SP6651AEU-L/TR - Exar Corporation

SP6651A

FEATURES

■DFN Package (3mm x 3mm)

■Ultra-low 20µA Quiescent Current

■98% Efficiency Possible

■800mA Output Current

■2.7V to 5.5V Input Voltage Range

■Output Adjustable Down to 1.0V

■No External FET’s Required

■1.25A Inductor Peak Current Limit

■100% Duty Ratio Low Dropout Operation

■80µA Light Load Quiescent Current

in Dropout

■Over Temperature Protection

■Logic Shutdown Control

■Programmable UVLO and Adaptive

Battery Low Output

High Efficiency 800mA Sync hr onous Buc k Regulator

APPLICATIONS

■ PDA's

■ DSC's

■ MP3 Players

■USB Devices

■Point of Use Power

The SP6651A is a 800mA synchronous buck regulator which is ideal for portable applications that

use a Li-Ion or 3 cell alkaline/NiCD/NiMH input. The SP6651A’s proprietary control loop, 20µA

light load quiescent current, and 0.3Ω power switches provide excellent efficiency across a wide

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

SP6651A seamlessly transitions into 100% duty ratio operation further extending useful battery

life. The SP6651A is protected against overload and short circuit conditions with a precise

inductor peak current limit. Other features include programmable under voltage lockout and low

battery detection, externally programmed output voltage down to 1.0V, logic level shutdown

control, and 140°C over temperature shutdown.

BLON

22µF

10µHV

OUT

800mA

2.7V to 5.5V Input

10Ω

1µF

SP6651A

VIN

BLON

GND

OUT

GND

22µF

OUT

VIN

22pF

200K

Ideal for portable designs powered with Li Ion battery

TYPICAL APPLICATION SCHEMATIC

DESCRIPTION

SP6651A

10 Pin DFN

BLON

GND

OUT

Now Available in Lead Free Packaging

PARAMETER MIN TYP MAX UNITS CONDITIONS

Input Voltage Operating UVLO 5.5 V Result of IQ measurement at VIN=PVIN=5.5V

Range

Minimum Output Voltage 1.0 V

FB Set Voltage, Vr 0.784 0.800 0.816 V 25°C, IO=200mA Close Loop. LI = 10µH,

COUT = 22µF

Overall Accuracy Measured at VIN=5.5V, no load and

(-40°C to 85°C) ±5%V

IN=3.6V, 200mA load, Close Loop

(0°C to 70°C) ±4

On-Time Constant - KON 1.5 2.25 3.0 V*µsClose Loop, LI = 10µH,COUT = 22µF

Min, TON=KON/(VIN-VOUT)

Off-Time Constant - KOFF 1.6 2.4 3.2 V*µsInductor current limit tripped, VFB=0.5V

