Datasheet LT1308A, LT1308B Datasheet (Linear Technology)

Download

Page 1

LT1308A/LT1308B

Final Electrical Specifications

High Current, Micropower

Single Cell, 600kHz

DC/DC Converters

FEATURES

■

5V at 1A from a Single Li-Ion Cell

■

5V at 800mA in SEPIC Mode from Four NiCd Cells

■

Fixed Frequency Operation: 600kHz

■

Boost Converter Outputs up to 34V

■

Starts into Heavy Loads

■

Automatic Burst ModeTM Operation at Light Load (LT1308A)

■

Continuous Switching at Light Loads (LT1308B)

■

Low V

■

Pin-for-Pin Upgrade Compatible with LT1308

■

Lower Quiescent Current in Shutdown: 1µA (Max)

■

Improved Accuracy Low-Battery Detector

Switch: 300mV at 2A

CESAT

Reference: 200mV ±2%

APPLICATIONS

■

GSM/CDMA Phones

■

Digital Cameras

■

LCD Bias Supplies

■

Answer-Back Pagers

■

GPS Receivers

■

Battery Backup Supplies

■

Handheld Computers

August 1999

DESCRIPTION

The LT®1308A/LT1308B are micropower, fixed frequency step-up DC/DC converters that operate over a 1V to 10V input voltage range. They are improved versions of the LT1308 and are recommended for use in new designs. The LT1308A features automatic shifting to power saving Burst Mode operation at light loads and consumes just 140µA at no load. The LT1308B features continuous switching at light loads and operates at a quiescent current of 2.5mA. Both devices consume less than 1µA in shutdown.

Low-battery detector accuracy is significantly tighter than the LT1308. The 200mV reference is specified at ±2% at room and ±3% over temperature. The shutdown pin enables the device when it is tied to a 1V or higher source and does not need to be tied to VIN as on the LT1308. An internal VC clamp results in improved transient response and the switch voltage rating has been increased to 36V, enabling higher output voltage applications.

The LT1308A/LT1308B are available in the 8-lead SO and 14-lead TSSOP packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.

TYPICAL APPLICATION

C1 47µF

Li-Ion CELL

C1: AVX TAJC476M010 C2: AVX TPSD227M006 D1: IR 10BQ015

Figure 1. LT1308B Single Li-Ion Cell to 5V/1A DC/DC Converter

LBI

SHDNSHUTDOWN

L1: MURATA LQH6N4R7 *R1: 169k FOR V 887k FOR V

4.7µH

LT1308B

47k

100pF

LBO

GND

OUT

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

R1* 309k

R2 100k

= 3.3V

= 12V

5V 1A

C2 220µF

EFFICIENCY (%)

1308A/B F01

Converter Efficiency

95 90 85 80 75 70 65 60 55 50

VIN = 3.6V

VIN = 1.5V

10 100 1000

LOAD CURRENT (mA)

VIN = 4.2V

VIN = 2.5V

1308A/B F01a

Page 2

LT1308A/LT1308B

1 2 3 4

8 7 6 5

TOP VIEW

LBO LBI V

SHDN

GND

S8 PACKAGE

8-LEAD PLASTIC SO

LUTEXI TIS

WUW

ARB

(Note 1)

VIN, SHDN, LBO Voltage ......................................... 10V

SW Voltage............................................... –0.4V to 36V

FB Voltage ....................................................... VIN + 1V

VC Voltage ................................................................ 2V

LBI Voltage ................................................. –0.1V to 1V

Current into FB Pin .............................................. ±1mA

PACKAGE

TOP VIEW

SHDN

GND

F PACKAGE

14-LEAD PLASTIC TSSOP

(Note 6)

= 125°C, θJA = 80°C/W

JMAX

RDER I FOR ATIO

ORDER PART

LBO

LBI

NUMBER

LT1308ACF LT1308BCF

Operating Temperature Range

Commercial ............................................ 0°C to 70°C

Extended Commerial (Note 2) ........... –40°C to 85°C

Industrial ........................................... –40°C to 85°C

Storage Temperature Range................ –65°C to 150°C

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

ORDER PART

NUMBER

LT1308ACS8 LT1308AIS8 LT1308BCS8 LT1308BIS8

S8 PART MARKING

= 125°C, θJA = 80°C/W

JMAX

1308A 1308AI

1308B 1308BI

Consult factory for Military grade parts.

