ELM185xB Laser Diode Driver■General description

http://www.elm-tech.com

ELM185xB is a bipolar type laser diode driver IC with internal APC circuit which consists of a reference
voltage source, an error amplifier, and a thermal shutdown circuit for protection. With reference voltage source,
the output of laser is comparatively stable during the change of power voltage and temperature. With its small
package, ELM185xB is possible to be assembled within small areas on the board. When control loop damage
occurs, ELM185xB is also capable of limiting the laser drive current; limited current value can be adjusted by
an external resister on ILM. KLD output drive current can reach up to 400mA (max.). For avoidance of damageof laser diode, the Zener diode which is included in ELM185xB is able to absorb 8V surge between VCC-GND.
ELM185xB is able to drive various types of laser diode modules (LDM); please refer to applicable laser
diode modules for further information. ELM185xB can not only drive laser diode by APC control, but also
by constant current with internal constant current setup function; therefore, ELM185xB can also be used as
constant current driver for laser diode, high luminous LED, etc.

■Features• Low voltage operation: 2.0V
• Low current consumption operation : Typ.1mA• Laser drive current: Max.400mA• Internal voltage reference: Typ.0.30V• Thermal shutdown circuit: Typ.150°C• Package: SOT-26, WSON6-2x2• Zener diode for surge absorption included■Application• Driver for laser diode in laser pointer, laser level, etc.
• Driver for constant load current such as LED, etc.

■Maximum absolute ratings
Parameter

Symbol

Limit

Unit

Operation voltage
CMP voltage
ILM voltage

VCC

GND-0.3 to 7.0

VVcmp
Vilm

GND-0.3 to 7.0
GND-0.3 to 7.0

VV

KLD voltage
AMD voltage
KLD current

Vkld
Vamd
Ikld

GND-0.3 to 18.0
GND-0.3 to VCC+0.3
500

VVmA

Power dissipation

Pd

Operation temperature
Storage temperature

TopTstg

300 (SOT-26)
1000 (WSON6-2x2)-30 to +85-40 to +125

mW
°C°C

Rev.1.6
1 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com■Selection guide
ELM185xB-S
Symbol

ELM185 x B - S↑ ↑ ↑a b c

B: SOT-26,
G: WSON6-2x2

aPackageb

Product version

BcTaping direction

S: Refer to PKG file

■Pin configuration
SOT-26(TOP VIEW)
651Pin No.

Pin Name

12AMDGND

345CMP
ILM
VCC

6KLD

567Pin No.
1Pin Name
KLD

2123

VCC
ILM

4CMP

567

GND
AMD
EP

423

WSON6-2x2(TOP VIEW)
65447
1233

WSON6-2x2(BOTTOM VIEW)
654471256Connection of EP is to GND(recommended) or NC

73321

Rev.1.6
2 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com■Block diagram
VCC

KLD

CMP

GND

Pin description+-AMD

CONTROL
AMP

VREF
ILD

CURRENT
LIMIT CMP

DRIVERCONTROL+-DRIVERNPN TR

ILM

VREF
LIMIT

PinNameAMD

MD current input

CMP
ILM

phase compensation input of phase compensation capacitor for control feedback loop stabilization
LD current limit input of detection of laser diode driver drive current limit

KLD
VCC
GND

LD drive output
power input
groundContent
connected to anode of monitoring diodeconnected to cathode of laser diodepower input of IC
ground of IC