Min, TOFF=KOFF/VOUT Measured at VOUT = 2V

Off-Time Blanking 100 ns

PMOS Switch Resistance 0.3 0.6 ΩIPMOS = 200mA

NMOS Switch Resistance 0.3 0.6 ΩINMOS = 200mA

Inductor Current Limit 1.0 1.25 1.50 A VFB=0.5V

LX Leakage Current 0.01 3 µAD0=D1=0

Power Efficiency 96 % VOUT=2.5V, IO=200mA

92 VOUT=3.3V, IO=800mA

Minimum Guaranteed Load 800 900 mA

Current

VIN Quiescent Current 20 30 µAV

OUT=3.3V, VIN=3.6V and VIN= 5.5V

VIN Shutdown Current 1 500 nA D1=D0=0V

VOUT Quiescent Current 2 5 µAV

OUT = 3.3V

VOUT Shutdown Current 1 500 nA D1=D0=0V

UVLO 2.55 2.70 2.85 D1=0V, D0=VIN

Undervoltage Lockout 2.70 2.85 3.00 V D1=VIN, D0=0V

Threshold, VIN falling 2.85 3.00 3.15 D1=VIN, D0=VIN

UVLO hysteresis 40 mV

Battlo Trip Voltage, VIN falling 265 300 335 mV Measured as VIN-VOUT

Battlo Trip Voltage Hysteresis 9 mV

BLON Low Output Voltage 0.4 V VIN=3.3V, ISINK=1mA

BLON Leakage Current 1 µAV

BLON=3.6V

Over-Temperature 140 °C

Rising Trip Point

Over-Temperature Hysteresis 14 °C

D1,D0 Leakage Current 1 500 nA

D1,D0 Input Threshold Voltage 0.60 0.90 V High to Low Transition

1.25 1.8 V Low to High Transition

FB Leakage Current 1 100 nA FB=1V

VIN=UVIN=VSDN=3.6V, VOUT=VFB, IO = 0mA, TAMB = -40°C to +85°C, typical values at 27°C unless otherwise noted.

PVIN,VIN .............................................................................................. 6V

All other pins .............................................................. -0.3V to VIN+0.3V

PVIN, PGND, LX current ........................................................................ 2A

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

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

Lead Temperature (Soldering, 10 sec) ....................................... 300 °C

Thermal Resistance øJA:

10-Pin MSOP....................................................................128°C/W

10-Pin DFN ........................................................................68°C/W

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.

ELECTRICAL CHARACTERISTICS

PIN DESCRIPTION

PIN NUMBER PIN NAME DESCRIPTION

1PV

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

IN Internal supply voltage. Control circuitry powered from this pin.

3BLON Open drain battery low output. (VIN-VO) less than 300mV pulls this

node to ground. (VIN-VO) above threshold, this node is open.

4D1Digital mode control input. See table I for definition.

5D0Digital mode control input. See table I for definition.

6FBExternal feedback network input connection. Connect a resistor from

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

regulates to the internal bandgap reference voltage of 0.8V.

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

and off times.

8GND Internal ground pin. Control circuitry returns current to this pin.

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

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

capacitor to create regulated output voltage.

FUNCTIONAL DIAGRAM

D1 D0

00Shutdown. All internal circuitry is disabled and the power switches are opened.

01Device enabled, falling UVLO threshold =2.70V

10Device enabled, falling UVLO threshold =2.85V

11Device enabled, falling UVLO threshold =3.00V

Table 1. Operating Mode Definition

Zero_X

DRVON

Min Ton

BLON

OVR_I

MIN Ton

OVR_IK

OFF

OUT

Vin

OFF

UVLO

BLANK = Tblank(=100ns) or Toff = Koff/Vout

OUT

ILIM/M

REF

VOLOW

FB +-

RAMP

RST

GND

TSD

BLANK

300mV

-C

UVLO

TONOVER Internal Supply

REF'

OVR_I

OUT

-C

DRVON

BLANK

ILIM/M

VOLOW

-C

TONOVER Min Ton =

OUT)

Ref One-Shot

DRVON

-C

Block

FB'

GND

REF

Vos

DRIVER

DRVON

=100ns

100

0.1 1.0 10.0 100.0 1000.0

ILoad (mA)

Efficiency (%)

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

3.20

3.25

3.30

3.35

3.40

0 200 400 600 800 1000

ILoad (mA)

Vout (V)

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

100

200

300

400

500

3.0 3.3 3.6 3.9 4.2

Vin (V)

Iin (uA)

Tamb = 85°C

Tamb = 25°C

Tamb = -40°C

1.45

1.47

1.49

1.51

1.53

1.55

0200 400 600 800 1000

ILoad (mA)

Vout (V)

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

3.0 3.3 3.6 3.9 4.2

Vin (V)

Iin (µA)

Tamb = 85°C

Tamb = 25°C

Tamb = -40°C

100

1.0 10.0 100.0 1000.0

ILoad (mA)

Efficiency (%)

600.

