Datasheet

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LTC3522

3522fa

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Synchronous 400mA

Buck-Boost and 200mA

Buck Converters

The LTC

3522 combines a 400mA buck-boost DC/DC con-

verter with a 200mA synchronous buck DC/DC converter in

a tiny 3mm × 3mm package. The 1MHz switching frequency

minimizes the solution footprint while maintaining high

efﬁ ciency. Both converters feature internal soft-start and

compensation, simplifying the design process.

The buck converter is current mode controlled and utilizes

an internal synchronous rectiﬁ er for high efﬁ ciency. The

buck converter supports 100% duty cycle operation to

extend battery life. If the PWM pin is held low, the buck

converter automatically transitions from Burst Mode opera-

tion to PWM mode. With the PWM pin held high, the buck

converter remains in low noise, 1MHz PWM mode.

The buck-boost converter provides continuous conduc-

tion operation to maximize efﬁ ciency and minimize noise.

At light loads, the buck-boost converter can be placed in

Burst Mode operation to improve efﬁ ciency and reduce

no-load standby current.

The LTC3522 provides a 1A shutdown mode, overtem-

perature shutdown and current limit protection on both

converters. The LTC3522 is available in a 16-pin low proﬁ le

3mm × 3mm QFN package.

■

Dual High Efﬁ ciency DC/DC Converters:

Buck-Boost (V

OUT

: 2.2V to 5.25V, I

OUT

: 400mA

for V

> 3V, V

OUT

= 3.3V)

Buck (V

OUT

: 0.6V to V

, I

OUT

: 200mA)

■

2.4V to 5.5V Input Voltage Range

■

Pin Selectable Burst Mode

Operation

■

25μA Total Quiescent Current for Both Converters in

Burst Mode Operation

■

Independent Power Good Indicator Outputs

■

Integrated Soft-Start

■

Thermal and Overcurrent Protection

■

<1µA Quiescent Current in Shutdown

■

Small 0.75mm × 3mm × 3mm QFN Package

■

Flash-Based MP3 Players

■

Medical Instruments

■

Digital Cameras

■

PDAs, Handheld PCs

■

Personal Navigation Devices

, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology

Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents, including 6404251 and 6166527.

IN1

IN2

SW2

FB2

OUT1

LTC3522

SHDN2

137k

68.1k

L1: COILCRAFT MSS6132-8.2μH

L2: COILCRAFT MSS6132-4.7μH

4.7μF

6.8μF

4.7μF

12pF

Li-Ion

4.7μH

8.2μH

OUT1

3.3V

300mA

(400mA

> 3V)

OUT2

1.8V

200mA

2.4V TO 4.2V

432k

3522 TA01a

SHDN1

PWM

SW1A

SW1B

FB1

PGOOD2

PGOOD1

PGND1 GND PGND2

OFF

PWM

BURST

(V)

2.4

EFFICIENCY (%)

5.4

3522 TA01b

3.4

4.4

100

BUCK-BOOST

OUT

= 100mA

OUT

= 3.3V

BUCK

OUT

= 100mA

OUT

= 1.8V

Efﬁ ciency vs V

Summary of content (20 pages)

