SDSDQAB-016G-859 19NM - SANDISK - Datasheet.Directory

MIC2870

1.5A Synchronous Boost Flash LED Driver

with I2C Inter f ace

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

September 5, 2013

Revision 1.0

General Description

The MIC2870 is a high-current, high-efficiency flash LED

driver for one or two high-brightness camera flash LEDs.

The LED driver current is generated by an integrated

inductive boost converter with 2MHz switching frequency

which allows the use of a very-small inductor and output

capacitor. These features make the MIC2870 an ideal

solution for high-resolution camera phone LED flashlight

driver applications.

MIC2870 supports two 750mA white-LEDs (WLEDs) or a

single 1.5A WLED configuration. When two WLEDs are

connected, their currents are matched automatically.

MIC2870 operates in either flash or torch modes that can

be controlled through either an I2C interface or external

pins. The brightness in the flash and torch mode can be

adjusted via t wo externa l resistors individ uall y. High -speed

mode I2C interface provides a simple control at a clock

speed up to 3.4MHz to support most camera functions

such as auto-focus, white balance, and image capture

(flash mode).

The MIC2870 is available in 16-pin, 2mm × 2mm TQFN

package with a junction temperature range of −40°C to

+125°C.

Datasheets and support documentation are available on

Micrel’s web site at: www.micrel.com.

Features

• Up to 1.5A flash LED driving current

− 2.7V to 5.0V input voltage range

• High-efficiency 2MHz VF adaptive boost driver

• Configurable 1 or 2 channel(s) WLED driver

• LED driving current soft-start

• Control through I2C interface or external pins

• Flash inhibit function for GSM pulse synchronization

• True load disconnect

• Flash time-out protection

• 1µA shutdown current

• Available in 16-pin 2mm × 2mm TQFN package

Applications

• Camera phones/mobile handsets

• Cellular phones/smart phones

• LED light for image capture/auto focus/white balance

• Handset video light (torch li ght)

• Digital cameras

• Portable applications

Typical Applic ation

Micrel, Inc.

MIC2870

September 5, 2013

2 Revision 1.0

Ordering Information

Part Number Marking Temperature Range Package

(1)

Lead Finish

MIC2870YFT 70H –40°C to +125°C 16-Pin 2mm × 2mm TQFN NiPdAu

Note:

1. Package is a GREEN, RoHS-compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.

2. Thin QFN pin 1 identifier = “▲”.

Pin Configuration

16-Pin 2mm × 2mm TQFN

(Top View)

Pin Description

Pin Number Pin Name Pin Function

1 SCL High-Speed Mode (3.4MHz) I²C Clock Input.

2 VIN Supply Input. Connect a low-ESR ceramic capacitor of at least 4.7µF to PGND. A small capacitor

of 100nF between VIN and AGND is highly recommended.

3 FEN Flash-Mode Enable Pin. A LOW-to-HIGH transition initiates the flash mode and flash-mode timer.

If FEN is left floating, it is pulled-down internally by a built-in 1µA current source when the device

is enabled.

4 FI

Flash Inhibit. When FI is pulled HIGH, both LED currents are changed from the flash-mode

current level to the torch-mode current level. If FI is left floating, it is pulled-down internally by a

built-in 1µA current source when the device is enabled. This function is generally used to reduce

instantaneous battery load current by synchronizing with the handset’s GSM pulse off time.

5 FRSET

Flash-Mode Current Level Programming. Connect a resistor from FRSET to AGND to set the

maximum current in the flash mode. For example, a 10kΩ resistor sets the LED sink current to its

maximum value of 750mA per channel. FRSET can be grounded if the default maximum flash-

mode current (750mA) is desired. FRSET, however, cannot be left floating and the maximum

resistance is limited to 80kΩ

6 AGND Analog Ground. Reference ground for FRSET and TRSET pins.

Micrel, Inc.

MIC2870

September 5, 2013

3 Revision 1.0

Pin Description (Continued)

Pin Number Pin Name Pin Function

7, 15 PGND Power Ground. PGND is used for the switching NMOS and PMOS of boost converter, and pow er

ground for LED current sin ks.

8 TRSET

Torch-Mode Current Level Programming. Connect a resistor from TRSET to AGND to set the

maximum current in the torch mode. For example, a 10kΩ resistor sets the LE D sink curr ent to its

maximum value of 187.5mA per channel. TRSET can be grounded if the default maximum torch-

mode current (187.5mA) is desired. TRSET, however, cann o t be left float ing and the maximum

resistance is limited to 80kΩ.

9 LED2 Channel 2 LED Current Sink. Connect the LED anode to OUT and cathode to LED2.

10 LED1 Channel 1 LED Current Sink. Connect the LED anode to OUT and cathode to LED1.

11 TEN Torch-Mode Enable. Initiates torch mode when TEN is HIGH. If TEN is left floating, it is pulled-

down internally by a built-in 1µA current source when the device is enab led.

12 OUT Boost Converter Output.

13 EN

Enable (IC). The MIC2870 is in standby mode when EN is asserted HIGH. If EN is driven low for

more than 1s, the IC is shut down. Alternatively, the I2C int erface can be used for

enabling/disabling the IC through the master control/status register. EN is pulled down by an

internal resistor.

14 SW Inductor Connection. It is connected to the internal power MOSFETs.

16 SDA High-Speed Mode (3.4MHz) I²C Data Input/Output.

EP ePad Exposed Heat Sink Pad. Connect to PGND ground plane for best thermal perfo rma nce . This pin

is internally connected to PGND.

