Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Holder TSSOP 16 EP

LT1976/LT1976B

1976bfg

■

High Voltage Power Conversion

■

14V and 42V Automotive Systems

■

Industrial Power Systems

■

Distributed Power Systems

■

Battery-Powered Systems

■

Wide Input Range: 3.3V to 60V

■

1.5A Peak Switch Current (LT1976)

■

100μA Quiescent Current (LT1976)**

■

1.6mA Quiescent Current (LT1976B)

■

Low Shutdown Current: I

< 1μA

■

Power Good Flag with Programmable Threshold

■

Load Dump Protection to 60V

■

200kHz Switching Frequency

■

Saturating Switch Design: 0.2Ω On-Resistance

■

Peak Switch Current Maintained Over

Full Duty Cycle Range*

■

1.25V Feedback Reference Voltage

■

Easily Synchronizable

■

Soft-Start Capability

■

Small 16-Pin Thermally Enhanced TSSOP Package

High Voltage 1.5A, 200kHz

Step-Down Switching Regulator

with 100μA Quiescent Current

*Protected by U.S. Patents, including 6498466

**See Burst Mode Operation section for conditions

The LT

1976/LT1976B are 200kHz monolithic step-down

switching regulators that accept input voltages up to 60V.

A high efficiency 1.5A, 0.2Ω switch is included on the die

along with all the necessary oscillator, control and logic

circuitry. Current mode topology is used for fast transient

response and good loop stability.

Innovative design techniques along with a new high volt-

age process achieve high efficiency over a wide input

range. Efficiency is maintained over a wide output current

range by employing Burst Mode operation at low currents,

utilizing the output to bias the internal circuitry, and by

using a supply boost capacitor to fully saturate the power

switch. The LT1976B does not shift into Burst Mode

operation at low currents, eliminating low frequency out-

put ripple at the expense of efficiency. Patented circuitry

maintains peak switch current over the full duty cycle

range.* Shutdown reduces input supply current to less

than 1μA. External synchronization can be implemented

by driving the SYNC pin with logic-level inputs. A single

capacitor from the C

pin to the output provides a

controlled output voltage ramp (soft-start). The devices

also have a power good flag with a programmable thresh-

old and time-out and thermal shutdown protection.

The LT1976/LT1976B are available in a 16-pin TSSOP

package with Exposed Pad leadframe for low thermal

resistance.

SHDN

BOOST

BIAS

PGFB

LT1976

4.7μF

100V

CER

330pF

0.33μF

0.1μF

33μH

4148

1μF

SYNC

GND

100μF

6.3V

TANT

OUT

3.3V

3.3V TO 60V

10MQ60N

1500pF

10k

165k

100k

1976 TA01

47pF

14V to 3.3V Step-Down Converter with

100μA No Load Quiescent Current

LT1976 Efficiency and Power

Loss vs Load Current

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (W)

3.3V

1000

1976 TA02

100

10000

100

0.1

0.01

0.001

EFFICIENCY

TYPICAL

POWER LOSS

LT1976 Supply Current vs

Input Voltage

INPUT VOLTAGE (V)

SUPPLY CURRENT (μA)

100

30 40

1976 F05

150

125

OUT

= 3.3V

= 25°C

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

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

Burst Mode is a registered trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Summary of content (28 pages)