PAGE 1
LTC3522 Synchronous 400mA Buck-Boost and 200mA Buck Converters FEATURES DESCRIPTION ■ The LTC®3522 combines a 400mA buck-boost DC/DC converter with a 200mA synchronous buck DC/DC converter in a tiny 3mm × 3mm package. The 1MHz switching frequency minimizes the solution footprint while maintaining high efﬁciency. Both converters feature internal soft-start and compensation, simplifying the design process. ■ ■ ■ ■ ■ ■ ■ ■ Dual High Efﬁciency DC/DC Converters: Buck-Boost (VOUT: 2.2V to 5.
PAGE 2
LTC3522 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) PGND1 SW2 SHDN2 PVIN2 TOP VIEW PVIN1, PVIN2 Voltage .................................... –0.3V to 6V SW1A, SW1B, SW2 Voltage DC............................................................ –0.3V to 6V Pulsed < 100ns ........................................... –1V to 7V Voltage, All Other Pins ................................. –0.3V to 6V Operating Temperature Range (Note 2) ... –40°C to 85°C Maximum Junction Temperature (Note 5) ............
PAGE 3
LTC3522 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. PVIN1 = PVIN2 = 3.6V, VOUT1 = 3.3V unless otherwise noted. PARAMETER CONDITIONS Maximum Duty Cycle VFB2 = 0.54V ● MIN Minimum Duty Cycle VFB2 = 0.66V ● PGOOD Threshold VFB2 Falling TYP MAX 100 –11.3 Power Good Hysteresis UNITS % –7.7 0 % –4.1 % 2.5 % Buck-Boost Converter ● Output Voltage 2.2 5.
PAGE 4
LTC3522 TYPICAL PERFORMANCE CHARACTERISTICS Buck-Boost Efﬁciency, Li-Ion to 3.3V Buck Efﬁciency, Li-Ion to 2.5V 160 100 Burst Mode OPERATION 90 80 40 60 Burst Mode POWER LOSS 30 VIN = 4.2V VIN = 2.7V 20 EFFICIENCY (%) PWM Mode 0 1 PWM Mode 60 40 100 80 50 Burst Mode POWER LOSS 40 VIN = 3.7V VIN = 4.2V L: COILCRAFT MSS6132-8.2μH 30 20 20 L: COILCRAFT MSS6132-4.7μH 0 1000 100 10 LOAD CURRENT (mA) 10 120 70 10 60 40 20 0 1000 0 1 100 10 LOAD CURRENT (mA) 3522 G02 3522 G01 L = 4.
PAGE 5
LTC3522 TYPICAL PERFORMANCE CHARACTERISTICS 0.4 0.3 0.2 0.1 0 –0.1 –0.2 –0.3 –0.4 20 40 60 80 100 120 140 TEMPERATURE (°C) Buck-Boost Maximum Load Current, Burst Mode Operation 0.5 90 0.4 80 MAXIMUM LOAD CURRENT (mA) 0.5 –0.5 –40 –20 0 Buck Feedback Voltage vs Temperature CHANGE IN FEEDBACK VOLTAGE FROM 20°C (%) CHANGE IN FEEDBACK VOLTAGE FROM 20°C (%) Buck-Boost Feedback Voltage vs Temperature 0.3 0.2 0.1 0 –0.1 –0.2 –0.3 –0.
PAGE 6
LTC3522 PIN FUNCTIONS FB2 (Pin 1): Feedback Voltage for the Buck Converter Derived from a Resistor Divider on the Buck Output Voltage. The buck output voltage is given by the following equation where R1 is a resistor between FB2 and ground and R2 is a resistor between FB2 and the buck output voltage: ⎛ R2⎞ VOUT = 0.594V ⎜1+ ⎟ ⎝ R1⎠ PWM (Pin 2): Logic Input Used to Choose Between Burst and PWM Mode Operation for Both Converters. This pin cannot be left ﬂoating.
PAGE 7
LTC3522 PIN FUNCTIONS SW1B (Pin 10): Buck-Boost Switch Node That Must be Connected to One Side of the Buck-Boost Inductor. SW1A (Pin 11): Buck-Boost Switch Node That Must be Connected to One Side of the Buck-Boost Inductor. VOUT1 (Pin 12): Buck-Boost Output Voltage Node. This pin should be connected to a low ESR output capacitor. The capacitor should be placed as close to the IC as possible and should have a short return to ground.
PAGE 8
LTC3522 BLOCK DIAGRAM 10 12 VOUT1 SW1B D A B C FILTER + – 0.85A 0.250A + – 0A + – PGND1 PGND2 IZERO 0.9V REVERSE ILIMIT SW1A FB1 1.00V PVIN2* PWM OSCILLATOR INTERNAL VCC 5 SOFT-START RAMP SHDN1 15 6 + – VOUT1 BUCK-BOOST PWM LOGIC GATE DRIVES PGOOD1 FORWARD ILIMIT 11 PVIN1* + + – 8 7 2 UVLO 14 SW2 GATE DRIVES BUCK PWM LOGIC SHDN2 16 PGND1 0A + – ZERO CROSSING 0.4A + – + 1 FB2 0.594V –gm + + 1.00V 0.594V ILIMIT SLOPE COMPENSATION 0.9V 0.
PAGE 9
LTC3522 OPERATION The LTC3522 combines a synchronous buck DC/DC converter and a 4-switch buck-boost DC/DC converter in a single 3mm × 3mm QFN package. The buck-boost converter utilizes a proprietary switching algorithm which allows its output voltage to be regulated above, below or equal to the input voltage. The buck converter provides a high efﬁciency lower voltage output and supports 100% duty cycle operation to extend battery life.
PAGE 10
