SP6656ER3TR_技术文档

SP6656

High Efficiency 400mA Synchronous Buck Regulator

with Dynamically Adjustable Voltage Output

FEATURES

P_VIN

VIN

10

9

1

2

3

4

5

LX

P

■ 98% Efficiency Possible

■ Offered in small 2.4 x 2.5mm DFN

■ Ultra-low 20µA Quiescent Current

■ 625mA Inductor Peak Current Limit

■ Guaranteed Minimum 400mA Output

Current

SP6656

GND

8

GND

OVSO

OVSI

EN

10 Pin DFN

7

V

OUT

6

FB

Now Available in Lead Free Packaging

■ 2.7V to 5.5V Input Voltage Range

APPLICATIONS

■ Cell Phones

■ PDA's

■ Output Adjustable Down to 1.0V

■ 100% Duty Ratio Low Dropout

Operation

■ DSC's

■ 80µA Light Load Quiescent Current in

Dropout

■ MP3 Players

■ USB Devices

■ Point of Use Power

■ Dynamic Adjustable Output Voltage

■ Ideal for portable designs powered with

Li Ion battery

DESCRIPTION

The SP6656 is a 400mA synchronous buck regulator that is ideal for portable applications that

useaLi-Ionor3cellalkaline/NiCD/NiMHinput. TheSP6656’sproprietarycontrolloop, 20µAlight

loadquiescentcurrent,and0.3Ωpowerswitchesprovideexcellentefficiencyacrossawiderange

of output currents. As the input battery supply decreases towards the output voltage the SP6656

seamlessly transitions into 100% duty ratio operation further extending useful battery life. The

SP6656 is protected against overload and short circuit conditions with a precise inductor peak

current limit. Other features include externally programmable output voltage down to 1.0V,

dynamicallyadjustableoutputvoltage, logiclevelshutdowncontrol, and140°Covertemperature

shutdown.

TYPICAL APPLICATION SCHEMATIC

2.7V to 5.5V Input

VI

V_OUT

400mA

3.2 x 1.6 x 1.55mm

L1

10Ω

VO

C_IN

R_VIN

SP6656

C_OUT

10µF

10µH

LX

P_VIN

V_IN

CV_IN

1µF

10µF

P_GND

CF

GND

V_OUT

OVSO

OVSI

EN

22pF

R_F

R_I

FB

R_S

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

1

ABSOLUTE MAXIMUM RATINGS

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.

PV ,V_IN.............................................................................................. 6V

All ^Io^Nther pins .............................................................. -0.3V to V_IN+0.3V

PV_IN, P_GND, LX current ........................................................................ 2A

Storage Temperature .................................................. -65 °C to 150 °C

Operating Temperature ................................................. -40°C to +85°C

ELECTRICAL CHARACTERISTICS

V_IN= UV_IN= V_EN= 3.6V, V_OUT= V_FB, I_O= 0mA, T_AMB= -40°C to +85°C, typical values at 25°C unless otherwise noted

.

PARAMETER

MIN

TYP

MAX UNITS CONDITIONS

Input Voltage Operating

UVLO

5.5

V

Range

Minimum Output Voltage

FB Set Voltage, Vr

1.0

0.784

V

0.800

0.816

25°C, I_O= 200mA Close Loop. L_I= 10µH,

C_OUT= 22µF

Overall Accuracy

(-40°C to 85°C)

(0°C to 70°C)

Measured at V_IN= 5.5V, no load and

±5

±4

3.0

%

V_IN=3.6V, 200mA load, Close Loop

On-Time Constant - K_ON

1.5

1.6

2.25

2.4

V*µs

Close Loop, L_I= 10µH,C_OUT= 22µF

Min, T_ON=K_ON/(V_IN-V_OUT

)

