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LTC1159

LTC1159-3.3/LTC1159-5

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Operation from 4V to 40V Input Voltage

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Ultrahigh Efficiency: Up to 95%

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A Supply Current in Shutdown

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High Efficiency Maintained Over Wide Current Range

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Current Mode Operation for Excellent Line and Load

Transient Response

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Very Low Dropout Operation: 100% Duty Cycle

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Short-Circuit Protection

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Synchronous FET Switching for High Efficiency

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Adaptive Non-Overlap Gate Drives

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Available in SSOP and SO Packages

The LTC

1159 series is a family of synchronous step-down

switching regulator controllers featuring automatic Burst

Mode

operation to maintain high efficiencies at low

output currents. These devices drive external complemen-

tary power MOSFETs at switching frequencies up to 250kHz

using a constant off-time current-mode architecture.

A separate pin and on-board switch allow the MOSFET

driver power to be derived from the regulated output

voltage providing significant efficiency improvement when

operating at high input voltages. The constant off-time

current-mode architecture maintains constant ripple cur-

rent in the inductor and provides excellent line and load

transient response. The output current level is user pro-

grammable via an external current sense resistor.

The LTC1159 automatically switches to power saving

Burst Mode operation when load current drops below

approximately 15% of maximum current. Standby current

is only 300µA while still regulating the output and shut-

down current is a low 20µA.

High Efficiency Synchronous

Step-Down Switching Regulators

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Step-Down and Inverting Regulators

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Notebook and Palmtop Computers

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Portable Instruments

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Battery-Operated Digital Devices

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Industrial Power Distribution

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Avionics Systems

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Telecom Power Supplies

Figure 1. High Efficiency Step-Down Regulator

LOAD CURRENT (A)

0.02

EFFICIENCY (%)

100

0.2 2

LTC1159 • TA01

= 10V

= 20V

FIGURE 1 CIRCUIT

LTC1159-5 Efficiency

0.15µF

CAP

P-DRIVE

EXTV

LTC1159-5

SHDN1

S-GND

P-GATE

SHDN2

SENSE

–

SENSE

P-GND

N-GATE

0.01µF

Si9410DY

0.1µF

1N4148

Si9435DY

MBRS140T3

33µH

SENSE

0.05Ω

OUT

5V/2A

OUT

220µF

100µF

100V

3.3µF

0V = NORMAL

>2V = SHUTDOWN

3300pF

300pF

LTC1159 • F01

*COILTRONICS CTX33-4-MP

Burst Mode is a trademark of Linear Technology Corporation.

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

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (20 pages)