PAGE 1
LT1976/LT1976B High Voltage 1.5A, 200kHz Step-Down Switching Regulator with 100μA Quiescent Current U FEATURES DESCRIPTIO ■ The LT®1976/LT1976B are 200kHz monolithic step-down switching regulators that accept input voltages up to 60V. A high efficiency 1.5A, 0.2Ω switch is included on the die along with all the necessary oscillator, control and logic circuitry. Current mode topology is used for fast transient response and good loop stability. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Wide Input Range: 3.3V to 60V 1.
PAGE 2
LT1976/LT1976B U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN, SHDN, PG, BIAS .............................................. 60V BOOST Pin Above SW ............................................ 35V BOOST Pin Voltage ................................................. 68V SYNC, CSS, PGFB, FB ................................................ 6V Operating JunctionTemperature Range LT1976EFE/LT1976BEFE (Note 2) ... – 40°C to 125°C LT1976IFE/LT1976BIFE (Note 2) .....
PAGE 3
LT1976/LT1976B ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full –40°C to 125°C operating temperature range, otherwise specifications are at TJ = 25°C. VIN = 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V, FB/PGFB = 1.25V, CSS/SYNC = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS IPK SW Current Limit LT1976 LT1976B MIN TYP MAX UNITS 1.5 1.2 2.4 2.5 3.5 4 A A 0.2 0.
PAGE 4
LT1976/LT1976B ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full –40°C to 140°C operating temperature range, otherwise specifications are at TJ = 25°C. VIN = 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V, FB/PGFB = 1.25V, CSS/SYNC = 0V unless otherwise noted. SYMBOL PARAMETER IPK SW Current Limit CONDITIONS MIN ● BOOST = OPEN Ω 150 200 260 kHz 90 92 1.5 230 SYNC = 0.
PAGE 5
LT1976/LT1976B U W TYPICAL PERFOR A CE CHARACTERISTICS LT1976B Efficiency and Power Loss vs Load Current LT1976 Efficiency and Power Loss vs Load Current 100 10 1.30 1.29 EFFICIENCY EFFICIENCY 0.1 TYPICAL POWER LOSS 25 EFFICIENCY (%) 50 5V 3.3V 0.1 50 TYPICAL POWER LOSS 1.27 1.26 1.25 1.24 1.23 0.01 25 0.01 POWER LOSS (W) 3.3V POWER LOSS (W) 5V 1.28 1 75 1 VOLTAGE (V) 75 EFFICIENCY (%) FB Voltage 100 10 1.22 1.21 0 0.1 0 0.1 0.
PAGE 6
LT1976/LT1976B U W TYPICAL PERFOR A CE CHARACTERISTICS PGFB Threshold Switch Peak Current Limit PG Sink Current 1.20 3.5 250 1.18 1.16 PEAK SWITCH CURRENT (A) 200 CURRENT (μA) VOLTAGE (V) 1.14 1.12 1.10 1.08 150 100 1.06 1.04 50 3.0 2.5 2.0 1.02 1.
PAGE 7
LT1976/LT1976B U W TYPICAL PERFOR A CE CHARACTERISTICS LT1976B VC Switching Threshold vs Temperature Minimum On Time 700 Boost Current vs Load Current 500 50 450 45 400 40 BOOST CURRENT (mA) 500 350 ON TIME (ns) VC VOLTAGE (V) 600 400 300 300 LOAD CURRENT = 0.5A 250 200 LOAD CURRENT = 1A 150 200 100 0 –50 –30 –10 10 30 50 70 TEMPERATURE (˚C) 5 0 90 110 6 2.5 2.0 LOAD CURRENT = 1.25A 1.5 LOAD CURRENT = 250mA 1.0 VOUT = 5V BOOST DIODE = DIODES INC. B1100 2.5 3 3.
PAGE 8
LT1976/LT1976B U W TYPICAL PERFOR A CE CHARACTERISTICS LT1976 Step Response VOUT 100mV/DIV 1A IOUT 500mA/DIV 0A TIME (1ms/DIV) VIN = 12V VOUT = 3.3V COUT = 47μF IDC = 250mA 1976 G18 U U U PI FU CTIO S NC (Pins 1, 3, 5): No Connection. Pins 1, 3, 5 are electrically isolated from the LT1976. They may be connected to PCB traces to aid in PCB layout. SW (Pin 2): The SW pin is the emitter of the on-chip power NPN switch. This pin is driven up to the input pin voltage during switch on time.
PAGE 9
LT1976/LT1976B U U U PI FU CTIO S CSS (Pin 9): A capacitor from the CSS pin to the regulated output voltage determines the output voltage ramp rate during start-up. When the current through the CSS capacitor exceeds the CSS threshold (ICSS), the voltage ramp of the output is limited. The CSS threshold is proportional to the FB voltage (see Typical Performance Characteristics) and is defeated for FB voltage greater than 0.9V (typical). See Soft-Start section in Applications Information for details.
PAGE 10