Off-Time Constant - K_OFF

3.2

Inductor current limit tripped, VFB = 0.5V

Measured at V_OUT= 1V

Min, T_OFF=K_OFF/V_OUT

Off-Time Blanking

100

250

0.3

ns

µs

Ω

Turn On Time

400

0.6

400mA Load

I_PMOS= 200mA

I_NMOS= 200mA

VFB = 0.5V

PMOS Switch Resistance

NMOS Switch Resistance

Inductor Current Limit

Power Efficiency

0.3

0.6

Ω

500

400

625

750

mA

%

96

V_OUT= 2.5V, I_O= 200mA

92

V_OUT= 3.3V, I_O= 400mA

Minimum Guaranteed Load

Current

500

mA

V_INQuiescent Current

V_INShutdown Current

V_OUTQuiescent Current

V_OUTShutdown Current

20

1

2

1

30

500

5

µA

nA

µA

nA

V_OUT= 3.3V, V_IN= 3.6V and V_IN= 5.5V

EN = 0.0V

V_OUT= 3.3V

EN = 0.0V

500

UVLO

Undervoltage Lockout

Threshold, V_INfalling

2.55

0.60

2.70

2.85

V

EN = V_IN,

UVLO hysteresis

40

50

5

mV

nA

°C

OVSO Output Voltage

OVSO Leakage Current

100

V_IN= EN; Iovso =1mA; OVSI = 1 = Vcc

V_IN= EN; Vovso= 3.6V;OVSI= 0.0V= GND

Over-Temperature

140

Rising Trip Point

Over-Temperature Hysteresis

EN Leakage Current

14

1

°C

500

nA

EN Input Threshold Voltage

0.90

V

High to Low Transition

Low to High Transition

FB =1V

EN = 0.0V, V_IN= 3.6V

1.25

1.8

100

5

V

FB Leakage Current

LX Leakage

1

3

nA

µA

LX = 0.0V, LX = V_IN+ 0.2V

OVSI Leakage Current

OVSI Input Threshold Voltage 0.60

1

500

1.8

nA

V

0.90

High to Low Transition

Low to High Transition

1.25

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

2

PIN DESCRIPTION

PIN NUMBER

PIN NAME

P_VIN

V_IN

OVSO

DESCRIPTION

1

2

3

Input voltage power pin. Inductor charging current passes through this pin.

Internal supply voltage. Control circuitry powered from this pin.

Output Voltage Selection Output. OVSI = 1 pulls this node to

GND, OVSI = 0, this node is open.

4

5

OVSI

EN

Output Voltage Select Input. See table 1 for definition.

EN = 1, device is enabled. EN = 0, All internal circuitry is disabled and

power switches are opened.

6

7

FB

External feedback network input connection. Connect a resistor from

FB to ground and FB to V_OUTto set the output voltage. This pin

regulates to the internal bandgap reference voltage of 0.8V.

V_OUT

Output voltage sense pin. Used by the timing circuit to set minimum on

and off times.

8

9

10

GND

P_GND

LX

Internal ground pin. Control circuitry returns current to this pin.

Power ground pin. Synchronous rectifier current returns through this pin.

Inductor switching node. Inductor tied between this pin and the output

capacitor to create regulated output voltage.

V_OUT

VO

OVSI

OVSO

Output Voltage

0

Open

V_{OUT_LOW}= 0.8 (R_I+R_F) / R_I

CF

R_F

22pF

1

Short to GND

V_{OUT_HIGH}= 0.8 (R_A+R_F)/R_A

FB

OVSO

R_S

Table 1. Output Voltage Selection

R_I

R_IR_S

Note: R_A=

R_I+R_S

FUNCTIONAL DIAGRAM

P_VIN

V_OUT

V_IN

DRVON

VOLOW

Internal Supply

T_ONOVER

MIN Ton

T_ONOVER

Min T_ON

=

K_ON/(V_IN

-

V_OUT

)

Min Ton

OVR_I

M

1

Vos

+

VOLOW

REF'

DRVON

+

-

REF

-

+

C

ILIM/M

R

Q

_

Q

C

DRIVER

-

V_RAMP

S

FB'

+

-

FB

OVR_I

RST

DRVON

LX

+

REF

UVLO

Zero_X

C

One-Shot

=100ns

Ref

-

TSD

ILIM/M

Block

P_GND

BLANK

EN

T_OFF

=

OVSI

GND

K_OFF/V_OUT

OVR_I

OVSO

DRVON

BLANK

BLANK = T_BLANK(=100ns) or T_OFF= K_OFF/V_OUT

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

3

TYPICAL PERFORMANCE CHARACTERISTICS

Refer to the typical application schematic, T_AMB= +27°C

100

95

90

85

80

75

70

65

60

100

95

90

85

80

75

70

65

60

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

0.1

1.0

10.0

100.0

1000.0

0.1

1.0

10.0

ILoad (mA)

100.0

1000.0

ILoad (mA)

Efficiency vs. Load, V_OUT=3.3V

Efficiency vs Load, V_OUT= 1.5V

1.55

1.53

1.51

1.49

1.47

1.45

3.45

3.40

3.35

3.30

3.25

3.20

3.15

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

0

100

200

300

400

500

0

100

200

300

400

500

ILoad (mA)

Line/Load Rejection, V_OUT= 3.3V

Line/Load Rejection, V_OUT= 1.5V

500

400

300

200

100

0

50

Tamb = 85C

Tamb = 25C

Tamb = -40C

Tamb = 85C

Tamb = 25C

Tamb = -40C

40

30

20

10

0

3.0

3.3

3.6

Vin (V)