Vi=3.6V

Vi=3.9V

Vi=4.2V

Vi=5.0V

Figure 1. Efficiency vs Load, VOUT = 3.3V Figure 2. Efficiency vs Load, VOUT = 1.5V

Figure 3. Line/Load Rejection, VOUT = 3.3V Figure 4. Line/Load Rejection, VOUT = 1.5V

Figure 5. No Load Battery Current, VOUT=3.3V Figure 6. No Load Battery Current, VOUT=1.5V

TYPICAL PERFORMANCE CHARACTERISTICS

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

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

3.6 3.9 4.2 4.5 4.8 5.1 5.4

Vin (V)

Kon (V*usec)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4

Vin (V)

Kon (V*usec)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

3.6 3.9 4.2 4.5 4.8 5.1 5.4

Vin (V)

Koff (V*usec)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4

Vin (V)

Koff (V*usec)

Figure 7. KON vs VIN, VOUT=3.3V Figure 8. KON vs VIN, VOUT=1.5V

Figure 9. KOFF vs VIN, VOUT=3.3V Figure 10. KOFF vs VIN, VOUT=1.5V

TYPICAL PERFORMANCE CHARACTERISTICS: Continued

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

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

3.5 4.0 4.5 5.0

Vin (V)

Frequency (KHz)

Vout = 3.3V

Measured

Vout = 3.3V

Calculated

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

3.4 3.8 4.2 4.6 5.0

Vin (V)

Frequency (KHz)

Vout = 1.5V

Measured

Vout = 1.5V

Calculated

Figure 11. Ripple Frequency vs. VIN, IOUT=600mA,

VOUT=3.3V Figure 12. Ripple Frequency vs. VIN, IOUT=600mA,

VOUT=1.5V

CH.2=V

OUT

50mV/div . AC

CH.4=I

OUT

0.5A/div

CH.2=V

OUT

50mV/div . AC

CH.4=I

0.5A/div

CH.1=V

SHDN

10V/div.

CH.2=V

OUT

1V/div . AC

CH.4=ILx

0.5A/div

CH.1=V

SHDN

10V/div.

CH.2=V

OUT

2V/div . AC

CH.4=ILx

0.5A/div

Figure 15. Load Step, IOUT=0.4A to 0.8A, VOUT=3.3V Figure 16. Load Step, IOUT=0.4A to 0.8A, VOUT=1.5V

Figure 17. Start up from SHDN, IOUT=0.6A, VOUT=3.3V Figure 18. Start up from SHDN, IOUT=0.6A, VOUT=1.5V

TYPICAL PERFORMANCE CHARACTERISTICS: Continued

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

CH.1=V

2.5V/div

CH.2=V

OUT

2.0V/div

CH.4=I

0.5A/div

CH.1=V

2.5V/div

CH.2=V

OUT

5.0V/div

CH.4=I

0.5A/div

Figure 13. VIN Start up, IOUT=0.6A, VOUT=3.3V Figure 14. VIN Start up, IOUT=0.6A, VOUT=1.5V

THEORY OF OPERATION

The SP6651A is a high efficiency synchronous

buck regulator with an input voltage range of

+2.7V to +5.5Vand an output that is adjustable

between +1.0V and VIN. The SP6651A features

a unique on-time control loop that runs in dis-

continuous conduction mode (DCM) or con-

tinuous conduction mode (CCM) using syn-

chronous rectification. Other features include

over-temperature shutdown, over-current pro-

tection, digitally controlled enable and under-

voltage lockout, a battery low indicator, and an

external feedback pin.

The SP6651A operates with a light load quies-

cent current of 20µA using a 0.3Ω PMOS main

switch and a 0.3Ω NMOS synchronous switch.

It operates with excellent efficiency across the

entire load range, making it an ideal solution for

battery powered applications and low current

step-down conversions. The part smoothly tran-

sitions into a 100% duty cycle under heavy load/

low input voltage conditions.

