Datasheet

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LTC3548

3548fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

■

PDAs/Palmtop PCs

■

Digital Cameras

■

Cellular Phones

■

Portable Media Players

■

PC Cards

■

Wireless and DSL Modems

High Efﬁ ciency: Up to 95%

Very Low Quiescent Current: Only 40μA

Low Output Ripple Burst Mode

Operation

2.25MHz Constant-Frequency Operation

High Switch Current: 0.7A and 1.2A

No Schottky Diodes Required

Low R

DS(ON)

Internal Switches: 0.35Ω

Current Mode Operation for Excellent Line

and Load Transient Response

Short-Circuit Protected

Low Dropout Operation: 100% Duty Cycle

Ultralow Shutdown Current: I

< 1μA

Output Voltages from 5V down to 0.6V

Power-On Reset Output

Externally Synchronizable Oscillator

Small Thermally Enhanced MSOP and 3mm × 3mm

DFN Packages

Dual Synchronous,

400mA/800mA, 2.25MHz

Step-Down DC/DC Regulator

The LTC

3548 is a dual, constant-frequency, synchronous

step down DC/DC converter. Intended for low power ap-

plications, it operates from 2.5V to 5.5V input voltage

range and has a constant 2.25MHz switching frequency,

allowing the use of tiny, low cost capacitors and inductors

with a proﬁ le ≤1mm. Each output voltage is adjustable

from 0.6V to 5V. Internal synchronous 0.35Ω, 0.7A/1.2A

power switches provide high efﬁ ciency without the need

for external Schottky diodes.

A user selectable mode input is provided to allow the user

to trade-off noise ripple for low power efﬁ ciency. Burst

Mode operation provides high efﬁ ciency at light loads,

while pulse-skipping mode provides low noise ripple at

light loads.

To further maximize battery runtime, the P-channel

MOSFETs are turned on continuously in dropout (100%

duty cycle), and both channels draw a total quiescent cur-

rent of only 40μA. In shutdown, the device draws <1μA.

Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators

RUN2 V

= 2.8V

TO 5.5V

OUT2

= 2.5V

AT 400mA

OUT1

= 1.8V

AT 800mA

RUN1

POR

SW1

FB1

GND

FB2

SW2

MODE/SYNC

LTC3548

10μF 100k

RESET

33pF68pF

2.2μH4.7μH

887k 604k

301k280k

4.7μF 10μF

3548 TA01

LOAD CURRENT (mA)

EFFICIENCY (%)

100

POWER LOSS (mW)

1000

100

0.1

10 100 1000

3548 TA02

= 3.3V, V

OUT

= 1.8V

Burst Mode OPERATION

CHANNEL 1, NO LOAD ON CHANNEL 2

POWER LOSS

EFFICIENCY

LTC3548 Efﬁ ciency Curve

L, LT, LTC, LTM, Linear Technology, the Linear logo 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 5481178, 6127815, 6304066, 6498466, 6580258

6611131..

Summary of content (16 pages)

