ST LED2000 User Manual

3 A monolithic step-down current source with synchronous

VFQFPN8 4x4

SO8

!-V

Features

■ 3.0 V to 18 V operating input voltage range

■ 850 kHz fixed switching frequency

■ 100 mV typ. current sense voltage drop

■ PWM dimming

■ ± 7% output current accuracy

■ Synchronous rectification

■ 95 mΩ HS / 69 mΩ LS typical R

■

Peak current mode architecture

■ Embedded compensation network

■ Internal current limiting

■ Ceramic output capacitor compliant

■ Thermal shutdown

Applications

■ High brightness LED driving

■ Halogen bulb replacement

■ General lighting

■ Signage

DS(on)

LED2000

rectification

Datasheet — production data

Description

The LED2000 is an 850 kHz fixed switching
frequency monolithic step-down DC-DC converter
designed to operate as precise constant current
source with an adjustable current capability up to
3 A DC. The embedded PWM dimming circuitry
features LED brightness control. The regulated
output current is set connecting a sensing resistor
to the feedback pin. The embedded synchronous
rectification and the 100 mV typical R
voltage drop enhance the efficiency performance.
The size of the overall application is minimized
thanks to the high switching frequency and
ceramic output capacitor compatibility. The device
is fully protected against thermal overheating,
overcurrent and output short-circuit.

SENSE

The LED2000 is available in VFQFPN 4 mm x 4
mm 8-lead package, and standard SO8.

Figure 1. Typical application circuit

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July 2012 Doc ID 023432 Rev 2 1/39

This is information on a product in full production.

,,

2323 #/54#/54

www.st.com

39

Contents LED2000

Contents

1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.1 Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.2 Voltage monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.3 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.4 Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.5 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Application notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6.1 Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6.2 G

6.3 Error amplifier compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6.4 LED small signal model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6.5 Total loop gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.6 Dimming operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.7 eDesign studio software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

(s) control to output transfer function . . . . . . . . . . . . . . . . . . . . . . . . . 12

CO

6.5.1 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.6.1 Dimming frequency vs. dimming depth . . . . . . . . . . . . . . . . . . . . . . . . . 20

7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.1 Component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.1.1 Sensing resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.1.2 Inductor and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.1.3 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2/39 Doc ID 023432 Rev 2

LED2000 Contents

7.2 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

7.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

9 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

10 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Doc ID 023432 Rev 2 3/39

List of tables LED2000

List of tables

Table 1. Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Table 2. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 3. Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 4. Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 5. Uncompensated error amplifier characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 6. Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Table 7. List of ceramic capacitors for the LED2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table 8. Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Table 9. Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Table 10. VFQFPN8 (4x4x1.08 mm) mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Table 11. SO-8 mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Table 12. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4/39 Doc ID 023432 Rev 2

LED2000 List of figures

List of figures

Figure 1. Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Pin connection (top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 3. LED2000 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 4. Internal circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5. Block diagram of the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 6. Transconductance embedded error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 7. Equivalent series resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 8. Load equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 9. Module plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 10. Phase plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 11. Dimming operation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 12. LED current falling edge operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 13. Dimming signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 14. eDesign studio screenshot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 15. Equivalent circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 16. Layout example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 17. Switching losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 18. Constant current protection triggering Hiccup mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 19. Demonstration board application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 20. PCB layout (component side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 21. PCB layout (bottom side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 22. Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 23. Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 24. Dimming operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 25. LED current rising edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 26. LED current falling edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 27. Hiccup current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 28. Efficiency vs. IOUT (VIN 32 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 29. Thermal shutdown protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 30. VFQFPN8 (4x4x1.08 mm) package dimensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 31. SO8 package dimensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Doc ID 023432 Rev 2 5/39

Pin settings LED2000

1

45

8

SW

PGND

VINA

VINSW

GND

AGND

FB

NC

VFQFPN

SO8 -BW

DIM

DIM

AM12893v1

1 Pin settings

1.1 Pin connection

Figure 2. Pin connection (top view)

