Datasheet

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LTC3445

3445fa

Buck Regulator

■

High Efficiency: Up to 93%

■

600mA Output Current (V

CC1

= 3V, V

OUT

= 1.3V)

■

Programmable Output Voltage: 0.85V to 1.55V

■

2.5V to 5.5V Input Voltage Range

■

1.5MHz Constant Frequency or Spread Spectrum

Option

■

Soft-Start

LDOs

■

Two LDO Regulators: 0.3V Dropout at 50mA

PowerPath Controller

■

Dynamically Regulates V

BATT

■

Standard (100kHz) or Fast Mode (400kHz)

■

24-Lead (4mm × 4mm) QFN Package

C Controllable

Buck Regulator with Two LDOs

in a 4mm × 4mm QFN

■

Intel’s Microprocessor Supply (PXA27X)

■

Portable Instruments

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

The LTC

3445 contains a high efficiency monolithic syn-

chronous current mode buck regulator, two LDO regula-

tors, a PowerPath

controller and an I

interface.

The buck regulator has a 6-bit programmable output range

of 0.85V to 1.55V. Also, the buck regulator uses either a

constant (1.5MHz) or a spread spectrum switching fre-

quency. Using the spread spectrum option allows for a

lower noise regulated output as well as low noise at the

input. In addition, the regulated output voltage slew rate is

programmable via the I

C interface.

The LTC3445 contains two LDO voltage regulators. The

regulator output voltages are externally resistor program-

mable. Each LDO is capable of delivering up to 50mA.

The LTC3445 contains control circuitry (PowerPath) for

automatic back-up battery selection. V

BACKUP

is typically

a coin cell.

Typical supply current during operation is only 360µA and

drops to 27µA in shutdown. The 2.5V to 5.5V input

voltage range makes the LTC3445 ideal for single Li-Ion

battery-powered applications. Automatic Burst Mode

operation increases efficiency at light loads, further ex-

tending battery life.

Burst Mode is a registered trademark of Linear Technology Corporation.

PowerPath is a trademark of Linear Technology Corporation.

C is a trademark of Philips Electronics N.V.

Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815, 6498466,

6611131, Spread Spectrum patent pending.

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

2.2µH

705k

604k

4.7µF

CER

4.7µF

CER

10µF

CER

1.3V

0.85V

TO 1.55V

TYP

CC2

GND

LTC3445

CC1

nBATT_FAULT

CC1

BATTFAULT

4.7µF

CER

BATT

TRACK

COIN

CELL

BACKUP

LDO1

LDO1FB

LDO2

LDO2FB

RUN

SDA

C BUS

PWR_EN

CC1

OR GND

CC1

OR GND

SCL

ADD7

ADD6

PGOOD

_FAULT

20k

3445 TA01

503k

604k

10µF

CER

1.1V

BACKUP

20k

BACKUP

Efficiency and Power Loss

vs Load Current, V

CC1

= 3.6V

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (mW)

100

0.1 10 100 1000

3445 TA01b

DAC MAX

DAC MIN

DAC MAX

100

1000

1.0

0.1

EFFICIENCY

POWER LOSS

Summary of content (24 pages)