PAGE 1
LTC1159 LTC1159-3.3/LTC1159-5 High Efficiency Synchronous Step-Down Switching Regulators U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®1159 series is a family of synchronous step-down switching regulator controllers featuring automatic Burst ModeTM operation to maintain high efficiencies at low output currents. These devices drive external complementary power MOSFETs at switching frequencies up to 250kHz using a constant off-time current-mode architecture.
PAGE 2
LTC1159 LTC1159-3.3/LTC1159-5 W W W AXI U U ABSOLUTE RATI GS (Note 1) Input Supply Voltage (Pin 2) ..................... – 15V to 60V VCC Output Current (Pin 3) .................................. 50mA Continuous Pin Currents (Any Pin) ...................... 50mA Sense Voltages ......................................... – 0.3V to 13V Shutdown Voltages ................................................... 7V EXTVCC Input Voltage .............................................
PAGE 3
LTC1159 LTC1159-3.3/LTC1159-5 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VSHDN1 = 0V (Note 3), unless otherwise noted.
PAGE 4
LTC1159 LTC1159-3.3/LTC1159-5 ELECTRICAL CHARACTERISTICS Note 6: The LTC1159C, LTC1159C-3.3, and LTC1159C-5 are not tested and not quality assurance sampled at – 40°C and 85°C. These specifications are guaranteed by design and/or correlation. The LTC1159I, LTC1159I-3.3 and LTC1159I-5 are guaranteed and tested over the – 40°C to 85°C operating temperature range. Note 7: The logic-level power MOSFETs shown in Figure 1 are rated for VDS(MAX) = 30V.
PAGE 5
LTC1159 LTC1159-3.3/LTC1159-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Current Sense Threshold Voltage Off-Time vs VOUT 160 500 70 140 60 120 400 300 200 SENSE VOLTAGE (mV) 80 OFF-TIME (µs) EXTVCC – VCC (mV) EXTVCC Switch Drop 600 50 40 30 20 100 LTC1159-5 10 MAXIMUM THRESHOLD 100 80 60 40 MINIMUM THRESHOLD 20 LTC1159-3.
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LTC1159 LTC1159-3.3/LTC1159-5 W FU CTIO AL DIAGRA Internal divider broken at VFB for adjustable versions. U U VIN SHDN2 EXTVCC VCC P-GATE CAP LOW DROPOUT 4.5V REGULATOR VCC LOW DROP SWITCH 550k P-DRIVE 550k N-GATE SENSE + SENSE – PGND – V + R Q – S C + + 25mV TO 150mV + VTH1 – VOS T 13k – VTH2 100k 1.
PAGE 7
LTC1159 LTC1159-3.3/LTC1159-5 U OPERATIO (Refer to Functional Diagram) increases, the output voltage decreases slightly. This causes the output of the gain stage to increase the current comparator threshold, thus tracking the load current. The sequence of events for Burst Mode operation is very similar to continuous operation with the cycle interrupted by the voltage comparator.
PAGE 8
LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO 1400 0.20 VOUT = 5V 0.18 1200 CT CAPACITANCE (pF) 0.16 RSENSE (Ω) 0.14 0.12 0.10 0.08 0.06 0.04 1000 800 VIN = 48V 600 VIN = 24V 400 200 VIN = 12V 0.02 0 0 0 1 3 4 2 MAXIMUM OUTPUT CURRENT (A) 5 0 50 150 100 FREQUENCY (kHz) Once the frequency has been set by CT, the inductor L must be chosen to provide no more than 0.025V/RSENSE of peak-to-peak inductor ripple current.
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LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO inductor ripple current and consequent output voltage ripple which can cause Burst Mode operation to be falsely triggered in the LTC1159. Do not allow the core to saturate! The MOSFET dissipations at maximum output current are given by: Molypermalloy (from Magnetics, Inc.) is a low loss core material for toroids, but it is more expensive than ferrite. A reasonable compromise from the same manufacturer is Kool Mµ.
PAGE 10
LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO In continuous mode, the source current of the P-channel MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: [V (V – V )]1/2 I CIN Required IRMS ≈ MAX OUT IN OUT VIN This formula has a maximum at VIN = 2VOUT, where IRMS = IMAX/2.
PAGE 11
LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO discharged bypass capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem if the load switch resistance is low and it is driven quickly. The only solution is to limit the rise time of the switch drive so that the load rise time is limited to approximately 25 • CLOAD.