1.2 Pin description

Table 1. Pin description

Package/pin

Type Description

VFQFPN S08-BW

13VINAAnalog circuitry power supply connection

Dimming control input. Logic low prevents the switching

24DIM

35FB

4 6 AGND Analog circuitry ground connection

5 - NC Not connected

68VIN

7 1 SW Regulator switching pin

8 2 PGND Power ground

- 7 GND Connect to AGND

activity, logic high enables it. A square wave on this pin
implements LED current PWM dimming. Connect to VIN
not used (see Section 6.6)

Feedback input. Connect a proper sensing resistor to set the
LED current

Power input voltage

SW

if

A

6/39 Doc ID 023432 Rev 2

LED2000 Maximum ratings

2 Maximum ratings

Table 2. Absolute maximum ratings

Symbol Parameter Value Unit

V

INSW

V

INA

V

DIM

V

SW

V

PG

V

FB

I

FB

P

TOT

T

OP

T

stg

3 Thermal data

Table 3. Thermal data

Symbol Parameter Value Unit

R

thJA

Maximum thermal resistance
junction-ambient

Power input voltage -0.3 to 20

Input voltage -0.3 to 20

Dimming voltage -0.3 to V

Output switching voltage -1 to V

Power Good -0.3 to V

INA

IN

V

IN

Feedback voltage -0.3 to 2.5

FB current -1 to +1 mA

Power dissipation at TA < 60 °C 2 W

Operating junction temperature range -40 to 125 °C

Storage temperature range -55 to 150 °C

VFQFPN 40

(1)

SO8-BW 65

°C/W

1. Package mounted on demonstration board.

Doc ID 023432 Rev 2 7/39

Electrical characteristics LED2000

4 Electrical characteristics

TJ=25 °C, VCC=12 V, unless otherwise specified.

Table 4. Electrical characteristics

Value

Symbol Parameter Test conditions

Min. Typ. Max.

Unit

Operating input voltage
range

V

IN

Device ON level 2.6 2.75 2.9

Device OFF level 2.4 2.55 2.7

R

DSON

R

DSON

V

I

I

FB

LIM

FB

Feedback voltage

VFB pin bias current

High-side switch on-

-P
resistance

Low-side switch on-

-N
resistance

Maximum limiting current

Oscillator

F

SW

Switching frequency 0.7 0.85 1 MHz

D Duty cycle

DC characteristics

I

Q

Quiescent current 1.5 2.5 mA

Dimming

(1)

318

V

Tj=25 °C 90 97 104

mV

Tj=125 °C 90 100 110

(1)

=750 mA 95 mΩ

I

SW

600 nA

ISW=750 mA 69 mΩ

(2)

(2)

0 100 %

5A

Switching activity 1.2

V

DIM

DIM threshold voltage

Switching activity
prevented

I

DIM

DIM current 2 μA

Soft-start

T

SS

Soft-start duration 1 ms

Protection

Thermal shutdown 150

T

SHDN

1. Specifications referred to TJ from -40 to +125 °C. Specifications in the -40 to +125 °C temperature range
are assured by design, characterization and statistical correlation.

2. Guaranteed by design.

Hystereris 15

8/39 Doc ID 023432 Rev 2

0.4

V

°C

LED2000 Functional description

WSNIVANIV

OSC

E/A

DRIVER

DRIVER

DMD

OTP

MOSFET

CONTROL

LOGIC

REGULATOR

DIMMING

I_ S ENSE

COMP

PWM

OCP
REF

0.1V

SOFT-START

Vsum

Vc

OCP

UVLO

Vdrv

_p

Vdrv

_n

I2V

R

SENSE

SW

GNDP

GNDADIMFB

AM12894v1

5 Functional description

The LED2000 is based on a “peak current mode” architecture with fixed frequency control.
As a consequence, the intersection between the error amplifier output and the sensed
inductor current generates the control signal to drive the power switch.