LT1976/LT1976B W BLOCK DIAGRA 4 VIN INTERNAL REF UNDERVOLTAGE LOCKOUT 10 14 15 BIAS THERMAL SHUTDOWN 2.4V SLOPE COMP Σ 200kHz OSCILLATOR + CURRENT COMP – SYNC SHDN BOOST ANTISLOPE COMP + R SHDN COMP S – SWITCH Q LATCH DRIVER CIRCUITRY SW 1.3V 9 12 CSS FB SOFT-START BURST MODE DETECT LT1976 ONLY FOLDBACK DETECT VC CLAMP 6 2 – ERROR AMP 1.25V 11 13 + VC PG PGFB 16 + PG COMP 1.12V 1.2V CT CLAMP – GND 17 7 PGND 8 CT 1976 BD Figure 1.
PAGE 11
LT1976/LT1976B W BLOCK DIAGRA power from the VIN pin, but if the BIAS pin is connected to an external voltage higher than 3V bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. High switch efficiency is attained by using the BOOST pin to provide a voltage to the switch driver which is higher than the input voltage, allowing switch to be saturated. This boosted voltage is generated with an external capacitor and diode.
PAGE 12
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO FEEDBACK PIN FUNCTIONS More Than Just Voltage Feedback The feedback (FB) pin on the LT1976 is used to set output voltage and provide several overload protection features. The first part of this section deals with selecting resistors to set output voltage and the remaining part talks about frequency foldback and soft-start features. Please read both parts before committing to a final design. The FB pin is used for more than just output voltage sensing.
PAGE 13
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO capacitive loads or high input voltages can cause a high input current surge during start-up. The soft-start function reduces input current surge by regulating switch current via the VC pin to maintain a constant voltage ramp rate (dV/dt) at the output. A capacitor (C1 in Figure 2) from the CSS pin to the output determines the maximum output dV/dt. When the feedback voltage is below 0.
PAGE 14
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO Table 3. Surface Mount Solid Tantalum Capacitor ESR and Ripple Current E CASE SIZE AVX TPS ESR MAX (Ω) RIPPLE CURRENT (A) 0.1 to 0.3 0.7 to 1.1 0.1 to 0.3 0.7 to 1.1 0.2 0.5 D CASE SIZE AVX TPS filter capacitor CF in parallel with the RC/CC network, along with a small feedforward capacitor CFB, is suggested to control possible ripple at the VC pin.
PAGE 15
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO Example: with VIN = 12V, VOUT = 3.3V, L = 33μH, ESR = 0.08Ω, ESL = 10nH: (3.3)(12 – 3.3) = 0.362A IP-P = (12)(33e − 6)(200e3) di 12 = = 3.63e5 dt 3.3e – 5 VRIPPLE = (0.362A)(0.08) + (10e – 9)(363e3) = 0.0289 + 0.003 = 32mVP-P MAXIMUM OUTPUT LOAD CURRENT Maximum load current for a buck converter is limited by the maximum switch current rating (IPK). The current rating for the LT1976 is 1.5A.
PAGE 16
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO 1. Choose a value in microhenries from the graph of maximum load current. Choosing a small inductor with lighter loads may result in discontinuous mode of operation, but the LT1976 is designed to work well in either mode. Table 4. Inductor Selection Criteria VENDOR/ PART NUMBER VALUE (μH) IRMS(A) DCR (Ω) HEIGHT (mm) UP2B-150 15 2.4 0.041 6 UP2B-330 33 1.7 0.062 6 UP2B-470 47 1.4 0.139 6 UP2B-680 68 1.2 0.179 6 UP2B-101 100 0.
PAGE 17
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO Short-Circuit Considerations The LT1976 is a current mode controller. It uses the VC node voltage as an input to a current comparator which turns off the output switch on a cycle-by-cycle basis as this peak current is reached. The internal clamp on the VC node, nominally 2.2V, then acts as an output switch peak current limit. This action becomes the switch current limit specification.
PAGE 18
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO VOUT 0.5V/DIV Example: For VOUT = 3.3V, VIN = 12V CSS = GND CSS = 0.1μF ⎛ 3.3⎞ (125μA + 12.5μA + 0..5μA) IIN( AVG) = 45μA + 5μA + ⎜ ⎟ ⎝ 12 ⎠ (0.8) CSS = 0.1μF = 45μA + 5μA + 47μA = 97μA TIME (1ms/DIV) 1976 F04 Figure 4.
PAGE 19
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO drops to 15μA. The PG pin will be active low during the “on” portion of the SHDN waveform due to the CT capacitor discharge when SHDN is taken low. See the Power Good section for further information. The effect of reverse leakage and forward drop on efficiency for various Schottky diodes is shown in Table 4.