LECTRICAL C CHARA TERIST

ICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.1V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OSC

Quiescent Current Not Switching, LT1308A 140 240 µA

Feedback Voltage ● 1.20 1.22 1.24 V FB Pin Bias Current (Note 3) ● 27 80 nA Reference Line Regulation 1.1V ≤ VIN ≤ 2V ● 0.03 0.4 %/V

Minimum Input Voltage 0.92 1 V Error Amp Transconductance ∆I = 5µA60µmhos Error Amp Voltage Gain 100 V/V Switching Frequency VIN = 1.2V ● 500 600 700 kHz Maximum Duty Cycle ● 82 90 % Switch Current Limit Duty Cyle = 30% (Note 4) 2 3 4.5 A Switch V

CESAT

Burst Mode Operation Switch Current Limit VIN = 2.5V, Circuit of Figure 1 400 mA (LT1308A)

= VIN, unless otherwise noted.

SHDN

Switching, LT1308B 2.5 4 mA V

= 0V (LT1308A/LT1308B) 0.01 1 µA

SHDN

≤ 10V 0.01 0.2 %/V

2V ≤ V

ISW = 2A (25°C, 0°C), VIN = 1.5V 290 350 mV

= 2A (70°C), VIN = 1.5V 330 400 mV

Page 3

LT1308A/LT1308B

LECTRICAL C CHARA TERIST

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.1V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Shutdown Pin Current V

LBI Threshold Voltage 196 200 204 mV

LBO Output Low I LBO Leakage Current V LBI Input Bias Current (Note 5) V Low-Battery Detector Gain 3000 V/V Switch Leakage Current VSW = 5V ● 0.01 10 µA

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. Industrial Grade –40°C to 85°C. VIN = 1.2V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V I

g A f

m V

OSC

Quiescent Current Not Switching, LT1308A ● 140 240 µA

Feedback Voltage ● 1.19 1.22 1.25 V FB Pin Bias Current (Note 3) ● 27 80 nA Reference Line Regulation 1.1V ≤ VIN ≤ 2V ● 0.05 0.4 %/V

Minimum Input Voltage 0.92 1 V Error Amp Transconductance ∆I = 5µA60µmhos Error Amp Voltage Gain 100 V/V Switching Frequency ● 500 600 750 kHz Maximum Duty Cycle ● 82 90 % Switch Current Limit Duty Cyle = 30% (Note 4) 2 3 4.5 A Switch V

CESAT

Burst Mode Operation Switch Current Limit VIN = 2.5V, Circuit of Figure 1 400 mA (LT1308A)

Shutdown Pin Current V

LBI Threshold Voltage 196 200 204 mV

LBO Output Low I LBO Leakage Current V LBI Input Bias Current (Note 5) V Low-Battery Detector Gain 3000 V/V Switch Leakage Current VSW = 5V ● 0.01 10 µA

ICS

= VIN, unless otherwise noted.

SHDN

= 1.1V ● 25µA

SHDN

= 6V ● 20 35 µA

SHDN

= 0V ● 0.01 0.1 µA

SHDN

● 194 200 206 mV

= 50µA ● 0.1 0.25 V

SINK

= 250mV, V

LBI

= 150mV 33 100 nA

LBI

= VIN, unless otherwise noted.