Micrel, Inc.

MIC2870

September 5, 2013

4 Revision 1.0

Absolute Maximum Ratings(3)

Supply Voltage (VIN) ..................................... −0.3V to +6.0V

Enable Input Voltage

(VEN, VFEN, VFI, VTEN) ....................... −0.3V to VIN + 0.3V

VOUT, VLED1, and VLED2 .................................... −0.3V to 6.0V

I2C I/O (VSCL, VSDA) ................................ −0.3V to VIN + 0.3V

VFRSET and VTRSET .................................. −0.3V to VIN + 0.3V

VSW ................................................................. −0.3V to 6.0V

Power Dissip ati on(5) (PDISS) ....................... Internally Limited

Lead Temperature (soldering, 10s) .......................... +260°C

Junction Temperature (TJ) ........................ −40°C to +150°C

Storage Temperature (TS) ......................... −40°C to +150°C

ESD Rating(6) ................................. 2kV HBM and 150V MM

Operating Ratings(4)

Supply Voltage (VIN) ..................................... +2.7V to +5.0V

Enable Input Voltage (VEN, VFEN, VFI, VTEN) ............ 0V to VIN

I2C I/O (VSCL, VSDA) ................................................. 0V to VIN

Junction Temperature (TJ) .......................... −40°C to 125°C

Package Thermal Resistance(5)

2mm × 2mm TQFN (θJA) .................................... 80°C/W

Electrical Characteristics(7)

VIN = 3.6V; L = 1μH, COUT = 2.2μF, RFRSET = 10kΩ, RTRSET = 10kΩ, ILED = 100mA; TA = 25°C, bold values ind icat e −40°C ≤ TJ ≤ 125°C,

unless otherw ise not ed.

Symbol Parameter Condition Min. Typ. Max. Units

Powe r Su pply

VIN Input Voltage 2.7 5.0 V

IVIN Quiescent Current VLED1 = VLED2 > 200mV, not sw itching 0.9 mA

VLED1 = VLED2 = 7 0mV, boost keeps switching 4.2

IVIN(SD) Shutdown Current VEN = 0 V 0.6 µA

ISW(SD) SW Pin Shutdown Current VEN = 0 V 1 5 µA

UVLO_Rise UVLO Threshold (Rising) 2.35 2.5 2.65 V

UVLO_Hyst UVLO Hysteresis 300 mV

VOUT Output Voltage VIN ≥ VOUT VIN V

VOUT > VIN 5.2

VOVP

Overvoltage Protection

Threshold VOUT > VIN 5.26 5.38 5.6 V

Overvoltage Protection

Hysteresis 60 mV

OVP Blanking Time 24 µs

DMAX Maximum Duty Cycle 80 85 90 %

DMIN Minimum Duty Cycle 5.5 %

ISW_OC Sw itch Current Lim it VIN = VOUT = 2.7V 3.35 4.5 5.65 A

Notes:

3. Exceeding the absolute maximum ratings may damage the device.

4. The device is not guarant eed to function outside its operat i ng ratings.

5. The maxim um allowable power dissi pation of any TA (ambient temperature) is PDISS(max) = (TJ(max) – TA) / θJA. Exceeding the maximum allowable power

dissipati on will result in excessi ve die tem perat ure, and the regulat or will go into thermal shutdown.

6. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF.

7. Specific at i on for packaged product only

Micrel, Inc.

MIC2870

September 5, 2013

5 Revision 1.0

Electrical Characteristics(7) (Continued)

VIN = 3.6V; L = 1μH, COUT = 2.2μF, RFRSET = 10kΩ, RTRSET = 10kΩ, ILED = 100mA; TA = 25°C, bold values ind icat e −40°C ≤ TJ ≤ 125°C,

unless otherw ise not ed.

Symbol Parameter Condition Min. Typ. Max. Units

FSW Oscillator Frequency 1.8 2.0 2.2 MHz

RON(N) Switch On-Resistance VVIN = 2.7 V, ISW = 750 mA 80 mΩ

RON(P) VSW = 2.7 V, IOUT = 750 mA 80

ILK(N) NMOS Switch Leakage

Current VEN = 0 V, VIN = Vsw = VOUT = 5 V

1 5 µA

ILK(P) PMOS Switch Leakage

Current VEN = 0 V, VIN = VOUT = 5 V, Vsw = 0 V

1 5 µA

RDCHG Auto-Discharge NMOS

Resistance VEN = 0 V, IOUT = −1 mA 160 Ω

TSD Overtemperature Shutdown

Threshold 160 °C

TSD_HYST Overtemperature Shutdown

Hysteresis 25 °C

TFLASH_TIMEOUT Flash Safety Timeout

Shutdown Maximum timeout setting 1.25 s

Current Sink Channels

AccuLED_Ch Channel Current Accuracy VLED1 = VLED2 = 890mV,

ILED1 = ILED2 = 750mA −10 10 %

MatchLED_Ch Channel Current Matching VLED1 = VLED2 = 890mV,

ILED1 = ILED2 = 750mA −5 5 %

VDROPOUT Current Sink Dropout Boost is in regulation 100 mV

ILK_LED1 LED1 Leakage Current VIN = 3.6 V, VEN = 0 V, VLED1 = 3.6 V 0.05 µA

ILK_LED2 LED2 Leakage Current VIN = 3.6 V, VEN = 0 V, VLED2 = 3.6 V 0.05 µA

VFRSET FRSET Pin Voltage RFRSET = 10kΩ, flash mode 0.970 1.00 1.030 V

IFRSET FRSET Current So urcing FRSET pin is shorted to groun d,

flash mode 90 100 110 µA

VTRSET TRSET Pin Voltage RTRSET = 10kΩ, torch mode 0.970 1.00 1.030 V

ITRSET TRSET Current Sourcing TRSET pin is shorted to groun d, torch

mode 90 100 110 µA

Micrel, Inc.