PAGE 1
LTC3445 I2C Controllable Buck Regulator with Two LDOs in a 4mm × 4mm QFN U FEATURES DESCRIPTIO Buck Regulator ■ High Efficiency: Up to 93% ■ 600mA Output Current (V CC1 = 3V, VOUT = 1.3V) ■ Programmable Output Voltage: 0.85V to 1.55V ■ 2.5V to 5.5V Input Voltage Range ■ 1.5MHz Constant Frequency or Spread Spectrum Option ■ Soft-Start LDOs ■ Two LDO Regulators: 0.
PAGE 2
LTC3445 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO LDO1FB LDO1 VCC2 LDO2 LDO2FB TOP VIEW 24 23 22 21 20 19 VTRACK 1 18 VCC BATT VBACKUP 2 17 FB VCC1 3 16 NC 25 PGOOD 4 15 RUN 13 NC NC 9 10 11 12 GND 8 VCC1 7 ADD6 14 SW SDA 6 NC ADD7 5 SCL VCC1, VCC2, SDA, SCL Voltages .................. – 0.3V to 6V RUN, VTRACK, VBACKUP, PGOOD, ADD7, ADD6, FB, VCC BATT, BATTFAULT Voltages .............................. – 0.3V to VCC1 SW Voltage ............................
PAGE 3
LTC3445 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC1 = VCC2 = 3.6V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS IS Additional Input DC Bias Current For Buck (Note 4) Active Mode VOUT = 90%, ILOAD = 0A Sleep Mode VOUT = 103%, ILOAD = 0A MIN TYP MAX µA µA 220 6 ● 1.2 1.5 300 UNITS fOSC Nominal Oscillator Frequency VOUT = 100% VOUT = 0V 1.
PAGE 4
LTC3445 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC1 = VCC2 = 3.6V, unless otherwise noted.
PAGE 5
LTC3445 U W TYPICAL PERFOR A CE CHARACTERISTICS 100 1000 100 90 EFFICIENCY 80 80 50 10 DAC MAX 40 POWER LOSS 30 1.0 20 DAC MIN 10 DAC MAX 1 50 10 30 DAC MAX 20 1 VCC2 LEAKAGE CURRENT (µA) BUCK OUTPUT (V) 1.540 1.520 1.500 1.480 100 0.700 –100 500 700 300 LOAD CURRENT (mA) 0.6 0.4 0.2 –10 30 70 110 TEMPERATURE (°C) 0.8 0.6 0.4 0.
PAGE 6
LTC3445 U W TYPICAL PERFOR A CE CHARACTERISTICS Buck (DAC = Min) 100mA to 300mA Load Step Slew Rates DAC Min to DAC Max Buck (DAC = Max) 100mA to 400mA Load Step BUCK VOLTAGE 50mV/DIV BUCK VOLTAGE 50mV/DIV 200mV/DIV LOAD CURRENT 100mA/DIV LOAD CURRENT 100mA/DIV 100µs/DIV 20µs/DIV 3445 G13 Buck Switching Frequency vs VCC1 Buck Switching Frequency vs Temperature 1.56 1.52 1.48 1.44 Soft-Start (DAC = Min and Max) 4.7Ω Load 2.5 3.5 4.5 5.5 1.540 BUCK OUTPUTS 500mV/DIV 1.520 1.500 1.
PAGE 7
LTC3445 U W TYPICAL PERFOR A CE CHARACTERISTICS LDO Reference Voltage vs Load Current LDO Reference Voltage vs Temperature 0.604 0mA 0.598 0.596 0.594 0.592 0.590 1.202 1.201 0.606 LDO OUTPUT VOLTAGE (V) LDO REFERENCE VOLTAGE (V) 0.600 0.604 VCC2 = 2.5V 0.602 VCC2 = 5.5V 0.600 0.598 0 25 50 75 100 125 150 TEMPERATURE (°C) 1.200 1.199 10mA 1.198 50mA 1.197 1.196 1.195 0.596 0 10 20 30 40 50 60 LOAD CURRENT (mA) 70 80 1.194 2.5 3.1 3.7 4.
PAGE 8
LTC3445 U U U PI FU CTIO S VTRACK (Pin 1): Supply Sense that VCC BATT Tracks when above 3V. Must be ≤ VCC1. NC (Pin 13): Not Connected. VBACKUP (Pin 2): Back-Up Battery Input. RUN (Pin 15): Chip Enable. 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. In shutdown, all functions are disabled, drawing <35µA supply current. Do not leave RUN floating. Must be ≤ VCC1. VCC1 (Pins 3, 10): Power Supply (2.5V to 5.5V). Both VCC1 pins must be connected externally to the 2.5V to 5.
PAGE 9
LTC3445 W FU CTIO AL DIAGRA S U U VCC CIN1 3 10 VCC1 VCC1 PWR_EN 15 6 8 VCC1 OR GND VCC1 OR GND 5 9 RUN SDA SCL ADD7 ADD6 I2C VREF DAC STRAPPABLE STRAPPABLE SLEW CONTROL BUCK REGULATOR SOFT-START VOUT CONTROL 0.
