Datasheet

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LTC3407-2

34072fc

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.

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Dual Synchronous, 800mA,

2.25MHz Step-Down

DC/DC Regulator

The LTC

3407-2 is a dual, constant-frequency, synchro-

nous step down DC/DC converter. Intended for low power

applications, 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 ≤1.2mm. Each output voltage is adjustable

from 0.6V to 5V. Internal synchronous 0.35Ω, 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 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.

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

High Efﬁ ciency: Up to 95%

Very Low Quiescent Current: Only 40μA

2.25MHz Constant-Frequency Operation

High Switch Current: 1.2A 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

LTC3407-2 Efﬁ ciency Curve

RUN2 V

= 2.5V*

TO 5.5V

OUT2

= 2.5V

AT 800mA

OUT1

= 1.8V

AT 800mA

RUN1

POR

SW1

FB1

GND

FB2

SW2

MODE/SYNC

LTC3407-2

10μF

100k

RESET

C4, 22pFC5, 22pF

2.2μH

887k

604k

301k

280k

10μF

3407 TA01

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

OUT

CONNECTED TO V

FOR V

b 2.8V

LOAD CURRENT (mA)

EFFICIENCY (%)

100

10 100 1000

3407 TA02

= 3.3V

Burst Mode OPERATION

NO LOAD ON OTHER CHANNEL

2.5V

1.8V

Summary of content (16 pages)