Description :The internal APC circuit of ELM185xB controls the output of laser oscillation at constant value with thefeedback of monitor photo diode light output current. Monitor photo diode light current will be changed tovoltage by resistance and becomes the input of AMD; this voltage is set to be 0.3V, which is the same as thereference voltage inside IC. It is possible to acquire constant laser output by the laser diode drive current whichis controlled by this voltage; hence, laser light output can be adjusted by the resistor connected to AMD.
Laser diode drive current can be changed to voltage by resistance connected to ILM, and the increase of thisvoltage is limited under current limit voltage (Typ.0.15V). ILM is also capable of avoiding the damage ofovermuch drive current of laser diode which is caused by control loop abnormality.
For stability of control return loop, a phase compensation capacitor is required to be connected to CMP. Please
set to small value at least above 3nF when making ON/OFF control with fast speed.
Laser diode is driven by the open collector output of NPN transistor inside ELM185xB; therefore, drive current(Max.18V) higher than power voltage of IC can be added as drive voltage of laser diode. ELM recommends
inserting resistance between laser diode module (LDM) and KLD if the drive voltage is high so as to disperse
power loss.
By monitor current detection function of ELM185xB, AMD can be used as ON/OFF control pin. It is also
possible to control switching of laser diode when the input source is from external control signal; the ON/OFFcontrol will become 0.3V threshold voltage.
By 7V voltage, the Zener diode between power and ground of ELM185xB is able to absorb power surge;
meanwhile, the Zener diode is also capable of decreasing the damage of surge by clipping the surge voltage ofpower line.
Rev.1.6
3 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com■Electrical characteristics
Parameter
Operation voltage

SymbolVCC

Condition

Min.
2.0

Current consumption
AMDreference voltage

ICCVamd

Vamd temperature
characteristics

ΔVamd
ΔTop

VCC=3.6V

KLD current
KLD leak current

IDkld
ILkld

VCC=2.7V, Vkld=1.0V
VCC=5.5V

400

ILM current limit voltage

Vilm

VCC=3.6V

0.13

Max. external clock frequency
AMD input current

Fext
Iamd

VCC=3.6V
VCC=5.5V, Vamd=1.0V

Zener diode avalanche voltage

ZDBV

VCC=3.6V
VCC=3.6V

0.285

Typ.

Max.
6.5

Unit
V

13mA

0.300

0.315

V

±200

ppm/°C
1.0mA
μA

0.17

V-0.5

20
0.5

kHz
μA

6.8

8.0

V

0.15

■Marking
SOT-26
SymbolMark

Contenta, b, c

2NW

Series : 185
Package : SOT-26d0 to 9 and
A to Z ( I, O, X excepted)

Assembly lot No.

Symbol185

Mark185

Content185 seriesa, b, c0 to 9 and
A to Z ( I, O, X excepted)

Assembly lot No.

�WSON6-2x2

Rev.1.6
4 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com■Application circuit example 1 (continuous drive circuit)

Circuit that laser diode is driven by constant output continuously. LDM, which is the combination of laser
diode (LD) and monitor diode (MD), is commonly used.
Based on various ways of handling poles and common pins, there are many different types of internal wireof anode and cathode of LDM. Examples which LDM can be easily connected to ELM185xB are shown as
following three application circuits.
Proper values for external parts depend on characteristics of a laser diode. Table 2 shows example values incase of using a laser diode which have 35mA forward current and 0.1mA photo current at target power output.

circuit (1)
V1

D2

D1MD
LDM

LDC2

C1

VR1

R2

R1circuit (2)
V1

D2

D1MD

LDC2LDMC1VR1R2

R1circuit (3)Tr1

V1Tr2D2D1MD

LDC2VCC

LDM

KLD

CMP
C1AMDILM

GND

VR1R2

R1

Rev.1.6
5 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com
Typical Electric characteristics of LDM
Parameter
Symbol

Min.

Typ.

Max.

table 1
Unit

Action current

Iop

-35

50mA

Monitor current

Im

0.05

0.10

0.30mA

Recommendation of absolute ratings of each circuit when using the LDM of table 1
Recommended absolute
No.
parts
Notes
ratings
R1 *1
fixed resistor
1.0kΩ
LD output adjustment
VR1 *2
adjustable resistor
5.0kΩ
LD output adjustment
R2 *3

fixed resistor

2.2Ω

C1C2
Tr1 Tr2

ceramic capacitor
electrolysis, ceramic, etc.
PNP transistor

3300pF1μF to 100μF
small signal transistor

table 2current limit setting (no limit under 0Ω)
control loop stabilization
power stabilization
monitor current mirror circuit* 1 R1=0.3/ Im (Max.)* 2 (R1 + VR1) = 0.3/ Im (Min.)* 3 R2=0.15/ Iop (Max.)x0.75■Application circuit example 2 (Pulse drive circuit)
For application circuit of intermittent diode output controlled by external signal, please refer to application
circuit (4).
Max. frequency can set to be on/off by limit of response speed of laser diode output control loop is 20kHz.By
using logic gate, the control of on/off is easy; it is required that the resistances of R1, R3 and VR1 are muchlarger than the output resistance of logic gate.

