ILC6381CP-50 - Impala Linear Corporation

100mA boost converter in 5-lead SOT-89 package using

both PFM and PWM conversion techniques. In normal

operation the ILC6380 runs in PWM mode running at one of

three fixed frequencies. At light loads the ILC6380 senses

when the duty cycle drops to approximately 10%, and auto-

matically switches into a power-saving PFM switching tech-

nique. This maintains high efficiencies both at full load and

in system sleep conditions.

Only 3 external components are needed to complete the

switcher design, and standard voltage options of 2.5, 3.3,

and 5.0V at ±2.5% accuracy feature on-chip phase com-

pensation and soft-start design.

ILC6381 drives an external transistor for higher current switch-

er design, with all of the features and benefits of the ILC6380.

ILC6380/81

SOT-89 Step-up Dual-Mode Switcher with Shutdown

Impala Linear Cor por ation

Impala Linear Corporation 1

(408) 574-3939 www.impalalinear.com Sept 1999

ILC6380/1 1.4

!85% efficiency at 50mA

!Start-up voltages as low as 900mV

!±2.5% accurate outputs

!Complete switcher design with only 3 external

components

!50, 100 and 180kHz switching frequency versions

available

!Shutdown to 0.5µA Iq

!External transistor option allows several hundred

milliamp switcher design

!Cellular Phones, Pagers

!Portable Cameras and Video Recorders

!Palmtops and PDAs

SOT -89-5

( TOP VIEW)

132

VOUT CE

VSS

N/C

SOT -89-5

(T OP VI EW )

132

VOUT CE

EXT

VSS

N/C

ILC6380CP-25

2.5V ± 2.5%@50kHz

ILC6380CP-33

3.3V ± 2.5%@50kHz

ILC6380CP-50

5.0V ± 2.5%@50khz

ILC6380CP-25

2.5V ± 2.5%@100kHz

ILC6380CP-33

3.3V ± 2.5%@100kHz

ILC6380CP-50

5.0V ± 2.5%@100kHz

ILC6380CP-25

2.5V ± 2.5%@180kHz

ILC6380CP-33

3.3V ± 2.5%@180kHz

ILC6380CP-50

5.0V ± 2.5%@180kHz

ILC6381CP-25

2.5V ± 2.5%@50kHz, external xtor

ILC6381CP-33

3.3V ± 2.5%@50kHz, external xtor

ILC6381CP-50

5.0V ± 2.5%@50kHz, external xtor

ILC6381BP-25

2.5V ± 2.5%@100kHz, external xtor

ILC6381BP-33

3.3V ± 2.5%@100kHz, external xtor

ILC6381BP-50

5.0V ± 2.5%@100kHz, external xtor

ILC6381AP-25

2.5V ± 2.5%@180kHz, external xtor

ILC6381AP-33

3.3V ± 2.5%@180kHz, external xtor

ILC6381AP-50

5.0V ± 2.5%@180kHz, external xtor

VLX

LIMI TER

PWM/PFM Controll e d

BUFFER

VSS

EXT

CHIP ENABLE

OS C

50/100/180KHz

VDD

VOUT

Phase com p

Vref

Slow St ar t

VDD is int ernal ly connec ted to the V OUT pin.

*Standard product offering comes in tape & reel, quantity

1000 per reel, orientation right for SOT-89

General Description Package Features

Applications

Block Diagram

Pin Package Configurations

Ordering Information

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ILC6380/1 1.4

Parameter

Symbol

Ratings

Units

VOUT Input Voltage

VOUT

Voltage on pin LX

VLX

Current on pin LX

ILX

400

Voltage on pin EXT

VEXT

VSS-0.3~VOUT+0.3

Current on pin EXT

IEXT

±50

CE Input Voltage

VCE

Continuous Total Power Dissipation

500

Operating Ambient Temperature

TOPR

-30~+80

°C

Storage Temperature

TSTG

-40~+125

°C

Stresses above those listed under ABSOLUTE MAXIMUM RATINGS may cause permanent device failure. Functionality at

or above these limits is not implied. Exposure to absolute maximum ratings for extended periods may affect device reliabil-

ity. Operating ranges define those limits between which the functionality of the device is guaranteed.