3.9

4.2

3.0

3.3

3.6

3.9

4.2

Vin (V)

No Load Battery Current, V_OUT=3.3V

No Load Battery Current, V_OUT=1.5V

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

4

TYPICAL PERFORMANCE CHARACTERISTICS

Refer to the typical application schematic, T_AMB= +27°C

4.7uH Efficiency at 3.3Vout

(L1 = LQH32CN4R7)

4.7uH Efficiency at 1.8Vout

(L1 = LQH32CN4R7)

100

90

80

70

60

50

100

90

80

70

60

50

Vin=3.0V

Vin=3.6V

Vin=4.2V

Vin=3.6V

Vin=4.2V

0.1

1

10

Iout (mA)

100

1000

0.1

1

10

100

1000

Iout (mA)

4.7uH Efficiency at 1.8Vout

(L1 = LQH31CN4R7)

4.7uH Efficiency at 3.3Vout

(L1 = LQH31CN4R7)

100

90

80

70

60

50

100

90

80

70

60

50

Vin=3.0V

Vin=3.6V

Vin=4.2V

Vin=3.6V

Vin=4.2V

0.1

1

10

Iout (mA)

100

1000

0.1

1

10

Iout (mA)

4.7uH Efficiency at 1.8Vout

(L1 = LQH2MCN4R7)

Efficiency at 3.3Vout

(L1 = LQH2MCN4R7)

100

90

80

70

60

50

100

90

80

70

60

50

Vin=3.0V

Vin=3.6V

Vin=4.2V

Vin=3.6V

Vin=4.2V

0.1

1

10

0.1

1

10

Iout (mA)

100

1000

Iout (mA)

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

5

TYPICAL PERFORMANCE CHARACTERISTICS

Refer to the typical application schematic, T_AMB= +27°C

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

3.6

3.9

4.2

4.5

4.8

5.1

5.4

3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4

Vin (V)

K_ONvs V_IN, V_OUT=3.3V

K_ONvs V_IN, V_OUT=1.5V

3.5

3.0

2.5

2.0

3.5

3.0

2.5

2.0

1.5

1.0

1.5

1.0

0.5

0.0

0.5

0.0

3.6

3.9

4.2

4.5

4.8

5.1

5.4

3.0

3.3

3.6

3.9

4.2

4.5

4.8

5.1

5.4

Vin (V)

K_OFFvs V_IN, V_OUT=3.3V

K

_OFFvs V_IN, V_OUT=1.5V

700.0

600.0

500.0

700.0

600.0

500.0

400.0

300.0

400.0

300.0

200.0

100.0

0.0

200.0

100.0

Vout = 3.3V

Measured

Vout = 1.5V

Measured

Vout = 1.5V

Calculated

Vout = 3.3V

Calculated

0.0

3.5

3.4

3.8

4.2

Vin (V)

4.6

5.0

4.0

4.5

5.0

Vin (V)

Ripple Frequency vs. V_IN, I_OUT=0.4A, V_OUT=3.3V

Ripple Frequency vs. V_IN, I_OUT=0.4A, V_OUT=1.5V

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

6

TYPICAL PERFORMANCE CHARACTERISTICS

Refer to the typical application schematic, T_AMB= +27°C

CH.1=V_IN

5.0V/DIV.

CH.2=V_OUT

0.5V/DIV.

CH.1=V_SHDN

5.0V/DIV.

CH.2=V_OUT

2.0V/DIV.

CH.4=I_LX

0.5A/DIV.

CH.4=I_IN

0.5A/DIV.

V

_INStart up,V_IN=4.2V, I_OUT=0.4A, V_OUT=1.5V

V_INStart up, V_IN=4.2V, I_OUT=0.4A, V_OUT=3.3V

Load Step, V_IN=4.2V, I_OUT=0.1A to 0.4A, V_OUT=3.3V

Load Step, V_IN=4.2V, I_OUT=0.1A to 0.4A, V_OUT=1.5V

CH.1=V_SHDN

5.0V/DIV.

CH.2=V_OUT

2.0V/DIV.

CH.4=I_LX

0.5A/DIV.

Start up from SHDN, V_IN=5V ,I_OUT=0.4A, V_OUT=3.3V

Start up from SHDN, V_IN=5V, I_OUT=0.4A, V_OUT=1.5V

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

7

THEORY OF OPERATION

RAMP: CCM OPERATION

The SP6656 is a high efficiency synchro-

nous buck regulator with an input voltage

range of +2.7V to +5.5V and an output that

is adjustable between +1.0V and V_IN. The

SP6656 features a unique on-time control

loop that runs in discontinuous conduction

mode(DCM)orcontinuousconductionmode

(CCM) using synchronous rectification.