SHDN

Switching, LT1308B V

= 0V (LT1308A/LT1308B) ● 0.01 1 µA

SHDN

2V ≤ V

≤ 10V ● 0.01 0.2 %/V

ISW = 2A (25°C, –40°C), VIN = 1.5V 290 350 mV

= 2A (85°C), VIN = 1.5V 330 400 mV

= 1.1V ● 2 5µA

SHDN

= 6V ● 20 35 µA

SHDN

= 0V 0.01 0.1 µA

SHDN

= 50µA ● 0.1 0.25 V

SINK

= 250mV, V

LBI

= 150mV 33 100 nA

LBI

= 5V ● 0.01 0.1 µA

LBO

● 2.5 4 mA

● 193 200 207 mV

= 5V ● 0.01 0.1 µA

LBO

Page 4

LT1308A/LT1308B

LECTRICAL C CHARA TERIST

ICS

Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.

Note 2: The LT1308ACS8 and LT1308BCS8 are designed, characterized and expected to meet the industrial temperature limits, but are not tested at –40°C and 85°C. I grade devices are guaranteed.

Note 3: Bias current flows into FB pin.

Note 4: Switch current limit guaranteed by design and/or correlation to

static tests. Duty cycle affects current limit due to ramp generator (see Block Diagram).

Note 5: Bias current flows out of LBI pin. Note 6: Connect the four GND pins (Pins 4–7) together at the device.

Similarly, connect the three SW pins (Pins 8–10) together and the two V pins (Pins 11, 12) together at the device.

TYPICAL PERFORMANCE CHARACTERISTICS

LT1308B

3.3V Output Efficiency

95 90 85 80 75 70

EFFICIENCY (%)

65 60 55 50

1 100 1000

VIN = 1.8V

LOAD CURRENT (mA)

VIN = 2.5V

VIN = 1.2V

1308A/B G01

LT1308A

3.3V Output Efficiency

95 90 85 80 75 70

EFFICIENCY (%)

65 60 55 50

VIN = 1.8V

1 100 1000

LOAD CURRENT (mA)

VIN = 2.5V

VIN = 1.2V

1308A/B G02

LT1308A 5V Output Efficiency

95 90

VIN = 3.6V

85 80 75 70

EFFICIENCY (%)

65 60 55 50

LOAD CURRENT (mA)

VIN = 4.2V

VIN = 1.5V

10 100 1000

VIN = 2.5V

1308A/B G03

LT1308B 12V Output Efficiency

90 85 80 75 70 65

EFFICIENCY (%)

60 55 50

1 100 1000

VIN = 5V

VIN = 3.3V

LOAD CURRENT (mA)

1308A/B G04

OUT

100mV/DIV

AC COUPLED

LOAD

LT1308A Transient Response Circuit of Figure 1

VIN = 3.6V 100µs/DIV V

= 5V

OUT

= 220µF 1308 G05

OUT

Switch Saturation Voltage vs Current

500

400

(mV)

300

CESAT

200

SWITCH V

100

0.5

SWITCH CURRENT (A)

1.0

25°C

1.5

85°C

–40°C

2.0

1308 G06

Page 5

PIN FUNCTIONS

LT1308A/LT1308B

UUU

VC (Pin 1): Compensation Pin for Error Amplifier. Connect a series RC from this pin to ground. Typical values are 47kΩ and 100pF. Minimize trace area at VC.

FB (Pin 2): Feedback Pin. Reference voltage is 1.22V. Connect resistive divider tap here. Minimize trace area at FB. Set V

according to: V

OUT

= 1.22V(1 + R1/R2).

OUT

SHDN (Pin 3): Shutdown. Ground this pin to turn off switcher. To enable, tie to 1V or more. SHDN does not need to be at VIN to enable the device.

GND (Pin 4): Ground. Connect directly to local ground plane. Ground plane should enclose all components associated with the LT1308. PCB copper connected to Pin 4 also functions as a heat sink. Maximize this area to keep chip heating to a minimum.

