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Date: 7/20/05

SP7648

FEATURES

True Shutdown

700mA Output Current at 3.3V Input; 4.2V

output

92% Efficiency from 2.7V

to 3.3V

OUT

Wide Input Voltage Range: 2.7V to 4.5V

5V Fixed or Adjustable Output

0.3

Switch

Integrated Synchronous Rectifier:0.3

Anti-Ringing Switch Technology

Programmable Inductor Peak Current

Logic Shutdown Control

Low 0.8V or 0.288V Reference Voltage

Small 10 pin DFN or MSOP Package

Low Reference High Efficiency Boost Regulator

APPLICATIONS

LED Driver

Camera Flash

Handheld Portable Devices

DESCRIPTION

The SP7648 is an ultra-low quiescent current, high efficiency step-up DC-DC converter ideal for
single cell Li-Ion or dual cell alkaline battery applications to drive various LEDs. The SP7648
combines low quiescent current and excellent light-load efficiency of PFM control. The SP7648
features synchronous rectification, a 0.3

charging switch, an anti-ringing inductor switch, under-

voltage lockout and programmable inductor peak current. The device can be shut down by a
1nA active LOW shutdown pin. A very low 0.288V reference voltage is optimized for driving a
constant current load.

TYPICAL APPLICATION CIRCUIT

Now Available in Lead Free Packaging

SP7648

10 Pin DFN

OUT

GND

FLASH

SHDN

NC (Test)

LIM

BATT

Preliminary

4.7

SP7648

BATT

FLASH

OUT

1.0K

ON/OFF

SHDN

GND

0.33

LIM

(2.7 - 4.5V)

FLASH

470pF

LIM

Date: 7/20/05

LX, Vo, V

BATT

, FLASHOUT, FB to GND pin ...................... -0.3 to 6.0V

SHDN, FLASH ..................................................... -0.3V to V

BATT

+1.0V

Vo, GND, LX Current ....................................................................... 2A
Reverse V

BATT

Current .............................................................. 220mA

Forward V

BATT

Current .............................................................. 500mA

Storage Temperature .................................................. -65

C to 150

PARAMETER

MIN

TYP

MAX

UNITS

CONDITIONS

Input Voltage Operating Range, V

BATT

2.7

4.5

After Startup

Output Voltage Range, V

OUT

2.7

5.5

Under Voltage Lock-out/UVLO

0.5

0.61

0.7

Output Voltage, V

4.6

5.0

5.4

Internal Feedback Divider

Shutdown Current into V

SDO

500

SHDN

= ZeroV

Shutdown Current into V

BATT,

SDB

250

750

SHDN

= ZeroV, V

BATT

= 2.7V

Efficiency

BATT

= 2.7V, I

OUT

= 200mA, R

LIM

= 2k

Inductor Peak Current Limit, I

650

800

1000

LIM

= 2k

, I

= 1600/R

LIM

1600

LIM

= 1k

, I

= 1600/R

LIM

Output Current (Note 2)

800

BATT

= 2.7V, R

LIM

=1k

400

BATT

= 2.7V, R

LIM

=2k

200

BATT

= 2.7V, R

LIM

= 4k

Minimum Off-Time Constant K

OFF

0.5

1.0

1.5

OFF

OUT

- V

BATT

)

Maximum On-Time Constant K

2.0

3.5

5.0

BATT

)

Enable Valid to Output Stable (Note 3)

300

500

LOAD

= 1mA

NMOS

Switch Resistance

0.30

0.6

NMOS

= 100mA

PMOS

Switch Resistance

0.30

0.6

PMOS

= 100mA

FB Set Voltage, V

0.76

0.8

0.84

External feedback Flash = 0

0.266

0.288

0.310

External feedback Flash = 1

FB Input Current

100

=1.3V

SHDN Input Voltage (Note 1)

0.5

BATT

= 2.7V

2.0

BATT

= 2.7V

SHDN Input Current

100

LX Pin Leakage

FLASH Threshold V

0.4

1.0

ELECTRICAL SPECIFICATIONS

BATT

SHDN

= 3.6V, V

=ZeroV, I

LOAD

= 0mA, T

AMB

= -40

C to +85

C, V

OUT

= 5.0V, typical values at 27

C unless

otherwise noted. The

denotes the specifications which apply over full operating temperature range -40ºC to +85

C, unless

otherwise specified.

Operating Temperature ................................................ -40

C to +85

ESD Rating ........................................................................ 1.5kV HBM

These are stress ratings only and functional operation of the device at
these ratings or any other above those indicated in the operation sections
of the specifications below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect reliability.