PAGE 12
LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO 4. EXTVCC Connected to an External Supply. If an external supply is available in the 5V to 12V range, it may be used to power EXTVCC providing it is compatible with the MOSFET gate drive requirements. There are no restrictions on the EXTVCC voltage relative to VIN. EXTVCC may be higher than VIN providing EXTVCC does not exceed the 15V absolute maximum rating. In LTC1159N and LTC1159S applications with VOUT > 5.
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LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO the same process as in conventional applications, using either the internal divider (LTC1159-3.3, LTC1159-5) or an external divider with the adjustable version. Figure 15 in the Typical Applications shows a synchronous 12V to –12V converter that can supply up to 1A with better than 85% efficiency.
PAGE 14
LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO certain types of inductors in high current (IOUT > 5A) applications when they are lightly loaded. An external offset is put in series with the SENSE – pin to subtract from the built-in 0.025V offset. An example of this technique is shown in Figure 7. Two 100Ω resistors are inserted in series with the leads from the sense resistor.
PAGE 15
LTC1159 LTC1159-3.3/LTC1159-5 U W U U APPLICATIO S I FOR ATIO 1) Are the signal and power grounds segregated? The LTC1159 signal ground must connect separately to the (–) plate of COUT. The other ground pin(s) should return to the source of the N-channel MOSFET, anode of the Schottky diode and (–) plate of CIN, which should have as short lead lengths as possible.
PAGE 16
LTC1159 LTC1159-3.3/LTC1159-5 U TYPICAL APPLICATIO S VIN 8V TO 20V 5V 1N4148 + 1N4148 IRF7205 1 0.15µF 2 0.1µF 3 4 5 + 3.3µF 6 1000pF 7 0.047µF 8 2k P-GATE CAP VIN SHDN2 VCC EXTVCC L* 15µH 16 15 ITH VFB SENSE – SENSE + VOUT 2.5V/5A 4 3 14 + IRF7201 P-DRIVE N-GATE LTC1159 12 VCC PGND SGND 1µF WIMA RSENSE** 1 0.02Ω 2 SHUTDOWN 13 CT 47µF 25V × 2 OS-CON IRF7201 330µF 6.
PAGE 17
LTC1159 LTC1159-3.3/LTC1159-5 U TYPICAL APPLICATIO S VIN 15V TO 40V 12V + 0.33µF MPSA06 0.1µF 1N4148 1200µF 50V × 2 LXF 1N4148 SMP40P06 HEAT SINK 1µF WIMA MPSA56 1 2 0.15µF 3 P-GATE CAP VIN SHDN2 VCC EXTVCC 16 L* 22µH 15 14 + 13 P-DRIVE N-GATE LTC1159-5 5 12 VCC PGND 7 + 10µF 750pF 0.047µF 8 CT SGND ITH SHDN1 SENSE – VOUT 5V/10A 4 3 1N4148 4 6 RSENSE** 1 0.
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LTC1159 LTC1159-3.3/LTC1159-5 U TYPICAL APPLICATIO S VIN 5.5V TO 24V BAS16 + BAS16 Si9435DY 47µF 25V × 2 OS-CON Si9435DY 1µF WIMA T* 0.22µF 2 3 CAP VIN SHDN2 VCC EXTVCC 16 • 15 0V = NORMAL >2V = SHUTDOWN 14 • 4 13 P-DRIVE N-GATE LTC1159 5 12 VCC PGND + 2.2µF 6 1000pF 7 2200pF 8 CT SGND ITH VFB SENSE – 5V OUTPUT • Si9410DY + Si9410DY MBRS140T3 1µF BAS16 100k 220µF 10V × 2 AVX 11 10 56pF 24.9k 1% 0.01µF 1k 102k 1% 9 SENSE + 124k 1% 1k 100Ω + 0.
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LTC1159 LTC1159-3.3/LTC1159-5 U PACKAGE DESCRIPTIO N Package 16-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) 0.770* (19.558) MAX 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 0.255 ± 0.015* (6.477 ± 0.381) 0.130 ± 0.005 (3.302 ± 0.127) 0.300 – 0.325 (7.620 – 8.255) 0.020 (0.508) MIN 0.009 – 0.015 (0.229 – 0.381) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 0.045 – 0.065 (1.143 – 1.651) ) 0.065 (1.651) TYP 0.125 (3.175) MIN 0.018 ± 0.003 (0.457 ± 0.076) 0.100 (2.
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LTC1159 LTC1159-3.3/LTC1159-5 U TYPICAL APPLICATIO VIN = 12V Q1 Si9435 1N4148 0.1µF + 330µF 35V NICHICON 0.15µF 0.1µF 3 4 1N5818 5 6 7 5V OR 3.3V CT 390pF Q3 TP0610L SHUTDOWN 6800pF 8 CAP VIN SHDN2 EXTVCC LTC1159 P-DRIVE N-GATE VCC 3.3µF VCC CT PGND SGND VFB (SHDN1) ITH SENSE – SENSE + Q2 Si9410 16 MBRS140 15 L* 100µH 14 13 12 11 OUTPUT –12V/1A 10 200pF 10.5k Q4 2N7002 90.5k 9 1k 1000pF + 2 P-GATE + 1 150µF 16V × 2 OS-CON 20k 100Ω 510k 100Ω 3 1 5.