Datasheet

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LTC3419

3419fa

OUTPUT CURRENT (mA)

EFFICIENCY (%)

100

POWER LOSS (W)

0.1

0.01

0.001

0.0001

0.1 10 100 1000

3419 TA01b

OUT

= 1.2V

OUT

= 1.8V

OUT

= 2.5V

= 3.6V

Cellular Telephones

Digital Still Cameras

Wireless and DSL Modems

Portable Media Players

PDAs/Palmtop PCs

FEATURES

APPLICATIONS

DESCRIPTION

Dual Monolithic 600mA

Synchronous Step-Down

Regulator

The LTC

3419 is a dual, 2.25MHz, constant-frequency,

synchronous step-down DC/DC converter in a tiny

3mm × 3mm DFN package. 100% duty cycle provides

low dropout operation, extending battery life in portable

systems. Low output voltages are supported with the 0.6V

feedback reference voltage. Each regulator can supply

600mA output current.

The input voltage range is 2.5V to 5.5V, making it ideal

for Li-Ion and USB powered applications. Supply current

during operation is only 35μA and drops to <1μA in

shutdown. A user-selectable mode input allows the user

to trade off between high efﬁ ciency Burst Mode operation

and pulse-skipping mode.

An internally set 2.25MHz switching frequency allows the

use of tiny surface mount inductors and capacitors. Internal

soft-start reduces inrush current during start-up. Both

outputs are internally compensated to work with ceramic

output capacitors. The LTC3419 is available in a low proﬁ le

(0.75mm) 3mm × 3mm DFN package. The LTC3419 is also

available in a ﬁ xed output voltage conﬁ guration selected

via internal resistor dividers (see Table 2).

Dual Monolithic Buck Regulator in 8-Lead 3 × 3 DFN

High Efﬁ ciency Dual Step-Down Outputs: Up to 96%

600mA Current per Channel at V

= 3V

Only 35μA Quiescent Current During Operation

(Both Channels)

2.25MHz Constant-Frequency Operation

2.5V to 5.5V Input Voltage Range

Low Dropout Operation: 100% Duty Cycle

No Schottky Diodes Required

Internally Compensated for All Ceramic Capacitors

Independent Internal Soft-Start for Each Channel

Available in Fixed Output Versions

Current Mode Operation for Excellent Line and Load

Transient Response

0.6V Reference Allows Low Output Voltages

User-Selectable Burst Mode

Operation

Short-Circuit Protected

Ultralow Shutdown Current: I

< 1μA

Available in Small MSOP or 3mm × 3mm DFN-8

Packages

, 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. Protected by U.S. Patents,

including

5481178, 6127815, 6304066, 6498466, 6580258, 6611131.

Efﬁ ciency and Power Loss

vs Output Current

RUN2 RUN1

LTC3419

FB2

SW2

SW1

MODE

FB1

22pF 22pF

GND

2.5V TO 5.5V

OUT2

1.8V AT

600mA

OUT1

2.5V AT

600mA

3419 TA01

118k 187k

59k 59k

3.3

μH3.3μH

10μF

μF

TYPICAL APPLICATION

Summary of content (16 pages)

