AS1337A-BTDT - Austriamicrosystems

AS1337

200mA, DC-DC Step-Up Converter with Buck Mode

www.austriamicrosystems.com/DC-DC_Step-Up/AS1337 Revision 1.05 1 - 15

Datasheet

1 General Description

The AS1337 is a synchronous, fixed frequency, highefficiency

DC-DC boost converter capable of supplying 3.3V @ 200mA

from two AA Cells. Compact size and minimum external parts

requirements make these devices perfect for modern portable

devices. The AS1337 offers automatic powersave mode to

increase efficiency at light loads. For input voltages higher

than VOUT the AS1337 will switch in a step down mode, so

that a Buck Boost function is realized.

The AS1337A offers a shutdown mode where the battery is

connected directly to the output enabling the supply of real-

time-clocks or memories.

In the shutdown mode of the AS1337B the battery is discon-

nected and the output is discharged.

The AS1337 offers a POK (open-drain) feature which detects

output power fail of 10%.

The AS1337 is available in a TDFN (3x3mm) 8-pin package.

2 Key Features

 Input Voltage Range: 0.65V to 4.5V

 Low Start-Up Voltage: 0.85V

 Output Voltage Range: 2.5V to 5.0V

 Delivers 200mA @ 3.3V (from two AA Cell)

 up to 97% Efficiency

 High-Speed Fixed-Frequency: 1.2MHz

 Single-Cell Operation

 Internal PMOS Synchronous Rectifier

 Automatic Powersave Operation

 Anti-Ringing Control Minimizes EMI

 Logic Controlled Shutdown (< 1µA)

 TDFN (3x3mm) 8-pin Package

3 Applications

The AS1337 is ideal for low-power applications where ultra-

small size is critical as in medical diagnostic equipment, hand-

held instruments, pagers, digital cameras, remote wireless

transmitters, MP3 players, LCD bias supplies, cordless

phones, GPS receivers, and PC cards.

Table 1. Standard Products

Model Operation Mode

AS1337A Battery Connected in Shutdown

AS1337B Battery Disconnected in Shutdown and

Output Discharged

VIN = 2xAA

1.6V to 3.6V

Figure 1. AS1337 - Ty pical Application Diagram – Dual Cell to 3.3V Synchronous Boost Converter

2x AA Cell Range

3.6V

1.6V

VOUT=3.3V

Buck Mode

Boost Mode

AS1337

COUT

22µF

4.7µH VOUT = 3.3V

GND

VIN

PGND

POK

VIN Curve

LX VOUT

Off

CIN

10µF

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AS1337

Datasheet - Pin Assignments

4 Pin Assignments

Figure 2. Pin Assignments (Top View)

Pin Descriptions

Table 2. Pin Descriptions

Pin Name Pin Number Description

VOUT 1Output Voltage. Bias is derived from VOUT when VOUT exceeds VIN. PCB trace length from

VOUT to the output filter capacitor(s) should be as short and wide as is practical.

LX 2

Switch Pin. Connect an inductor between this pin and VIN. Keep the PCB trace lengths as short

and wide as is practical to reduce EMI and voltage overshoot. If the inductor current falls to zero,

or pin EN is low , an internal 100Ω anti-ringing switch is connected from this pin to VIN to minimize

EMI.

Note: An optional Schottky diode can be connected between this pin and VOUT.

PGND 3Power Ground. Provide a short, direct PCB path between this pin and the output capacitor(s).

GND 4Ground

EN 5

Enable Pin. Logic controlled enable input.

1 = Normal operation

0 = Shutdown

Note: In a typical application, EN should be connected to VIN through a 1MΩ

pull-up resistor.

POK 6POK. High when VOUT is within regulation.

VIN 7

Input Voltage. The AS1337 gets its start-up bias from VIN unless VOUT exceeds VIN, in which

case the bias is derived from VOUT. Thus, once started, operation is completely independent

from VIN. Operation is only limited by the output power level and the internal series resistance of

the supply.

FB 8Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to this pin.