MIC2870

September 5, 2013

6 Revision 1.0

Electrical Characteristics(7) (Continued)

VIN = 3.6V; L = 1μH, COUT = 2.2μF, RFRSET = 10kΩ, RTRSET = 10kΩ, ILED = 10 0mA; TA = 25°C, bold valu es ind ica te −40°C ≤ TJ ≤ 125°C,

unless otherw ise not ed.

Symbol Parameter Condition Min. Typ. Max. Units

EN / FEN / TEN / FI Control Pins

VEN_ON EN On Threshold Boost convert er and chip log ic ON 1.5 V

VEN_OFF EN Off Threshold Boost convert er and chip log ic ON 0.4 V

VFEN_ON FEN On Threshold FLASH ON 1.5 V

VFEN_OFF FEN Off Threshold FLASH OFF 0.4 V

VTEN_ON TEN On Threshold TORCH ON 1.5 V

VTEN_OFF TEN Off Threshold TORCH OF F 0.4 V

VFI_ON FI On Threshold FLASH INHIBIT ON 1.5 V

VFI_OFF FI Off Threshold FLASH INHIBIT OFF 0.4 V

EN Pin Current VEN = 5V 2 5 µA

FEN/TEN/FI Pin Current VFEN = VTEN = VFI = 5V 1 5 µA

tBlank_EN_Off EN OFF Blanking Time EN pin should be driven low for more

than this time before the IC enters sleep

mode 0.90 1.10 1.30 s

I2C Interface (SCL / SDA Pins) (Guaranteed by Design)

fSCL Maximum Operating

Frequency 3.4 MHz

VIL Low-Level Input Voltage 0.4 V

VIH High-Level Input Voltage 1.5 V

RSDA_DN SDA Pulled-Down

Resistance 20 Ω

Additional Protection Features

VTH_LEDOPEN LED1 / LED2 Open Detect

Threshold 15 25 40 mV

TBLANK_OPEN Open Detect Blanking Time 65 µs

TRETRY_OPEN Open Retry Timeout 100 ms

VTH_LEDSHORT Short Trigger Threshold VOUT − MAX[VLED1,VLED2], VOUT = 3.6V 400 600 800 mV

VHYST_LEDSHORT Short Trigger Hysteresis 200 mV

TBLANK_SHORT Short Trigger Blanking

Time 30 µs

TRETRY_ SHORT Short Retry Timeout 100 ms

Micrel, Inc.

MIC2870

September 5, 2013

7 Revision 1.0

Typical Characteris tics

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-40 -20 020 40 60 80 100 120

SHUTDOWN CURRENT (µA)

TEMPERATURE (°C)

Shutdown Current

vs. Temperature

0.87

0.88

0.89

0.90

0.91

0.92

0.93

0.94

-40 -20 020 40 60 80 100 120

QUIESCENT CURRENT (µA)

TEMPERATURE (°C)

Quiescent Current (Linear Mode)

vs. Temperature

LINEAR MODE NOT SWITCHING

LED1

= V

LED2

> 200mV

4.10

4.15

4.20

4.25

4.30

4.35

4.40

4.45

4.50

-40 -20 020 40 60 80 100 120

QUIESCENT CURRENT (µA)

TEMPERATURE (°C)

Quiescent Current (Boost Mode)

vs. Temperature

BOOST MODE SWITCHING

LED1

= V

LED2

= 70mV

185

186

187

188

189

190

-40 -20 020 40 60 80 100 120

TORCH MODE LED CURRENT (mA)

TEMPERATURE (°C)

Tor c h Mode LED1 and LED2

Current vs. Temperature

TORCH MODE

L = 1µH

OUT

= 2.2

LED

= 187.5mA

LED

= 890mV

TRSET

= 10k

600

650

700

750

800

850

-40 -20 020 40 60 80 100 120

FLASH MODE LED CURRENT (mA)

TEMPERATURE (°C)

Flash Mode LED1 and LED2

Current vs. Temperature

FLASH MODE

L = 1µH

OUT

= 2.2µF

LED

= 750mA

LED

= 890mV

FRSET

= 10kΩ

100

150

200

250

010 20 30 40 50 60 70 80

TORCH MODE ILED(MAX) (mA)

TRSET RESISTOR (kΩ)

Torch Mode I

LED(MAX)

(Dual LEDs) vs. TRSET Resistor

L = 1 µH

OUT

= 2.2µF

DUAL LEDs

LED

PER CHANNEL

= 25°C

100

200

300

400

500

600

700

800

010 20 30 40 50 60 70 80

FLASH MODE ILED(MAX) (mA)

FRSET RESISTOR (kΩ)

Flash Mode ILED(MAX)

(Dual LEDs) vs. FRSET Resistor

L = 1 µH

OUT

= 2.2µF

DUAL LEDs

LED

PER CHANNEL

= 25°C

100

150

200

250

300

350

400

010 20 30 40 50 60 70 80

TORCH MODE I

LED(MAX)

(mA)

TRSET RESISTOR (kΩ)

Torch Mode I

LED(MAX)

(Single LED) vs. TRSET Resistor

L = 1 µH

OUT

= 2.2µF

SINGLE LED

LED1

LED2

= 25°C

200

400

600

800

1000

1200

1400

1600

010 20 30 40 50 60 70 80

FLASH MODE ILED(MAX) (mA)

FRSET RESISTOR (kΩ)

Flash Mode ILED(MAX)

(Single LED) vs. FRSET Resistor

L = 1 µH

OUT

= 2.2µF

SINGLE LED

LED1

LED2

= 25°C

Micrel, Inc.