Other features include over-temperature

shutdown, over-current protection, an ex-

ternal feedback pin, digitally controlled en-

able and output voltage selection.

DRVON

I(L1)

FB’

REF, FB

V

OS

REF’

The SP6656 operates with a light load qui-

escent current of 20µA using a 0.3Ω PMOS

main switch and a 0a.3Ω NMOS synchro-

nous switch. It operates with excellent effi-

ciency across the entire load range, making

it an ideal solution for battery powered ap-

plications and low current step-down con-

versions. The part smoothly transitions into

a 100% duty cycle under heavy load/low

input voltage conditions.

RAMP: DCM OPERATION

DRVON

I(L1)

FB’

REF, FB

V

OS

On-Time Control - Charge Phase

REF’

The SP6656 uses a precision comparator

and a minimum on-time to regulate the

output voltage and control the inductor cur-

rent under normal load conditions. As the

feedback pin drops below the regulation

point, the loop comparator output goes high

and closes the main switch. The minimum

on-timer is triggered, setting a logic high for

the duration defined by:

operation in both CCM and DCM operation.

In either CCM or DCM, the negative going

ramp voltage (V_RAMPin the functional dia-

gram) is added to FB and this creates the

FB's signal. This FB signal is applied to the

negative terminal of the loop comparator.

To the positive terminal of the loop com-

parator is applied the REF voltage of 0.8V

plus an offset voltage Vos to compensate

for the DC level of V_RAMPapplied to the

negative terminal. The result is an internal

ramp with enough negative going offset

(approximately 50mV) to trip the loop com-

parator whenever FB falls below regulation.

KON

V_IN- V_OUT

.

T_ON

=

where:

K_ON= 2.25V*µSec constant

V_IN= V_INpin voltage

V_OUT= V_OUTpin voltage

To accommodate the use of ceramic and

other low ESR capacitors, an open loop

ramp is added to the feedback signal to

mimic the inductor current ripple. The fol-

lowing waveforms describe the ideal ramp

The output of the loop comparator, a rising

VOLOW, causes a SET if BLANK = 0 and

OVR_I = 0. This starts inductor charging

(DRVON = 1) and starts the minimum on-

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

8

THEORY OF OPERATION

timer. The minimum on-timer times out and

indicatesDRVONcanberesetifthevoltage

loop is satisfied. If V_OUTis still below the

regulation point RESET is held low until

V_OUTis above regulation. Once RESET

occurs T_ONminimum is reset, and the T_OFF

one-shot is triggered to blank the loop com-

parator from starting a new charge cycle for

a minimum period. This blanking period

occurs during the noisy LX transition to

discharge, where spurious comparator

states may occur. For T_OFF> T_BLANKthe

loop is in a discharge or wait state until the

loopcomparatorstartsthenextchargecycle

by DRVON going high.

that are greater than half the minimum cur-

rent ripple. The current ripple, I_LR, is defined

by the equation:

KON

VIN - VOUT - IOUT * RCH

I_LR

≈

*

L

V_IN- V_OUT

where:

L = Inductor value

I_OUT= Load current

R

_CH= PMOS on resistance, 0.3Ω typ.

If the I_OUT* R_CHterm is negligible compared

with (V_IN- V_OUT), the above equation simpli-

fies to:

KON

I_LR

≈

If an over current occurs during charge the

loop is interrupted and DRVON is RESET.

The off-time one-shot pulse width is wid-

ened to T_OFF= K_OFF/ V_OUT, which holds the

loop in discharge for that time. At the end of

the off-time the loop is released and con-

trolled by VOLOW. In this manner maxi-

mum inductor current is controlled on a

cycle-by-cycle basis. An assertion of UVLO

(undervoltagelockout)orTSD(thermalshut-

down) holds the loop in no-charge until the

fault has ended.

L

For most applications, the inductor current

ripple controlled by the SP6656 is constant

regardless of input and output voltage.

The maximum loop frequency in CCM is

defined by the equation:

(VIN - VOUT) * (VOUT + IOUT * RDC)

≈

F_LP

K_ON[V_IN+ I_OUT(R_DC- R_CH)]

*

where:

F

_LP= CCM loop frequency

On-Time Control - Discharge Phase

R_DC= NMOS on resistance, 0.3Ω typ.

The discharge phase follows with the high

side PMOS switch opening and the low side

NMOSswitchclosingtoprovideadischarge

path for the inductor current. The decreas-

ing inductor current and the load current

cause the output voltage to drop. Under

normal load conditions when the inductor

current is below the programmed limit, the

off-timewillcontinueuntiltheoutputvoltage

falls below the regulation threshold, which

initiates a new charge cycle via the loop

comparator.