ABSOLUTE MAXIMUM RATINGS

Note 1: SHDN must transition faster than 1V/100mS for proper operation.

Note 2: Output Current I =

{

VIN

}

X Efficiency x

{

Inductor Peak Current - Inductor Ripple Current

}

VOUT

Note 3: Guaranteed by Design.

Date: 7/20/05

PIN DESCRIPTION

PIN NUMBER

PIN NAME

DESCRIPTION

BATT

Battery Voltage. The startup circuitry is powered by this pin. Battery

Voltage is used to calculate switch off time: T

OFF

= K

OFF

/ (V

OUT

BATT

). When the battery voltage drops below 0.61V the SP7648

goes into an undervoltage lockout mode (UVLO), where the part is shut

down.

FLASH

Reference Control Input. Internal Reference defaults to 0.8V if FLASH

= LOW and 0.288V if FLASH = HIGH.

NC (Test)

No connection. This pin is bonded out for test purposes only and

must be left floating in all applications.

LIM

Current Limit Resistor. By connecting a resistor R

LIM

from this pin to

ground the inductor peak current is set by I

PEAK

=1600/R

LIM

. The range

for R

LIM

is 9k

(for 180mA) to 1.K

(for 1.6A).

SHDN

Shutdown Not. Tie this pin high to V

BATT,

for normal operation. Pull

this pin to ground to disable all circuitry inside the chip.

Feedback. Connect this pin to GND for fixed +5V operation. Connect

this pin to a resistor voltage divider between V

OUT

and GND for

adjustable output operation.

GND

Ground. Connect to ground plane.

PGND

Power Ground. The inductor charging current flows out of this pin.

Inductor Switching Node. Connect one terminal of the inductor to the

positive terminal of the battery. Connect the second terminal of the

inductor to this pin. The inductor charging current flows into LX,

through the internal charging N-channel FET, and out the PGND pin.

OUT

Output Voltage. The inductor current flows out of this pin during

switch off-time. It is also used as the internal regulator voltage supply.

Connect this pin to the positive terminal of the output capacitor.

Date: 7/20/05

_________________________DETAILED

DESCRIPTION

The SP7648 is a step-up DC-DC converter
with an input voltage operation range from
2.7V to 4.7V. In addition to the main 0.3

internal NMOSFET switch the SP7648 has
an internal synchronous rectifier, thereby
increasing efficiency and reducing the space
and cost of an external diode. An internal
inductive-damping switch significantly re-
duces inductive ringing for low noise-high
efficiency operation. If the supply voltage
drops below 0.61V the SP7648 goes into
under voltage lockout, thus opening both
internal switches. The inductor peak current
is externally programmable to allow for a
range of inductor values.

__________________________ CIRCUIT

LAYOUT

Printed circuit board layout is a critical part of
a power supply design. Poor designs can
result in excessive EMI on the feedback
paths and on the ground planes with applica-
tions involving high switching frequencies
and large peak currents. Excessive EMI can
result in instability or regulation errors. All
power components should be placed on the
PC board as closely as possible with the
traces kept short, direct, and wide (>50mils
or 1.25mm). Extra copper on the PC board
should be integrated into ground as a pseudo-
ground plane. On a multilayer PC board,
route the star ground using component-side
copper fill, then connect it to the internal
ground plane using vias. For the SP7648

THEORY OF OPERATION

devices, the inductor and input & output filter
capacitors should be soldered with their
ground pins as close together as possible in
a star-ground configuration. The V

OUT

must be bypassed directly to ground as
close to the SP7648 devices as possible
(within 0.2in or 5mm). The DC-DC converter
and any digital circuitry should be placed on
the opposite corner of the PC board as far
away from sensitive RF and analog input
stages. Noisy traces, such as from the LX
pin, should be kept away from the voltage-
feedback V

node and separated from it

using grounded copper to minimize EMI.
See the SP7648EB Evaluation Board
Manual for PC Board Layout design details.

________________ CONTROL SCHEME

A minimum off-time, current limited pulse
frequency modulation (PFM) control scheme
combines the high output power and effi-
ciency of a pulse width modulation (PWM)
device with the ultra low quiescent current of
the traditional PFM. At low to moderate
output loads the PFM control provides higher
efficiency than traditional PWM converters
are capable of delivering. At these loads the
switching frequency is determined by a mini-
mum off-time (T

OFF

, MIN) and a maximum

on-time (T

, MAX) where:

OFF

< K

OFF

/ (V

OUT

- V

BATT

)