MIC2870

September 5, 2013

8 Revision 1.0

Typical Characteristics (Continued)

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.5 3.7 3.9 4.1 4.3

TORCH MODE I

LED(MAX)

ACCURACY (%)

INPUT VOLTAGE (V)

Torch Mode I

LED(MAX)

Accuracy vs. Input Voltage

RTRSET = 51kΩ

RTRSET = 62kΩ

RTRSET = 39kΩ

RTRSET = 30kΩ

RTRSET = 20kΩ

RTRSET = 10kΩ

RTRSET = 82kΩ

RTRSET = 75kΩ

1.80

1.85

1.90

1.95

2.00

2.05

2.10

2.15

2.20

2.5 3.0 3.5 4.0 4.5

SWITCHING FREQUENCY (MHz)

INPUT VOLTAGE (V)

Boost Switching Frequency

vs. Input Voltage

-40°C

125°C

75°C

25°C

L = 1 µH

OUT

= 2.2µF

LED1

+ I

LED2

= 1.5A

100

2.6 3.0 3.4 3.8 4.2 4.6 5.0

EFFICIENCY (%)

INPUT VOLTAGE (V)

WLED Output Power Efficiency

vs. Input Voltage

L = 1µH

OUT

= 2.2µF

= 25°C

LED

= 150mA

LED

= 375mA

LED

= 780mA

LED

= 1.2A

LED

= 1.5A

Micrel, Inc.

MIC2870

September 5, 2013

9 Revision 1.0

Functional Characteristics

Micrel, Inc.

MIC2870

September 5, 2013

10 Revision 1.0

Functional Characteristics (Continued)

Micrel, Inc.

MIC2870

September 5, 2013

11 Revision 1.0

Functional Characteristics (Continued)

Micrel, Inc.

MIC2870

September 5, 2013

12 Revision 1.0

Functional Diagram

Figure 1. Simplified MIC2870 Functional Block Diagram

Micrel, Inc.

MIC2870

September 5, 2013

13 Revision 1.0

Functional Description

VIN

The input supply provides power to the internal

MOSFETs gate drive an d contr ols circu itry for the s witch-

mode r egulator. The operat ing i npu t vo lta ge rang e is f rom

2.7V to 5.0V. A 4.7µF low-ESR ceramic input capacitor

should be connected from VIN to AGND as close to

MIC2870 as pos sib le to ens ure a clean s uppl y voltage for

the device. The minimum voltage rating of 10V is

recom m ended for the input c apac itor.

The MIC2870 has internal low-side and synchronous

MOSFET switches. The switch node (SW) between the

internal MOSFET switches connects directly to one end

of the inductor and provides the current paths during

switching cycles. The other end of the inductor is

connected to the input supply voltage. Due to the high-

speed switching on this pin, the switch node should be

routed away from sensitive nodes wherever possible.

AGND

This is the gr ound path f or the int erna l bias ing and cont rol

circuitr y. The cur rent lo op of the analog ground s houl d be

separated from that of the power ground (PGND). AGND

should be connected to PGND at a single point.

PGND

The power ground pin is the ground path for the high

current in the boost switch and the ground path of the

LED curre nt sink s. The curr ent loop f or the power gr ound

should be as small as possible and separate from the

AGND loop as applicable.

OUT

Boost converter output pin which is connected to the

anode of t he LED. A lo w-ESR ceram ic capac itor of 2.2µF

or larger should be connected from OUT to PGND as

close as possible to the MIC2870. The minimum voltage

rating of 10V is recommended for the output capacitor.

LED1/LED2

The current sink pins for the LED(s). The LED anode is

connected to the OUT pin and the LED cathode is

connected to the LED1/LED2 pin(s).

This is the enable pin of the MI C2870. The MIC 2870 is in

standby mode when the EN pin is asserted high. If this

pin is driven low for more than 1s, the IC is shutdown.

Alternatively, the I2C interface can be used for

enabling/disabling the IC through the master

control/status register. EN is pulled down by an internal

resistor.

FEN

FEN is the hardware enable pin for flash mode. A logic

low-to-hig h transitio n on FEN pin initiates the f lash mode.

If FEN pin is left floating, it is pulled down internally by a

built-in 1µA current source when the device is enabled.

Flash mode is terminated when FEN is pulled low or left

floating, and the flash control register is cleared.

TEN

TEN is the hardware enable pin for torch mode. A logic

low-to-hig h transit ion on T EN pin ini tiates the t orch mode.

If TEN pin is left floating, it is pulled down internally by a

built-in 1µA current source when the device is enabled.

Torch mode is terminated when TEN is pulled low or left

floating, and the torch control register is cleared.