Ignoring conduction losses simplifies the

loop frequency to:

1

VOUT

≈

F_LP

*

* (V_IN- V_OUT)

K_ON

V_IN

AND’ing the loop comparator and the on-

timer reduces the switching frequency for

load currents below half the inductor ripple

current. This increases light load efficiency.

The minimum on-time insures that the in-

ductor current ripple is a minimum of K_ON/L,

more than the load current demands. The

converter goes in to a standard pulse fre-

quency modulation (PFM) mode where the

switching frequency is proportional to the

load current.

The inductor current “floats” in continuous

conduction mode. During this mode the

inductor peak current is below the pro-

grammed limit and the valley current is

above zero. This is to satisfy load currents

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

9

THEORY OF OPERATION

Low Dropout and Load Transient

Operation

shot. The off-time one shot forces the loop

into the discharge phase for a minimum

T_OFFtime causing the inductor current to

decrease. At the end of the off-time, loop

control is handed back to the AND logic

function on-time signal. If the output voltage

is still low, charging begins until the output

is in regulation or the current limit has been

reached again. During startup and overload

conditions, the converter behaves like a

current source at the programmed limit mi-

nus half the current ripple. The minimum

T_OFFis controlled by the equation:

UsingANDlogicfunctiontheloopcompara-

tor also increases the duty ratio past the

idealD=V_OUT/V_INuptoandincluding100%.

Under a light to heavy load transient, the

loop comparator will hold the main switch

on longer than the minimum on timer until

the output is brought back into regulation.

Also, as the input voltage supply drops

down close to the output voltage, the main

MOSFETresistancelosswilldictateamuch

higher duty ratio to regulate the output.

Eventually as the input voltage drops low

enough, the output voltage will follow, caus-

ing the loop comparator to hold the con-

verter at 100% duty cycle.

KOFF

T_{OFF (MIN)}

=

V_OUT

This mode is critical in extending battery life

when the output voltage is at or above the

minimum usable input voltage. The dropout

voltage is the minimum (V_IN-V_OUT) below

whichtheoutputregulationcannotbemain-

tained. The dropout voltage of SP6656 is

equal to I_L* (0.3Ω+ R_L1) where 0.3Ω is the

typical R_DS(ON)of the P-Channel MOSFET

and R_Lis the DC resistance of the inductor.

Under-Voltage Lockout

The SP6656 is equipped with a program-

mable under-voltage lockout to protect the

input battery source from excessive cur-

rents when substantially discharged. When

the input supply is below the UVLO thresh-

old both power switches are open to pre-

ventinductorcurrentfromflowing. Thelevel

of falling input voltage has a typical hyster-

esis of 120mV to prevent chattering due to

the impedance of the input source.

The SP6656 has been designed to operate

in dropout with a light load Iq of only 80µA.

The on-time control circuit seamlessly op-

erates the converter between CCM, DCM,

and low dropout modes without the need for

compensation. The converter’s transient

response is quick since there is no compen-

sated error amplifier in the loop.

Under-Current Detection

The synchronous rectifier is comprised of

aninductordischargeswitch,avoltagecom-

parator, and a driver latch. During the off-

time, positive inductor current flows into the

PGND pin 9 through the low side NMOS

switch to LX pin 10, through the inductor

and the output capacitor, and back to pin 9.

The comparator monitors the voltage drop

across the discharge NMOS. As the induc-

tor current approaches zero, the channel

voltage sign goes from negative to positive,

causing the comparator to trigger the driver

latch and open the switch to prevent induc-

tor current reversal. This circuit along with

the on-timer puts the converter into PFM

mode and improves light load efficiency

Inductor Over-Current Protection

To reduce the light load dropout Iq, the

SP6656 over-current system is only en-

abled when I_L1> 400mA. The inductor over-

current protection circuitry is programmed

to limit the peak inductor current to 0.625A.

This is done during the on-time by compar-

ing the source to drain voltage drop of the

PMOS passing the inductor current with a

second voltage drop representing the maxi-

mum allowable inductor current. As the two

voltages become equal, the over-current

comparatortriggersaminimumoff-timeone

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

10

THEORY OF OPERATION

when the load current is less than half the

inductor ripple current defined by K_ON/L.

delay to allow the regulator circuitry to rees-

tablish itself. Power conversion begins with

the assertion of the internal reference ready

signal which occurs approximately 150µs

after the enable signal is received.