circuit (4)
V1

D2

D1

MD
LDM

LD

C2

C1

R3
Pulse in

VR1

R2

R1

* For pulse drive, please add resister to AMD pin in circuit (1) to control signal of pulse drive.
* Adjustable resistor (VR1) is inserted in the place as shown above in order to adjust monitor current; pulsedrive control signal shall be added between R1 and VR1.
* R3: resistor of the input of pulse drive control signal. VCC is set to be higher than Vamd=0.30V(Typ.)
VCC * R1 / (R3 + R1) > Vamde.g.) when VCC=3.3V, R1=1kΩ, R3 < R1 * (VCC-Vamd)/Vamd = 1kΩ * (3.3-0.3)/0.3 = 10kΩ.
* The control signal is logic level; laser light will be switched off when the signal is H and switched on when itis L.
Rev.1.66 / 10ELM185xB Laser Diode Driver
http://www.elm-tech.com• Pulse drive wave
This drive wave is tested base upon standard circuit (4) under the conditions that R1=22kΩ, R2=2.2Ω,R3=220kΩ, VR1=0, C1=3300pF, C2=1μF, V1=3.6V

ch3
ILM wave= current wave
ch2
AMD wave
ch1
control signal pulse in

Ch1 2.00V/div
Ch3 100mV/div

Ch2 500mV/div
50.0μs/div■Application circuit example 3 (Drive circuit with detection circuit of single fault mode)
Based on different applications of laser, it is required that laser output can be maintained in safety region whensingle fault error happens. The example of single fault detection circuit is shown as application circuit (5).
If any of following 3 conditions happens, laser output of ELM185xB will be overmuch when single fault of all
pin occurs:1) Ground short fault happens to KLD (Ground current will be flowed directly from laser and thus result inovermuch of laser diode light output.)2) Ground short fault happens to AMD (laser diode light output will be overmuch since output is judged to be 0)
3) VCC short fault happens to CMP (laser diode light output will be overmuch since circuit cannot be controlled.)
If any of these 3 conditions is detected, laser drive will be stopped forcibly and become single fault detection
circuit. Meanwhile, the condition when single fault occurs is the same as initial power input, solutions (start-upcircuit) of error detection for normal action when the circuit starts is required additionally.
For example of this safety circuit, please refer to application (5).When abnormality occurs, ELM742NBC, thecomparator will detect the error, the latch which is composed by ELM7SU04BW will be turned reversely,and ELM23401CA, P-ch MOS will be off and thus shut down the power. When comparison voltage of
3 comparators is under 0.9V of KLD, under 0.1V of AMD, and above 2.5V of CMP, it will be judged asabnormality by OR condition of the comparator and thus the power will be shut down. This circuit is only forreference use; confirmation of safety standard fit actions on actual application is still required.
Start-up circuit consists of time constant of R1 and C1.The ratio of disperse voltage of R3, R4, R5, R8 is
required to be changed with power voltage. For best solution, ELM recommends using ELM742NBC as thevoltage detector, ELM7SU04BW as the latch and ELM23401CA as the transistor.
This circuit is for reference use only; additional inspection of safety standard suitableness is required.
It is possible to insert detection circuit as shown in circuit (2) and (3) in this circuit.
Rev.1.6
7 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com

circuit (5)ELM7SU04BWA2*1ELM23401CA+ V1R1100k A1M15V

ELM742NBC
U1+R2100k

U2C10.1�

C310�

D2D1MDLDU3*2R3100k+R468k+R833k

2.5V
0.9V
0.1V

R52.2kVCC
KLD
AMDR63k

ELM185xB

GND

ILM
R7
2.2

CMP
C23300p*1. Pch MOSFET having higher capability than Vds: 10V, Ids: 1A can be used.
*2. Or an equivalent Nch open-drain output CMOS voltage comparator.

