Datasheet

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LTC3532

3532fc

Micropower Synchronous

Buck-Boost DC/DC Converter

The LTC

3532 is a high efﬁ ciency, ﬁ xed frequency, buck-

boost DC/DC converter that operates from input voltages

above, below or equal to the output voltage. The topology

incorporated in the IC provides a continuous transfer

function through all operating modes, making the product

ideal for single lithium-ion, multicell alkaline or NiMH ap-

plications where the output voltage is within the battery

voltage range.

The device includes two 0.36Ω N-channel MOSFET

switches and two 0.42Ω P-channel switches. Switching

frequencies up to 2MHz are programmed with an external

resistor. Quiescent current is only 35μA in Burst Mode

operation, maximizing battery life in portable applica-

tions. Automatic Burst Mode operation allows the user

to program the load current for Burst Mode operation or

to control it manually.

Other features include a 1

A shutdown, soft-start control,

thermal shutdown, and peak current limit. The LTC3532 is

available in a low proﬁ le (0.75mm) 10-lead (3mm × 3mm)

DFN and 10-lead MSOP packages.

■

Miniature Hard Disk Drive Power Supply

■

MP3 Players

■

Handheld Instruments

■

Digital Cameras

■

Handheld Terminals

■

Single Inductor

■

Regulated Output with Input Voltages Above, Below

or Equal to the Output

■

Wide V

Range: 2.4V to 5.5V

■

OUT

Range: 2.4V to 5.25V

■

Up to 500mA Peak Output Current

■

Synchronous Rectiﬁ cation: Up to 95% Efﬁ ciency

■

Manual or Programmable Automatic Burst Mode

Operation

■

Output Disconnect in Shutdown

■

Programmable Oscillator: 300kHz to 2MHz

■

Pin Compatible with LTC3440

■

Small Thermally Enhanced 10-Lead (3mm × 3mm)

DFN and 10-Lead MSOP Packages

Miniature Hard Disk Drive Power Supply

APPLICATIO S

FEATURES

DESCRIPTIO

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.

SW1

SHDN/SS

BURST

SW2

OUT

GND

LTC3532

3532 TA01

43.2k

0.01μF

200k

4.7μF

Li-Ion

2.5V TO 4.2V

4.7μH

OUT

3.3V

100mA

TO 500mA

(PEAK)

10μF

33pF

1k340k

12.1k

220pF

200k

OUT

200mV/DIV

LOAD

100mA/DIV

100μs/DIV

= 3V

OUT

= 3.3V

LOAD

= 50mA TO 300mA

3532 TA01b

Summary of content (16 pages)