On-Time Control - Charge Phase

The SP6651A uses a precision comparator and

a minimum on-time to regulate the output volt-

age and control the inductor current under nor-

mal 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:

TON = KON

VIN - VOUT

where:

KON = 2.25V*µsec constant

VIN = VIN pin voltage

VOUT = VOUT pin 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 following waveforms de-

scribe the ideal ramp operation in both CCM and

DCM operation.

In either CCM or DCM, the negative going

ramp voltage (VRAMP in the functional diagram)

is added to FB and this creates the FB's signal.

This FB signal is applied to the negative termi-

nal of the loop comparator. To the positive

terminal of the loop comparator is applied the

REF voltage of 0.8V plus an offset voltage Vos

to compensate for the DC level of VRAMP ap-

plied 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.

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-timer.

The minimum on-timer times out and indicates

DRVON can be reset if the voltage loop is

satisfied. If VOUT is still below the regulation

DRVON

REF, FB

REF’

FB’

I(L1)

RAMP: DCM OPERATION

DRVON

REF, FB

REF’

FB’

I(L1)

RAMP: CCM OPERATION

point RESET is held low until VOUT is above

regulation. Once RESET occurs TON minimum

is reset, and the TOFF one-shot is triggered to

blank the loop comparator from starting a new

charge cycle for a minimum period. This blank-

ing period occurs during the noisy LX transition

to discharge, where spurious comparator states

may occur. For TOFF > TBLANK the loop is in a

discharge or wait state until the loop comparator

starts the next charge cycle by DRVON going

high.

If an over current occurs during charge the loop

is interrupted and DRVON is RESET. The off-

time one-shot pulse width is widened to TOFF =

KOFF / VOUT, which holds the loop in discharge

for that time. At the end of the off-time the loop

is released and controlled by VOLOW. In this

manner maximum inductor current is controlled

on a cycle-by-cycle basis. An assertion of UVLO

(undervoltage lockout) or TSD (thermal shut-

down) holds the loop in no-charge until the fault

has ended.

On-Time Control - Discharge Phase

The discharge phase follows with the high side

PMOS switch opening and the low side NMOS

switch closing to provide a discharge path for

the inductor current. The decreasing inductor

current and the load current cause the output

voltage to drop. Under normal load conditions

when the inductor current is below the pro-

grammed limit, the off-time will continue until

the output voltage falls below the regulation

threshold, which initiates a new charge cycle via

the loop comparator.

The inductor current “floats” in continuous con-

duction mode. During this mode the inductor

peak current is below the programmed limit and

the valley current is above zero. This is to satisfy

load currents that are greater than half the mini-

mum current ripple. The current ripple, ILR, is

defined by the equation:

ILR ≈ KON * VIN - VOUT - IOUT * RCH

L VIN - VOUT

where:

L = Inductor value

IOUT = Load current

RCH = PMOS on resistance, 0.3Ω typ.

If the IOUT * RCH term is negligible compared

with (VIN - VOUT), the above equation simplifies

to:

ILR ≈ KON

For most applications, the inductor current ripple

controlled by the SP6651A is constant regard-

less of input and output voltage. Because the

output voltage ripple is equal to:

VOUT (ripple) = ILR * RESR

where:

RESR = ESR of the output capacitor

the output ripple of the SP6651A regulator is

independent of the input and output voltages.

For battery powered applications, where the

battery voltage changes significantly, the

SP6651A provides constant output voltage ripple

through-out the battery lifetime. This greatly

simplifies the LC filter design.

The maximum loop frequency in CCM is de-

fined by the equation:

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

KON * [VIN + IOUT * (RDC - RCH)]

where:

FLP = CCM loop frequency

RDC = NMOS on resistance, 0.3Ω typ.

Ignoring conduction losses simplifies the loop

frequency to:

FLP ≈ 1 * VOUT * (VIN - VOUT)

KON VIN

AND’ing the loop comparator and the on-timer

reduces the switching frequency for load cur-

rents below half the inductor ripple current. This

increases light load efficiency. The minimum

on-time insures that the inductor current ripple

THEORY OF OPERATION : Continued

is a minimum of KON/L, more than the load

current demands. The converter goes in to a

standard pulse frequency modulation (PFM)

mode where the switching frequency is propor-

tional to the load current.