Thermal Shutdown

Theconverterwillopenbothpowerswitches

if the die junction temperature rises above

140°C.Thediemustcooldownbelow126°C

before the regulator is re-enabled. This fea-

ture protects the SP6656 and surrounding

circuitry from excessive power dissipation

due to fault conditions.

Output Voltage Selection

The OVSI (Output Voltage Selection Input)

pin is internally driving a NMOS Gate which

Drain (OVSO pin) is used to short circuit R_S

and then achieve a higher output voltage (

see table 1 for calculation, page 3)

Shutdown/Enable Control

External Feedback Pin

The EN pin of the device is a logic level

control pin that shuts down the converter

when logic is low, or enables the converter

when logic is high. When the converter is

shut down, the power switches are opened

and all circuit biasing is extinguished leav-

ingonlyjunctionleakagecurrentsonsupply

pins 1 and 2. After pin 5 is brought high to

enable the converter, there is a turn on

The FB pin 6 is compared to an internal

reference voltage of 0.8V to regulate the

SP6656 output. The output voltage can be

externally programmed within the range

+1.0Vto+5.0VbytyingaresistorfromFBto

ground and FB to V_OUT(pin7). See the

applications section for resistor selection

information.

APPLICATION INFORMATION

INDUCTORS - SURFACE MOUNT

Inductor Specification

Size

Inductance

(uH)

Series R

Isat

Inductor Type

Manufacturer

Manufacturer/Part No.

L x W

(mm)

Ht.

(mm)

1.55

1.8

ohms

0.150

0.65

(A)

Website

4.7

10

22

Murata LQH32CN4R7M53L

Murata LQH31CN4R7M03L

Murata LQH2MCN4R7M02L

Murata LQH32CN100K53L

TDK RLF5018T-100MR94

Coilcraft LPO6013-103K

Murata LQH32CN220K21

TDK RLF5018T-220MR63

Coilcraft LPO6013-223K

0.65

0.34

0.30

0.45

0.94

0.70

0.25

0.63

0.45

3.2x2.5

3.2x1.6

2.0x1.6

3.2x2.5

5.6x5.2

6.0x5.4

3.2x2.5

5.6x5.2

6.0x5.4

Unshielded Ferrite Core

www.murata.com

www.tdk.com

0.80

0.9

0.300

0.056

0.300

0.710

0.130

0.520

1.55 Unshielded Ferrite Core

2.0

1.3

2.0

1.3

Shielded Ferrite Core

Unshielded Ferrite Core

Shielded Ferrite Core

Unshielded Ferrite Core

www.coilcraft.com

www.murata.com

www.tdk.com

www.coilcraft.com

CAPACITORS - SURFACE MOUNT

Capacitor Specification

Ripple

Current

(A) @

45C

Capacitance

(uF)

Manufacturer/Part No.

ESR

ohms

(max)

0.003

0.005

Size

Voltage

Capacitor

Type

Manufacturer

L x W

Ht.

(mm)

1.25

(mm)

(V)

6.3

Website

www.tdk.com

www.murata.com

www.tdk.com

www.murata.com

10

4.7

TDK C2012X5R0J106M

Murata GRM21BR60J106KE01

TDK C2012X5R0J475M

1.00

2.0x1.2

X5R Ceramic

1.00

Murata GRM21BR60J475KE01

1.00

Note: Components highlighted in bold are those used on the SP6656 Evaluation Board.

Table 2 Component Selection

Inductor Selection

ForthetypicalSP6656applicationcircuitwith

inductor size of 10µH, and K_ONof 2V*µsec,

the SP6656 current ripple would be about

200mA,andwouldbefairlyconstantfordiffer-

ent input and output voltages, simplifying the

selectionofcomponentsfortheSP6656power

circuit. Other inductor values could be se-

lected, as shown in Table 2 Components

Selection. Using a larger value than 10µH in

an attempt to reduce output voltage ripple

would reduce inductor current ripple and may

The SP6656 uses a specially adapted mini-

mumon-timecontrolofregulationutilizinga

precision comparator and bandgap refer-

ence. This adaptive minimum on-time con-

trol has the advantage of setting a constant

current ripple for a given inductor size.

Fromtheoperationssectionithasbeenshown:

KON

≈

Inductor Current Ripple, I_LR

L

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

11

APPLICATION INFORMATION

less,aninternalrampvoltageV_RAMPhasbeen

added to the FB signal to reliably trip the loop

comparator (as described in the Operations

section).

not produce as stable an output ripple. For

largerinductorswiththeSP6656,whichhas

a peak inductor current of 0.625A, most

15µH or 22µH inductors would have to be

larger physical sizes, limiting their use in

small portable applications. Smaller values

like10µHwouldmoreeasilymeetthe0.625A

limit and come in small case sizes, and the

increased inductor current ripple of almost

200mA would produce very stable regula-

tion and fast load transient response at the

expense of slightly reduced efficiency.

