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LTC3535

3535fa

TYPICAL APPLICATION

DESCRIPTION

Dual Channel 550mA 1MHz

Synchronous Step-Up

DC/DC Converter

The LTC

3535 is a dual channel, synchronous, ﬁxed fre-

quency step-up DC/DC converter with output disconnect.

Extended battery life in single AA/AAA powered products

is realized with a 680mV start-up voltage and operation

down to 500mV once started.

A switching frequency of 1MHz minimizes solution foot-

print by allowing the use of tiny, low proﬁle inductors

and ceramic capacitors. The current mode PWM design

is internally compensated, reducing external parts count.

The LTC3535 features Burst Mode operation at light load

conditions allowing it to maintain high efﬁciency over a

wide range of load. Anti-ring circuitry reduces EMI by

damping the inductor in discontinuous mode. Additional

features include a low shutdown current of under 1µA and

thermal shutdown.

The LTC3535 is housed in a 3mm × 3mm × 0.75mm

DFN package.

Efﬁciency vs Load Current

FEATURES

APPLICATIONS

Medical Instruments

Noise Canceling Headphones

Energy Harvesting

Bluetooth Headsets

Two Independent Step-Up Converters

Each Channel Delivers 3.3V at 100mA from a Single

Alkaline/NiMH Cell or 3.3V at 200mA from Two Cells

Start-Up Voltage: 680mV

1.5V to 5.25V V

OUT

Range

Up to 94% Efﬁciency

Output Disconnect

1MHz Fixed Frequency Operation

> V

OUT

Operation

Integrated Soft-Start

Current Mode Control with Internal Compensation

Burst Mode

Operation with 9µA I

Each Channel

Internal Synchronous Rectiﬁer

Logic Controlled Shutdown (I

< 1µA)

Anti-Ring Control

Low Proﬁle (3mm × 3mm × 0.75mm)

12-Lead DFN Package

LOAD CURRENT (mA)

0.01

EFFICIENCY (%)

1000

3535 TA01b

0.1 1

100

OUT

= 3.3V

= 1.2V

OUT

= 1.8V

3535 TA01

OFF ON

4.7µH

0.8V

TO 1.5V

OUT1

1.8V

100mA

OUT2

3.3V

50mA

10µF

511k

2.2µF

4.7µH

1.78M

SW1

IN1

LTC3535

OUT1

OUT2

FB1

FB2

SW2GND GND

SHDN1

IN2

SHDN2

L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

Summary of content (16 pages)