Low Dropout and Load Transient Operation

AND’ing the loop comparator also increases the

duty ratio past the ideal D= VOUT /VIN up to and

including 100%. 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 regu-

lation.

Also, as the input voltage supply drops down

close to the output voltage, the main MOSFET

resistance loss will dictate a much higher duty

ratio to regulate the output. Eventually as the

input voltage drops low enough, the output

voltage will follow, causing the loop compara-

tor to hold the converter at 100% duty cycle.

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 (VIN -VOUT) below

which the output regulation cannot be main-

tained. The dropout voltage of SP6651A is equal

to IL* (0.3Ω+ RL1) where 0.3Ω is the typical

RDS(ON) of the P-Channel MOSFET and RL is

the DC resistance of the inductor.

The SP6651A has been designed to operate in

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

on-time control circuit seamlessly operates the

converter between CCM, DCM, and low drop-

out modes without the need for compensation.

The converter’s transient response is quick since

there is no compensated error amplifier in the loop.

Inductor Over-Current Protection

To reduce the light load dropout Iq, the SP6651A

over-current system is only enabled when IL1 >

400mA. The inductor over-current protection

circuitry is programmed to limit the peak induc-

tor current to 1.25A. This is done during the on-

time by comparing the source to drain voltage

drop of the PMOS passing the inductor current

with a second voltage drop representing the

maximum allowable inductor current. As the

two voltages become equal, the over-current

comparator triggers a minimum off-time one

shot. The off-time one shot forces the loop into

the discharge phase for a minimum TOFF time

causing the inductor current to decrease. At the

end of the off-time, loop control is handed back

to the AND’d 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 over-

load conditions, the converter behaves like a

current source at the programmed limit minus

half the current ripple. The minimum TOFF is

controlled by the equation:

TOFF (MIN) = KOFF

VOUT

Under-Voltage Lockout

The SP6651A is equipped with a programmable

under-voltage lockout to protect the input bat-

tery source from excessive currents when sub-

stantially discharged. When the input supply is

below the UVLO threshold both power switches

are open to prevent inductor current from flow-

ing. The three levels of falling input voltage

UVLO threshold are shown in Table 1, with a

typical hysteresis of 120mV to prevent chatter-

ing due to the impedance of the input source.

During UVLO, BLON is forced low.

Under-Current Detection

The synchronous rectifier is comprised of an

inductor discharge switch, a voltage compara-

tor, 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 inductor current approaches zero,

the channel voltage sign goes from negative to

positive, causing the comparator to trigger the

THEORY OF OPERATION: Continued

For the typical SP6651A application circuit with

inductor size of 10µH, and KON of 2V*µsec, the

SP6651A current ripple would be about 200mA,

driver latch and open the switch to prevent

inductor current reversal. This circuit along

with the on-timer puts the converter into PFM

mode and improves light load efficiency when

the load current is less than half the inductor

ripple current defined by KON/L.

Thermal Shutdown

The converter will open both power switches if

the die junction temperature rises above 140°C.

The die must cool down below 126°C before the

regulator is re-enabled. This feature protects the

SP6651A and surrounding circuitry from exces-

sive power dissipation due to fault conditions.

Shutdown/Enable Control

The D0, D1 pins 4,5 of the device are logic level

control pins that according to Table 1 shut down

the converter when both are a logic low, or

enables the converter when either are a logic

high. When the converter is shut down, the

power switches are opened and all circuit bias-

ing is extinguished leaving only junction leak-

age currents on supply pins 1 and 2. After pins

4 or 5 are brought high to enable the converter,

there is a turn on delay to allow the regulator

circuitry to re-establish itself. Power conversion

begins with the assertion of the internal refer-

ence ready signal which occurs approximately

150µs after the enable signal is received.