PAGE 10
LTC3445 W FU CTIO AL DIAGRA S U U VCC1 VFB PEAK CURRENT LEVEL REFERENCE EA RS VREF ICOMP OSC S Q R QB PFET L SW LOGIC L BURST NFET IRCOMP 3445 F02 Figure 2.
PAGE 11
LTC3445 WU W TI I G DIAGRA SDA tSU(DAT) tSU(STA) tHD(DAT) tLOW tBUF tHD(STA) tSUSTO 3445 TD SCL tHIGH tHD(STA) tr tf START CONDITION REPEATED START CONDITION STOP CONDITION START CONDITION I2C Fast Mode Timing Specifications (for Reference) SYMBOL PARAMETER fI2C(MAX) Maximum I2C Operating Frequency MIN tBUF Bus Free Time Between Stop and Start Condition 1.3 µs tHD(RSTA) Hold Time After (Repeated) Start Condition 0.6 µs tSU(RSTA) Repeated Start Condition Setup Time 0.
PAGE 12
LTC3445 U OPERATIO (refer to Figure 1) Burst Mode Operation 1400 1300 In Burst Mode operation, the peak current of the inductor is set to approximately 200mA regardless of the output load. Each burst event can last from a few cycles at light loads to almost continuous cycling with short sleep intervals at moderate loads. In between these burst events, the power MOSFETs and any nonessential circuitry are turned off, reducing the buck regulator’s quiescent current to 6µA.
PAGE 13
LTC3445 U OPERATIO (refer to Figure 1) SPR = 00 (Spread Spectrum OFF) NOISE 10dBm/DIV SPR = 10 NOISE 10dBm/DIV START FREQ: 100kHz, RBW: 10kHz, STOP FREQ: 30MHz START FREQ: 100kHz, RBW: 10kHz, STOP FREQ: 30MHz SPR = 01 SPR = 11 NOISE 10dBm/DIV NOISE 10dBm/DIV START FREQ: 100kHz, RBW: 10kHz, STOP FREQ: 30MHz START FREQ: 100kHz, RBW: 10kHz, STOP FREQ: 30MHz Figure 4. LTC3445 Output Noise Spectrum micro-steps. The table below shows the register settings and corresponding slew rates.
PAGE 14
LTC3445 U OPERATIO (refer to Figure 1) When VCC1 rises above 2.8V, the PowerPath’s LDO is enabled and set to the lesser of 3V or VCC1. Once VTRACK is 3V or higher, it controls the PowerPath’s LDO output (VCC BATT) voltage to within 200mV of VTRACK. Note that VTRACK needs to be less than or equal to VCC1. When VTRACK falls below 3V, VCC1 is used to regulate the PowerPath’s LDO (VCC BATT) to 3V. When VCC1 falls below 2.4V, the PowerPath LDO is disconnected and VBACKUP is connected to VCC BATT.
PAGE 15
LTC3445 U OPERATIO (refer to Figure 1) be able to control the data line to acknowledge communications from the master, and some devices will need to able to send data back to the master; they will be in control of the data line while they are doing so. Many slave devices will have no need to stretch the clock signal and will have no ability to pull the clock line low, which is the case with the LTC3445. The START and STOP Conditions When the bus is not in use, both SCL and SDA must be high.
PAGE 16
LTC3445 U OPERATIO (refer to Figure 1) data line is also left high by the slave and master after a slave has transmitted a byte of data to the master in a read operation, but this is a not-acknowledge that indicates that the data transfer is successful.
PAGE 17
LTC3445 U W U U APPLICATIO S I FOR ATIO BUCK REGULATOR The basic LTC3445 application circuit is shown on the first page of this data sheet. External component selection is driven by the load requirement and begins with the selection of L followed by CIN and COUT. Table 1 MANUFACTURER PART NUMBER Inductor Selection For most applications, the value of the inductor will fall in the range of 1µH to 4.7µH. Its value is chosen based on the desired ripple current.