■Application circuit example 4 (white LED constant current drive circuit)
Example of application of ELM185xBA as LED constant current drive current is shown as circuit (6).
This circuit is white LED drive circuit which is driven by constant current with external resistance of ILM.
Since the voltage limit of KLD can reach 18V, it is possible to design several LEDs in series connection. The
VCC voltage is controlled to be constant by internal Zener diode of ELM185xB.

circuit (6)
+ V1
12V

White LEDR1
4.7k C1

D3
D21�

D1

R2100k

W1Switch

R7
4.7�

C210n

This circuit is designed by 3 series-connected white LEDs with power of 12V.
In this circuit, AMD is not used to control light feedback, but on/off only. Current control, which is constantcurrent type, is monitored by the voltage of ILM. Capacitors of 0.1μF-0.01μF for anti-oscillation are connected
to CMP. Resistance of R7 is set by constant current value; it will be 34mA under 4.7Ω. This value is calculatedby the formula that Iout=0.16/R7. The power of ELM185xB will be lowered from 12V to 7V by R1 and internal
Zener. Light will be turned on when the switch of W1 is ON, and be off when it is OFF.

Rev.1.68 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com■Notice

1. Safety standard
For different applications of laser diode, it is sometimes required that the application should obey the safety
standard which is ruled by the law. Please make complete confirmation about which safety or law should beobeyed while designing the circuit. ELM185xB drives laser diode by the conditions which is set by external
circuit; please confirm the actual output of light by instruments such as light power meter.
2. Laser diode damaged caused by surge voltage
Laser diode can be easily damaged by static or surge voltage when the power is turned on/off because of its low
surge resistance. ELM185xB includes Zener for absorption of surge; for best protection, ELM recommends
connecting ELM185xB and laser diode in the shortest distance.

connection in shortest distance
LDKA

654KLD

VCC

ILM

ELM185xB
AMD

GND

CMP

123

■Applicable laser diode modules
Type 1Type 2Type 3

1 : LD cathode2 : LD anode, MD cathode3 : MD anode

1 : LD anode2 : LD cathode, MDcathode3 : MD anode

1 : LD anode2 : LD cathode, MD anode3 : MD cathode

It is possible to connect separate LD and MD to ELM185xB.
When connecting different LDMs other than these 3 types, additional parts are required.

Rev.1.69 / 10

ELM185xB Laser Diode Driver
http://www.elm-tech.com■Electrical characteristics
1. Icc consumption current
characteristics of power voltage vs.
consumption current

Icc
AVcc vs Icc

485�

3Icc (mA)

Icc consumption current test circuit

Vcc V2654KLD

VCC

ILM

ELM185xB25�

-30�

1AMDGNDCMP1230.1��

204
6Vcc (V)810

2. Vamd standard voltage
power voltage vs. AMD standard voltage

Vamd standard voltage test circuit

Vcc - Vamd

0.35

0.3

654KLD

VCCILM

Vamd (V)ELM185xB
85�

-30�

25�

0.25

0.2

AMDGND

CMP

123Vamd V
864Vcc (V)2

3. Ikld constant current
KLD output current voltage characteristics

Ikld constant current test circuit
Ikld
A

Vkld - Ikld

160
140

Ikld (mA)

120

1�

100

2.2�

Vkld V80

54KLD

VCC

ILM

40
205Vkld (V)

10RILM

ELM185xB

4.7�

600

5.0V

6AMD

GND

CMP1230.1��

15* When Vkld, Ikld are large, protection circuit operates according to the heat generation of IC;
the limit will be determined by heat characteristic of actual assembly.
Rev.1.6
10 / 10