PAGE 1
LTC3535 Dual Channel 550mA 1MHz Synchronous Step-Up DC/DC Converter DESCRIPTION FEATURES n n n n n n n n n n n n n n n Two Independent Step-Up Converters Each Channel Delivers 3.3V at 100mA from a Single Alkaline/NiMH Cell or 3.3V at 200mA from Two Cells VIN Start-Up Voltage: 680mV 1.5V to 5.
PAGE 2
LTC3535 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW VIN1, VIN2 Voltage.......................................... –0.3V to 6V SW1, SW2 Voltage DC............................................................. –0.3V to 6V Pulsed <100ns.......................................... –0.3V to 7V SHDN1, SHDN2, FB1, FB2 Voltage................ –0.3V to 6V VOUT1, VOUT2................................................. –0.3V to 6V Operating Temperature Range (Notes 2, 5).................................
PAGE 3
LTC3535 ELECTRICAL CHARACTERISTICS (For each channel) The l denotes the specifications which apply over the specified operating temperature range of –40°C to 85°C, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted. PARAMETER CONDITIONS Minimum Duty Cycle VFB = 1.3V MIN TYP MAX 0.75 1 1.25 0 l Switching Frequency UNITS l SHDN Pin Input High Voltage % MHz 0.8 V SHDN Pin Input Low Voltage 0.
PAGE 4
LTC3535 TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted. Efficiency vs Load Current and VIN for VOUT = 5V 100 10 50 POWER LOSS 40 30 1 VIN = 1.2V VIN = 2.4V VIN = 3.6V VIN = 4.2V 20 10 0 0.01 0.1 VOUT = 1.8V 1000 250 200 VOUT = 5V 150 100 100 0.1 50 0 0.5 0.01 1000 1 10 100 LOAD CURRENT (mA) L = 4.7µH 1.0 1.5 2.0 2.5 3.0 3.5 VOUT = 1.8V L = 4.7µH LOAD CURRENT (mA) 80 60 50 40 30 40 LEAVE BURST 20 ENTER BURST 15 10 20 5 10 2.0 2.5 3.
PAGE 5
LTC3535 TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted. Oscillator Frequency Change vs Temperature RDS(ON) vs VOUT 0.90 10 0.85 8 0.80 0.65 PMOS 0.60 0.55 0.50 0.45 NMOS 0.40 4 2 0 –2 –4 –6 0.30 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 5.0 4.5 –10 –50 –30 –10 10 30 50 TEMPERATURE (°C) 1.0 0.9 70 0.7 –50 90 0.80 10.0 0.25 0.75 9.5 0 0.70 1mA LOAD –0.25 0.65 NO LOAD 0.60 8.0 –0.75 0.55 7.5 80 100 0.
PAGE 6
LTC3535 TYPICAL PERFORMANCE CHARACTERISTICS (Each Channel) TA = 25°C, unless otherwise noted. Load Step Response (from Burst Mode Operation) Load Step Response (Fixed Frequency) VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED LOAD CURRENT 50mA/DIV LOAD CURRENT 50mA/DIV VIN = 3.6V 100µs/DIV VOUT = 5V 20mA TO 170mA STEP COUT = 10µF 3535 G19 VIN = 3.
PAGE 7
LTC3535 PIN FUNCTIONS VOUT1 (Pin 1): Output Voltage Sense and Drain of the Internal Synchronous Rectifier for Channel 1. PCB trace length from VOUT1 to the output filter capacitor (4.7µF minimum) should be as short and wide as possible. SW1 (Pin 2): Switch Pin for Channel 1. Connect inductor between SW1 and VIN1. Keep PCB trace lengths as short and wide as possible to reduce EMI.
PAGE 8
LTC3535 BLOCK DIAGRAM VIN1 0.8V TO 5V L1 4.7µH CIN 2.2µF 10 2 VIN1 SW1 VOUT VSEL VBEST WELL SWITCH VB VOUT1 VOUT1 1.5V TO 5.25V 1 ANTI-RING 11 SHDN1 SHUTDOWN SHUTDOWN GATE DRIVERS AND ANTI-CROSS CONDUCTION FB1 – + 4M Σ IPK UVLO IZERO IZERO COMP CLK1 1MHz OSC R1 ERROR AMP SLEEP COMP START-UP LOGIC COUT1 10µF SLOPE COMP + – IPK COMP VREF1 VREF R2 12 + – MODE CONTROL VREF CLAMP 5 VIN2 0.8V TO 5V CIN2 2.2µF TSD THERMAL SHUTDOWN L2 4.
PAGE 9
LTC3535 OPERATION (Refer to Block Diagram) The LTC3535 is a dual channel 1MHz synchronous boost converter housed in a 12-lead 3mm × 3mm DFN package. Each channel is identical and fully independent. They can operate from the same source, or from different voltage sources. In addition, their output voltages can be tied together to allow operation of a single output from two different input sources.
PAGE 10
LTC3535 OPERATION (Refer to Block Diagram) the test mode being engaged. Refer to Figure 1 for two possible implementations. LTC3535 Zero Current Comparator LTC3535 VIN 4M ±30% 4M ±30% SHDN R SHDN 3535 F01 VCNTRL 1M R > (VCNTRL/VIN + 0.4) – 1)MΩ independent of input or output voltage, unless VOUT falls below 0.7V, in which case the current limit is cut in half. ZETEX ZC2811E 1M VCNTRL Figure 1.
PAGE 11
LTC3535 OPERATION (Refer to Block Diagram) Burst Mode OPERATION Each channel of the LTC3535 will enter Burst Mode operation at light load current and return to fixed frequency PWM mode when the load increases. Refer to the Typical Performance Characteristics to see the output load Burst Mode threshold current vs VIN. The load current at which Burst Mode operation is entered can be changed by adjusting the inductor value.
PAGE 12
LTC3535 APPLICATIONS INFORMATION COMPONENT SELECTION Table 1. Recommended Inductors Inductor Selection The LTC3535 can utilize small surface mount chip inductors due to their fast 1MHz switching frequency. Inductor values between 3.3µH and 6.8µH are suitable for most applications. Larger values of inductance will allow slightly greater output current capability (and lower the Burst Mode threshold) by reducing the inductor ripple current.
PAGE 13
LTC3535 APPLICATIONS INFORMATION 4.7µF to 10µF output capacitor is sufficient for most applications. Larger values may be used to obtain extremely low output voltage ripple and improve transient response. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Y5V types should not be used. Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery.
PAGE 14
LTC3535 PACKAGE DESCRIPTION DC Package 12-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1725 Rev A) 0.70 ± 0.05 3.50 ± 0.05 2.10 ± 0.05 2.38 ± 0.05 1.65 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 2.25 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ± 0.10 (4 SIDES) R = 0.115 TYP 7 0.40 ± 0.10 12 2.38 ± 0.10 1.65 ± 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 ± 0.05 6 1 0.23 ± 0.
PAGE 15
LTC3535 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 9/10 Updated Applications section 1 Updated Pin Configuration 2 Updated Note 6 3 Updated Pins 3, 6 and 13 text 7 Updated Shutdown section 9, 10 Corrected CHOLD capacitor value in Typical Application 13 Added new Typical Application and Updated Related Parts table 16 3535fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 16
LTC3535 TYPICAL APPLICATION 3.3V Converter Operates from a Single Cell or from Harvested Thermal Energy, as Low as 1°C ∆T TEG FERROTEC 9500/127/100B COILCRAFT LPR6235-752SML T1 1:100 47µF • COILCRAFT XFL4020-472 4.7µH SINGLE AAA CELL 1nF C1 • VSTORE + VOUT2_EN 330pF C2 LTC3108 VOUT 2.35V PEAK SW D1A + C1 1.5mF SHDN1 VIN2 VOUT1 3.3V VOUT2 10µF LTC3535 FB2 1M 4.7µH 1µF 1µF 3535 TA03 COILCRAFT XFL4020-472 D1B GND 1.78M 30.1k SHDN2 VLDO VOUT FB1 2.