ELM186CxA 120mA laser diode driver

http://www.elm-tech.com■General description

ELM186CxA is a bipolar IC with APC drive circuit for laser diode(LD) applications. It can drive up to 120mAof LD forward current. Laser output power is controlled at constant value by a function of APC.
It consist of a band gap reference and an APC circuit. Laser power is adjusted by an external resistor which
defines output laser power. ELM186CxA application circuit occupies only small area on PCB by SC-70-5 small
package and a few external passive parts.
Four versions, ELM186C1A, ELM186C2A, ELM186C3A and ELM186C4A are prepared to drive all kinds oflaser diode modules(LDMs) which have 4 combinations of each pin’s polarity. All types of LDMs which havepins of LD cathode/LD anode and MD cathode/MD anode can be driven by a suitable version of ELM186CxA.
ELM186CxA consumes 0.6mA typ, and operates from 3.0V to 12.0V VCC.

■Features■Application• External adjustment for output laser power• Internal voltage reference: Typ.1.25V• Operation voltage: 3.0V to 12.0V• Low power consumption: Typ.0.6mA• LD drive current: Max.120mA• Package: SC-70-5 (5 Pin)

• Laser pointers• Laser levels• Other LD applications■Maximum absolute ratings
ParameterOperation voltage
Power dissipation
Operation temperature range
Storage temperature range

SymbolVcc
PdTopTstg

Limit
13.0300-40 to +85-55 to +150

Unit
VmW°C°C■Selection guide
ELM186CxA-x
SymbolabcdPackage

C: SC-70-5

1 : type1
2 : type2
Pin configuration type 3 : type3
4 : type4(Refer to pin configuration)
Product version
A
Taping direction
S, N: Refer to PKG file

ELM186C x A - x↑↑↑ ↑ab c dRev.1.1
1/8

ELM186CxA 120mA laser diode driver
http://www.elm-tech.com■Pin configuration
SC-70-5(TOP VIEW)

Pin No.
12345

type1
ELM186C1A
ALD
GND
VCC
IREF
AMD

Pin name

type2
ELM186C2A
ALD
GND
VCC
IREF
KMD

type3
ELM186C3A
KLD
GND
VCC
IREF
AMD

type4
ELM186C4A
KLD
GND
VCC
IREF
KMD

■Block diagram
ELM186C1A

CURRENTAMP

ELM186C2A

CURRENTAMP

DRIVERCONTROL

VREF

VREF

(EMITTER FOLLOWER AMP)

(EMITTER FOLLOWER AMP)

ELM186C3A

CURRENTAMP

DRIVERCONTROL

ELM186C4A

CURRENTAMP

DRIVERCONTROL

DRIVERCONTROL

VREF

VREF

(EMITTER FOLLOWER AMP)

(EMITTER FOLLOWER AMP)

Pin descriptions
Pin Name
Function
Description
ALD
LD drive output Connect to anode of laser diodes. Emitter output of internal NPN transistor.
KLD
LD drive output Connect to cathode of laser diodes. Collector output of internal NPN transistor.
AMD MD current input Connect to anode of monitor diode. Sinks photo current from monitor diode.
KMD MD current input Connect to cathode of monitor diode. Sources photo current to monitor diode.
Connect an external resistor from IREF to GND. Emitter output of reference voltage
IREF
Iref setting
source. The current at the resistor is copied to be a reference current for APC operation.
VCC
Power input
Power input of IC.
GND
GroundGround of IC.
Rev.1.1
2/8

ELM186CxA 120mA laser diode driver
http://www.elm-tech.com
Internal blocks and operation :ELM186CxA consists of a reference voltage circuit, a reference current generator, a current operation circuit
and a LD driving output transistor.
The reference current generator has a function to generate reference current for APC function defined by an
external resistor at IREF pin. The current operational circuit controls output current to the LD in conditionof flowing same current between the reference current and the photo current from a monitor diode's anode orcathode. The output transistor is a 120mA capable NPN bipolar transistor.
ELM186CxA has two types of output, ALD is an emitter output for LD anode drive and KLD is a collector
output for LD cathode drive. Two photo current polarity inputs are prepared. AMD is connected to an anodeof the monitor diode. KMD is connected to the cathode of monitor diode. AMD is a input pin to an anode ofinternal PN diode, and KMD is a input pin to a cathode of internal PN diode. Each diode works as a part ofcurrent mirrors.
ELM186CxA works as follows.
The reference current which defines output power of the LD is generated as a constant value by a band gap
reference and a external resistor. The monitor current is proportional to the laser power. When ELM186CxA isin operation, the laser monitor current is compared with the reference current by a current operational amplifier.
The difference current is maginified in very large amplitude. The amplified current is output to drive the laser
diode. Consequently the output current is increased when the monitor current is smaller than the reference. And
the output current is decreased when the monitor current is larger. Eventually the laser output is controlled in aconstant power defined by the external resistor. The control error is caused from current gain of the amplifier.
AMD/KMD current is recommended to be less than 1000µA. Since the reference voltage is approximately 1.25 V,
the IREF pin resistance in that case is 1.25 kΩ or more.