Notes:

1. The Schottky diode (S.D.), in figure 3 must be type MA735, with Reverse current (IR) < 1.0µA at reverse voltage (VR)=10.0V

2. “Supply Current 1” is the supply current while the oscillator is continuously oscillating. In actual operation the oscillator

periodically operates which results in less average power consumption.

The current that is actually provided by external VIN source is represented by “No-Load Input Current(IIN)”

3. Switching frequency is determined by delay time of internal comparator to turn Lx “off”, and minimum “on” time as determined

by MAXDTY spec.

Parameter

Sy mbol

Conditions

Min

Typ

Max

Units

Output Voltage

VOUT

4.875

5.000

5.125

Input Voltage

VIN

Oscillation Startup

Voltage

VST

LX = 10kΩ pull-up to 5V, VOUT = VST

0.8

Operation Startup

Voltage

VST1

IOUT = 1mA

0.9

No-Load Input Current

IIN

IOUT = 0mA (See Note 1)

23.0

46.0

µA

Supply Current 1

(See Note 2)

IDD 1

LX = 10kΩ pull-up to 5V, VOUT = 4.5V

78.6

131.1

µA

Supply Current 2

IDD 2

LX = 10kΩ pull-up to 5V, VOUT = 5.5V

6.9

13.8

µA

LX Switch-On

Resistance

RSWON

LX = 10kΩ pull-up to 5V, VOUT = 4.5V

1.3

2.3

Ω

LX Leakage Current

ILXL

No external components, VOUT = VLX = 10V

1.0

µA

Oscillator Freq.

FOSC

LX = 10kΩ pull-up to 5V, VOUT = 4.5V,

Measuring of LX waveform

100

115

kHz

Maximum Duty Ration

MAXDTY

LX = 10kΩ pull-up to 5V, VOUT = 4.5V,

Measuring of LX on-time

PFM Duty Ration

PFMDTY

VIN = 4.75V, Measuring of LX on-time

Stand-by Current

ISTB

LX = 10kΩ pull-up to 5V, VOUT =4.5V

0.5

µA

CE “High” Voltage

VCEH

LX = 10kΩ pull-up to 5V, VOUT = 4.5V,

Existence of LX Oscillation

0.75

CE “Low” Voltage

VCEL

LX = 10kΩ pull-up to 5V, VOUT = 4.5V,

Stopped LX Oscillation

0.20

CE “High” Current

ICEH

LX = 10kΩ pull-up to 5V, VOUT = VCE = 4.5V

0.25

µA

CE “Low” Current

ICEL

LX = 10kΩ pull-up to 5V, VOUT = 4.5V,

VCE = 0V

-0.25

µA

LX Limit Voltage

VLXLMT

LX = 10kΩ pull-up to 5V, VOUT = 4.5V,

FOSC > FOSC x 2 (See Note 2)

0.7

1.1

Efficiency

EFFI

Slow Start Time

TSS

msec

VOUT = 5.0V, FOSC = 100kHz TA- 25°C. Unless otherwise specified, VIN = VOUT x 0.6, IOUT = 50mA. See schematic, figure 3

Absolute Maximum Ratings (TA= 25°C)

Electrical Characteristics

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ILC6380/1 1.4

VOUT = 5.0V, FOSC = 100kHz TA= 25°C. Unless otherwise specified, VIN = VOUTX0.6, IOUT = 50mA. See the schematic, figure 4.