FI is the flash inhibit pin. When this pin is high in flash

mode, both LED1 and LED2 currents are changed from

the flash-mode current level to the torch-mode current

level. When this pin is lo w, both LED 1 and LE D2 currents

are changed from torch-mode current level back to the

original flash-mode current level.

FRSET

The flash-mode maximum LED current level is

programmed through FRSET. A resistor connected from

FRSET to AGND sets the maximum current in the flash

mode. FRSET can be grounded for the default flash-

mode c ur rent of 0. 75A. For best c urr ent ac cur acy, a 0.1%

tolerance r esistor is r ec om mended. FRSET canno t b e left

floating and the maximum resistance is limited to 80kΩ.

TRSET

The torch-mode maximum LED current level is

programmed through TRSET. A resistor connected from

the TRSET pin to AG ND se ts the m axim um curr ent in the

torch mode. TRSET can be grounded for the default

torch-mode current of 187.5mA. For best current

accuracy, a 0.1% tolerance resistor is recommended.

TRSET cannot be left floating and the maximum

resistance is limited to 80kΩ.

SCL

I2C clock input pin prov ides a ref erence cloc k for clocking

in the data signal. This is a high-speed mode up to

3.4MHz input pin, and requires a 4.7kΩ pull-up resistor.

SDA

I2C data input/output pin allows for data to be written to

and read from the MIC2870. This is a high-speed mode

up to 3.4MHz I2C pin, and requires a 4.7kΩ pull-up

resistor.

Micrel, Inc.

MIC2870

September 5, 2013

14 Revision 1.0

Application Information

The MIC2870 can drive one or two high-current flash

WLEDs in either flash mode or torch mode. Two W LEDs

can be used to optimize the light output and beam

shaping through the optical lens/reflector assembly. In

this case, the two channels, up to 750mA each, are

matched to within 10% for optimal flash illumination.

When the two channels are combined to drive a single

high-brightness WLED, the maximum current is 1.5A. If

one of the channels is left floating, MIC2870 senses the

circuit condition automatically and allows the other

channel to operate.

Flash Mode

The maximum current level in the flash mode is 750mA

per channel. This current level can be adjusted through

an external resistor connecting to FRSET according to

the following equation:

FRSET

LED(MAX)

7500

Eq. 1

Alternatively, the default maximum value of 750mA per

channel is used when FRSET is grounded.

The flash-mode current can be initiated at the preset

FRSET brightness level by asserting FEN high or by

setting t he I2C flash control register (addres s 01h) for the

desired flash duration, subjected to the flash safety

timeout setting. The flash-mode current is terminated

when FEN is brought low and the I2C flash register is

cleared.

The flash inhibit (FI) pin can be used to synchronize the

flash current to a handset GSM pulse event to prevent

excess ive battery droop. W hen FEN and FI pins ar e both

HIGH, the f lash-mode c urrent is lim ited t o the t orch-mode

current setting. The FI pin is also functional when the

flash-mode current is enabled through the I2C flash

Flash-mode current can be adjusted to a fraction of the

maximum flash-mode level (either default or set by the

FRSET resistor) by selecting the desired flash current

level percentage in the flash control register (address

01h) through the I2C interface. The flash current is the

product of the maximum flash current setting and the

percentage selected in the flash register.

The flash s af et y timeout featur e aut omatically shuts down

the flash current if the flash mode is enabled for an

extended period of time. Refer to the flash safety timer

setting in Table 4.

Torch Mode

The maximum torch-mode current level can be adjusted

through an ext ernal resistor connecting to the TR SET pin

according to Equation 2:

TRSET

LED(MAX) 4R

7500

Eq. 2

Alternat ivel y, the def ault m ax imum value of 187.5 m A per

channel is used when the TRSET pin is grounded. The

torch-mode operation is activated by asserting TEN high

or by setting the I2C torch register (address 02h) for the

desired duration. The torch-mode current is terminated

when TEN is brought low and the I2C torch register is

cleared.

Like the flash-mode current, the torch-mode current can

be set to a fraction of the maximum torch-mode level

(either default or set by the TRSET resistor) by selecting

the desired torch current level percentage in the torch

torch cur rent is the product of the m axim um t orch current

setting and the percentage selected in the torch register.

Overvoltage Protection

When the output voltage rises above the overvoltage

protection (OVP) threshold, the MIC2870 is turned off

automatically to avoid permanent damage to the IC.

Open-Circuit Detection

The open-circuit detector (OCD) is active only when the

LED current regulator is turned on. When the external

LED is missing or fails open, the LED1/2 pin voltage is

pulled to near the groun d potential b y the internal curr ent

sink. If both LEDs are open or missing, the open-circuit

detector would force the boost regulator and LED curr ent

regulator to turn off. The MIC2870 will try to turn on the

boost regulator and LED current regulator again after a

100ms timeout. However, in most practical cases, the

boost output v olt ag e wou ld r ise abo ve the O V P thres h old,

when both LED channels have an open fault. The OVP

function woul d cause the MIC2870 to shut down.

Short-Circuit Detection

Like the OCD, the short-circuit detector is active only

when the current regulator is turned on. If either one or

both of the external LEDs fail a short, the short-circuit

detector would force the MIC2870 to turn off. The

MIC2870 will try to turn on the boost regulator and LED

current r egulator agai n after a 100m s timeout. If t he short

condition persists, the whole cycle repeats again.

Prolonged operation in short-circuit condition is not

recommended as it can damage the device.

Micrel, Inc.