BLOCK DIAGRAM

OUT

R1 (EXTERNAL)

R2 (EXTERNAL)

R5 40k

R6 40k

–

ERROR

Q2 ×10

R3 30k

R4 140k

AMPLIFIER

RAMP

GENERATOR

600kHz

OSCILLATOR

Figure 2. LT1308A/LT1308B Block Diagram

*HYSTERESIS IN LT1308A ONLY

SW (Pin 5): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to keep EMI down.

VIN (Pin 6): Supply Pin. Must have local bypass capacitor right at the pin, connected directly to ground.

LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between –100mV and 1V. Low-battery detector does not function with SHDN pin grounded. If not used, float LBI pin.

LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 50µA. A 1MΩ pull-up is recommended. LBO is high impedance when SHDN is grounded.

SHDN

LBO

0.03Ω

–

1308 BD

GND

BIAS

–

COMPARATOR

–

ENABLE

200mV

SHUTDOWN

LBI

–

DRIVER

A = 3

Page 6

LT1308A/LT1308B

WUU

APPLICATIONS INFORMATION

OPERATION

The LT1308A combines a current mode, fixed frequency PWM architecture with Burst Mode micropower operation to maintain high efficiency at light loads. Operation can be best understood by referring to the block diagram in Figure

2. Q1 and Q2 form a bandgap reference core whose loop is closed around the output of the converter. When VIN is 1V, the feedback voltage of 1.22V, along with an 80mV drop across R5 and R6, forward biases Q1 and Q2’s base collector junctions to 300mV. Because this is not enough to saturate either transistor, FB can be at a higher voltage than VIN. When there is no load, FB rises slightly above

1.22V, causing VC (the error amplifier’s output) to decrease. When VC reaches the bias voltage on hysteretic comparator A1, A1’s output goes low, turning off all circuitry except the input stage, error amplifier and lowbattery detector. Total current consumption in this state is 120µA. As output loading causes the FB voltage to decrease, A1’s output goes high, enabling the rest of the IC. Switch current is limited to approximately 400mA initially after A1’s output goes high. If the load is light, the output voltage (and FB voltage) will increase until A1’s output goes low, turning off the rest of the LT1308A. Low frequency ripple voltage appears at the output. The ripple frequency is dependent on load current and output capacitance. This Burst Mode operation keeps the output regulated and reduces average current into the IC, resulting in high efficiency even at load currents of 1mA or less.

If the output load increases sufficiently, A1’s output remains high, resulting in continuous operation. When the LT1308A is running continuously, peak switch current is controlled by VC to regulate the output voltage. The switch is turned on at the beginning of each switch cycle. When the summation of a signal representing switch current and a ramp generator (introduced to avoid subharmonic oscillations at duty factors greater than 50%) exceeds the V signal, comparator A2 changes state, resetting the flip-flop and turning off the switch. Output voltage increases as switch current is increased. The output, attenuated by a resistor divider, appears at the FB pin, closing the overall loop. Frequency compensation is provided by an external series RC network connected between the VC pin and ground.

Low-battery detector A4’s open-collector output (LBO) pulls low when the LBI pin voltage drops below 200mV. There is no hysteresis in A4, allowing it to be used as an amplifier in some applications. The entire device is disabled when the SHDN pin is brought low. To enable the converter, SHDN must be at 1V or greater. It need not be tied to VIN as on the LT1308.

The LT1308B differs from the LT1308A in that there is no hysteresis in comparator A1. Also, the bias point on A1 is set lower than on the LT1308B so that switching can occur at inductor current less than 100mA. Because A1 has no hysteresis, there is no Burst Mode operation at light loads and the device continues switching at constant frequency. This results in the absence of low frequency output voltage ripple at the expense of efficiency.