PAGE 1
LTC3548 Dual Synchronous, 400mA/800mA, 2.25MHz Step-Down DC/DC Regulator FEATURES n n n n n n n n n n n n n n n DESCRIPTION High Efﬁciency: Up to 95% Very Low Quiescent Current: Only 40μA Low Output Ripple Burst Mode® Operation 2.25MHz Constant-Frequency Operation High Switch Current: 0.7A and 1.2A No Schottky Diodes Required Low RDS(ON) Internal Switches: 0.
PAGE 2
LTC3548 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN Voltages .................................................– 0.3V to 6V VFB1, VFB2 Voltages ...........................– 0.3V to VIN +0.3V RUN1, RUN2 Voltages ................................ – 0.3V to VIN MODE/SYNC Voltage .......................– 0.3V to VIN + 0.3V SW1, SW2 Voltage ...........................– 0.3V to VIN + 0.3V POR Voltage .................................................– 0.3V to 6V Operating Temperature Range (Note 2)....
PAGE 3
LTC3548 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.6V, unless otherwise speciﬁed. (Note 2) SYMBOL PARAMETER CONDITIONS MIN ΔVLOADREG Output Voltage Load Regulation (Note 3) 0.5 IS Input DC Supply Current Active Mode Sleep Mode Shutdown (Note 4) VFB1 = VFB2 = 0.5V VFB1 = VFB2 = 0.63V, MODE/SYNC = 3.6V RUN = 0V, VIN = 5.5V, MODE/SYNC = 0V 700 40 0.
PAGE 4
LTC3548 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise speciﬁed. Oscillator Frequency vs Temperature Efﬁciency vs Input Voltage 100 2.5 Oscillator Frequency vs Supply Voltage 10 VIN = 3.6V 8 95 FREQUENCY DEVIATION (%) 2.4 100mA FREQUENCY (MHz) 90 EFFICIENCY (%) 10mA 85 1mA 80 800mA 75 70 60 2 3 4 2.2 2.1 VOUT = 1.8V, CHANNEL 1 Burst Mode OPERATION CIRCUIT OF FIGURE 3 65 2.
PAGE 5
LTC3548 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency vs Load Current Efﬁciency vs Load Current 100 2.7V Efﬁciency vs Load Current 100 3.6V 100 95 90 4.2V EFFICIENCY (%) 80 70 60 VOUT = 2.5V, CHANNEL 1 50 Burst Mode OPERATION NO LOAD ON OTHER CHANNEL CIRCUIT OF FIGURE 3 40 1 10 100 LOAD CURRENT (mA) 95 3.6V 90 2.7V EFFICIENCY (%) 90 EFFICIENCY (%) TA = 25°C unless otherwise speciﬁed. 85 4.2V 80 75 70 1000 VOUT = 1.
PAGE 6
LTC3548 BLOCK DIAGRAM REGULATOR 1 MODE/SYNC 6 BURST CLAMP VIN SLOPE COMP 0.6V EA VFB1 ITH BURST SLEEP S – + 5Ω ICOMP + 0.35V – 1 EN – + Q RS LATCH R 0.55V – UVDET Q SWITCHING LOGIC AND BLANKING CIRCUIT UV + ANTI SHOOTTHRU 4 SW1 + OVDET – + 0.65V OV IRCMP SHUTDOWN – 11 GND VIN PGOOD1 RUN1 8 POR 2 0.
PAGE 7
LTC3548 OPERATION This decrease causes the error ampliﬁer to increase the ITH voltage until the average inductor current matches the new load current. The main control loop is shut down by pulling the RUN pin to ground. Low Current Operation By selecting MODE/SYNC (Pin 6), two modes are available to control the operation of the LTC3548 at low currents. Both modes automatically switch from continuous operation to the selected mode when the load current is low.
PAGE 8
LTC3548 APPLICATIONS INFORMATION The inductor value will also have an effect on Burst Mode operation. The transition from low current operation begins when the peak inductor current falls below a level set by the burst clamp. Lower inductor values result in higher ripple current which causes this to occur at lower load currents. This causes a dip in efﬁciency in the upper range of low current operation. In Burst Mode operation, lower inductance values will cause the burst frequency to increase. required.
PAGE 9