The output voltage can be adjusted from 2.5V to 5V by: VOUT = 1.23V[1 + (R1/R2)]

GND 9Exposed Pad Ground

5EN

3PGND

2LX

1VOUT

6POK

7VIN

8FB

AS1337

GND 9GND

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AS1337

Datashee t - A b s o l u t e M a x i mu m R a t i n g s

5 Absolute Maximum Ratings

Stresses beyond those listed in Table 3 may cause permanent damage to the device. These are stress ratings only, and functional operation of

the device at these or any other conditions beyond those indicated in Section 6 Electrical Characteristics on page 4 is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

Table 3. Absolute Maximum Ratings

Parameter Min Max Units Notes

Electrical Parameters

VIN to GND -0.3 5.5 V

FB to GND -0.3 5 V

All other pins to GND -0.3 6 V

Input Current (latch-up immunity) -100 100 mA Norm: JEDEC 78

Electrostatic Discharge

Human Body Model 2 kV Norm: MIL 883 E method 3015

Temperature Ranges and Storage Conditions

Storage Temperature Range -55 +150 ºC

Package Body Temperature +260 ºC

The reflow peak soldering temperature (body

temperature) specified is in accordance with IPC/

JEDEC J-STD-020 “Moisture/Reflow Sensitivity

Classification for Non-Hermetic Solid State

Surface Mount Devices”.

The lead finish for Pb-free leaded packages is

matte tin (100% Sn).

Humidity non-condensing 5 85 %

Moisture Sensitive Level 1 Represents a max. floor life time of unlimited

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AS1337

Datasheet - Electrical Characteristics

6 Electrical Characteristics

VIN

= V

= +1.2V, V

OUT

= +3.3V, Typ values @ T

AMB

= +25ºC (unless otherwise specified);

Table 4. Electrical Characteristics

Symbol Parameter Conditions Min Typ Max Units

TAMB Operating Temperature Range -45 +85 °C

Input

Minimum Start-Up Voltage ILOAD = 1mA 0.85 1.15 V

Minimum Operating Voltage EN = VIN 1

1. Minimum VIN operation after start-up is only limited by the battery’s ability to provide the necessary power as it enters a deeply dis-

charged state.

0.65 0.85 V

VIN Maximum Input Voltage 4.5 V

Output Voltage Adjust Range 2.5 5 V

Regulation

VFB Feedback Voltage 1.192 1.23 1.268 V

IFB Feedback Input Current VFB = 1.25V 1 nA

Operating Current

IQPWS Quiescent Current VFB = 1.4V 2

2. IQPWS is measured at VOUT. Multiply this value by VOUT/VIN to get the equivalent input (battery) current.

Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality

Control) methods.

20 35 µA

ISHDN Shutdown Current EN = GND, VIN = 3.3V 0.01 1 µA

Switches

INMOSSWL NMOS Switch Leakage 0.01 1 µA

IPMOSSWL PMOS Switch Leakage AS1337B only 0.01 1 µA

RONNMOS NMOS Switch On Resistance VOUT = 3.3V 0.35 Ω

VOUT = 5V 0.20

RONPMOS PMOS Switch On Resistance VOUT = 3.3V 0.45 Ω

VOUT = 5V 0.30

INMOS NMOS Current Limit 850 mA

Max Duty Cycle VFB = 1V 80 87 %

fSW Switching Frequency 0.95 1.2 1.5 MHz

Shutdown

VIH Enable Input Threshold 1V

VIL 0.3

IEN EN Input Current EN = 5.0V 0.01 1 µA

Power-OK

POK Voltage Low IPOK=1mA 0.1 0.4 V

POK Leakage Current VPOK = VIN or VOUT 1 100 nA

Power-OK Threshold Falling Edge 86 88 91 %

Thermal Protection

TENM Overtemperature Protection 145 ºC

ΔTENM Overtemperature Protection Hysteresis 10 ºC

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AS1337

Datasheet - Typical Operating Characteristics

7 Typical Operating Characteristics

VOUT = 3.3V, CIN = 10µF, COUT = 22µF, L1 = 4.7µH, TAMB = +25°C (unless otherwise specified).