PAGE 1
LTC3419 Dual Monolithic 600mA Synchronous Step-Down Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n n n High Efﬁciency Dual Step-Down Outputs: Up to 96% 600mA Current per Channel at VIN = 3V Only 35μA Quiescent Current During Operation (Both Channels) 2.25MHz Constant-Frequency Operation 2.5V to 5.
PAGE 2
LTC3419 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (VIN) ............................. –0.3 to 6V VFB1, VFB2 ........................................ –0.3V to VIN + 0.3V RUN1, RUN2, MODE ........................ –0.3V to VIN + 0.3V SW1, SW2 ....................................... –0.3V to VIN + 0.3V P-Channel SW Source Current (DC) (Note 2).......800mA N-Channel SW Source Current (DC) (Note 2) ......800mA Peak SW Source and Sink Current (Note 2) .............1.
PAGE 3
LTC3419 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating junction temperature range, otherwise speciﬁcations are at TA = 25°C, VIN = 3.6V, unless otherwise noted. SYMBOL PARAMETER VIN VIN Operating Voltage VUV VIN Undervoltage Lockout IFB Feedback Pin Input Current CONDITIONS MIN ● TYP 2.5 MAX UNITS 5.5 V VIN Low to High ● 2.1 2.
PAGE 4
LTC3419 TYPICAL PERFORMANCE CHARACTERISTICS Burst Mode Operation TA = 25°C, VIN = 3.6V, unless otherwise noted. Pulse Skip Mode Operation Efﬁciency vs Input Voltage 100 SW 2V/DIV SW 2V/DIV IOUT = 100mA 90 EFFICIENCY (%) 80 VOUT 50mV/DIV AC-COUPLED VOUT 50mV/DIV AC-COUPLED IL 100mA/DIV IL 100mA/DIV IOUT = 10mA 60 IOUT = 0.1mA 3419 G02 5μs/DIV 40 VIN = 3.6V VOUT = 1.8V ILOAD = 5mA VIN = 3.6V VOUT = 1.8V ILOAD = 25mA 70 50 3419 G01 2μs/DIV IOUT = 1mA IOUT = 600mA VOUT = 1.8V 30 2.
PAGE 5
LTC3419 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency vs Load Current Efﬁciency vs Load Current 100 100 90 90 90 80 80 80 70 70 70 60 50 40 60 50 40 30 30 20 20 VIN = 2.7V VIN = 3.6V VIN = 4.2V 10 VOUT = 1.2V 0 0.1 10 100 1 OUTPUT CURRENT (mA) EFFICIENCY (%) 100 EFFICIENCY (%) EFFICIENCY (%) Efﬁciency vs Load Current VOUT = 1.8V 0 0.1 10 100 1 OUTPUT CURRENT (mA) 1000 2.5 1000 3419 G12 Load Regulation 2.0 VOUT = 1.2V VOUT = 1.8V VOUT = 2.5V Burst Mode OPERATION VOUT = 1.
PAGE 6
LTC3419 TYPICAL PERFORMANCE CHARACTERISTICS Load Step TA = 25°C, VIN = 3.6V, unless otherwise noted. Load Step Load Step VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED IL 500mA/DIV IL 500mA/DIV IL 500mA/DIV ILOAD 500mA/DIV ILOAD 500mA/DIV ILOAD 500mA/DIV 3419 G19 20μs/DIV VIN = 3.6V VOUT = 1.8V ILOAD = 0A TO 600mA PIN FUNCTIONS 20μs/DIV VIN = 3.6V VOUT = 1.8V ILOAD = 40mA TO 600mA 3419 G20 20μs/DIV 3419 G21 VIN = 3.6V VOUT = 1.
PAGE 7
LTC3419 FUNCTIONAL DIAGRAM REGULATOR 1 MODE 3 BURST CLAMP 5 VIN SLOPE COMP VFB1 – – 1 EA 0.6V VSLEEP + – SLEEP ITH + ICOMP + BURST S Q RS LATCH SOFT-START R Q SWITCHING LOGIC AND BLANKING CIRCUIT ANTI SHOOTTHRU 4 SW1 + IRCMP – SHUTDOWN RUN1 2 SLEEP2 0.
PAGE 8
LTC3419 OPERATION The LTC3419 uses a constant-frequency, current mode architecture. The operating frequency is set at 2.25MHz. Both channels share the same clock and run in-phase. The output voltage is set by an external resistor divider returned to the VFB pins. An error ampliﬁer compares the divided output voltage with a reference voltage of 0.6V and regulates the peak inductor current accordingly.