PAGE 1
LTC3532 Micropower Synchronous Buck-Boost DC/DC Converter DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Single Inductor Regulated Output with Input Voltages Above, Below or Equal to the Output Wide VIN Range: 2.4V to 5.5V VOUT Range: 2.4V to 5.
PAGE 2
LTC3532 W W U W ABSOLUTE AXI U RATI GS (Note 1) BURST, VIN, VOUT, VC, FB ................................... –0.3V to 6V RT ..................................................................... 0V to 5V SHDN/SS ..................................................... –0.3V to 6V SW1, SW2 DC............................................................ –0.3V to 6V Pulsed < 100ns ........................................ –0.3V to 7V Operating Temperature Range (Note 2)....
PAGE 3
LTC3532 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = VOUT = 3.6V, RT = 64.9k, unless otherwise speciﬁed. PARAMETER CONDITIONS TYP MAX PMOS Switch Leakage Switches A and D MIN 0.1 10 NMOS Switch On Resistance Switches B and C 0.36 Ω PMOS Switch On Resistance Switches A and D 0.
PAGE 4
LTC3532 U W TYPICAL PERFOR A CE CHARACTERISTICS Peak Current Clamp and Limit vs VIN 100 1.6 98 1.4 INPUT CURRENT (A) 96 94 92 90 88 86 Automatic Burst Threshold vs RBURST 70 60 1.2 LOAD CURRENT (mA) Efﬁciency vs Frequency EFFICIENCY (%) TA = 25°C, unless otherwise speciﬁed. ILIMIT 1.0 ICLAMP 0.8 0.6 40 LEAVE BURST 30 0.4 84 20 0.2 82 VIN = 3.6V VOUT = 3.3V 80 1500 500 1000 FREQUENCY (kHz) VOUT = 3.3V VIN = 3.6V VOUT = 3.3V 0 2.4 2000 3.4 5.4 4.
PAGE 5
LTC3532 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Pins Before Entering Buck Mode TA = 25°C, unless otherwise speciﬁed. Output Ripple at 100mA Load SW1 2VDIV VOUT 50mV/DIV Burst Mode, Boost VIN = 2.4V SW1 5V/DIV VIN = 3.6V SW2 5V/DIV VIN = 4.5V VOUT 100mV/DIV VOUT 50mV/DIV SW2 2VDIV VOUT 50mV/DIV 40ns/DIV INDUCTOR CURRENT 500mA/DIV 3535 G13 VIN = 4V VOUT = 3.3V ILOAD = 100mA 400ns/DIV 3535 G14 4μs/DIV 3535 G15 VIN = 2.4V VOUT = 3.3V ILOAD = 20mA COUT = 22μF VOUT = 3.
PAGE 6
LTC3532 U U U PI FU CTIO S SHDN/SS (Pin 8): Combined Soft-Start and Shutdown. Grounding this pin shuts down the IC. Tie to >1.5V to enable the IC and >2.4V to ensure the error amp is not clamped from soft-start. For Burst Mode operation, this pin must be pulled up to within 0.5V of VIN. An RC from the shutdown command signal to this pin will provide a softstart function by limiting the rise time of the VC pin. VOUT = 1.
PAGE 7
LTC3532 U OPERATIO The LTC3532 provides high efﬁciency, low noise power for applications such as portable instrumentation, digital cameras, and MP3 players. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on VC determines the output duty cycle of the switches. Since VC is a ﬁltered signal, it provides rejection of frequencies well below the switching frequency.
PAGE 8
LTC3532 U OPERATIO 88% DMAX BOOST VOUT 1– (150ns • f) V4 (≈2.05V) VIN = V3 (≈1.65V) The point at which the 4-switch region ends is given by: A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK FOUR SWITCH PWM BUCK/BOOST REGION V2 (≈1.55V) D ON, C OFF PWM AB SWITCHES BUCK REGION Boost Region (VIN < VOUT) V1 (≈0.9V) 0% DUTY CYCLE VIN = VOUT(1 – D) = VOUT(1 – 150ns • f) V 3532 F02 INTERNAL CONTROL VOLTAGE, VCI Figure 2.
PAGE 9
LTC3532 U OPERATIO VIN VOUT VIN VOUT 7 6 7 6 SW1 + L A D – 4 SW2 B C 250mA 3 SW1 – dI ≈ – VOUT L dt + L 4 SW2 B 0mA C 3532 F03 T1 5 5 GND GND Figure 3. Inductor Charge Cycle During Burst Mode Operation Note that the peak efﬁciency during Burst Mode operation is less than the peak efﬁciency during ﬁxed frequency because the part enters full-time 4-switch mode (when servicing the output) with discontinuous inductor current as illustrated in Figures 3 and 4.
PAGE 10
LTC3532 U OPERATIO be minimized. Note that if the load current applied during forced Burst Mode operation (BURST pin is grounded) exceeds the current that can be supplied, the output voltage will start to droop and the IC will automatically come out of Burst Mode operation and enter ﬁxed frequency mode, raising VOUT. Once regulation is achieved, the IC will then enter Burst Mode operation once again, and the cycle will repeat, resulting in about 4% output ripple.
PAGE 11
LTC3532 U U W U APPLICATIO S I FOR ATIO 1 RT LTC3532 2 BURST peak inductor currents in the 1A to 2A region. To minimize radiated noise, use a shielded inductor. See Table 1 for a suggested list of inductor suppliers. VC 10 FB 9 3 SW1 SHDN/SS 8 4 SW2 VIN 7 5 GND VOUT 6 Table 1. Inductor Vendor Information GND 3532 F06 Figure 6. Recommended Component Placement. Traces Carrying High Current are Direct. Trace area at FB and VC Pins are Kept Low.
PAGE 12
LTC3532 U W U U APPLICATIO S I FOR ATIO Table 2. Capacitor Vendor Information Operating Frequency Selection SUPPLIER WEB SITE AVX www.avxcorp.com Murata www.murata.com Sanyo www.sanyovideo.com Taiyo Yuden www.t-yuden.com TDK www.component.tdk.com Higher operating frequencies allow the use of a smaller inductor and smaller input and output ﬁlter capacitors, thus reducing board area and component height.
PAGE 13
LTC3532 U U W U APPLICATIO S I FOR ATIO The loop gain is typically rolled off before the RHP zero frequency. A simple Type I compensation network can be incorporated to stabilize the loop, but at a cost of reduced bandwidth and slower transient response. To ensure proper phase margin using Type I compensation, the loop must be crossed over a decade before the LC double pole. The unity-gain frequency of the error ampliﬁer with the Type I compensation is given by: the output ﬁlter.
PAGE 14
LTC3532 U TYPICAL APPLICATIO S Three Cell to 3.3V at 300mA Buck-Boost Converter With Automatic Burst Mode Operation and Soft-Start VOUT 3.3V 300mA L1 4.7μH SW1 VIN 2.7V TO 4.5V SHDN R7 200k SW2 VIN VOUT SHDN/SS BURST C4 150pF VC VC RT R6 12.1k GND C2 150pF 0.01μF C5 4.7nF 200k R9 1k FB FB LTC3532 BURST RT C1 4.7μF SW1 R1 340k SW2 C3 22μF R2 200k R4 86.6k 3532 TA02 Li-Ion to 5V Boost Converter with Output Disconnect D1 DMBRM 110LT3 L1 2.2μH SW1 VIN 2.5V TO 4.
PAGE 15
LTC3532 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN 1103 5 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.200 REF 0.25 ± 0.05 1 0.50 BSC 2.38 ±0.05 (2 SIDES) 2.38 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 16
LTC3532 U TYPICAL APPLICATIO Low Proﬁle Li-Ion to 3.3V at 300mA Converter with Automatic Burst Mode Operation VOUT 3.3V 300mA L1 2.2μH SW1 VIN 2.5V TO 4.2V SW1 SHDN/SS LTC3532 BURST RT R3 200k C1 4.7μF R9 1k VOUT VIN BURST SW2 R1 340k SW2 FB VC GND RT R4 28.7k FB C4 68pF VC R6 12.1k C2 220pF C3 10μF R2 200k C5 0.01μF L1: COILCRAFT LPO6610-222M 3532 TA04 RELATED PARTS PART NUMBER DESCRIPTION LTC3440 600mA IOUT, 2MHz, Synchronous Buck- VIN: 2.5V to 5.5V, VOUT(RANGE): 2.5V to 5.