The difference between the two devices is clearly illustrated in Figure 3. The top two traces in Figure 3 shows an LT1308A/LT1308B circuit, using the components indicated in Figure 1, set to a 5V output. Input voltage is 3V. Load current is stepped from 50mA to 800mA for both circuits. Low frequency Burst Mode operation voltage ripple is observed on Trace A, while none is observed on Trace B.

At light loads, the LT1308B will begin to skip alternate cycles. The load point at which this occurs can be decreased by increasing the inductor value. However, output ripple will continue to be significantly less than the LT1308A output ripple. Further, the LT1308B can be forced into micropower mode, where IQ falls from 3mA to 200µA by sinking 40µA or more out of the VC pin. This stops switching by causing A1’s output to go low.

TRACE A: LT1308A

, 100mV/DIV

OUT

AC COUPLED

TRACE B: LT1308B

, 100mV/DIV

OUT

AC COUPLED

800mA

LOAD

50mA

= 3V 200µs/DIV 1308 F03

(CIRCUIT OF FIGURE 1)

Figure 3. LT1308A Exhibits Burst Mode Operation Output Voltage Ripple at 50mA Load, LT1308B Does Not

Page 7

LT1308A/LT1308B

WUU

APPLICATIONS INFORMATION

LAYOUT HINTS

The LT1308A/LT1308B switch current at high speed, mandating careful attention to layout for proper performance.

You will not get advertised performance with careless layouts

ment for a boost (step-up) converter. Follow this closely in your PC layout. Note the direct path of the switching loops. Input capacitor C1 package. As little as 10mm of wire or PC trace from CIN to VIN will cause problems such as inability to regulate or oscillation.

The negative terminal of output capacitor C2 should tie close to Pin 4 of the LT1308A/LT1308B. Doing this reduces dI/dt in the ground copper which keeps high frequency spikes to a minimum. The DC/DC converter ground should tie to the PC board ground plane at one place only, to avoid introducing dI/dt in the ground plane.

A SEPIC (Single-Ended Primary Inductance Converter) schematic is shown in Figure 5. This converter topology produces a regulated output over an input voltage range that spans (i.e., can be higher or lower than) the output. Recommended component placement for a SEPIC is shown in Figure 6.

COMPONENT SELECTION Inductors

Suitable inductors for use with the LT1308A/LT1308B must fulfill two requirements. First, the inductor must be able to handle current of 2A steady-state, as well as support transient and start-up current over 3A without inductance decreasing by more than 50% to 60%. Second, the DCR of the inductor should have low DCR, under 0.05Ω so that copper loss is minimized. Acceptable inductance values range between 2µH and 20µH, with 4.7µH best for most applications. Lower value inductors are physically smaller than higher value inductors for the same current capability.

Table 1 lists some inductors we have found to perform well in LT1308A/LT1308B application circuits. This is not an exclusive list.

. Figure 4 shows recommended component place-

must

be placed close (<5mm) to the IC

Table 1

VENDOR PART NO. VALUE PHONE NO.

Murata LQH6C4R7 4.7µH 770-436-1300 Sumida CDRH734R7 4.7µH 847-956-0666 Coiltronics CTX5-1 5µH 561-241-7876

Capacitors

Equivalent Series Resistance (ESR) is the main issue regarding selection of capacitors, especially the output capacitors.

The output capacitors specified for use with the LT1308A/ LT1308B circuits have low ESR and are specifically designed for power supply applications. Output voltage ripple of a boost converter is equal to ESR multiplied by switch current. The performance of the AVX TPSD227M006 220µF tantalum can be evaluated by referring to Figure 4. When the load is 800mA, the peak switch current is approximately 2A. Output voltage ripple is about 60mV

, so the ESR of the output capacitor is 60mV/2A or 0.03Ω.

Ripple can be further reduced by paralleling ceramic units. Table 2 lists some capacitors we have found to perform

well in the LT1308A/LT1308B application circuits. This is not an exclusive list.

Table 2

VENDOR SERIES PART NO. VALUE PHONE NO.