Figure 3. Efficiency vs. IOUT - Down Conversion Mode Figure 4. Efficiency vs. IOUT - Step-up Mode

100

0.1 1 10 100 1000

Out put Curr ent ( mA)

Efficiency (%)

Vin = 3.5V

Vi n = 4.0V

100

0.1 1 10 100 1000

Output Current (mA )

Efficiency (%)

Vin = 1.5V

Vi n = 2.0V

Vi n = 3.0V

Figure 5. Efficiency vs. Input Voltage Figure 6. Output Current vs. Input Voltage

100

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Input Voltage ( V)

Efficiency (%)

Iou t = 1m A

Iou t = 10m A

Iou t = 30mA

Iou t = 100mA

Iout = 200mA 0

100

200

300

400

500

0.5 1 1.5 2 2.5 3 3.5 4 4.5

Input Voltage ( V)

Output Current (mA)

Figure 7. Min. Operating Voltage vs. Temperature Figure 8. Switching Frequency vs. Temperature

0.35

0.45

0.55

0.65

0.75

0.85

-45 -30 -15 0 15 30 45 60 75 90

T emperat ur e ( °C)

Minim um Operating Voltage (V )

0.9

1.1

1.2

1.3

1.4

1.5

-45 -30 -15 0 15 30 45 60 75 90

Temperat ur e (°C)

Switching F requency (MHz

)

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AS1337

Datasheet - Typical Operating Characteristics

Figure 9. Output Voltage vs. Temp.; ILOAD = 1mA Figure 10. Load Transient Response; VIN = 1.8V

3.1

3.15

3.2

3.25

3.3

3.35

3.4

3.45

3.5

-45 -30 -15 0 15 30 45 60 75 90

T emperat ur e ( °C)

Out put Voltage ( V )

1ms/Div

VOUT

IOUT

100mV/Div

10mA 100mA

Figure 11. Load Transient Response; VIN = 3.0V Figure 12. Load Transient Response; VIN = 3.6V

1ms/Div

VOUT

IOUT

100mV/Div

10mA 100mA

1ms/Div

VOUT

IOUT

100mV/Div

10mA 100mA

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AS1337

Datasheet - Detailed Description

8 Detailed Description

The AS1337 can operate from a single-cell input voltage (VIN) below 1V, and features fixed frequency (1.2MHz) and current mode PWM control

for exceptional line- and load-regulation. With low RDS(ON) and gate charge internal NMOS and PMOS switches, the device maintains high-effi-

ciency from light to heavy loads.

Modern portable devices frequently spend extended time in low-power or standby modes, switching to high power-drain only when certain func-

tions are enabled. The AS1337 is ideal for portable devices since it maintains high-power conversion efficiency over a wide output power range,

thus increasing battery life in these types of applications.

In addition to high-efficiency at moderate and heavy loads, the AS1337 includes an automatic powersave mode that improves efficiency of the

power converter at light loads. The powersave mode is initiated if the output load current falls below a factory programmed threshold.

The Overtemperature protection circuitry turn-off both switches for a short time when the temperature reaches 145ºC in the device .

Figure 13. AS1337 - Bl ock Diagram

AS1337

–

Start Up

OSC

PWM

Control

A/B

MUX

Slope

Compensator

1.2MHz

Ramp

Generator

–

Powersave

Operation

Control

–

Shutdown

Control

PWM

Comp

–

1.23V

Ref

Sync Drive

Control

VOUT

Good

2.3V

gm Error

Amp

Shutdown

Powersave

0.35Ω0.45Ω

330kΩ

560kΩ

CFF*

COUT

4.7µF

3.3V

Output

CIN

1µF

1.5V

Single

Cell

* Optional

Current

Sense

80kΩCP2

2.5pF

150pF

PGND

VIN 1

VOUT

4.7µH

POK

GND

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AS1337

Datasheet - Detailed Description

Low-Voltage Start-Up and Soft Start

The AS1337 requires a VIN of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the internal switches and provides

a soft start function, where the inductor current during start up is limited for a certain time. This soft start and in rush current limitation feature pro-

vides also a smooth curve of VOUT after start up and makes the overshoot of VOUT minimal. To achieve this, a 100pF capacitor as CFF is

needed (see Figure 13 on page 7) to speed up the feedback loop.

After a certain time a bigger inductor current is allowed and the soft start is disabled.

Low-Noise Fixed-Frequency Operation

Oscillator

The AS1337 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components.

Current Sensing

A signal representing the internal NMOS-switch current is summed with the slope compensator. The summed signal is compared to the error

amplifier output to provide a peak current control command for the PWM. Peak switch current is limited to approximately 850mA independent of

VIN or VOUT.

