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LTC3544

3544fa

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Cellular Telephones

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Personal Information Appliances

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Wireless and DSL Modems

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Digital Still Cameras

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Media Players

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Portable Instruments

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Quad Synchronous

Step-Down Regulator: 2.25MHz,

300mA, 200mA, 200mA, 100mA

The LTC

3544 is a quad, high efficiency, monolithic

synchronous buck regulator using a constant-frequency,

current mode architecture. The four regulators operate

independently with separate run pins. The 2.25V to 5.5V

input voltage range makes the LTC3544 well suited for

single Li-Ion/polymer battery-powered applications.

100% duty cycle provides low dropout operation, ex-

tending battery runtime in portable systems. Low ripple

Burst Mode

operation increases efﬁ ciency at light loads,

further extending battery runtime with typically only 20mV

of ripple.

Switching frequency is internally set to 2.25MHz, allowing

the use of small surface mount inductors and capacitors.

The internal synchronous switches increase efﬁ ciency

and eliminate the need for external Schottky diodes. Low

output voltages are easily supported with the 0.8V feedback

reference voltage.

The LTC3544 is available in a low proﬁ le (0.75mm) (3mm

× 3mm) QFN package.

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High Efﬁ ciency: Up to 95%

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Four Independent Regulators Provide Up to 300mA,

200mA, 200mA and 100mA Output Current

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2.25V to 5.5V Input Voltage Range

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2.25MHz Constant-Frequency Operation

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No Schottky Diodes Required

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Extremely Low Channel-to-Channel Transient

Crosstalk

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Low Ripple (20mV

P-P

) Burst Mode Operation:

= 70μA (All Channels On)

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0.8V Reference Allows Low Output Voltages

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Shutdown Mode Draws <1µA Supply Current

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Current Mode Operation for Excellent Line and Load

Transient Response

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Overtemperature Protected

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Low Proﬁ le (3mm × 3mm) 16-Lead QFN Package

, 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, 6580258, 6304066, 6127815, 6498466, 6611131, 5994885.

4.7μH 3.3μH

10μH

93.1k

107k

4.7μF

CER

4.7μF

CER

3.3μH

133k

59k

107k 118k

3544B TA01a

4.7μF

CER

4.7μF

CER

4.7μF

CER

OUT3

0.8V

200mA

OUT1

1.2V

100mA

OUT2

1.5V

200mA

2.25V TO 5.5V

OUT4

1.8V

300mA

RUN200B

SW200B

FB200B

RUN200A

SW200A

FB200A

RUN300

SW300

FB300

RUN100

SW100

FB100

LTC3544

GNDA PGND

100k

High Efﬁ ciency Quad Step-Down Converter

LOAD CURRENT (A)

EFFICIENCY (%)

POWER LOSS (W)

100

0.0001 0.01 0.1 1

3544 TA01b

0.1

0.01

0.001

0.0001

0.001

= 2.7V

= 3.6V

= 4.2V

OUT

= 2.5V

= 25°C

EFFICIENCY

LOSS

Efﬁ ciency vs Load Current, 300mA

Channel, All Other Channels Off

Summary of content (16 pages)