Battery Low Indicator

The BLON function is a differential measure-

ment of (VIN -VOUT) which causes the open

drain NMOS on pin 3 to sink current to ground

when (VIN -VOUT) < 300mV. Tying a resistor

from pin 3 to VIN or VOUT creates a logic level

battery low indicator. A low bandwidth com-

parator and 3% hysteresis filter the input voltage

ripple to prevent noisy transitions at the thresh

old. BLON is forced Low when in UVLO.

External Feedback Pin

The FB pin 6 is compared to an internal refer-

ence voltage of 0.8V to regulate the SP6651A

output. The output voltage can be externally

programmed within the range +1.0V to +5.0V

by tying a resistor from FB to ground and FB to

VOUT (pin7). See the applications section for

resistor selection information.

Inductor Selection

The SP6651A uses a specially adapted mini-

mum on-time control of regulation utilizing a

precision comparator and bandgap reference.

This adaptive minimum on-time control has the

advantage of setting a constant current ripple

for a given inductor size. From the operations

section it has been shown:

Inductor Current Ripple, ILR ≈ KON

THEORY OF OPERATION: Continued

APPLICATION INFORMATION

and would be fairly constant for different input and

output voltages, simplifying the selection of com-

ponents for the SP6651A power circuit. Other

inductor values could be selected, 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 not produce as stable an output ripple.

For larger inductors with the SP6651A, which

has a peak inductor current of 1.25A, most

15µH or 22µH inductors would have to be larger

physical sizes, limiting their use in small por-

table applications. Smaller values like 6.8µH

would more easily meet the 1.25A limit and

come in small case sizes, and the increased

For the 22µF POSCAP with 0.04Ω ESR, and a

10µH inductor yielding 200mA inductor current

ripple ILR, the VOUT ripple would be 8mVpp.

Since 8mV is a very small signal level, the actual

value would probably be larger due to noise and

layout issues, but this illustrates that the SP6651A

output ripple can be very low indeed. To improve

stability, a small ceramic capacitor, CF = 22pF

should be paralleled with the feedback voltage

divider RF, as shown on the typical application

schematic on page 1. Another function of the

output capacitance is to hold up the output voltage

during the load transients and prevent excessive

overshoot and undershoot. The typical perfor-

mance characteristics curves show very good load

step transient response for the SP6651A with the

recommended output capacitance of 22µF ce-

ramic.

The input capacitor will reduce the peak current

drawn from the battery, improve efficiency and

significantly reduce high frequency noises in-

duced by a switching power supply. The typical

input capacitor for the SP6651A is 22µF ceramic,

POSCAP or Aluminum Polymer. These capaci-

tors will provide good high frequency bypassing

and their low ESR will reduce resistive losses for

higher efficiency. An RC filter is recommended

for the VIN pin 2 to effectively reduce the noise for

the ICs analog supply rail which powers sensitive

circuits. This time constant needs to be at least 5

times greater than the switching period, which is

calculated as 1/FLP during the CCM mode. The

typical application schematic uses the values of

RVIN = 10Ω and CVIN = 1µF to meet these require-

ments.

APPLICATION INFORMATION: Continued

inductor current ripple of almost 300mA would

produce very stable regulation and fast load

transient response at the expense of slightly

reduced efficiency.

Other inductor parameters are important: the in-

ductor current rating and the DC resistance. When

the current through the inductor reaches the level

of ISAT, the inductance drops to 70% of the

nominal value. This non-linear change can cause

stability problems or excessive fluctuation in in-

ductor current ripple. To avoid this, the inductor

should be selected with saturation current at least

equal to the maximum output current of the con-

verter plus half the inductor current ripple. To

provide the best performance in dynamic condi-

tions such as start-up and load transients, inductors

should be chosen with saturation current close to

the SP6651A inductor current limit of 1.25A.

DC resistance, another important inductor charac-

teristic, directly affects the efficiency of the con-

verter, so inductors with minimum DC resistance

should be chosen for high efficiency designs.