ILC6380

123

VOUT

GND

VIN

ILC6381

123

VOUT

VIN

L: 100µH ( SUMIDA, CD-54)

SD: Diode (Schottky diode; MATSUSHITA MA735)

CL: 16V 47µF (Tantalum Capacitor; NICHICON, F93)

L: 47µH ( SUMIDA, CD-54)

SD: Diode (Schottky diode; MATSUSHITA MA735)

CL: 16V 47µF (Tantalum Capacitor; NICHICON, F93)

RB: 1kW

CB: 3300pF

Tr: 2SC3279, 2SDI628G

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Output Voltage

VOUT

Test Circuit of Figure 2

4.875

5.000

5.125

Input Voltage

VIN

Oscillation Startup Voltage

VST2

VOUT = VST2

0.8

Operation Startup Voltage

VST1

IOUT = 1mA

0.9

Supply Current 1

(See Note 2)

IDD 1

EXT = 10kΩ pull-up to 5V,

VOUT = 4.5V

78.6

131.1

µA

Supply Current 2

IDD 2

EXT = 10kΩ pull-up to 5V,

VOUT = 5.5V

6.9

13.8

µA

EXT “High” On-Resistance

REXTH

EXT = 10kΩ pull-up to 5V,

VOUT = 4.5V, VEXT = VOUT – 0.4V

Ω

EXT “Low” On-Resistance

REXTL

EXT = 10Ω pull-up to 5V,

VOUT = 4.5V, VEXT = VOUT - 0.4V

Ω

Oscillator Frequency

FOSC

EXT = 10kΩ pull-up to 5V, VOUT =

4.5V, Measuring of EXT waveform

100

115

kHz

Maximum Duty Ratio

MAXDTY

EXT = 10kΩ pull-up to 5V, VOUT =

4.5V, Measuring of EXT high state

CE “High” Voltage

VCEH

EXT = 10kΩ pull-up to 5V, VOUT =

4.5V, Existence of Oscillation

0.75

CE “Low” Voltage

VCEL

EXT = 10kΩ pull-up to 5V, VOUT =

4.5V, Stopped EXT Oscillation

0.20

CE “High” Current

ICEH

EXT: 10kΩ pull-up to 5V,

VOUT = 4.5V, VCE = VOUT X 0.95V

0.25

µA

CE “Low” Current

ICEL

EXT = 10kΩ pull-up to 5V,

VOUT = 4.5V, VCE = 0V

-0.25

µA

Efficiency

EFFI

Slow Start Time

TSS

msec

Notes:

1. The Schottky diode (S.D.), in figure 3 must be type MA735, with Reverse current (IR) < 1.0µA at reverse voltage (VR)=10.0V

2. “Supply Current 1” is the supply current while the oscillator is continuously oscillating. In actual operation the oscillator periodically

operates which results in less average power consumption.

The current that is actually provided by external VIN source is represented by “No-Load Input Current (IIN)”

Electrical Characteristics ILC6380BP-50

Typical Applications

Figure 3 Figure 4

SOT-89 Step-up Dual-Mode Switcher with Shutdown

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ILC6380/1 1.4

The ILC6380 performs boost DC-DC conversion by controlling the

switch element shown in the circuit below

When the switch is closed, current is built up through the inductor.

When the switch opens, this current has to go somewhere and is

forced through the diode to the output. As this on and off switch-

ing continues, the output capacitor voltage builds up due to the

charge it is storing from the inductor current. In this way, the out-

put voltage gets boosted relative to the input. The ILC6380 moni-

tors the voltage on the output capacitor to determine how much

and how often to drive the switch.

In general, the switching characteristic is determined by the output

voltage desired and the current required by the load. Specifically

the energy transfer is determined by the power stored in the coil

during each switching cycle.

PL = ƒ(tON, VIN)

The ILC6380 and ILC6381 use a PWM or Pulse Width Modulation

technique. The parts come in one of three fixed internal frequen-

cies: 50, 100, or 180kHz. The switches are constantly driven at

these frequencies. The control circuitry varies the power being

delivered to the load by varying the on-time, or duty cycle, of the

switch. Since more on-time translates to higher current build-up in

the inductor, the maximum duty cycle of the switch determines the

maximum load current that the device can support. The ILC6380

and ILC6381 both support up to 87% duty cycles, for maximum

usable range of load currents.

There are two key advantages of the PWM type controllers. First,

because the controller automatically varies the duty cycle of the

switch’s on-time in response to changing load conditions, the

PWM controller will always have an optimized waveform for a

steady-state load. This translates to very good efficiency at high

currents and minimal ripple on the output. [Ripple is due to the out-

put cap constantly accepting and storing the charge received from

the inductor, and delivering charge as required by the load. The

“pumping” action of the switch produces a sawtooth-shaped volt-

age as seen by the output.]