Zero Current Comparator

The zero current comparator monitors the inductor current to the output and shuts off the PMOS synchronous rectifier once this curren t d r ops t o

20mA (approx.). This prevents the inductor current from reversing polarity and results in improved converter efficiency at light loads.

Anti-Ringing Control

Anti-ringing control circuitry prevents high-frequency ringing on pin LX as the inductor current approaches zero. This is accomplished by damp-

ing the resonant circuit formed by the inductor and the capacitance on pin LX.

Setting Output Voltage

A voltage divider from VOUT to GND programs the output voltage from 2.5V to 5V via pin FB as:

VOUT = 1.23V(1 + (R1/R2)) (EQ 1)

Powersave Operation

In light load conditions, the integrated powersave feature removes power from all circuitry not required to monitor VOUT. When VOUT has

dropped approximately 1% from nominal, the AS1337 powers up and begins normal PWM operation.

COUT (see Figure 13 on page 7) recharges, causing the AS1337 to re-enter powersave mode as long as the output load remains below the pow-

ersave threshold. The frequency of this intermittent PWM is proportional to load current; i.e., as the load current drops further below the power-

save threshold, the AS1337 turns on less frequently. When the load current increases above the powersave threshold, the AS1337 will resume

continuous, seamless PWM operation.

Note: An optional capacitor (CFF) between pins VOUT and FB in some applications can reduce VOUTp-p ripple and input quiescent current

during powersave mode. Typical values for CFF range from 15pF to 220pF.

Buck Mode

Both devices, the AS1337A and the AS1337B, offer a low power buck mode for VIN > VOUT operation. The switching during buck mode is simi-

lar to boost mode, but with forced reduction of some energy internal to be able to provide a buck conversion.

Shutdown

When pin EN is low the AS1337 is switched off and <1µA current is drawn from battery; when pin EN is high the device is switched on. If EN is

driven from a logic-level output, the logic high-level (on) should be referenced to VOUT to avoid intermittently switching the device on.

Note: If pin EN is not used, it should be connected directly to pin VOUT.

Caution: Because of the feedthrough the out put voltage is the same as the input voltage during shutdown. If VIN >

VOUT the output voltage will jump to the value of the input voltage when the device switches into shutdown.

During normal operation the device is in down conve r sion mode.

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AS1337

Datasheet - Detailed Description

Shutdown Battery Feedthrough (AS1337A)

In shutdown the battery input of the AS1337A is connected to the output through the inductor and the small internal synchronous rectifier P-FET.

This allows the input battery to provide backup power for devices such as an idle microcontroller, memory, or real-time-clock, without the usual

diode forward drop. In this way a separate backup battery is not needed.

Shutdown Battery Disconnect (AS1337B)

The AS1337B is designed to allow true output disconnect by opening both P-channel MOSFET rectifiers. During Shutdown VOUT is discharged

via the internal NMOS transistor and connected to GND.

POK Function

The POK output indicates if the output voltage is within 88% (typ.) of the nominal voltage level. As long as the output voltage is within regulation

the open-drain POK output is high impedance. The POK output can be tied to VIN or to VOUT or to any external voltage up to VIN or VOUT via a

pull-up resistance (see Figure 1 on page 1). If the output voltage drops below 88% (typ.) of the nominal voltage the POK pin is pulled to GND.

Note: It is important to consider that in shutdown mode the POK output is pulled to VIN in order to save current.

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AS1337

Datasheet - Application Information

9 Application Information

The AS1337 is perfectly suited for LED matrix displays, bar-graph displays, instrument-panel meters, dot matrix displays, set-top boxes, white

goods, professional audio equipment, medical equipment, industrial controllers to name a few applications.

Along with Figure 1 on page 1, Figure 14 and Figure 15 depict a few of the many applications for which the AS1337 converters are perfectly

suited.

Figure 14. Single AA Cell to 3.3V Synchronous Boost Converter

Figure 15. Single Lithium Cell to 5V

VIN = 1.5V

AS1337

COUT

22µF

4.7µH VOUT = 3.3V

GND

VIN

PGND

POK

VOUT

Off

CIN

10µF

560kΩ

330kΩ

Lithium-Ionen Cell

AS1337

COUT

22µF

4.7µH VOUT = 5.0V

GND

VIN

PGND

POK

VOUT

Off

CIN

10µF

680kΩ

220kΩ

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AS1337

Datasheet - Application Information

Component Selection

Only three power components are required to complete the design of the buck-boost converter , except the additional two resistors for the voltage

divider to set VOUT. The high operating frequency and low peak currents of the AS1337 allow the use of low value, low profile inductors and tiny

external ceramic capacitors.