■Electrical characteristics
Parameter
Operating voltage
Current consumption
IREF reference voltage
IREF current range
ALD output current
KLD output current
ALD leak current
KLD leak current
AMD input current
KMD input current■MarkingSymbol
Vcc
Icc
Vref
Iref
Io_aldIo_kldIl_aldIl_kldIi_amdIi_kmdCondition

VCC=+5V, Top=25°C, unless otherwise noted

Vcc=5.0V, Iref register=22kΩ
Vcc=5.0V, Iref register=22kΩ

Min.
3.0
0.3
1.15

Typ.
0.6
1.2550-120

Max.
12.0
1.2
1.35
120
1.0-1.0-1000

50-50

1000

Unit
VmA
V
µA
mA
mA
µA
µA
µA
µA

SC-70-5Symbol
adc

MarkM
1 to 40 to 9 andA to Z ( I, O, X excepted)

ContentSeries : 186
Pin type display
Assembly lot No.
Rev.1.1

3/8

ELM186CxA 120mA laser diode driver
http://www.elm-tech.com■Appliation circuits

LDMs are used in many LD applications. A LDM contain a laser diode and a monitor diode in one package.
These two diodes are optically connected inside the package. The monitor diode is a PN diode generates photocurrent to measure photo power from the LD.
ELM186CxA can drive 4 kinds of laser diode modules(LDMs) having different polarity pins.
Each ELM186CxA can drive only corresponding polarity of laser diodes(LD) and monitor diodes(MD). Table1
shows ELM186CxA and laser diode modules (LDM) combinations.
Table 1 :No.

Laser diode module pinsMDLD1LD

2: LD anode, common, MD cathodeELM186C2A(Fig.4) or ELM186C4A(Fig.8): LD cathode, common, MD anode

ELM186C1A(Fig.1) or ELM186C3A(Fig.5): LD cathode, common, MD cathodeELM186C2A(Fig.3) or ELM186C4A(Fig.7): Other LDM without a common pin

All ELM186CxA

MD

LD

5

ELM186C1A(Fig.2) or ELM186C3A(Fig.6)

MD

LD

4

: LD anode, common, MD anode
MD

LD

3

Parts number of ELM186CxA

MD

LD anode driving applications
ELM186C1A and C2A are used when LD anode is driven. ALD is NPN emitter follower output. LD anodedriving application only requires a resister for output power definition. Only a noise absorbing capacitor at VCC
is recommended.
Operation voltage is 5V or higher because it is necessary to have the sum of IC operation voltage and to LD
forward voltage. LD anode drive has advantages on heat dissipation and fewer RC parts. The cases of LD modules can be directly grounded in Fig.1 for good heat dissipation.
ELM186C2A needs to have a compensation capacitor and a resistor at KMD pin for stable operation in Fig.3and Fig4.
LD anode driving application circuits Fig.1, Fig.2, Fig.3, Fig.4.
Fig.2