The other key advantage of the PWM type controllers is that the

radiated noise due to the switching transients will always occur at

the (fixed) switching frequency. Many applications do not care

much about switching noise, but certain types of applications,

especially communication equipment, need to minimize the high

frequency interference within their system as much as is possible.

Using a boost converter requires a certain amount of higher fre-

quency noise to be generated; using a PWM converter makes that

noise highly predictable; thus easier to filter out.

Dual Mode Operation

But there are downsides of PWM approaches, especially at very

low currents. Because the PWM technique relies on constant

switching and varying duty cycle to match the load conditions,

there is some point where the load current gets too small to be

handled efficiently. An actual switch consumes some finite amount

of current to switch on and off; at very low currents this can be of

the same magnitude as the load current itself, driving switching

efficiencies down to 50% and below. The ILC6380 and ILC6381

overcome this limitation by automatically switching over to a PFM,

or Pulse Frequency Modulation, technique at low currents. This

technique conserves power loss by only switching the output if the

current drain requires it. As shown in the diagram below , the wave-

form actually skips pulses depending on the power needed by the

output. [This technique is also called “pulse skipping” because of

this characteristic.]

In the ILC6380 and ILC6381, this switchover is internally set to be

at the point where the PWM waveform hits approximately 10%

duty cycle. So the PFM mode is running at 10% duty cycle at the

rated frequency; for 100kHz part this means a constant on-time of

1msec. This not only is ideal for efficiency at these low currents,

but a 10% duty cycle will have much better output ripple charac-

teristics than a similarly configured PFM part, such as the ILC6390

and ILC6391.

The Dual-Mode architecture was designed specifically for those

applications, like communications, which need the spectral pre-

dictability of a PWM-type DC-DC converter, yet which also needs

the highest efficiencies possible, especially in Shutdown or

Standby mode. [For other conversion techniques, please see the

ILC6370/71 and ILC6390/91 datasheets.]

Other Considerations

The other limitation of PWM techniques is that, while the funda-

mental switching frequency is easier to filter out since it’s constant,

the higher order harmonics of PWM will be present and may have

to be filtered out, as well. Any filtering requirements, though, will

vary by application and by actual system design and layout, so

generalizations in this area are difficult, at best.

However, PWM control for boost DC-DC conversion is widely

used, especially in audio-noise sensitive applications or applica-

tions requiring strict filtering of the high frequency components.

Impala’s products give very good ef ficiencies of 85% at 50mA out-

put (5V product), 87% maximum duty cycles for high load condi-

tions, while maintaining very low shutdown current levels of

VSET

VOUT

Switch Waveform

Functions and Operation

SOT-89 Step-up Dual-Mode Switcher with Shutdown

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ILC6380/1 1.4

0.5mA. The only difference between the ILC6380 and ILC6381

parts is that the 6381 is configured to drive an external transistor

as the switch element. Since larger transistors can be selected for

this element, higher effective loads can be regulated.

Start-up Mode

The ILC6380 has an internal soft-start mode which suppresses

ringing or overshoot on the output during start-up. The following

diagram illustrates this start-up condition’s typical performance:

External Components and Layout Consideration

The ILC6380 is designed to provide a complete DC-DC convertor

solution with a minimum of external components. Ideally, only

three externals are required: the inductor, a pass diode, and an

output capacitor.

The inductor needs to be of low DC Resistance type, typically 1Ω

value. Toroidal wound inductors have better field containment (less

high frequency noise radiated out) but tend to be more expensive.

Some manufacturers like Coilcraft have new bobbin-wound induc-

tors with shielding included, which may be an ideal fit for these

applications. Contact the manufacturer for more information.

The inductor size needs to be in the range of 47mH to 1mH. In

general, larger inductor sizes deliver less current, so the load cur-

rent will determine the inductor size used.

For load currents higher than 10mA, use an inductor from 47mH

to 100mH. [The 100mH inductor shown in the datasheet is the

most typical used for this application.]