LTC3548 APPLICATIONS INFORMATION tantalum capacitors are all available in surface mount packages. The OS-CON semiconductor dielectric capacitor available from Sanyo has the lowest ESR (size) product of any aluminum electrolytic at a somewhat higher price. Special polymer capacitors, such as Sanyo POSCAP, Panasonic Special Polymer (SP), and Kemet A700, offer very low ESR, but have a lower capacitance density than other types.
PAGE 10
LTC3548 APPLICATIONS INFORMATION stray capacitance to cause noise problems and reduce the phase margin of the error amp loop. To improve the frequency response, a feed-forward capacitor CF may also be used. Great care should be taken to route the VFB line away from noise sources, such as the inductor or the SW line. Power-On Reset The POR pin is an open-drain output which pulls low when either regulator is out of regulation. When both output voltages are above –8.
PAGE 11
LTC3548 APPLICATIONS INFORMATION the losses in LTC3548 circuits: 1) VIN quiescent current, 2) switching losses, 3) I2R losses, 4) other losses. 1. The VIN current is the DC supply current given in the Electrical Characteristics which excludes MOSFET driver and control currents. VIN current results in a small (<0.1%) loss that increases with VIN, even at no load. 2. The switching current is the sum of the MOSFET driver and control currents.
PAGE 12
LTC3548 APPLICATIONS INFORMATION Design Example Board Layout Considerations As a design example, consider using the LTC3548 in an portable application with a Li-Ion battery. The battery provides a VIN = 2.8V to 4.2V. The load requires a maximum of 800mA in active mode and 2mA in standby mode. The output voltage is VOUT = 2.5V. Since the load still needs power in standby, Burst Mode operation is selected for good low load efﬁciency.
PAGE 13
LTC3548 APPLICATIONS INFORMATION VIN = 2.5V* TO 5.5V VIN C1 10μF RUN2 VIN VOUT2 = 2.5V* AT 400mA C3 4.7μF LTC3548 SW2 C1, C2, C3: TAIYO YUDEN JMK212BJ106MG C3: TAIYO YUDEN JMK212BJ475MG GND R1 301k RUN1 POR L1 L2 VOUT1 = 1.8V AT 800mA VOUT2 SW1 SW2 C5 R2 604k L1: MURATA LQH32CN2R2M11 L2: MURATA LQH32CN4R7M23 COUT2 VFB1 VFB2 R4 C2 10μF VOUT1 C4 VFB1 VFB2 VIN LTC3548 C4, 33pF R3 280k RUN2 MODE/SYNC SW1 C5, 68pF R4 887k CIN POWER-ON RESET L1 2.2μH POR MODE/SYNC L2 4.
PAGE 14
LTC3548 TYPICAL APPLICATIONS 1mm Proﬁle Core and I/O Supplies Efﬁciency vs Load Current VIN = 3.6V TO 5.5V 100 RUN2 VIN MODE/SYNC VOUT2 = 3.3V AT 400mA R5 100k RUN1 SW2 L1 2.2μH SW1 C5, 68pF C4, 33pF 3.3V 90 POWER-ON RESET POR LTC3548 L2 4.7μH 95 EFFICIENCY (%) C1* 10μF VOUT1 = 1.8V AT 800mA 1.8V 85 80 75 70 C3 4.
PAGE 15
LTC3548 PACKAGE DESCRIPTION MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev C) BOTTOM VIEW OF EXPOSED PAD OPTION 2.794 p 0.102 (.110 p .004) 5.23 (.206) MIN 0.889 p 0.127 (.035 p .005) 1 0.05 REF 10 DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 3.00 p 0.102 (.118 p .004) (NOTE 3) 10 9 8 7 6 DETAIL “A” 0o – 6o TYP 1 2 3 4 5 GAUGE PLANE 0.53 p 0.152 (.021 p .006) DETAIL “A” 0.18 (.007) 0.497 p 0.
PAGE 16
LTC3548 TYPICAL APPLICATION 2mm Height Lithium-Ion Single Inductor Buck-Boost Regulator and a Buck Regulator VIN = 2.8V TO 4.2V C1 10μF RUN2 VIN MODE/SYNC L2 15μH D1 VOUT2 = 3.3V AT 100mA M1 C6 22μF POWER-ON RESET L1 2.2μH POR SW1 C5, 22pF R4 887k C3 4.7μF R5 100k LTC3548 SW2 + RUN1 C1, C2: TAIYO YUDEN JMK316BJ106ML C3: MURATA GRM21BR60J475KA11B C6: KEMET C1206C226K9PAC D1: PHILIPS PMEG2010 C4, 33pF VFB1 VFB2 R3 196k VOUT1 = 1.