Fig.1

C1C1

0.1~10�F

0.1~10�F

3351

1
D2

D1

MD

LD

542

R1poweradjust

D2

D1

MD

LD

AMD

ALD

VCC

GND
2IREF

4R1poweradjust

R4
voltage shift for MD

Rev.1.1
4/8

ELM186CxA 120mA laser diode driver
http://www.elm-tech.com
Fig.3

Fig.4

C1

C110~47�F

10~47�F
33
R2 10k�

51
D2

D1

MD

LD

KMD
ALD

VCC

GND
2IREF

R2 10k� 54

1

R1poweradjust

D2

D1

MDLD

KMD

ALD

VCC

IREF

4GND
2R1
poweradjust

C2

C2
1000pF

1000pF

Method of determining circuit constants (Figures 1 to 4)
The laser diode module is assumed to have the characteristics of drive current IF = 40mA, forward voltage VF= 2.2V, and monitor current IM = 100μA at the rated 5mW operation.
In the case of Fig.1:
Supply voltage VCC = VF + 3V = 5.2V or more, reference resistor R1 = VREF / IM = 1.25V / 100μA =12.5kΩ, and supply capacitor C1 is 0.1μF to 10μF.
In the case of Fig.2 (Use a voltage drop of 1V on R4 to reverse bias MD) :Power supply voltage VCC = VF + 4V = 6.2V or more, reference resistance R1 = VREF / IM = 1.25V /100μA = 12.5kΩ, voltage shift resistance R4 = shift voltage / IF = 1V / 40mA = 25Ω, power supply capacitor
C1 is 0.1 μF to 10 μF, optional for power stabilization.
In the case of Fig. 3 (Add R2 and C2 for APC stabilization):
Power supply voltage VCC = VF + 3V = 5.2V or more, reference resistance R1 = VREF / IM = 1.25V /100μA = 12.5kΩ, stabilized CR is C = 1000pF, R = 10kΩ, power supply capacitor C1 is 10μF to 47μF, It is
optional for power stabilization.
In the case of Fig. 4 (Add R2 and C2 for APC stabilization):
Power supply voltage VCC = VF + 3V = 5.2V or more, reference resistance R1 = VREF / IM = 1.25V /100μA = 12.5kΩ, stabilized CR is C = 1000pF, R = 10kΩ, power capacitor C1 is 10μF to 47μF, It is optional
for power stabilization.
CR Example: R1 = 12kΩ (Iref = 100μA), R2 = 10kΩ to 2kΩ, C2 = 1000pF, R4 = 25Ω (Ild = 40 mA)

Rev.1.1
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http://www.elm-tech.com

LD cathode driving applications

ELM186C3A and C4A are used when LD cathode is driven. KLD is NPN Collector output. Power supply voltage is possible to down till 3V(forward voltage of LD +0.5V). A decoupling CR network for VCC pin and acompensation CR network for AMD/KMD pin are needed to keep APC loop stability.
Decoupling CR filter’s time constant is more than 1msec. Examples are 100Ω×10μF and etc. .
LD cathode driving application circuits Fig.5, Fig.6, Fig.7, Fig.8.
Fig.5

Fig.6
C1

R3 10010�FC20.1�F

35
D1

D2LDMD4R210k

1R4
voltage shift for MD

Fig.7

R1poweradjust

2Fig.8
C1

R4
voltage shift for MD
D1LD

D2
MD

C110�F345

R2 10kC2 1000pF

12

R1poweradjust

D1

D2LD

MD

R210k
510�F

C21000pF
3412

R1
power
adjustCR example : R1=12kΩ(Iref=100μA), C1=10μF, C2=0.1μF(ELM186C3A), C2=1000pF(ELM186C4A),
R2=10kΩ, R4=25Ω(Ild=40mA)
Tips for PCB design:
Consider low thermal resistance on PCB layout design. Thermal vias are recommended on PCB.
IREF pin to resistor connection should be a short line to reduce stray capacitance. Power lines toVCC and LD
are branched at input point of PCB to prevent influence of voltage drops on power lines. Ground plane is strongly recommended to get lower ground impedance by using a multi layers PCB.

Rev.1.1
6/8

ELM186CxA 120mA laser diode driver
http://www.elm-tech.com■Electrical characteristics curves
1. Power consumption
Vcc vs. Icc

Vcc vs. Icc

R1= 47k, 22k,10k, 4.7k, Top=25°C, test circuit 1

R1= 22k, Top=-30°C, 25°C, 80°C, test circuit 1
1

2.5

0.9
20.8

22k10k10.6

Vcc (mA)

Vcc (mA)

0.7
47k

1.5

4.7k

�30�

0.5

25�

0.4

80�

0.3

0.5

0.2
0.1

002

468101201402

46Vcc (V)8101214Vcc (V)

2. Voltage reference stability
Vcc vs. Iref voltage

Vcc vs. Iref voltage

R1= 47k, 22k,10k, 4.7k, Top=25°C, test circuit 1

R1= 22k, Top=-30°C, 25°C, 80°C, test circuit 1
1.35
1.3

1.5
1.45

1.25

1.35

47k

1.3

22k

1.25

10k

1.2

4.7k

Iref (V)

Iref (V)

1.4

1.2

�30�25�

1.15

80�

1.1

1.15
1.1

1.05

1.05

110

5

10015

Vcc (V)

2468101214

Vcc (V)

Iref resistor vs. AMD current

Iref resistor vs. KMD current

Iald=100mA, 33mA, 10mA, Top=25°C, test circuit 2

Iald=100mA, 33mA, 10mA, Top=25°C, test circuit 3

AMD current (A)KMD current (A)3. LD drive characteristics

R1 Iref resistor (Ω)

R1 Iref resistor (Ω)

Rev.1.1
7/8

ELM186CxA 120mA laser diode driver
http://www.elm-tech.com■Test circuits• Test circuit 1• Test circuit 2Vcc
5V
4

5
2

I_AMD

3

1

R1
power adjust

R2
load 10/33/100�

• Test circuit 3Vcc
5V
45
2

I_KMD

3

1R2
load 10/33/100�

R1
power adjust

Rev.1.1
8/8