Inductor Selection

The inductor should have low ESR to reduce the I²R power losses, and must be able to handle the peak inductor current without saturating.

High-frequency ferrite core inductor materials reduce frequency dependent power losses compared to less expensive powdered iron types,

which result in improved converter efficiency.

A 4.7µH to 15µH inductor value with a >850mA current rating and low DCR is recommended. For applications where radiated noise is a con-

cern, a toroidal or shielded inductor can be used.

Capacitor Selection

A 10µF capacitor is recommend for CIN as well as a 22µF for COUT. Small-sized ceramic capacitors are recommended. X5R and X7R ceramic

capacitors are recommend as they retain capacitance over wide ranges of voltages and temperatures.

Output Capacitor Selection

Low ESR capacitors should be used to minimize VOUT ripple. Multi-layer ceramic capacitors are recommended since they have extremely low

ESR and are available in small footprints. A 1 to 10µF output capacitor is sufficient for most applications. Larger values up to 22µF ma y be used

to obtain extremely low output voltage ripple and improve transient response.

An additional phase lead capacitor may be required with output capacitors larger than 10µF to maintain acceptable phase margin. X5R and X7R

dielectric materials are recommended due to their ability to maintain capacitance over wide voltage and temperature ranges.

Input Capacitor Selection

Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. Ceramic capacitors are recom-

mended for input decoupling and should be located as close to the device as is practical. A 4.7µF input capacitor is sufficient for most applica-

tions. Larger values may be used without limitations.

PCB Layout Guidelines

The high-speed operation of the AS1337 requires proper layout for optimum performance.

 A large ground pin copper area will help to lower the device temperature.

 A multi-layer board with a separate ground plane is recommended.

 Traces carrying large currents should be direct.

 Trace area at pin FB should be as small as is practical.

 The lead-length to the battery should be as short as is practical.

Table 5. Recommended External Components

Name Part Number Value Rating Type Size Manufacturer

CIN GRM219R60J106KE19 10µF 6.3V X5R 0805 Murata

www.murata.com

COUT GRM21BR60J226ME39 22µF 6.3V X5R 0805

L1 MOS6020-472ML 4.7µH 1.82A 50mΩ6.8x6.0x2.4mm Coilcraft

www.coilcraft.com

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AS1337

Datasheet - Package Drawings and Markings

10 Package Drawings and Markings

Figure 16. TDFN (3x3mm) 8-pin Marking

Table 6. Packaging Code YYWWIZZ

YY WW QZZ

last two digits of the current year manufacturing week plant identifier free choice / traceability code

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AS1337

Datasheet - Package Drawings and Markings

Figure 17. TDFN (3x3mm) 8-pin Package

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AS1337

Datasheet - Ordering Info rmation

11 Ordering Information

The device is available as the standard products listed in Table 7.

Note: All products are RoHS compliant and Pb-free.

Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect

For further information and requests, please contact us mailto:sales@austriamicrosystems.com

or find your local distributor at http://www.austriamicrosystems.com/distributor

Table 7. Ordering Information

Ordering Code Marking Descriptiom Delivery Form Package

AS1337A-BTDT ASSE 200mA, DC-DC Step-Up Converter with Buck Mode;

Battery Connect in Shutdown Tape and Reel TDFN (3x3mm) 8-pin

AS1337B-BTDT ASSF 200mA, DC-DC Step-Up Converter with Buck Mode;

Battery Disconnect in Shutdown and Output Discharged Tape and Reel TDFN (3x3mm) 8-pin

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AS1337

Datasheet

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Disclaimer

Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale.

austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding

the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at

any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for

current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range,

unusual environmental requirements, or high reliability applications, such as military, medical life-support or life-sustaining equipment are

specifically not recommended without additional processing by austriamicrosystems AG for each application. For shipments of less than 100

parts the manufacturing flow might show deviations from the standard production flow, such as test flow or test location.

The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However, austriamicrosystems AG shall not

be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use,

interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing,

performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of

austriamicrosystems AG rendering of technical or other services.

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