltage added to LD/PWM is within the range from 0.25V to 2.5V; the luminance would be 0% under
0.25V, and 100% under 2.5V. For PWM dimming function, ELM915BA is able to adjust the luminance by
digital signal when voltage of LD/PWM is under 0.25V.
LD/PWM-Luminance
120
100
LD/PWM(V)
Luminance (%)
80
60
40
20
0
5
PWM
0
0
0.5
1
1.5
2
2.5
3
T
LD/PWM (V)
6-4
Rev.1.1
ELM915BA
54V 1A switching LED driver
4) Buck topology application
Vin(dc)
12V
Open
LD/ VDD
PWM
RT
GND
SW
C
SBD
LED
350mA LEDx1
L
17.5μH
ELM915.BA
CS
Rt
100kΩ
Rs
0.6Ω
The above diagram shows buck topology circuit.
a) Vin = 12Vdc. b) Vled = 3.5V
LED average forward current is 350mA and ripple current range is 20%(280mA~420mA). If constant off time
is 700ns, then Rt is required to be 100kΩ.
Toff=0.7μs
420mA
350mA
±20%
280mA
D = Vled / Vin = 3.5 / 12 = 0.292,
ΔI = 140mA = Vled / L × Toff = 3.5 / L × 0.7μ,
The duty would be changed by Vin voltage.
5) Buck-boost topology application
Vin
12Vdc
Rs = 0.25 / Imax. = 0.25 / 420mA = 0.595 Ω
L = 3.5 × 0.7μ / 0.14 = 17.5μH
C1
10μF
25V
LED
LED
L
100μH
C2
10μF
25V
LED
LED
LED
LED
Vld/PWM
Dimming
LD VDD
PWM
RT
GND
SW
SBD
LEDx6
ELM915BA
CS
Rt
100kΩ
Rs
0.6Ω
6-5
Rev.1.1