PAGE 18
LTC3445 U W U U APPLICATIO S I FOR ATIO where f = operating frequency, COUT = output capacitance and ∆IL = ripple current in the inductor. For a fixed output voltage, the output ripple is highest at maximum input voltage since ∆IL increases with input voltage. that any DAC settings above 48 defaults to the 48 setting. The DAC controls the VOUT range of 0.85V to 1.55V in ~15mV steps. The default value for VOUT is 1.35V and is reset to this value whenever VCC1 comes up.
PAGE 19
LTC3445 U W U U APPLICATIO S I FOR ATIO 1000 Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to (∆ILOAD • ESR), where ESR is the effective series resistance of COUT. ∆ILOAD also begins to charge or discharge COUT, which generates a feedback error signal.
PAGE 20
LTC3445 U W U U APPLICATIO S I FOR ATIO prevent oscillations. The LTC3445 LDOs are micropower devices and output transient response will be a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide improved transient response for larger load current changes. PowerPath CONTROLLER The PowerPath circuitry in the LTC3445 is used to provide backup power from VBACKUP to the VCC BATT pin when VCC1 is low or disconnected. When VCC1 is below 2.
PAGE 21
LTC3445 U W U U APPLICATIO S I FOR ATIO As an example, consider the LTC3445 in dropout at an input voltage of 2.7V, an ambient temperature of 70°C, a buck load current of 600mA, LDO1 set to 1.3V with a load of 25mA, LDO2 set to 1.1V with a load of 15mA, and the PowerPath regulator at 2.5V with a load of 6µA. From the typical performance graph of switch resistance, the RDS(ON) of the P-channel switch at 70°C is approximately 0.52Ω.
PAGE 22
LTC3445 U W U U APPLICATIO S I FOR ATIO DESIGN EXAMPLE The buck regulator’s maximum load requirement for this application is 300mA. Although the default start-up voltage for the buck regulator is 1.35V, ripple current is greatest when the output voltage is programmed to 0.85V. For ripple currents of 200mA and the main battery at 4.2V, the required inductor value is 2.2µH (Equation 1). For best efficiency choose a 400mA or greater inductor with less than 0.3Ω series resistance.
PAGE 23
LTC3445 U PACKAGE DESCRIPTIO UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 4.50 ± 0.05 2.45 ± 0.05 3.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.23 TYP R = 0.115 (4 SIDES) TYP 23 24 0.75 ± 0.05 0.38 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 2.45 ± 0.10 (4-SIDES) (UF24) QFN 1103 0.200 REF 0.00 – 0.05 0.25 ± 0.05 0.50 BSC NOTE: 1.
PAGE 24
LTC3445 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1761 100mA, Low Noise Micropower, LDO VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, Dropout Voltage = 0.30V, IQ = 20µA, ISD < 1µA, VOUT = Adj, 1.5V, 1.8V, 2V, 2.5V, 2.8V, 3V, 3.3V, 5V, ThinSOTTM Package. Low Noise < 20µVRMS(P-P), Stable with 1µF Ceramic Capacitors LT1762 150mA, Low Noise Micropower, LDO VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, Dropout Voltage = 0.30V, IQ = 25µA, ISD < 1µA, VOUT = Adj, 2.5V, 3V, 3.3V, 5V, MS8 Package.