MIC2870

September 5, 2013

15 Revision 1.0

I2C Interface

Figure 2 shows the communications required for write

and read opera tions via the I2C interf ace. T he black lines

show master comm unications and the red lines show the

slave communications. During a write operation the

master m ust drive SD A an d SC L for a ll s tages ex cept the

acknowledgement (A) shown in red, which are provided

by the slave (MIC2870):

Figure 2. I2C Timing Example

The read operation begins firstly with a data-less write to

select the register address from which to read. Then a

restart sequence is issued, and then a read command

followed by the data read.

The MIC2870 responds to a slave address of hex 0xB4

and 0xB5 for write and read operations respectively, or

binary 1011010X (where X is the read/write bit).

The register address is eight bits wide and carries the

address of the MIC2870 register to be operated upon.

Only the lower three bits are used.

I²C Registers

MIC2870 contains three 8-bit read/write registers having

an address from 00h to 02h for operation control as

shown in Table 1. These registers are reset to their

default values in power-on-reset (POR) event. In other

words, the y hold their previous contents when the chip is

shutdown as long as supply voltage is above 1.5V

(typical).

Table 1. MIC2870 Register Map

Address Register

Name Description

00h Master

Control/

Status

Chip enable control and status

01h Flash

Control

Flash-mode current, flash-

mode enable, and flash timeout

control register

02h Torch

Control Torch-mode current and torch-

mode enable co ntrol r egi ster

Master Control / Status Register [00h]

The master control / status register allows the MIC2870

to be enabled by the I2C interface -- setting the ON [ ] bit

high has the same effect as asserting EN pin. The LED

short bit, LED_SHT[ ] is set if any or both of the LED is

shorted to OUT, while the LED open bit, LED_OP[ ] is

asserted only when both LED are open circuit. The

thermal shutdown bit, TSD[ ] is set when the junction

temperature of the MIC2870 is higher than 160°C.

Flash Control Register [01h]

The flash safety timer and flash-mode current are

configurable via the flash control register. Refer to flash

timeout duration s etting and f lash-mode cur rent setting in

Table 4 and Table 5.

Torch Control Register [02h]

The torch-mode current is configurable via the torch

control register. Refer to torch-mode current setting in

Table 7. The FI[ ] bit has th e sam e function as the FI pin.

When the FI[ ] bit is set, the flash-mode current is

reduced to the torch-mode current setting.

Micrel, Inc.

MIC2870

September 5, 2013

16 Revision 1.0

Table 2. Master Control Register [00h]

Bit D7 D6 D5 D4 D3 D2 D1 D0

Name Reserved ON LED_SHT LED_OP TSD

Access R R/W R

Default Value 0

Table 3. Flash Control Register [01h]

Bit D7 D6 D5 D4 D3 D2 D1 D0

Name FTMR FEN FCUR

Access R/W

Default Value 111 0 0000

Table 4. Flash Safety Timer Setting (FTMR)

111 1250

110 1093.75

101 937.5

100 781.25

011 625

010 468.75

001 312.5

000 156.25

Micrel, Inc.

MIC2870

September 5, 2013

17 Revision 1.0

Table 5. Flash-Mode Current Setting (FCUR)

Percentage of

Maximum Current / % Register Value

[D3:D0] of 01h Current per Channel (mA)

(RFRSET = 0Ω) Combined Current (mA)

(RFRSET = 0Ω)

100 0000 750.0 1500.0

90 0001 675.0 1350.0

80 0010 600.0 1200.0

70 0011 525.0 1050.0

63 0100 472.5 945.0

56 0101 420.0 840.0

50 0110 375.0 750.0

44.7 0111 335.3 670.5

39.8 1000 298.5 597.0

35.5 1001 266.3 532.5

31.6 1010 237.0 474.0

28.2 1011 211.5 423.0

25.1 1100 188.3 376.5

22.4 1101 168.0 336.0

20 1110 150.0 300.0

18 1111 135.0 270.0

Table 6. Torch Control Register [02h]

Bit D7 D6 D5 D4 D3 D2 D1 D0

Name Reserved FI TEN TCUR

Access RO R/W

Default Value 0 0000

Micrel, Inc.

MIC2870

September 5, 2013

18 Revision 1.0

Table 7. Torch-Mode Current Setting (TCUR)

Percentage of

Maximum Current (%) Register Value

[D3:D0] of 02h Current per Channel (mA)

(RTRSET = 0Ω) Combined Current (mA)

(RTRSET = 0Ω)

100 0000 187.5 375.0

90 0001 168.8 337.5

80 0010 150.0 300.0

70 0011 131.3 262.5

63 0100 118.1 236.3

56 0101 105.0 210.0

50 0110 93.8 187.5

44.7 0111 83.8 167.6

39.8 1000 74.6 149.3

35.5 1001 66.6 133.1

31.6 1010 59.3 118.5

28.2 1011 52.9 105.8

25.1 1100 47.1 94.1

22.4 1101 42.0 84.0

20 1110 37.5 75.0

18 1111 33.8 67.5

Micrel, Inc.

MIC2870

September 5, 2013

19 Revision 1.0

Component Selection

Inductor

Inductor selection is a balance between efficiency,

stability, cost, size, and rated current. Since the boost

converter is compensated internally, the recommended

inductance of L is limited from 1µH to 2.2µH to ensure

system stability. It is usually a good balance between

these considerations.