AVX TPS TPSD227M006 220µF, 6V 803-448-9411 AVX TPS TPSD107M010 100µF, 10V 803-448-9411 Taiyo Yuden X5R LMK432BJ226 22µF, 10V 408-573-4150 Taiyo Yuden X5R TMK432BJ106 10µF, 25V 408-573-4150

Diodes

We have found Motorola MBRS130 and International Rectifier 10BQ015 to perform well. For applications where V

exceeds 30V, use 40V diodes such as MBRS140 or

OUT

10BQ040.

P-

Page 8

LT1308A/LT1308B

WUU

APPLICATIONS INFORMATION

LBI

GROUND PLANE

SHUTDOWN

MULTIPLE

VIAs

GND

1 2

LT1308A LT1308B

3 4

Figure 4. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize Trace Area at Pin 1 (VC) and Pin 2 (FB). Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use Vias at One Location Only to Avoid Introducing Switching Currents into the Ground Plane

LBO

8 7 6 5

OUT

1308 F04

3V TO

10V

C1 47µF

C1: AVX TAJC476M016 C2: TAIYO YUDEN EMK325BJ475(X5R) C3: AVX TPSD227M006

SHDNSHUTDOWN

Figure 5. SEPIC (Single-Ended Primary Inductance Converter) Converts 3V to 10V Input to a 5V/500mA Regulated Output

47k

L1A

CTX10-2

LT1308B

GND

680pF

D1: IR 10BQ015 L1: COILTRONICS CTX10-2

4.7µF

CERAMIC

R2 100k

309k

L1B

OUT

5V 500mA

C3 220µF

6.3V

1308A/B F05

GROUND PLANE

SHUTDOWN

MULTIPLE

VIAs

LBI

LBO

1 2

3 4

LT1308A LT1308B

8 7 6 5

L1A L1B

GND

OUT

Figure 6. Recommended Component Placement for SEPIC

1308 F06

Page 9

LT1308A/LT1308B

WUU

APPLICATIONS INFORMATION

SHDN PIN

The LT1308A/LT1308B SHDN pin is improved over the LT1308. The pin does not require tying to VIN to enable the device, but needs only a logic level signal. The voltage on the SHDN pin can vary from 1V to 10V independent of VIN. Further, floating this pin has the same effect as grounding, which is to shut the device down, reducing current drain to 1µA or less.

LOW-BATTERY DETECTOR

The low-battery detector on the LT1308A/LT1308B features improved accuracy and drive capability compared to the LT1308. The 200mV reference has an accuracy of ±2% and the open-collector output can sink 50µA. The LT1308A/ LT1308B low-battery detector is a simple PNP input gain stage with an open-collector NPN output. The negative input of the gain stage is tied internally to a 200mV reference. The positive input is the LBI pin. Arrangement as a low-battery detector is straightforward. Figure 7 details hookup. R1 and R2 need only be low enough in value so that the bias current of the LBI pin doesn’t cause large errors. For R2, 100k is adequate. The 200mV reference can also be accessed as shown in Figure 8.

A cross plot of the low-battery detector is shown in Figure 9. The LBI pin is swept with an input which varies from 195mV to 205mV, and LBO with a 100k pull-up resistor, is displayed.

START-UP

The LT1308A/LT1308B can start up into heavy loads, unlike many CMOS DC/DC converters that derive operating voltage from the output (a technique known as “bootstrapping”). Figure 10 details start-up waveforms of Figure 1’s circuit with a 20Ω load and VIN of 1.5V. Inductor current rises to 3.5A as the output capacitor is charged. After the output reaches 5V, inductor current is about 1A. In Figure 11, the load is 5Ω and input voltage is 3V. Output voltage reaches 5V 500µs after the device is enabled. Figure 12 shows start-up behavior of Figure 5’s SEPIC circuit, driven from a 9V input with a 10Ω load. The output reaches 5V in about 1ms after the device is enabled.