> K

/ V

BATT

OFF

= 1.0V

= 3.5 V

Date: 7/20/05

THEORY OF OPERATION

Figure 1. Inductor Current vs. Load

At light loads (as shown in plot A in Figure 1)
the charge cycle will last the maximum value
for

: For a 3V battery this would be as

follows: T

= K

/ V

BATT

= 3.5V

S/ 3V =

1.17

S. The current built up in the coil during

the charge cycle gets fully discharged in the
discontinuous conduction mode (DCM).
When the current in the coil has reached
zero, the synchronous rectifier switch is
opened and the voltage across the coil (from
V

BATT

to LX) is shorted internally to eliminate

inductive ringing. With increasing load (as
shown in plot B in Figure 1) this inductor
damping time becomes shorter, because
the output will quickly drop below its regula-
tion point due to heavier load. If the load
current increases further, the SP7648 en-
ters continuous conduction mode (CCM)
where there is always current flowing in the
inductor. The charge time remains at maxi-
mum T

as long as the inductor peak

current limit is not reached as shown in plot
C in Figure 1. The inductor peak current limit
can be programmed by tying a resistor R

LIM

from the R

LIM

pin to ground where:

PEAK

= 1600 / R

LIM

When the peak current limit is reached the
charge time is short-cycled. In plot D of
Figure 1, the switch current reaches the
peak current limit during the charge period
which ends the charge cycle and starts the
discharge cycle. However, full load is not yet
achieved because at the end of the mini-
mum discharge time the output was still
within regulation. Maximum load is reached
when this discharge time has shrunk to the
minimum allowed value T

OFF

as shown in

Plot E of Figure 1.

_____________________ COMPONENT

SELECTION

Selection of capacitors for SP7648 power
supply circuits can be made through the use
of the Component Selection Table. Capaci-
tor equivalent series resistance (ESR) in the
range of 0.2 to 0.3

is a requirement for

obtaining sufficient output voltage ripple for
the SP7648 to properly regulate under its
load. For example, in the SP7648 applica-
tion circuit a 10

F, 10V, X5R, surface mount

ceramic output filter capacitor is used.
Ceramic capacitors have an ESR too low to
produce enough output ripple for the SP7648
to regulate the output; therefore, a 0.33

resistor is added in series with the 10

capacitor at the V

OUT

pin. Designers should

select input and output capacitors with a
rating exceeding the inductor current ripple,
which is typically set by the inductor value
and the K

value as given in the following

relationship:

L(RIPPLE)

= K

/L, where K

= 3.5V*

Inductor Current vs. Load

Ton Max.

Toff Min.

E. Iripple=Toff* (Vo

- Vi)/L

llim

Ton Max.

Toff Min.

D. Toff*= (Vo

- Vi)/L<Iripple<Ton*Vi/L

C. Iripple=Ton*Vi/L

B. Iripple=Ton*Vi/L

A. Iripple=Ton*Vi/L

Date: 7/20/05

For the example, a 10

H inductor would

have an inductor current ripple of 350mA,
while a 4.7

H inductor would have an in-

ductor current ripple value of 740mA. Do not
allow tantalum capacitors to exceed their
ripple-current ratings. An input filter capaci-
tor can reduce peak currents drawn from
the battery and improve efficiency. For
most applications, use the same capacitor
for the input and output.
Low-ESR tantalum capacitors are accept-
able provided they meet the ESR require-
ment of 0.2

to 0.3

. In selecting an

inductor, the saturation current specified for
the inductor needs to be greater than the
SP7648 peak current to avoid saturating
the inductor, which would result in a loss of
efficiency and could damage the inductor.
The SP7648 evaluation board uses a Wurth
4.7

H inductor with an I

SAT

value of 1.7A

and a DCR of 0.065

, which handles the

PEAK

of 1.6A of the SP7648 and will deliver

high efficiencies. Other inductors could be
selected provided their I

SAT

is greater than

the I

PEAK

of the SP7648.

THEORY OF OPERATION

______________ V

OUT

PROGRAMMING

The SP7648 can be programmed as either
a voltage source or a current source. To
program the SP7648 as voltage source, the
SP7648 requires 2 feedback resistors R1 &
R2 to control the output voltage. To set V

OUT

in the voltage mode, use the equation:

R1 = [(V

OUT

/0.8)-1] * R2, where flash < 0.4V,

R1 = [(V

OUT

/0.288)-1] * R2, where flash > 1.0V

_______________________ USING THE

LIM

FUNCTION

The peak inductor current, I

PEAK

, is pro-

grammed externally by the R

LIM

resistor

connected between the R

LIM

pin and GND.