Recommended inductors with low DC resistance

are listed in table 2. Preferred inductors for on

board power supplies with the SP6651A are mag-

netically shielded types to minimize radiated mag-

netic field emissions.

Capacitor Selection

The SP6651A has been designed to work with

very low ESR output capacitors (listed in Table 2

Component Selection) which for the typical appli-

cation circuit are 22µF ceramic, POSCAP or Alu-

minum Polymer. These capacitors combine small

size, low ESR and good value. To regulate the

output with low ESR capacitors of 0.01Ω or less,

an internal ramp voltage VRAMP has been added to

the FB signal to reliably trip the loop comparator

(as described in the Operations section).

Output ripple for a buck regulator is determined

mostly by output capacitor ESR, which for the

SP6651A with a constant inductor current ripple

can be expressed as:

VOUT (ripple) = ILR * RESR

APPLICATION INFORMATION: Continued

Output Voltage Program

The output voltage is programmed by the external

divider, as shown in the typical application circuit

on page 1. First pick a value for RI that is no larger

than 300K. Too large a value of RI will reduce the

AC voltage seen by the loop comparator since the

internal FB pin capacitance can form a low pass

filter with RF in parallel with RI. The formula for

RF with a given RI and output voltage is:

RF = ( VOUT - 1 ) • RI

0.8V

Output Voltage Ripple Frequency

An important consideration in a power supply

application is the frequency value of the output

ripple. Given the control technique of the

SP6651A (as described in the operations sec-

tion), the frequency of the output ripple will

vary when in light to moderate load in the

discontinuous or PFM mode. For moderate to

heavy loads greater than about 100mA inductor

current ripple, (for the typical 10µH inductor

application on 100mA is half the 200mA induc-

tor current ripple), the output ripple frequency

will be fairly constant. From the operations

section, this maximum loop frequency in con-

tinuous conduction mode is:

1 VOUT (VIN - VOUT)

FLP ≈KON

VIN

Data for loop frequency, as measured from

output voltage ripple frequency, can be found in

the typical performance curves.

Layout Considerations

Proper layout of the power and control circuits is

necessary in a switching power supply to obtain

good output regulation with stability and a mini-

mum of output noise. The SP6651A application

circuit can be made very small and 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

INDUCTORS SURFACE MOUNT

Inductor Specification

Inductance Manufacturer/Part No. Series R ΩI

SAT

(A) Size Inductor Type Manufacturer

(µH) LxW(mm) Ht. (mm) Website

10 Sumida CDRH5D28-100 0.048 1.30 5.7 x 5.5 3.0 Shielded Ferrite Core sumida.com

10 TDK RLF5018T-100MR94 0.056 0.94 5.6 x 5.2 2.0 Shielded Ferrite Core tdk.com

10 Coilcraft DO1608C-103 0.160 1.10 6.6 x 4.5 2.9 Unshielded Ferrite Core coilcraft.com

10 Coilcraft LPO6013-103 0.300 0.70 6.0 x 5.4 1.3 Unshielded Ferrite Core coilcraft.com

6.8 Sumida CDRH5D28-6R8 0.081 1.12 4.7 x 4.5 3.0 Shielded Ferrite Core sumida.com

6.8 TDK RLF5018T-6R8M1R1 0.47 1.10 5.6 x 5.2 2.0 Shielded Ferrite Core tdk.com

6.8 Coilcraft DO1608C-682 0.130 1.20 6.6 x 4.5 2.9 Unshielded Ferrite Core coilcraft.com

6.8 Coilcraft LPO6013-103 0.200 0.60 6.0 x 5.4 1.3 Unshielded Ferrite Core coilcraft.com

CAPACITORS - SURFACE MOUNT

Capacitor Specification

Capacitance Manufacturer/Part No. ESR RippleCurrent Size Voltage Capacitor Type Manufacturer