GSM AND CDMA PHONES

The LT1308A/LT1308B are suitable for converting a single Li-Ion cell to 5V for powering RF power stages in GSM or CDMA phones. Improvements in the LT1308A/LT1308B error amplifiers allow external compensation values to be reduced, resulting in faster transient response compared to the LT1308. The circuit of Figure 13 (same as Figure 1, printed again for convenience) provides a 5V, 1A output from a Li-Ion cell. Figure 14 details transient response at the LT1308A operating at a VIN of 4.2V, 3.6V and 3V. Ripple voltage in Burst Mode operation can be seen at 10mA load. Figure 15 shows transient response of the LT1308B under the same conditions. Note the lack of Burst Mode ripple at 10mA load.

LBI

R2 100k

BAT

Figure 7. Setting Low-Battery Detector Trip Point

–

200mV INTERNAL REFERENCE

GND

LT1308A

LT1308B

LBO

1308 F07

100k

TO PROCESSOR

R1 =

– 200mV

2µA

200k

BAT

2N3906

REF

200mV

Figure 8. Accessing 200mV Reference

10k

LBO

LBI

10µF

LT1308A LT1308B

GND

1308 F08

Page 10

LT1308A/LT1308B

WUU

APPLICATIONS INFORMATION

LBO

1V/DIV

195 200 205

Figure 9. Low-Battery Detector Input/Output Characteristic

OUT

2V/DIV

1A/DIV

SHDN

5V/DIV

(mV) 1308 F09

LBI

1ms/DIV

1308 F10

OUT

1V/DIV

2A/DIV

SHDN

5V/DIV

500µs/DIV

Figure 11. 5V Boost Converter of Figure 1. Start-Up from 3V Input into 5Ω Load

OUT

2V/DIV

2A/DIV

SHDN

5V/DIV

500µs/DIV

1308 F11

1308 F12

Figure 10. 5V Boost Converter of Figure 1. Start-Up from 1.5V Input into 20Ω Load

C1 47µF

Li-Ion CELL

C1: AVX TAJC476M010 C2: AVX TPSD227M006

Figure 13. Li-Ion to 5V Boost Converter Delivers 1A

4.7µH

LBI

SHDNSHUTDOWN

47k

D1: IR 10BQ015 L1: MURATA LQH6N4R7

LBO

LT1308B

GND

100pF

Figure 12. 5V SEPIC Start-Up from 9V Input into 10Ω Load

R1 309k

R2 100k

5V 1A

C2 220µF

1308A/B F13

Page 11

LT1308A/LT1308B

WUU

APPLICATIONS INFORMATION

OUT

VIN = 4.2V

OUT

VIN = 3.6V

OUT

VIN = 3V

LOAD

10mA

TRACES = 200µs/DIV

OUT

200mV/DIV

1308 F14

Figure 14. LT1308A Li-Ion to 5V Boost Converter Transient Response to 1A Load Step

PACKAGE DESCRIPTION

Dimensions in inches (millimeters) unless otherwise noted.

OUT

VIN = 4.2V

OUT

VIN = 3.6V

OUT

VIN = 3V

LOAD

10mA

TRACES = 100µs/DIV

OUT

200mV/DIV

1308 F15

Figure 15. LT1308B Li-Ion to 5V Boost Converter Transient Response to 1A Load Step

F Package

14-Lead Plastic TSSOP (4.4mm)

(LTC DWG # 05-08-1650)

4.30 – 4.48** (0.169 – 0.176)

° – 8°

0.09 – 0.18

(0.0035 – 0.0071)

NOTE: DIMENSIONS ARE IN MILLIMETERS

DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.152mm (0.006") PER SIDE

DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.254mm (0.010") PER SIDE

0.50 – 0.70

(0.020 – 0.028)

0.65

(0.0256)

BSC

0.18 – 0.30

(0.0071 – 0.0118)