The output capacitor is required to keep the

output voltage ripple small and to ensure

regulation loop stability. The output capaci-

tor must have low impedance at the switch-

ingfrequency.CeramiccapacitorswithX5R

or X7R dielectrics are recommended due to

their low ESR and high ripple current. The

output ripple ∆V^OUTis determined by:

Other inductor parameters are important: the

inductorcurrentratingandtheDCresistance.

Whenthecurrentthroughtheinductorreaches

the level of I_SAT, the inductance drops to 70%

of the nominal value. This nonlinear change

can cause stability problems or excessive

fluctuation in inductor current ripple. To avoid

this, the inductor should be selected with

saturation current at least equal to the maxi-

mum output current of the converter plus half

the inductor current ripple. To provide the

bestperformanceindynamicconditionssuch

as start-up and load transients, inductors

shouldbechosenwithsaturationcurrentclose

totheSP6656inductorcurrentlimitof0.625A.

∆V^OUT<=

.

1

*

VOUT * (VINMax - VOUT)

+

ESR

*

}

{

(8 ƒOSC COUT)

*

(

VINMax

L

ƒOSC)

*

To improve stability, a small ceramic capaci-

tor, C_F= 22pF should be paralleled with the

feedbackvoltagedividerRF, asshownonthe

typical application schematic on page 1. An-

other function of the output capacitance is to

hold up the output voltage during the load

transients and prevent excessive overshoot

andundershoot.Thetypicalperformancechar-

acteristics curves show very good load step

transient response for the SP6656 with the

recommended output capacitance of 10µF

ceramic.

DC resistance, another important inductor

characteristic, directly affects the efficiency of

the converter, so inductors with minimum DC

resistance should be chosen for high effi-

ciency designs. Recommended inductors

with low DC resistance are listed in Table 2.

Preferred inductors for on board power sup-

plies with the SP6656 are magnetically

shielded types to minimize radiated magnetic

field emissions.

The input capacitor will reduce the peak cur-

rent drawn from the battery, improve effi-

ciencyandsignificantlyreducehighfrequency

noises induced by a switching power supply.

The typical input capacitor for the SP6656 is

10µF ceramic. These capacitors will provide

good high frequency bypassing and their low

ESR will reduce resistive losses for higher

efficiency. An RC filter is recommended for

theV_INpin2toeffectivelyreducethenoisefor

the ICs analog supply rail which powers sen-

sitive circuits. This time constant needs to be

at least 5 times greater than the switching

period, which is calculated as 1/FLP during

theCCMmode. Thetypicalapplicationsche-

matic uses the values of R_VIN= 10Ω and C_VIN

= 1µF to meet these requirements.

Capacitor Selection

TheSP6656hasbeendesignedtowork with

very low ESR output capacitors (listed in

Table 2 Component Selection) which for the

typical application circuit are 10µF ceramic

capacitors. These capacitors combine small

size,lowESRandgoodvalue.Toregulatethe

output with low ESR capacitors of 0.01Ω or

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

12

APPLICATION INFORMATION

The output voltage is programmed by the external divider, as shown in the typical

application circuit on Page 1. Depending on the topology used, 1 or 2 voltages ,V_OUT

is set as follows:

1) Single V_OUT

V_OUT

VO

First pick a value for RI that is no larger than

300KΩ. ToolargeavalueofRIwillreducethe

ACvoltageseenbytheloopcomparatorsince

theinternalFBpincapacitancecanformalow

pass filter with RF in parallel with RI. The

formula for RF with a given RI and output

voltage is:

CF

R_F

R_I

22pF

FB

R_F= (V_OUT/ 0.8V - 1) (R_I)

*

2) Dual V_OUT(selectable)

First pick the lowest voltage that will be used

and utilize the same method as above.

V_OUT

VO

R_F= (V_{OUT_LOW}/ 0.8V - 1) (R_I) R_I≤ 300kΩ

CF

*

R_F

22pF

Then use the following equation to determine

R_S:

OVSO

FB

R_S

0.8 * RF

.

[R_I//R_S] =

R_I

V_{OUT_HIGH}- 0.8

R_{S =}

[RI//RS]

.

