Datasheet

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LTC3407

3407fa

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Dual Synchronous, 600mA,

1.5MHz Step-Down

DC/DC Regulator

The LTC

3407 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 1.5MHz switching frequency,

allowing the use of tiny, low cost capacitors and inductors

2mm or less in height. Each output voltage is adjustable

from 0.6V to 5V. Internal synchronous 0.35Ω, 1A 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 ripple noise for low power efﬁ ciency. Burst

Mode

operation provides high efﬁ ciency at light loads,

while pulse-skipping mode provides low ripple noise at

light loads.

To further maximize battery life, the P-channel MOSFETs

are turned on continuously in dropout (100% duty cycle),

and both channels draw a total quiescent current of only

40μA. In shutdown, the device draws <1μA.

LTC3407 Efﬁ ciency Curve

High Efﬁ ciency: Up to 96%

Very Low Quiescent Current: Only 40μA

1.5MHz Constant Frequency Operation

High Switch Current: 1A on Each Channel

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

PDAs/Palmtop PCs

Digital Cameras

Cellular Phones

Portable Media Players

PC Cards

Wireless and DSL Modems

Figure 1. 2.5V/1.8V at 600mA Step-Down Regulators

RUN2 V

= 2.5V

TO 5.5V

OUT2

= 2.5V

AT 600mA

OUT1

= 1.8V

AT 600mA

RUN1

POR

SW1

FB1

GND

FB2

SW2

MODE/SYNC

LTC3407

10μF

100k

RESET

C4, 22pFC5, 22pF

2.2μH

887k

442k

280k

10μF

3407 TA01

C1, C2, C3: TAIYO YUDEN JMK316BJ106ML L1, L2: MURATA LQH32CN2R2M33

LOAD CURRENT (mA)

EFFICIENCY (%)