The main internal blocks shown in the block diagram in Figure 3 are:

● High-side and low-side embedded power element for synchronous rectification

● A fully integrated sawtooth oscillator with a typical frequency of 850 kHz

● A transconductance error amplifier

● An high-side current sense amplifier to track the inductor current

● A pulse width modulator (PWM) comparator and the circuitry necessary to drive the

internal power element

● The soft-start circuitry to decrease the inrush current at power-up

● The current limitation circuit based on the pulse-by-pulse current protection with

frequency divider

● The dimming circuitry for output current PWM

● The thermal protection function circuitry.

Figure 3. LED2000 block diagram

5.1 Power supply and voltage reference

The internal regulator circuit consists of a startup circuit, an internal voltage pre-regulator,
the BandGap voltage reference and the bias block that provides current to all the blocks.
The starter supplies the startup current to the entire device when the input voltage goes high

Doc ID 023432 Rev 2 9/39

Functional description LED2000

STARTER

PREREGULATOR

IC BIAS

BANDGAP

VREF

VREG

Vcc

D00IN126

AM12895v1

and the device is enabled. The pre-regulator block supplies the BandGap cell with a pre­regulated voltage that has a very low supply voltage noise sensitivity.

5.2 Voltage monitor

An internal block continuously senses the VCC, V
good, the regulator begins operating. There is also a hysteresis on the V

Figure 4. Internal circuit

5.3 Soft-start

The startup phase is implemented ramping the reference of the embedded error amplifier in
1 ms typ. time. It minimizes the inrush current and decreases the stress of the power
components at power-up.

During normal operation a new soft-start cycle takes place in case of:

● Thermal shutdown event

● UVLO event.

and Vbg. If the monitored voltages are

ref

(UVLO).

CC

The soft-start is disabled when DIM input goes high in order to maximize the dimming
performance.

5.4 Error amplifier

The voltage error amplifier is the core of the loop regulation. It is a transconductance
operational amplifier whose non-inverting input is connected to the internal voltage
reference (100 mV), while the inverting input (FB) is connected to the output current sensing
resistor.

The error amplifier is internally compensated to minimize the size of the final application.

Table 5. Uncompensated error amplifier characteristics

Description Value

Transconductance 250 µS

Low frequency gain 96 dB

10/39 Doc ID 023432 Rev 2

LED2000 Functional description

Table 5. Uncompensated error amplifier characteristics (continued)

Description Value

C

C

R

C

The error amplifier output is compared with the inductor current sense information to
perform PWM control.

5.5 Thermal shutdown

The shutdown block generates a signal that disables the power stage if the temperature of
the chip goes higher than a fixed internal threshold (150 ± 10 °C typical). The sensing
element of the chip is close to the PDMOS area, ensuring fast and accurate temperature
detection. A 15 °C typical hysteresis prevents the device from turning ON and OFF
continuously during the protection operation.

195 pF

70 KΩ

Doc ID 023432 Rev 2 11/39

Application notes LED2000

V

IN

-

+

-

LC filter

V

REF

error

amplifier

FB

compensation

network

PWM

comparator

HS

switch

R

S

L

C

OUT

R

C

C

C

+

PWM control

Current sense

LS

switch

V

OUT

V

CONTROL

GCO(s)

A

O

(s)

α

LED

GCOs()

R

0

R

i

-------

1

1

R

0TSW

⋅

L

---------------------------

m

C

1D–()0.5–⋅[]⋅+

-------------------------------------------------------- ------------------------------------------

1

s

ω

z

-----+

⎝⎠

⎛⎞

1

s

ω

p

------+

⎝⎠

⎛⎞

---------------------

F

H

s()⋅⋅⋅=

6 Application notes

6.1 Closing the loop

Figure 5. Block diagram of the loop

6.2 GCO(s) control to output transfer function

The accurate control to output transfer function for a buck peak current mode converter can
be written as:

Equation 1

where R
sense circuitry, ω

represents the load resistance, Ri the equivalent sensing resistor of the current

0

the single pole introduced by the LC filter and ωz the zero given by the

p

ESR of the output capacitor.

F

(s) accounts for the sampling effect performed by the PWM comparator on the output of

H

the error amplifier that introduces a double pole at one half of the switching frequency.

12/39 Doc ID 023432 Rev 2