PAGE 1
LTC3407-2 Dual Synchronous, 800mA, 2.25MHz 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 95% Very Low Quiescent Current: Only 40μA 2.25MHz Constant-Frequency Operation High Switch Current: 1.2A on Each Channel No Schottky Diodes Required Low RDS(ON) Internal Switches: 0.
PAGE 2
LTC3407-2 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.
PAGE 3
LTC3407-2 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 TYP MAX UNITS VFB Feedback Voltage (Note 3) 0°C ≤ TA ≤ 85°C –40°C ≤ TA ≤ 85°C –40°C ≤ TA ≤ 125°C (Note 2) 0.588 0.585 0.585 0.6 0.6 0.6 0.612 0.612 0.612 V V V ΔVLINE REG Reference Voltage Line Regulation VIN = 2.5V to 5.5V (Note 3) 0.3 0.
PAGE 4
LTC3407-2 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 1mA 85 FREQUENCY (MHz) 10mA 800mA 80 75 70 60 2 4 3 2.3 2.2 2.1 VOUT = 1.8V Burst Mode OPERATION CIRCUIT OF FIGURE 1 65 FREQUENCY DEVIATION (%) 100mA 90 EFFICIENCY (%) 2.4 2.0 –50 –25 5 100 VIN = 3.6V –6 2 0.605 400 0.595 0.
PAGE 5
LTC3407-2 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency vs Load Current Efﬁciency vs Load Current Line Regulation 100 100 0.5 95 95 0.4 2.7V EFFICIENCY (%) 85 90 80 75 4.2V 85 4.2V 80 75 1000 VOUT = 1.5V Burst Mode OPERATION 65 NO LOAD ON OTHER CHANNEL CIRCUIT OF FIGURE 1 60 1 10 100 LOAD CURRENT (mA) 3407 G13 VOUT = 1.8V IOUT = 200mA TA = 25°C 0.3 70 70 VOUT = 1.2V Burst Mode OPERATION 65 NO LOAD ON OTHER CHANNEL CIRCUIT OF FIGURE 1 60 1 10 100 LOAD CURRENT (mA) 3.6V 2.
PAGE 6
LTC3407-2 BLOCK DIAGRAM REGULATOR 1 MODE/SYNC 6 BURST CLAMP VIN SLOPE COMP 0.6V + ITH EA VFB1 EN – SLEEP – 1 – + 57 ICOMP + 0.35V BURST S Q RS LATCH R 0.55V – Q UV UVDET SWITCHING LOGIC AND BLANKING CIRCUIT + OV IRCMP OVDET – 0.65V 4 SW1 + + ANTI SHOOTTHRU – 11 GND SHUTDOWN PGOOD1 RUN1 2 RUN2 9 0.
PAGE 7
LTC3407-2 OPERATION Low Current Operation Two modes are available to control the operation of the LTC3407-2 at low currents. Both modes automatically switch from continuous operation to the selected mode when the load current is low. To optimize efﬁciency, the Burst Mode operation can be selected. When the load is relatively light, the LTC3407-2 automatically switches into Burst Mode operation, in which the PMOS switch operates intermittently based on load demand with a ﬁxed peak inductor current.
PAGE 8
LTC3407-2 APPLICATIONS INFORMATION 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. Toroid or shielded pot cores in ferrite or permalloy materials are small and do not radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics.
PAGE 9
LTC3407-2 APPLICATIONS INFORMATION fer very low ESR, but have a lower capacitance density than other types. Tantalum capacitors have the highest capacitance density, but they have 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
LTC3407-2 APPLICATIONS INFORMATION 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 feedforward 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
LTC3407-2 APPLICATIONS INFORMATION Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3407-2 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.
PAGE 12
LTC3407-2 APPLICATIONS INFORMATION Design Example As a design example, consider using the LTC3407-2 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. First, calculate the inductor value for about 40% IOUT(MAX) at maximum VIN: 2.5V 2.
PAGE 13
LTC3407-2 TYPICAL APPLICATIONS Low Ripple Buck Regulators Using Ceramic Capacitors VIN = 2.5V TO 5.5V C1 10MF RUN2 VIN R5 100k RUN1 POWER-ON RESET POR C3 10MF SW2 L1 4.7MH SW1 C5, 22pF C4, 22pF VFB2 R4 887k R3 442k MODE/SYNC C1, C2, C3: TAIYO YUDEN JMK316BJ106ML VOUT1 = 1.2V AT 800mA VFB1 GND R1 604k R2 604k L1, L2: SUMIDA CDRH2D18/HP-4R7NC C2 10MF 3407 TA03 Efﬁciency vs Load Current 100 95 1.8V 90 EFFICIENCY (%) VOUT2 = 1.8V AT 800mA LTC3407-2 L2 4.7MH 85 1.
PAGE 14
LTC3407-2 TYPICAL APPLICATIONS Efﬁciency vs Load Current 1.2mm Height Core Supply 100 VIN = 3.6V TO 5.5V RUN2 VIN VOUT2 = 3.3V AT 800mA LTC3407-2 L2 2.2μH SW2 L1 2.2μH SW1 C5, 22pF C4, 22pF 3.3V 90 POWER-ON RESET POR MODE/SYNC 95 R5 100k RUN1 EFFICIENCY (%) C1* 4.7μF VOUT1 = 1.8V AT 800mA 85 1.8V 80 75 70 C3 4.7μF s2 R4 887k R3 196k VIN = 5V 65 Burst Mode OPERATION NO LOAD ON OTHER CHANNEL 60 1 10 100 LOAD CURRENT (mA) VFB1 VFB2 GND R1 301k R2 604k C2 4.
PAGE 15
LTC3407-2 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.
PAGE 16
LTC3407-2 TYPICAL APPLICATION 2mm Height Lithium-Ion Single Inductor Buck-Boost Regulator and a Buck Regulator VIN = 2.8V TO 4.2V C1 10μF VOUT2 = 3.3V AT 200mA VIN M1 R5 100k R4 887k POWER-ON RESET L1 2.2μH C4, 22pF VFB1 VFB2 R3 196k C1, C2, C3: TAIYO YUDEN JMK316BJ106ML C6: SANYO 6TPB47M D1: PHILIPS PMEG2010 L1: MURATA LQH32CN2R2M33 L2: TOKO A914BYW-100M (D52LC SERIES) M1: SILICONIX Si2302 VOUT1 = 1.