100

10 100 1000

3407 TA02

= 3.3V

Burst Mode OPERATION

NO LOAD ON OTHER CHANNEL

2.5V

1.8V

L, LT, LTC, LTM, Burst Mode, Linear Technology 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
LTC3407 Dual Synchronous, 600mA, 1.5MHz Step-Down DC/DC Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n High Efﬁciency: Up to 96% Very Low Quiescent Current: Only 40μA 1.5MHz Constant Frequency Operation High Switch Current: 1A on Each Channel No Schottky Diodes Required Low RDS(ON) Internal Switches: 0.
PAGE 2
LTC3407 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 Ambient Operating Temperature Range (Note 2) ...............
PAGE 3
LTC3407 ELECTRICAL CHARACTERISTICS The l 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 IS Input DC Supply Current Active Mode Sleep Mode Shutdown MIN VFB1 = VFB2 = 0.5V VFB1 = VFB2 = 0.63V, MODE/SYNC = 3.6V RUN = 0V, VIN = 5.5V, MODE/SYNC = 0V fOSC Oscillator Frequency VFBX = 0.
PAGE 4
LTC3407 TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency vs Temperature Efﬁciency vs Input Voltage Oscillator Frequency vs Supply Voltage 1.70 100 1.8 TA = 25°C FREQUENCY (MHz) 85 1.60 10mA 1mA OSCILLATOR FREQUENCY (MHz) 100mA 90 EFFICIENCY (%) TA = 25°C 1.65 95 600mA 80 75 1.55 1.50 1.45 70 1.40 65 VOUT = 1.8V CIRCUIT OF FIGURE 1 60 4 5 2 3 INPUT VOLTAGE (V) 1.35 1.30 –50 –25 6 50 25 75 0 TEMPERATURE (°C) 100 1.5 1.4 1.3 1.2 125 2 RDS(ON) vs Input Voltage VIN = 3.
PAGE 5
LTC3407 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency vs Load Current Efﬁciency vs Load Current 100 95 3.3V 3.3V 2.7V 0.3 4.2V 80 75 70 VOUT ERROR (%) EFFICIENCY (%) 90 85 VOUT = 1.8V IOUT = 200mA TA = 25°C 0.4 95 2.7V 90 EFFICIENCY (%) Line Regulation 0.5 100 4.2V 85 80 75 70 0.2 0.1 0 –0.1 –0.2 –0.3 65 VOUT = 1.2V Burst Mode OPERATION CIRCUIT OF FIGURE 1 60 1 10 100 LOAD CURRENT (mA) 1000 65 VOUT = 1.
PAGE 6
LTC3407 BLOCK DIAGRAM REGULATOR 1 MODE/SYNC 6 BURST CLAMP VIN SLOPE COMP 0.6V EA VFB1 SLEEP ITH – + 5Ω ICOMP + 0.35V – 1 EN – + BURST S 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
LTC3407 OPERATION 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 Two modes are available to control the operation of the LTC3407 at low currents. Both modes automatically switch from continuous operation to to the selected mode when the load current is low. To optimize efﬁciency, the Burst Mode operation can be selected.
PAGE 8
LTC3407 APPLICATIONS INFORMATION 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. Inductor Core Selection Different core materials and shapes will change the size/ current and price/current relationship of an inductor.
PAGE 9
LTC3407 APPLICATIONS INFORMATION capacitors, such as Sanyo POSCAP, offer very low ESR, but have a lower capacitance density than other types. Tantalum capacitors have the highest capacitance density, but it has a larger ESR and it is critical that the capacitors are surge tested for use in switching power supplies. An excellent choice is the AVX TPS series of surface mount tantalums, available in case heights ranging from 2mm to 4mm.
PAGE 10
LTC3407 APPLICATIONS INFORMATION ⎛ R2 ⎞ VOUT = 0.6V ⎜1+ ⎟ ⎝ R1 ⎠ Keeping the current small (<5μA) in these resistors maximizes efﬁciency, but making them too small may allow 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.
PAGE 11
LTC3407 APPLICATIONS INFORMATION produce the most improvement. Percent efﬁciency can be expressed as: %Efﬁciency = 100% - (L1 + L2 + L3 + ...) where L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, 4 main sources usually account for most of the losses in LTC3407 circuits: 1)VIN quiescent current, 2) switching losses, 3) I2R losses, 4) other losses.
PAGE 12
LTC3407 APPLICATIONS INFORMATION the regulator operating in a 70°C ambient temperature is approximately: TJ = 2 • 0.153 • 45 + 70 = 84°C which is below the absolute maximum junction temperature of 125°C. Design Example As a design example, consider using the LTC3407 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 600mA in active mode and 2mA in standby mode. The output voltage is VOUT = 2.5V.
PAGE 13
LTC3407 TYPICAL APPLICATIONS Low Ripple Buck Regulators Using Ceramic Capacitors VIN = 2.5V TO 5.5V C1 10μF RUN2 VIN RUN1 R5 100k POWER-ON RESET POR C3 10μF LTC3407 L2 4.7μH L1 4.7μH SW2 SW1 C5, 22pF R4 887k C4, 22pF R3 442k VOUT1 = 1.2V AT 600mA VFB1 VFB2 MODE/SYNC R2 R1 604k 604k GND C1, C2, C3: TAIYO YUDEN JMK316BJ106ML L1, L2: MURATA LQH32CN4R7M11 C2 10μF 3407 TA03 Efﬁciency 100 95 VOUT = 1.8V 90 EFFICIENCY (%) VOUT2 = 1.8V AT 600mA 85 VOUT = 1.2V 80 75 70 65 60 VIN = 3.
PAGE 14
LTC3407 TYPICAL APPLICATIONS 2mm Height Core Supply VIN = 3.6V TO 5.5V C1 10μF RUN2 VIN MODE/SYNC VOUT2 = 3.3V AT 600mA C3 10μF SW2 POWER-ON RESET POR LTC3407 L2 4.7μH R5 100k RUN1 L1 2.2μH SW1 C5, 22pF R4 887k C4, 22pF VFB1 VFB2 R3 196k VOUT1 = 1.8V AT 600mA R2 R1 604k 301k GND C1, C2, C3: TAIYO YUDEN JMK316BJ106ML L1: MURATA LQH32CN2R2M33 L2: MURATA LQH32CN4R7M11 C2 10μF 3407 TA07 Efﬁciency vs Load Current 100 3.3V 95 EFFICIENCY (%) 90 1.
PAGE 15
LTC3407 PACKAGE DESCRIPTION DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev B) R = 0.125 TYP 0.40 ± 0.10 6 10 5 1 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN REV B 0309 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.200 REF 0.25 ± 0.05 1.65 ± 0.10 (2 SIDES) 0.50 BSC 2.38 ±0.05 (2 SIDES) 2.38 ±0.10 (2 SIDES) 0.00 – 0.
PAGE 16
LTC3407 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 R5 100k POWER-ON RESET POR LTC3407 L2 10μH D1 VOUT2 = 3.3V AT 200mA RUN1 L1 2.