For load currents of around 5mA, such as pagers, use an inductor

in the range of 100mH to 330mH. 220mH is the most typical value

used here.

For lighter loads, an inductor of up to 1mH can be used. The use

of a larger inductor will increase overall conversion efficiency, due

to the reduction in switching currents through the device.

For the ILC6381, using an external transistor, the use of a 47mH

inductor is recommended based on our experience with the part.

Note that these values are recommended for both 50kHz and

100kHz operation. If using the ILC6380 or ILC6381 at 180kHz,

the inductor size can be reduced to approximately half of these

stated values.

The capacitor should, in general, always be tantalum type, as tan-

talum has much better ESR and temperature stability than other

capacitor types. NEVER use electrolytics or chemical caps, as the

C-value changes below 0×C so much as to make the overall

design unstable.

Different C-values will directly impact the ripple seen on the output

at a given load current, due to the direct charge-to-voltage rela-

tionship of this element. Different C-values will also indirectly af fect

system reliability, as the lifetime of the capacitor can be degraded

by constant high current influx and outflux. Running a capacitor

near its maximum rated voltage can deteriorate lifetime as well;

this is especially true for tantalum caps which are particularly sen-

sitive to overvoltage conditions.

In general, then, this capacitor should always be 47mF, Tantalum,

16V rating.

The diode must be of shottkey type for fast recovery and minimal

loss. A diode rated at greater than 200mA and maximum voltage

greater than 30V is recommended for the fastest switching time

and best reliability over time. Different diodes may introduce dif-

ferent levels of high frequency switching noise into the output

waveform, so trying out several sources may make the most

sense for your system.

For the IL6381, much of the component selection is as described

above, with the addition of the external NPN transistor and the

base drive network. The transistor needs to be of NPN type, and

should be rated for currents of 2A or more. [This translates to

lower effective on resistance and, therefore, higher overall effi-

ciencies.] The base components should remain at 1kΩand

3300pF; any changes need to be verified prior to implementation.

As for actual physical component layout, in general, the more

compact the layout is, the better the overall performance will be. It

is important to remember that everything in the circuit depends on

a common and solid ground reference. Ground bounce can direct-

ly affect the output regulation and presents difficult behavior to

predict. Keeping all ground traces wide will eliminate ground

bounce problems.

It is also critical that the ground pin of CLand the VSS pin of the

device be the same point on the board, as this capacitor serves

two functions: that of the output load capacitor, and that of the

input supply bypass capacitor.

Layouts for DC-DC converter designs are critical for overall per-

formance, but following these simple guidelines can simplify the

task by avoiding some of the more common mistakes made in

these cases. Once actual performance is completed, though, be

sure to double-check the design on actual manufacturing proto-

type product to verify that nothing has changed which can affect

the performance.

VIN - Vf

VOUT MIN

T SOFT-START (~10msec)

t = 0

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ILC6380/1 1.4

RIPPLE VOLTAGE vs. OUTPUT CURRENT

OUTPUT VOLTAGE vs. OUTPUT CURRENT

ILC6380CP-30

3.2

3.1

3.0

2.9

2.8

2.7

2.6

00 40 80 120 160 200

OUTPUT CURRENT IOUT (mA)

INPUT VOLTAGE VIN (V)

OUTPUT CURRENT IOUT (mA)

OUTPUT VOLTAGE VOUT (V)

EFFICIENCY: EFFI (%)

RIPPLE Vr (mVp-p)

INPUT CURRENT (µA)

L = 1000µH

C = 47µF (Tantalum)

L = 1000µH

C = 47µF (Tantalum)

L = 1000µH

C = 47µF (Tantalum)

VIN = 1.0V

VIN = 1.5V

VIN = 2.0V

100

00 40 80 120 160

EFFICIENCY vs. OUTPUT CURRENT

L = 100µH

RL= 0

C = 47µF (Tantalum)

IOUT = 0 (no load)

1.0 1.2 1.4 1.6 1.8 2.0

INPUT CURRENT vs. INPUT VOLTAGE

100

00 40 80 120 160

Typical Performance Characteristics General conditions for all curves