PAGE 9
LTC3419 APPLICATIONS INFORMATION A general LTC3419 application circuit is shown in Figure 1. External component selection is driven by the load requirement, and begins with the selection of the inductor L. Once the inductor is chosen, CIN and COUT can be selected. Inductor Selection Although the inductor does not inﬂuence the operating frequency, the inductor value has a direct effect on ripple current.
PAGE 10
LTC3419 APPLICATIONS INFORMATION deviations do not offer much relief. Note that capacitor manufacturer’s ripple current ratings are often based on only 2000 hours lifetime. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet the size or height requirements of the design. An additional 0.
PAGE 11
LTC3419 APPLICATIONS INFORMATION Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ΔILOAD • ESR, where ESR is the effective series resistance of COUT. ΔILOAD also begins to charge or discharge COUT generating a feedback error signal used by the regulator to return VOUT to its steady-state value.
PAGE 12
LTC3419 APPLICATIONS INFORMATION The RDS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Characteristics curves. Thus, to obtain I2R losses: I2R losses = IOUT2 • (RSW + RL) 4. Other “hidden” losses, such as copper trace and internal battery resistances, can account for additional efﬁciency degradations in portable systems. It is very important to include these “system” level losses in the design of a system.
PAGE 13
LTC3419 APPLICATIONS INFORMATION VIN 2.5V TO 5.5V C1 RUN2 VIN RUN1 MODE LTC3419 L2 VOUT2 SW2 L1 VOUT1 SW1 CF2 CF1 VFB2 R4 COUT2 GND R3 VFB1 R1 R2 COUT1 3419 F02 BOLD LINES INDICATE HIGH CURRENT PATHS Figure 2. LTC3419 Layout Diagram (See Board Layout Checklist) CF1 CF2 R2 R1 R3 R4 VOUT1 VOUT2 COUT1 COUT2 VIA TO VIN L1 VFB1 VFB2 RUN1 RUN2 MODE SW2 SW1 L2 VIN VIA TO GND GND CIN 3419 F03 Figure 3.
PAGE 14
LTC3419 APPLICATIONS INFORMATION Using the same analysis for channel 2 (VOUT2 = 1.8V), the results are: 100 90 80 EFFICIENCY (%) L2 = 1.9μH R3 = 59k R4 = 118k 50 40 20 10 VIN = 2.7V VIN = 3.6V VIN = 4.2V VOUT = 1.8V 0 0.1 1 10 100 OUTPUT CURRENT (mA) Figure 4 shows the complete schematic for this example, along with the efﬁciency curve and transient response. 1000 100 90 C1 10μF L2 2.2μH RUN2 VIN RUN1 MODE LTC3419 SW2 80 L1 2.2μH VOUT1 2.5V AT 600mA SW1 CF2, 22pF EFFICIENCY (%) VOUT2 1.
PAGE 15
LTC3419 PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) R = 0.115 TYP 5 0.38 ± 0.10 8 0.675 ±0.05 3.5 ±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 (NOTE 6) (DD) DFN 1203 0.75 ±0.05 0.200 REF 0.25 ± 0.05 4 0.25 ± 0.05 1 0.50 BSC 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
LTC3419 TYPICAL APPLICATIONS Dual 600mA Buck Converter VIN 2.5V TO 5.5V VIN 2.5V TO 5.5V C1 10μF L2 3.3μH VOUT2 1.8V AT 600mA RUN2 VIN RUN1 MODE LTC3419 SW2 L1 3.3μH CF1, 22pF VFB2 R4 118k VOUT1 2.5V AT 600mA SW1 CF2, 22pF COUT2 10μF 1.8V/1.575V Dual 600mA Buck Converter R3 59k GND VFB1 R1 59k COUT1 10μF R2 187k C1 10μF L2 3.3μH VOUT2 1.8V AT 600mA RUN2 VIN RUN1 MODE LTC3419-1 SW2 COUT2 10μF VFB2 L1 3.