Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Converter, Converter/amplifier MSOP 10 EP

LTC3407-2

sn34072 34072fs

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

■

PDAs/Palmtop PCs

■

Digital Cameras

■

Cellular Phones

■

Portable Media Players

■

PC Cards

■

Wireless and DSL Modems

■

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 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, 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 profile ≤1.2mm. Each output voltage is adjustable

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

switches provide high efficiency 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 efficiency. Burst

Mode

operation provides high efficiency at light loads,

while Pulse Skip 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.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a registered trademark of Linear Technology Corporation.

LTC3407-2 Efficiency Curve

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

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

≤ 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 U FEATURES DESCRIPTIO ■ The LTC®3407-2 is a dual, constant frequency, synchronous 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 profile ≤1.2mm. Each output voltage is adjustable from 0.6V to 5V. Internal synchronous 0.35Ω, 1.
PAGE 2
LTC3407-2 W W U W ABSOLUTE AXI U RATI GS (Note 1) VIN Voltages.................................................– 0.3V to 6V VFB1, VFB2, RUN1, RUN2 Voltages ..................................... – 0.3V to VIN + 0.3V 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
LTC3407-2 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.
PAGE 4
LTC3407-2 U W TYPICAL PERFOR A CE CHARACTERISTICS Reference Voltage vs Temperature RDS(ON) vs Input Voltage 0.615 VIN = 3.6V 550 TA = 25°C 0.610 VIN = 2.7V 500 450 0.600 0.595 400 350 300 0.590 250 0.585 –50 –25 200 50 25 75 0 TEMPERATURE (°C) 100 MAIN SWITCH RDS(ON) (mΩ) 0.605 125 SYNCHRONOUS SWITCH 400 350 300 250 200 150 1 3 2 VIN = 3.6V VIN = 4.
PAGE 5
LTC3407-2 U U U PI FU CTIO S VFB1 (Pin 1): Output Feedback. Receives the feedback voltage from the external resistive divider across the output. Nominal voltage for this pin is 0.6V. RUN1 (Pin 2): Regulator 1 Enable. Forcing this pin to VIN enables regulator 1, while forcing it to GND causes regulator 1 to shut down. VIN (Pin 3): Main Power Supply. Must be closely decoupled to GND. SW1 (Pin 4): Regulator 1 Switch Node Connection to the Inductor. This pin swings from VIN to GND. GND (Pin 5): Main Ground.
PAGE 6
LTC3407-2 W BLOCK DIAGRA 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 Q 0.55V – UVDET 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
LTC3407-2 U OPERATIO 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 LTC3407-2 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.
PAGE 8
LTC3407-2 U W U U APPLICATIO S I FOR ATIO 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. Table 1.
PAGE 9
LTC3407-2 U U W U APPLICATIO S I FOR ATIO 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. 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 U W U U APPLICATIO S I FOR ATIO VOUT ⎛ R2 ⎞ = 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
LTC3407-2 U W U U APPLICATIO S I FOR ATIO 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 LTC3407-2 circuits: 1)VIN quiescent current, 2) switching losses, 3) I2R losses, 4) other losses.
PAGE 12
LTC3407-2 U W U U APPLICATIO S I FOR ATIO regulator operating in a 70°C ambient temperature is approximately: TJ = 2 • 0.272 • 45 + 70 = 94.5°C which is below the absolute maximum junction temperature of 125°C. 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.
PAGE 13
LTC3407-2 U TYPICAL APPLICATIO S Low Ripple Buck Regulators Using Ceramic Capacitors VIN = 2.5V TO 5.5V C1 10µF RUN2 VIN R5 100k RUN1 POWER-ON RESET POR C3 10µF SW2 L1 4.7µH SW1 C5, 22pF R4 887k C4, 22pF R3 442k VOUT1 = 1.2V AT 800mA VFB1 VFB2 MODE/SYNC C1, C2, C3: TAIYO YUDEN JMK316BJ106ML R2 R1 604k 604k GND L1, L2: SUMIDA CDRH2D18/HP-4R7NC C2 10µF 3407 TA03 Efficiency vs Load Current 100 95 1.8V 90 EFFICIENCY (%) VOUT2 = 1.8V AT 800mA LTC3407-2 L2 4.7µH 85 1.
PAGE 14
LTC3407-2 U TYPICAL APPLICATIO S 2mm Height Core Supply VIN = 3.6V TO 5.5V C1* 4.7µF RUN2 VIN MODE/SYNC VOUT2 = 3.3V AT 800mA C3 4.7µF ×2 R5 100k RUN1 POWER-ON RESET POR LTC3407-2 L2 2.2µH SW2 L1 2.2µH SW1 C5, 22pF R4 887k C4, 22pF VFB1 VFB2 R3 196k VOUT1 = 1.8V AT 800mA R2 R1 604k 301k GND C1, C2, C3: TDK C1608X5ROJ475M L1, L2: CMD4D11-2R2 *IF C1 IS GREATER THAN 3" FROM POWER SOURCE, ADDITIONAL CAPACITANCE MAY BE REQUIRED. C2 4.7µF ×2 3407 TA07 Efficiency vs Load Current 100 95 3.
PAGE 15
LTC3407-2 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 0.38 ± 0.10 6 10 5 1 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 5) PACKAGE OUTLINE (DD10) DFN 0403 0.25 ± 0.05 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 2.38 ±0.10 (2 SIDES) 0.00 – 0.
PAGE 16
LTC3407-2 U TYPICAL APPLICATIO 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 SW2 M1 + POWER-ON RESET POR LTC3407-2 L2 10µH D1 VOUT2 = 3.3V AT 200mA R5 100k RUN1 L1 2.