1 -

}

{

R_I

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

13

APPLICATION INFORMATION

Output Voltage Ripple Frequency

An important consideration in a power sup-

ply application is the frequency value of the

output ripple. Given the control technique of

the SP6656 (as described in the operations

section), the frequency of the output ripple

will vary when in light to moderate load in

the discontinuous or PFM mode. For mod-

erate to heavy loads greater than about

100mA inductor current ripple, (for the typi-

cal 10µH inductor application on 100mA is

half the 200mA inductor current ripple), the

output ripple frequency will be fairly con-

stant.Fromtheoperationssection,thismaxi-

mum loop frequency in continuous conduc-

tion mode is

Avoid injecting noise into the sensitive part of

circuit via the ground plane. Input and output

capacitors conduct high frequency current

through the ground plane. Separate the con-

trol and power grounds and connect them

together at a single point. Power ground

plane is shown in the figure titled PCB top

samplelayoutandconnectsthegroundofthe

C_OUTcapacitor to the ground of the

C_INcapacitor and then to the PGND pin 10.

The control ground plane connects from pin 9

GND to ground of the C_VINcapacitor and the

R_Iground return of the feedback resistor.

Thesetwoseparatecontrolandpowerground

planes come together in the figure titled PCB

top sample layout where SP6656 pin 9 GND

is connected to pin 10 PGND.

1

VOUT

(V_IN- V_OUT

)

≈

*

F_LP

K_ON

V_IN

Data for loop frequency, as measured from

outputvoltageripplefrequency,canbefound

in the typical performance curves.

Power loops on the input and output of the

converter should be laid out with the shortest

and widest traces possible. The longer and

narrower the trace, the higher the resistance

and inductance it will have. The length of

traces in series with the capacitors increases

its ESR and ESL and reduces their effective-

ness at high frequencies. Therefore, put the

1µF bypass capacitor as close to the V_INand

GND pins of the converter as possible, the

10µF C_INclose to the P_VINpin and the 10µF

output capacitor as close to the inductor as

possible. The external voltage feedback net-

work R_F, R_I, R_Sand feedforward capacitor C_F

shouldbeplacedveryclosetotheFBpin. Any

noise traces like the LX pin should be kept

away from the voltage feedback network and

separated from it by using power ground

copper to minimize EMI.

Layout Considerations

Properlayoutofthepowerandcontrolcircuits

is necessary in a switching power supply to

obtain good output regulation with stability

and a minimum of output noise. The SP6656

applicationcircuitcanbemadeverysmalland

reside close to the IC for best performance

and solution size, as long as some layout

techniques are taken into consideration. To

avoid excessive interference between the

SP6656 high frequency converter and the

other active components on the board, some

rules should be followed. Refer to the typical

application schematic on page 1 and the

sample PCB layout shown in the following

figures to illustrate how to layout a SP6656

power supply.

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

14

PACKAGE: 10 PIN DFN

D

D/2

E/2

A

A3

E

A1

Seating

Plane

SIDE VIEW

Pin1 Designator

to be within this

INDEX AREA

(D/2 x E/2)

TOP VIEW

1

2

3

4

5

L1

Pin 1

Indentification

INDEX AREA

(A/2 x B/2)

L

10

9

8

7

6

e

b

BOTTOM VIEW

2.5 x 2.4

10 Pin DFN

Dimensions in Inches

Conversion Factor:

1 Inch = 25.40 mm

Dimensions in Millimeters:

Controlling Dimension

SYMBOL

MIN

0.80

0.00

NOM

0.90

MAX

MIN

NOM

0.035

MAX

A

A1

A3

b

0.031

0.000

0.039

0.002

1.00

0.05

0.001

0.02

0.20 REF

0.25

0.008 REF

0.010

0.007

0.012

0.18

0.30

D

2.50 BSC

2.40 BSC

0.50 BSC

0.55

0.098 BSC

0.094 BSC

0.020 BSC

0.022

E

e

L

0.018

0.026

0.033

0.45

0.65

0.85

L1

0.030

0.75

SIPEX Pkg Signoff Date/Rev:

JL Nov1-05/ Rev A

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

15

ORDERING INFORMATION

Package Type

Part Number

Operating Temperature Range

SP6656ER3 ......... ...............................-40°C to +85°C ............................................................... 10 Pin DFN

SP6656ER3/TR ...................................-40°C to +85°C ............................................................... 10 Pin DFN

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

Example: SP6656ER3/TR = standard; SP6656ER3-L/TR = lead free

/TR = Tape and Reel

Pack quantity is 3,000 for DFN.

Sipex Corporation

Headquarters and

Sales Office

233 South Hillview Drive

Milpitas, CA 95035

TEL: (408) 934-7500

Solved By SipexTM

FAX: (408) 935-7600

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.

Date: 3/6/06

SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

16


型号：	SP6656ER3TR
厂家：	SIPEX CORPORATION
描述：	High Efficiency 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output 高效率400毫安同步降压稳压器具有动态可调电压输出稳压器
文件：	总16页 (文件大小：332K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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