A large inductance value reduces the peak-to-peak

inductor ripple current hence the output ripple voltage

and the LED ripple current. This also reduces both the

DC loss and th e tra nsition los s at t he sam e induc tor’s DC

resistance (DCR). However, the DCR of an inductor

usually increases with the inductance in the same

pack age size. This is due to the longer windings req uired

for an increase in inductance. Since the majority of the

input current passes through the inductor, the higher the

DCR the lower the efficiency is, and more significantly at

higher load currents. On the other hand, inductor with

smaller DCR but the same inductance usually has a

larger size. The saturation current rating of the selected

inductor m ust be higher than the m aximum peak inductor

current to be encountered and should be at least 20% to

30% higher than the average inductor current at

maximum output current.

Input Capacitor

A ceramic capacitor of 4.7µF or larger with low ESR is

recommended to reduce the input voltage ripple to

ensure a clean supply voltage for the device. The input

capacitor should be placed as close as possible to the

MIC2870 VIN pin with short trace for good noise

performance. X5R or X7R type ceramic capacitors are

recommended for better tolerance over tem perature. The

Y5V and Z5U type temper ature rating cer amic capacitor s

are not recommended due to their large reduction in

capacitance over temperature and increased resistance

at high fr equencies. T hese reduce their ability to fil ter out

high-frequency noise. The rated voltage of the input

capacitor should be at least 20% higher than the

maximum operating input voltage over the operating

temperature range.

Output Capacitor

Output capacitor selection is also a trade-off between

performance, size, and cost. Increasing output capacitor

will lead to an im proved transient respo nse, however, the

size and cost also increase. The output capacitor is

preferred in the range of 2.2µF to 10µF with ESR from

10mΩ to 50mΩ. X5R or X7R type ceramic capacitors are

recommended for better tolerance over temperature.

The Y5V and Z5U type ceramic capacitors are not

recommended due to their wide variation in capacitance

over temperature and increased resistance at high

frequencies. The rated voltage of the output capacitor

should be at least 20% higher than the maximum

operating output voltage over the operating temperature

range.

FRSET/TRSET Resistor

Since FRSET/TRSET resistor is used for setting the

maximum LED current in flash mode and torch mode

respectively, resistor type with 0.1% tolerance is

recommended for more accurate LED current setting.

Micrel, Inc.

MIC2870

September 5, 2013

20 Revision 1.0

Power Dissipation Consideration

As with all power devices, the ultimate current rating of

the output is limited by the thermal properties of the

device package and the PCB on which the device is

mounted. There is a simple, Ohm’s law type relationship

between thermal resistance, power dissipation and

temperature which are analogous to an electrical circuit:

Figure 3. Series Electrical Resistance Circuit

From this simple circuit we can calculate VX if we know

ISOURCE, VZ and the resistor values, RXY and RYZ using

Equation 3:

ZYZXYSOURCEXV)R(RIV ++×=

Eq. 3

Thermal circuits can be considered using this same rule

and can be drawn similarly by replacing current sources

with power dissipation (in watts), resistance with thermal

resistance (in °C/W) and voltage sources with

temperature (in °C).

Figure 4. Series Thermal Resistance Circuit

Now replacing the variables in the equation for VX, we

can find the junction temperature (TJ) from the power

dissipation, ambient temperature and the known thermal

resistance of the PCB (θCA) and the package (θJC).

ACAJCDISSJT ) (PT +θ+θ×=

Eq. 4

As can be seen in the diagram, total thermal resistance

θJA = θJC + θCA. Hence this can also be written as in

Equation 5:

AJADISSJ

T )(PT +θ×=

Eq. 5

Since effectively all of the power losses (minus the

inductor los ses) in the c onverter are d issipated with in the

MIC2870 package, PDISS can be calculated thus:

Linear Mode:

DCR

I]1

[PP

OUTOUTDISS

×−−×=













Eq. 6

Boost Mode:

DCR

[PP

OUT

OUTDISS

−

−−×= 























Eq. 7

Duty Cycle in Boost Mod e:

OUT

INOUT

D−

Eq. 8

where:

η = Efficiency taken from efficiency curves and DCR =

inductor DCR. θJC and θJA are found in the operating

ratings section of the data sheet.

W here the rea l b oar d area diff er s f rom 1” squar e, θCA (the

PCB thermal resistance) values for various PCB copper

areas can be tak en from Figure 5. Figure 5 is taken from

Designin g with Low Dr opou t Voltage Re gulat ors available

from the Micrel website.

Micrel, Inc.

MIC2870

September 5, 2013

21 Revision 1.0

Figure 5. Graph to Determine PC Board Area for a Given

PCB Thermal Resistance

Figure 5 shows the total area of a round or square pad,

centered on the device. The solid trace represents the

area of a squar e, si ngle si ded, hori zontal, s older m as ked,

copper PC board trace heat sink, measured in square

millimeters. No airflow is assumed. The dashed line

shows PC boards trace heat sink covered in black oil-

based paint and with 1.3m/sec (250 feet per minute)

airflow. This approaches a “best case” pad heat sink.

Conservative design dictates using the solid trace data,

which ind icates that a m aximum pad size of 5000 mm2 is

needed. This is a pad 71mm × 71mm (2.8 inches per

side).

Micrel, Inc.

MIC2870

September 5, 2013

22 Revision 1.0

PCB Layout Guidelines

PCB layout is critical to achieve reliable, stable and

efficient performance. A ground plane is required to

control EMI and m inimize the inductanc e in power, signa l

and return paths. The following guidelines should be

followed to ensure proper operation of the device:

IC (Integrated Circuit)

• Place th e IC clos e to th e point -of-load ( in th is cas e, th e

flash LED).