LTC3522 OPERATION Soft-Start The buck converter has an internal voltage mode soft-start circuit with a nominal duration of 600μs. The converter remains in regulation during soft-start and will therefore respond to output load transients which occur during this time. In addition, the output voltage rise time has minimal dependency on the size of the output capacitor or load current. Error Ampliﬁer and Compensation The LT3522 buck converter utilizes an internal transconductance error ampliﬁer.
PAGE 11
LTC3522 OPERATION VOUT1 LTC3522 + – 1V VOUT R2 FB1 R1 GND 3522 F02 Figure 2. Buck-Boost Error Ampliﬁer and Compensation response of the compensation network. The ratio of R2 to R1 must be set to program the desired output voltage but this still allows the value of R2 to be adjusted to optimize the transient response of the converter. Increasing the value of R2 generally leads to greater stability at the expense of reduced transient response speed.
PAGE 12
LTC3522 OPERATION has minimal dependency on the size of the output capacitor or load. During soft-start, the buck-boost converter is forced into PWM operation regardless of the state of the PWM pin. PGOOD1 Comparator The PGOOD1 pin is an open-drain output which indicates the status of the buck-boost converter. In Burst Mode operation (PWM = Low), the PGOOD1 open-drain output will pull low when the output voltage falls 10% below the regulation voltage. There is approximately 2.
PAGE 13
LTC3522 APPLICATIONS INFORMATION The basic LTC3522 application circuit is shown as the typical application on the front page of this data sheet. The external component selection is determined by the desired output voltages, output currents and ripple voltage requirements of each particular application. However, basic guidelines and considerations for the design process are provided in this section.
PAGE 14
LTC3522 APPLICATIONS INFORMATION Table 3. Buck Resistor Divider Values Table 2. Buck Output Capacitor Range VOUT CMIN CMAX VOUT R1 R2 CFF 0.6V 15μF 300μF 0.6V – 0 – 0.8V 15μF 230μF 0.8V 200k 69.8k 12pF 1.2V 10μF 150μF 1.0V 118k 80.6k 12pF 1.8V 6.8μF 90μF 1.2V 100k 102k 12pF 2.7V 6.8μF 70μF 1.5V 78.7k 121k 12pF 3.3V 6.8μF 50μF 1.8V 68.1k 137k 12pF 2.7V 63.4k 226k 18pF 3.3V 60.
PAGE 15
LTC3522 APPLICATIONS INFORMATION response. If a large inductor or small output capacitor is utilized the loop will be less stable and the phase margin can be improved by increasing the value of R2. Buck-Boost Inductor Selection To achieve high efﬁciency, a low ESR inductor should be utilized for the buck-boost converter. The inductor must have a saturation rating greater than the worst case average inductor current plus half the ripple current.
PAGE 16
LTC3522 APPLICATIONS INFORMATION of inductors that are well suited to many LTC3522 buck converter applications. Table 4. Representative Surface Mount Inductors MAX MANUFACTURER PART NUMBER VALUE CURRENT Taiyo Yuden Coilcraft Sumida CooperBussmann DCR HEIGHT NP035B-4R7M 4.7μH 1.2A 0.047Ω 1.8mm NP035B-6R8M 6.8μH 1.0A 0.084Ω 1.8mm MSS6132-472ML 4.7μH 1.8A 0.056Ω 3.2mm MSS6132-822ML 8.2μH 1.35A 0.070Ω 3.2mm CDRH2D14NP4R7N 4.7μH 1.0A 0.135Ω 1.55mm CDRH2D18/ HPNP-4R7N 4.7μH 1.2A 0.110Ω 2.
PAGE 17
LTC3522 APPLICATIONS INFORMATION KELVIN TO VOUT PAD BUCK VOUT UNINTERRUPTED GROUND PLANE MUST EXIST UNDER ALL COMPONENTS SHOWN IN BOLD AND UNDER TRACES CONNECTING TO THOSE COMPONENTS PGND1 (14) SW2 (14) SW1A (11) GND (3) SW1B (10) PGOOD2 (4) PGND2 (9) MINIMIZE TRACE LENGTH BUCK-BOOST VOUT KELVIN TO VOUT PAD VIA TO GROUND PLANE PVIN1 (8) PWM (2) SHDN1 (7) VOUT1 (12) PGOOD1 (6) FB2 (1) FB1 (5) DIRECT TIE BACK TO GND PIN SHDN2 (16) MINIMIZE TRACE LENGTH PVIN2 (15) VIA TO GROUND PLANE 352
PAGE 18
LTC3522 TYPICAL APPLICATION Li-Ion to 3V at 400mA and 1.2V at 200mA VIN 2.4V TO 4.2V + C3 4.7μF Li-Ion L1 6.8μH VOUT2 1.2V 200mA 499k COMBINED PGOOD OUTPUT C1 10μF 12pF L2 4.7μH PVIN1 PVIN2 SW1A SW2 102k FB2 SW1B LTC3522 VOUT1 1M 100k VOUT1 3V 300mA C2 4.
PAGE 19
LTC3522 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ±0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1.
PAGE 20
LTC3522 TYPICAL APPLICATION 3V at 400mA and 1.8V at 200mA with Sequenced Start-Up VIN 2.4V TO 4.2V VOUT2 1.8V 200mA + C3 4.7μF Li-Ion L1 8.2μH 499k SW1A SW2 C1 6.8μF 12pF L2 4.7μH PVIN1 PVIN2 137k FB2 SW1B LTC3522 VOUT1 1M 68.1k VOUT1 3V 300mA C2 4.