The peak inductor current is defined by:

PEAK

= 1600/R

LIM

The saturation current specified for the in-
ductor needs to be greater than the peak

INDUCTORS - SURFACE MOUNT

Inductor Specification

Inductance

Manufacturer/Part No.

Series R

Isat

Size LxWxH

Inductor Type

Manufacturer

(uH)

ohms

(A)

(mm)

Website

4.7

Wurth Elektronik 744042004

0.070

1.70

4.8x4.8x1.8

Shielded Ferrite Core

www.we-online.de

4.7

TDK SLF6025T-4R7M1R5-PF

0.031

1.50

6.0x6.0x2.5

Shielded Ferrite Core

www.tdk.com

4.7

Coilcraft MSS6122-4R7MX

0.065

1.85

6.1x6.1x2.2

Shielded Ferrite Core

www.coilcraft.com

6.8

Wurth Elektronik 744042006

0.080

1.50

4.8x4.8x1.8

Shielded Ferrite Core

www.we-online.de

6.8

TDK SLF6025T-6R8M1R3-PF

0.044

1.30

6.0x6.0x2.5

Shielded Ferrite Core

www.tdk.com

6.8

Coilcraft MSS6122-6R8MX

0.100

1.45

6.1x6.1x2.2

Shielded Ferrite Core

www.coilcraft.com

CAPACITORS - SURFACE MOUNT

Capacitor Specification

Capacitance

Manufacturer/Part No.

ESR

Ripple Current

Size LxWxH

Voltage

Capacitor

Manufacturer

(uF)

ohms (max)

10C Rise (A)

(mm)

(V)

Type

Website

TDK C2012X5R0J106M

0.020

1.70

2.0x1.2x1.35

6.3

X5R Ceramic

www.tdk.com

Murata GRM21BR60J106KE19L

0.020

1.70

2.0x1.2x1.35

6.3

X5R Ceramic

www.murata.com

MOSFETS - SURFACE MOUNT

MOSFET Specification

MOSFET

Manufacturer/Part No.

RDS(on)

Package

Manufacturer

type

ohms

(A)

Size

Website

NMOS

Vishay Si1400DL

0.190

1.70

SC70-6

www.vishay.com

NMOS

Fairchild FDN337N

0.070

2.20

SOT23-3

www.fairchildsemi.com

RESISTORS - LOW VALUE SURFACE MOUNT

Resistor Specification

Resistor

Manufacturer/Part No.

Resistance

Package

Manufacturer

Ref. Des.

ohms

(W)

Size

Website

Rc, R2

Vishay CRCW0603R33F

0.33

0.10

0603

www.vishay.com

Rc, R2

Vishay CRCW0603R22F

0.22

0.10

0603

www.vishay.com

Note: Components highlighted in bold are those used on the SP7648EB Evaluation Board.

30V, Vgs = 2.5V, Pd = 0.5W

MOSFET

Specifications

20V, Vgs = 2.5V, Pd = 0.5W

Resistor

Specifications

Thick Film 1% or 5%

Thick Film 1% or 5%

Table 1: Component Selection

Date: 7/20/05

current to avoid saturating the inductor,
which would result in a loss in efficiency and
could damage the inductor. The SP7648
evaluation board uses a R

LIM

value of 1K

for an I

PEAK

= 1.6A to allow the circuit to

deliver up to 700mA for V

= 3.3V and V

OUT

= 4.2V. Other values could be selected using
the above relationships.

_________________USING THE FLASH

CONTROL PIN

The SP7648 will regulate the output by the
equations above depending on the state of
the FLASH pin. When the FLASH pin is low
(<0.4V), the internal reference voltage is
defined as 0.8V. When the FLASH pin is
high (>0.4V), the internal reference voltage
is defined as 0.288V. This allows the use of
smaller values for the sense resistor for
current regulation mode. This improves effi-
ciency and reduces the physical size of the
sense resistor. An external MOSFET switch
can be used to change the sense resistor
when changing to the Flash Mode.

________________ HIGH BRIGHTNESS

WHITE LED

For the high brightness LumiLED white LED
application, the SP7648 is generally pro-
grammed as a current source. The bias
resistors R1 and R2 are used to set the
operating current of the white LED with the
equation:

R = V

where V

is 0.8V in torch mode and 0.288V

in flash mode, I

is the operating current of

THEORY OF OPERATION

the LED. To set the operating current to be
about 200mA in torch mode, the flash pin is
forced low, R2 is selected as 0.8V/ 0.2 = 4

as shown in the typical application circuit. To
set the operating current to 700mA in flash
mode, the flash pin is forced high, R is
selected as 0.288V/0.41

= 700mA. In real-

ity R in Flash includes the series MOSFET
R

DSON

and the parallel combination of R

shown by the formula:

R in Flash =

X (R

+ Q

DSON

)}

+ R

+ Q

DSON

}

If the SP7648 is powered up before the LED
is plugged in, the circuit will bring the feed-
back pin to ZeroV and the SP7648 has a
feature to set the output voltage to be 5V.
Once the LED is plugged in, the feedback
pin will go up to 0.8V in torch mode or 0.288V
in flash mode and begin to regulate. The
output voltage will go from 5V to V

where V

is the forward voltage of the LED.