PAGE 20
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO SHUTDOWN FUNCTION AND UNDERVOLTAGE LOCKOUT OPTIONAL VIN VIN BOOST VOUT LT1976 GND SW VBOOST – VSW = VOUT VBOOST(MAX) = VIN + VOUT (7a) VIN VIN BOOST LT1976 GND VOUT SW VBOOST – VSW = VIN VBOOST(MAX) = 2VIN (7b) VIN VIN BOOST VDC LT1976 GND VOUT SW DSS 1976 F07 VBOOST – VSW = VDC VBOOST(MAX) = VDC + VIN (7c) Figure 7. BOOST Pin Configurations A 0.33μF boost capacitor is recommended for most applications.
PAGE 21
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO LT1976 4 VIN + VIN COMP – 2.4V ENABLE R1 VOUT R3 15 R2 SHDN + SHDN COMP 3μA – 1.3V 1976 F08 Figure 8. Undervoltage Lockout See the Typical Performance Characteristics section for graphs of SHDN and VIN currents verses input voltage. SYNCHRONIZING Oscillator synchronization to an external input is achieved by connecting a TTL logic-compatible square wave with a duty cycle between 20% and 80% to the LT1976 SYNC pin.
PAGE 22
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO (ICT) from the CT pin into the external capacitor. When the voltage on the external capacitor reaches an internal clamp (VCT), the PG pin becomes a high impedance node. The VOUT 500mV/DIV PG 100k TO VIN VCT 500mV/DIV VSHDN 2V/DIV TIME (10ms/DIV) 1976 F09 Figure 9. Power Good PG at 80% VOUT with 100ms Delay resultant PG delay time is given by t = CCT • (VCT)/(ICT).
PAGE 23
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO LAYOUT CONSIDERATIONS LT1976 switch. When operating at higher currents and input voltages, with poor layout, this spike can generate voltages across the LT1976 that may exceed its absolute maximum rating. A ground plane should always be used under the switcher circuitry to prevent interplane coupling and overall noise.
PAGE 24
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO Board layout also has a significant effect on thermal resistance. Pin 8 and the exposed die pad, Pin 17, are a continuous copper plate that runs under the LT1976 die. This is the best thermal path for heat out of the package. Reducing the thermal resistance from Pin 8 and exposed pad onto the board will reduce die temperature and increase the power capability of the LT1976.
PAGE 25
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO HIGH TEMPERATURE OPERATION Extreme care must be taken when designing LT1976 applications to operate at high ambient temperatures. The LT1976H grade is designed to work at elevated temperatures but erratic operation can occur due to external components. Each passive component should be checked for absolute value and voltage ratings to ensure loop stability at temperature.
PAGE 26
LT1976/LT1976B U W U U APPLICATIO S I FOR ATIO The LT1976 uses current mode control. This alleviates many of the phase shift problems associated with the inductor. The basic regulator loop is shown in Figure 12. The LT1976 can be considered as two gm blocks, the error amplifier and the power stage. Figure 13 shows the overall loop response with a 330pF VC capacitor and a typical 100μF tantalum output capacitor.
PAGE 27
LT1976/LT1976B U TYPICAL APPLICATIO VIN 3.3V TO 60V VIN 4.7μF 100V CER 0.33μF 33μH SHDN 4148 SW 0.1μF LT1976B LT1976B Efficiency and Power Loss vs Load Current VOUT 3.3V 1A BOOST 100 10 EFFICIENCY 10MQ60N CSS 100pF 4700pF 1μF 16.5k 1% FB CT SYNC GND PGFB 10k 1% PG 100μF 6.3V TANT 1976 TA03 5V 3.3V 0.1 50 TYPICAL POWER LOSS POWER LOSS (W) 8.06k 1 75 VBIAS EFFICIENCY (%) VC 0.01 25 14V to 3.3V Non Burst Mode Step-Down Converter 0 0.1 1 100 1000 10 LOAD CURRENT (mA) 0.
PAGE 28
LT1976/LT1976B RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1074/LT1074HV 4.4A (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converters VIN: 7.3V to 45V/64V, VOUT(MIN): 2.21V, IQ: 8.5mA, ISD: 10μA, DD5/7, TO220-5/7 LT1076/LT1076HV 1.6A (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converters VIN: 7.3V to 45V/64V, VOUT(MIN): 2.21V, IQ: 8.5mA, ISD: 10μA, DD5/7, TO220-5/7 LT1676 60V, 440mA (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converter VIN: 7.4V to 60V, VOUT(MIN): 1.24V, IQ: 3.