PAGE 1
LTC3544 Quad Synchronous Step-Down Regulator: 2.25MHz, 300mA, 200mA, 200mA, 100mA FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efﬁciency: Up to 95% Four Independent Regulators Provide Up to 300mA, 200mA, 200mA and 100mA Output Current 2.25V to 5.5V Input Voltage Range 2.25MHz Constant-Frequency Operation No Schottky Diodes Required Extremely Low Channel-to-Channel Transient Crosstalk Low Ripple (20mVP-P) Burst Mode Operation: IQ = 70μA (All Channels On) 0.
PAGE 2
LTC3544 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) SW100 GNDA VCC RUN200B TOP VIEW 16 15 14 13 VFB200B 1 12 RUN100 VFB200A 2 11 VFB100 17 RUN200A 3 10 VFB300 SW200B 4 6 7 8 PGND PVIN SW300 9 5 SW200A Input Supply Voltage .....................................–0.3V to 6V RUNx ............................................. –0.3V to (VIN + 0.3V) VFBx ................................................ –0.3V to (VIN + 0.3V) SWx ............................................... –0.
PAGE 3
LTC3544 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 noted. SYMBOL PARAMETER CONDITIONS IS Input DC Bias Current Active Mode (Four Regulators Enabled) Sleep Mode (Four Regulators Enabled) MIN TYP MAX UNITS VFB = 0.7V, ILOAD = 0A, 2.25MHz 825 1100 μA VFB = 0.9V, ILOAD = 0A, 2.25MHz 70 80 μA 0.
PAGE 4
LTC3544 ELECTRICAL CHARACTERISTICS Note 3: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD)(68°C/W). Note 4: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature is active. Continuous operation above the speciﬁed maximum operating junction temperature may impair device reliability.
PAGE 5
LTC3544 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency vs Load Current 200mA Channel A. All Other Channels Off 100 90 90 80 80 70 70 60 50 40 30 100 VIN = 2.25V VIN = 3.6V VIN = 4.2V 90 80 70 60 50 40 10 0 0.0001 VIN = 2.25V VIN = 3.6V VIN = 4.2V VOUT = 1.8V TA = 25°C ALL OTHER CHANNELS OFF 0.01 0.1 0.001 LOAD CURRENT (A) 20 0 0.0001 40 10 0.01 0.1 0.001 LOAD CURRENT (A) 3544 G07 1 0 0.0001 VIN = 2.25V VIN = 3.6V VIN = 4.2V VOUT = 1.5V TA = 25°C ALL OTHER CHANNELS OFF 0.001 0.01 0.
PAGE 6
LTC3544 TYPICAL PERFORMANCE CHARACTERISTICS Load Step Response 100mA Channel Load Step Crosstalk VOUT100 50mV/DIV AC COUPLED VOUT100 1mV/DIV VOUT200A 1mV/DIV IL 100mA/DIV VOUT200B 1mV/DIV VOUT300 50mV/DIV ILOAD 100mA/DIV 3544 G17 VIN = 3.6V 40μs/DIV TA = 25°C 300mA LOAD STEP ON VOUT300 OTHER CHANNELS LOADED 50% OF MAXIMUM 3544 G16 VIN = 3.6V 20μs/DIV VOUT = 1.2V TA = 25°C ILOAD = 400μA TO 100mA PFET RDS(ON) vs Supply Voltage 1.2 NFET RDS(ON) vs Supply Voltage 1.0 TA = 25°C 1.0 0.8 0.
PAGE 7
LTC3544 PIN FUNCTIONS VFB200B (Pin 1): 200mA Regulator B Feedback Pin. This pin receives the feedback voltage from an external resistive divider across the output. RUN300 (Pin 9): 300mA Regulator Enable Pin. Forcing this pin to VIN enables the 300mA regulator, while forcing it to GND causes the regulator to shut off. VFB200A (Pin 2): 200mA Regulator A Feedback Pin. This pin receives the feedback voltage from an external resistive divider across the output. VFB300 (Pin 10): 300mA Regulator Feedback Pin.
PAGE 8
LTC3544 FUNCTIONAL DIAGRAMS 3 9 RUN200A 15 RUN300 14 16 GNDA VCC 12 RUN200B RUN100 SHDN 0.8V REF OSC RUN LOGIC SW200A 5 SW100 IBIAS200A POWER FETs POWER FETs VFB200A 2 VFB100 REG200A REG100 SW200B SW300 8 11 4 IBIAS200B IBIAS300 POWER FETs POWER FETs 10 13 IBIAS100 VFB200B VFB300 REG300 PVIN REG200B PGND 7 6 1 3544 FD01 REGULATOR BURST CLAMP 3 PVIN SLOPE COMP VFBx – – 1 EA 0.
PAGE 9
LTC3544 OPERATION (Refer to Functional Diagrams) The LTC3544 uses a constant-frequency current mode architecture. The operating frequency is set at 2.25MHz. All channels share the same clock and run in-phase. The output voltage for each regulator is set by an external resistor divider returned to the VFB pin. An error ampliﬁer compares the divided output voltage with a reference voltage of 0.8V and regulates the peak inductor current accordingly. VOUT100 VOUT200A VOUT200B VOUT300 RUNx VIN = 3.
PAGE 10
LTC3544 APPLICATIONS INFORMATION The basic LTC3544 application circuit is shown on the ﬁrst page of this data sheet. External component selection is driven by the load requirement and begins with the selection of L followed by CIN and COUT. Table 1. Representative Surface Mount Inductors Value (μH) DCR (Ω MAX) MAX DC CURRENT (A) Sumida CDH2D09B 10 6.4 4.7 3.3 0.47 0.32 0.218 0.15 0.48 0.6 0.7 0.85 3.0 × 2.8 × 1.0 Wurth TPC744029 10 6.8 4.7 3.3 0.50 0.38 0.210 0.155 0.50 0.65 0.80 0.95 2.8 × 2.
PAGE 11
LTC3544 APPLICATIONS INFORMATION voltage, the output ripple is highest at maximum input voltage since ΔIL increases with input voltage. Using Ceramic Input and Output Capacitors Higher value, lower cost, ceramic capacitors are now widely available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications.
PAGE 12
LTC3544 APPLICATIONS INFORMATION top and bottom MOSFET RDS(ON) and the duty cycle (DC) as follows: RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC) The RDS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Characteristics curves. Thus, to obtain I2R losses, simply add RSW to RL and multiply the result by the square of the average output current.
PAGE 13
LTC3544 APPLICATIONS INFORMATION PC Board Layout Checklist 3. Keep C8 and C9 as close to the part as possible. When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3544. These items are also illustrated graphically in Figures 3 and 4. Check the following in your layout: 4. Keep the switching nodes (SWx) away from the sensitive VFBx nodes. 5. Keep the ground connected plates of the input and output capacitors as close as possible. 1.
PAGE 14
LTC3544 APPLICATIONS INFORMATION Beginning with this channel, ﬁrst calculate the inductor value for about 35% ripple current (100mA in this example) at maximum VIN. Using a form of Equation 1: L4 = 200k are a good compromise between efﬁciency and immunity to any adverse effects of PCB parasitic capacitance on the feedback pins. Choosing 10μA with 0.8V feedback voltage makes R7 = 80k. A close standard 1% resistor is 76.8k. Using: 2.5V ⎛ 2.5V ⎞ 1– = 4.5µH 2.25MHz • 100mA ⎜⎝ 4.
PAGE 15
LTC3544 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ±0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1.
PAGE 16
LTC3544 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3405/LTC3405A 300mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converters 95% Efﬁciency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20μA, ISD < 1μA, ThinSOTTM Package LTC3406/LTC3406B 600mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converters 96% Efﬁciency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD < 1μA, ThinSOT Package LTC3407/LTC3407-2 Dual 600mA/800mA IOUT, 1.5MHz/2.