4.90 – 5.10*

(0.193 – 0.201)

14 13 12 11 10 9

13456

6.25 – 6.50

(0.246 – 0.256)

1.10

(0.0433)

MAX

0.05 – 0.15

(0.002 – 0.006)

F14 TSSOP 1299

Page 12

LT1308A/LT1308B

TYPICAL APPLICATION

SEPIC Converts 3V to 10V Input to a 5V/500mA Regulated Output 3.3V to 12V/300mA Step-Up DC/DC Converter

4.7µF

CERAMIC

GND

D1: IR 10BQ015 L1: COILTRONICS CTX10-2

R2 100k

309k

L1B

OUT

5V 500mA

C3 220µF

6.3V

C1: AVX TAJC476M010

1308A/B F05

C2: AVX TPSD107M016 D1: IR 10BQ015

Li-Ion CELL

47µF

4.7µH

LBI

SHDNSHUTDOWN

L1: MURATA LQH6N4R7

47k

LT1308B

100pF

LBO

GND

R1 887k

C2 100µF

R2 100k

1308A/B TA01

3V TO

10V

C1 47µF

C1: AVX TAJC476M016 C2: TAIYO YUDEN EMK325BJ475(X5R) C3: AVX TPSD227M006

SHDNSHUTDOWN

L1A

CTX10-2

LT1308B

47k

680pF

PACKAGE DESCRIPTION

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

× 45°

0.016 – 0.050

(0.406 – 1.270)

0°– 8° TYP

Dimensions in inches (millimeters) unless otherwise noted.

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

TYP

(LTC DWG # 05-08-1610)

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

BSC

0.228 – 0.244

(5.791 – 6.197)

0.189 – 0.197* (4.801 – 5.004)

0.150 – 0.157** (3.810 – 3.988)

SO8 1298

12V 300mA

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1302 High Output Current Micropower DC/DC Converter 5V/600mA from 2V, 2A Internal Switch, 200µA I LT1304 2-Cell Micropower DC/DC Converter 5V/200mA, Low-Battery Detector Active in Shutdown LT1307/LT1307B Single Cell, Micropower, 600kHz PWM DC/DC Converters 3.3V at 75mA from One Cell, MSOP Package LT1316 Burst Mode Operation DC/DC with Programmable Current Limit 1.5V Minimum, Precise Control of Peak Current Limit LT1317/LT1317B Micropower, 600kHz PWM DC/DC Converters 100µA IQ, Operate with VIN as Low as 1.5V LTC®1474 Micropower Step-Down DC/DC Converter 94% Efficiency, 10µA IQ, 9V to 5V at 250mA LTC1516 2-Cell to 5V Regulated Charge Pump 12µA IQ, No Inudctors, 5V at 50mA from 3V Input LTC1522 Micropower, 5V Charge Pump DC/DC Converter Regulated 5V ±4% Output, 20mA from 3V Input LT1610 Single-Cell Micropower DC/DC Converter 3V at 30mA from 1V, 1.7MHz Fixed Frequency LT1611 Inverting 1.4MHz Switching Regulator in 5-Lead SOT-23 –5V at 150mA from 5V Input, Tiny SOT-23 package LT1613 1.4MHz Switching Regulator in 5-Lead SOT-23 5V at 200mA from 4.4V Input, Tiny SOT-23 package LT1615 Micropower Step-Up DC/DC in 5-Lead SOT-23 20µA IQ, 36V, 350mA Switch LTC1682 Doubler Charge Pump with Low Noise LDO Adjustable or Fixed 3.3V, 5V Outputs, 60µV LT1949 600kHz, 1A Switch PWM DC/DC Converter 1.1A, 0.5Ω, 30V Internal Switch, VIN as Low as 1.5V

1308abis, sn1308ab LT/TP 0899 4K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1999

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear-tech.com

Output Noise

RMS