When the LED is open, the feedback pin
voltage will go to ZeroV and the output
voltage will go to 5V which will protect the
part from overvoltage at the output.

One approach to control LED brightness is
to apply a PWM signal to the SHDN input of
the SP7648. In this case, the output current
will be equal to the product of V

REF

/R1 and

the average duty cycle at the SHDN pin. An
optional 10K

potentiometer may also be

used for dimming the LED current by varying
the potentiometer between low brightness
and full brightness.

If the FB pin is pulled below 150mV the
output will default to 5V defined by an inter-
nal resistor divider.

Date: 7/20/05

TYPICAL PERFORMANCE CHARACTERISTICS

SP7648 for Luxeon I

100

200

300

400

500

600

700

800

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Vin (V)

Output current (mA)

Flash Mode,
Vf=3.6V

Torch Mode,
Vf=3.2V

SP7648 for Luxeon I

100

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Vin (V)

Efficiency (%)

Flash Mode,
Vf=3.6V

Torch Mode,
Vf=3.2V

SP7648 for AOT(2015HPW1915B)

100

200

300

400

500

600

700

800

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Vin (V)

Output current (mA)

Flash Mode,
Vf=3.9V

Torch Mode,
Vf=3.3V

SP7648 for AOT(2015HPW1915B)

100

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Vin (V)

Efficiency (%)

Flash Mode,
Vf=3.9V

Torch
Mode,Vf=3.3V

SP7648 for AOT(6060HPW0305BD)

100

200

300

400

500

600

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Vin (V)

Output current (mA)

Flash Mode,
Vf=4.2V

Torch Mode,
Vf=3.5V

SP7648 for AOT(6060HPW0305BD)

100

3.0

3.2

3.4

3.6

3.8

4.0

4.2

Vin (V)

Efficiency (%)

Flash Mode,
Vf=4.2V

Torch Mode,
Vf=3.5V

Date: 7/20/05

PACKAGE: 10 PIN DFN

MINIMUM

NOMINAL MAXIMUM MINIMUM

NOMINAL MAXIMUM

0.80

0.90

1.00

0.032

0.035

0.039

0.00

0.02

0.05

0.000

0.001

0.002

0.18

0.25

0.30

0.007

0.010

0.012

D
E

2.20

2.70

0.087

0.106

1.40

1.75

0.055

0.069

0.30

0.40

0.50

0.012

0.016

0.020

0.20

0.008

NOTE 1: PIN #1 INDICATOR MUST BE WITHIN THIS AREA AND CAN BE ANY SHAPE

(CONVERT UNIT 1MM = 0.0394INCH)

0.20 REF

0.008 REF

10-PIN 3X3MM DFN PACKAGE OUTLINE

JEDEC DOCUMENT MO-229 VARIATION VEED-5

0.50 BSC
3.00 BSC

DIMENSIONS IN MILLIMETERS

SYMBOL

(CONTROLLING UNIT)

DIMENSIONS IN INCHES

0.020 BSC
0.118 BSC
0.118 BSC

3.00 BSC

Date: 7/20/05

Corporation

ANALOG EXCELLENCE

Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.

Sipex Corporation

Headquarters and
Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600

Sales Office
22 Linnell Circle
Billerica, MA 01821
TEL: (978) 667-8700
FAX: (978) 670-9001
e-mail: sales@sipex.com

Part Number

Operating Temperature Range

Package Type

SP7648ER .................................................. -40

C to +85

C ........................................................... 10 Pin DFN

SP7648ER/TR ............................................ -40

C to +85

C .......................................................... 10 Pin DFN

SP7648EU .................................................. -40

C to +85

C ........................................................ 10 Pin MSOP

SP7648EU/TR ............................................ -40

C to +85

C ....................................................... 10 Pin MSOP

ORDERING INFORMATION

Available in lead free packaging. To order add "-L" suffix to part number.

Example: SP7648ER/TR = standard; SP7648ER-L/TR = lead free

/TR = Tape and Reel

Pack quantity is 2,500 for DFN and MSOP.

CLICK HERE TO ORDER SAMPLES

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