• Use fat traces to route the input and output power

lines.

• Analog ground (AGND) and power ground (PGND)

should be kept separate and connected at a single

location.

• The exposed pad (ePad) on the bottom of the IC m ust

be connected to the PGND ground plane of the PCB.

• 4 to 6 therm al vias m ust be placed on the PC B pad f or

exposed pad and connected it to the PGND ground

plane to ens ure a goo d PC B therm al resis tance can be

achieved.

VIN Decoupling Capacitor

• The VIN decoupling capacitor must be placed close to

the VIN pin of the IC and pref erably connected directl y

to the pin and not through any via. The capacitor m ust

be located right at the IC.

• The VIN decoupling capacitor should be connected to

analog ground (AGND).

• The VIN terminal is noise sensitive and the placement

of capacitor is very critical.

Inductor

• Keep both the inductor connections to the switch node

(SW) and input power line short and wide enough to

handle the switching current. Keep the areas of the

switching current loops small to minimize the EMI

problem.

• Do not route any digital lines underneath or close to

the inductor.

• Keep the switch node (SW) away from the noise

sensitive pi ns.

• To minimize noise, place a ground plane underneath

the inductor.

Output Capacitor

• Use wide and short traces to connect the output

capacitor to the OUT and PGND pins.

• Place several vias to the ground plane close to the

output capacitor ground terminal.

• Use either X5R or X7R temperature rating ceramic

capacitors. Do not use Y5V or Z5U type ceramic

capacitors.

Flash LED

• Use wide an d short trace t o connect the LED anode to

the OUT pin.

• Use wide and short trace to connect the LED cathode

to the LED1/LED2 pins.

• Make sure that the LED’s PCB land pattern can

provide sufficient PCB pad heat sink to the flash LED.

FRSET/TRSET Resistor

• The FRSET/TRSET resistor should be placed close to

the FRSET/TRSET pin and connected to AGND.

Micrel, Inc.

MIC2870

September 5, 2013

23 Revision 1.0

Typical Applic ation Schematic

Bill of Materials

Item Part Number Manufacturer Description Qty.

C3 0603ZD475KAT2A AVX(8) Ceramic Capacitor 4.7µF, 10V, X5R, 0603 1

C1608X5R1A475K080AC TDK(9)

0603ZD225KAT2A AVX

Ceramic Capacitor 2.2µF, 10V, X5R, 0603 1 GRM188R61A225KE34D Murata

(10)

C1608X5R1A225K080AC TDK

06033D104KAJ2A AVX

Ceramic Capacitor 0.1µF, 25V, X5R, 0603 1 GRM188R61C104KA01D Murata

C1608X5R1E104K TDK

0603ZD105KAT2A AVX

Ceramic Capacitor 1µF, 10V, X5R, 0603 1 GRM188R61A105KA61D Murata

C1608X5R1A105K080AC TDK

L1 CDRH4D28CLDNP-1R0PC Sumida(11) Inductor 1µH, 3.0A, 14mΩ, L5.1mm × W5.1mm × H3.0mm 1

LQH44PN1R0NP0L Murata Inductor 1µH, 2.45A, 36mΩ, L4.0mm × W4.0mm × H1.65mm

R1, R2 CRCW06034K70FKEA Vishay/Dale(12) Resistor 4.7kΩ, 1%, 1/10W, 0603 2

R3, R4 ERA3AEB103V Panasonic(13) Resistor 10kΩ, 0.1%, 1/10W, 0603 2

D1, D2 SML-LXL99UWC-TR/5 Lumex(14) LED SQ 5W COOL WHT 6000K SMD, 190lm 2

U1 MIC2870YFT Micrel, Inc.

(15)

1.5A Synchronous Boost Flash LED Driver with I

C Interface 1

Notes:

8. AVX: www.avx.com.

9. TDK: www.tdk.com.

10. Murata: www.murata.com.

11. Sumida: www.sumida.com.

12. Vishay: www.vishay.com.

13. Panasonic: www.panasonic.com.

14. Lumex: www.lumex.com.

15. Micrel, Inc.: www.micrel.com.

Micrel, Inc.

MIC2870

September 5, 2013

24 Revision 1.0

PCB Layout Recommendations

Top Layer

Bottom Layer

Micrel, Inc.

MIC2870

September 5, 2013

25 Revision 1.0

Package Information(16)

16-Pin 2mm × 2mm TQFN (FT)

Note:

16. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.

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TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com

Micrel makes no represent ations or warranties with respec t t o the accuracy or completeness of the information furnis hed in t his data sheet. This

informat i on is not intended as a warranty and Micrel does not assume responsibilit y for its use. Micrel reserves the right to change circuitry,

specificat i ons and descript i ons at any time without notice. No license, whether express , im plied, arisi ng by estoppel or otherwise, t o any intellectual

property rights is granted by this document. Except as provided in Micrel’s term s and condit i ons of sale for such products, Micrel assumes no liabil ity

whatsoever, and Micrel disclaims any express or impli ed warranty relati ng to t he sale and/or use of Micrel products including liabil ity or warranties

relating to fitness for a partic ular purpose, merchant abi lit y, or inf ri ngem ent of any patent, copyright or other intel l ect ual propert y right.

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can reasonably be expected to result in personal injury. Life support devices or systems are devices or syst ems that (a) are intended for surgical

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or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A

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