(µF) Ω (max) (A) @ 45°CLxW(mm) Ht. (mm) (V) Website

22 TDK C3216X5R0J226M 0.002 3.00 3.2 x 1.6 1.6 6.3 X5R Ceramic tdk.com

22 SANYO 6APA22M 0.040 1.90 7.3 x 4.3 2.0 6.3 POSCAP sanyovideo.com

47 TDK C3225X5R0J46M 0.002 4.00 3.2 x 1.6 1.6 6.3 X5R Ceramic tdk.com

47 SANYO 6TPA47M 0.040 1.90 6.0 x 3.2 2.8 6.3 POSCAP sanyovideo.com

Table 2 Component Selection

Note: Components highlighted in bold are those used on the SP6651A Evaluation Board.

APPLICATION INFORMATION: Continued

Figure 19. SP6651A PCB Component Sample Layout Figure 20. SP6651A PCB Top Sample Layout

Figure 21. SP6651A PCB Bottom Sample Layout

between the SP6651A 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 SP6651A power supply.

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 control and power

grounds and connect them together at a single

point. Power ground plane is shown in the figure

titled PCB top sample layout and connects the

ground of the COUT capacitor to the ground of the

CIN capacitor and then to the PGND pin 10. The

control ground plane connects from pin 9 GND to

ground of the CVIN capacitor and the RI ground

return of the feedback resistor. These two separate

control and power ground planes come together in

the figure titled PCB top sample layout where

SP6651A pin 9 GND is connected to pin 10

PGND.

Power loops on the input and output of the con-

verter 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 effectiveness at high frequencies. Therefore,

put the 1µF bypass capacitor as close to the VIN and

GND pins of the converter as possible, the 22µF

CIN close to the PVIN pin and the 22µF output

capacitor as close to the inductor as possible. The

external voltage feedback network RF, RI and

feedforward capacitor CF should be placed very

close to the FB pin. 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.

PACKAGE: 10 PIN MSOP

10-PIN MSOP

0.07 - -

Ø1

Seating Plane

E/2

Gauge Plane

A2 A

A1 b

- - 1.10

0.00 - 0.15

Dimensions in (mm)

10-PIN MSOP

JEDEC MO-187

(BA) Variation

0.75 0.85 0.95

0.17 - 0.27

0.08 - 0.23

3.00 BSC

4.90 BSC

3.00 BSC

0.4 0.60 0.80

0.95 REF

0.25 BSC

0.07 - -

0º - 8º

5º - 15º

Ø1

MIN NOM MAX

2.00 BSC

0.50 BSC

WITH PLATING

BASE METAL

(b)

Pin #1 indentifier must be indicated within this shaded area (D/2 * E1/2)

0 0

Section B-B

PACKAGE: 10 PIN DFN

Top View

D/2

Bottom View

E/2

Pin 1 identifier to be located within this shaded area.

Terminal #1 Index Area (D/2 * E/2)

Side View

AA1 A3

DIMENSIONS

(mm)

10 Pin DFN

(JEDEC MO-229,

VEED-5 VARIATION)

0.80 0.90 1.00

0.20 REF

2.20 - 2.70

3.00 BSC

1.40 - 1.75

0.30 0.40 0.50

0.20

0.18 0.25 0.30

3.00 BSC

0.50PITCH

SYMBOL MIN NOM MAX

00.02 0.05

- -

10 PIN DFN

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

ORDERING INFORMATION

Part Number Top Mark Operating Temperature Range Package Type

SP6651AEU..............6651AEU....................... -40°C to +85°C...................................................10 Pin MSOP

SP6651AEU/TR........6651AEU............ ........... -40°C to +85°C .................................................. 10 Pin MSOP

SP6651AER.............6651AER......................... -40°C to +85°C..................................................... 10 Pin DFN

SP6651AER/TR.......6651AER......................... -40°C to +85°C ..................................................... 10 Pin DFN

/TR = Tape and Reel

Pack quantity is 2500 for MSOP and 3,000 for DFN.

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

Example: SP6651AEU/TR = standard; SP6651AEU-L/TR = lead free