LTC3728LEGN-1#PBF Linear Technology, LTC3728LEGN-1#PBF Datasheet
LTC3728LEGN-1#PBF
Specifications of LTC3728LEGN-1#PBF
Available stocks
Related parts for LTC3728LEGN-1#PBF
LTC3728LEGN-1#PBF Summary of contents
Page 1
... L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. ...
Page 2
... SENSE2 SENSE2 GN PACKAGE 28-LEAD NARROW PLASTIC SSOP = 125°C, θ 95°C/W JMAX JA ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL LTC3728LEGN-1#PBF LTC3728LEGN-1#TRPBF LTC3728LIGN-1#PBF LTC3728LIGN-1#TRPBF LTC3728LEUH-1#PBF LTC3728LEUH-1#TRPBF LTC3728LIUH-1#PBF LTC3728LIUH-1#TRPBF LEAD BASED FINISH TAPE AND REEL LTC3728LEGN-1 LTC3728LEGN-1#TR LTC3728LIGN-1 LTC3728LIGN-1#TR LTC3728LEUH-1 LTC3728LEUH-1#TR ...
Page 3
ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T SYMBOL PARAMETER Main Control Loops V Regulated Feedback Voltage OSENSE1 Feedback Current VOSENSE1 Reference Voltage Line Regulation REFLNREG V Output Voltage Load Regulation LOADREG g Transconductance ...
Page 4
LTC3728L-1 ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T SYMBOL PARAMETER I Phase Detector Output Current PLLFLTR Sinking Capability Sourcing Capability 3.3V Linear Regulator V 3.3V Regulator Output Voltage 3.3OUT V 3.3V Regulator Load Regulation 3.3IL V 3.3V ...
Page 5
TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Input Voltage and Mode (Figure 13) 1000 800 600 BOTH CONTROLLERS ON 400 200 SHUTDOWN INPUT VOLTAGE (V) 3728L1 G04 Internal 5V LDO Line Regulation 5.1 I ...
Page 6
LTC3728L-1 TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation 0.0 FCB = 15V IN FIGURE 13 –0.1 –0.2 –0.3 –0 LOAD CURRENT (A) 3728L1 G13 Maximum Current Sense Threshold vs Temperature ...
Page 7
TYPICAL PERFORMANCE CHARACTERISTICS Input Source/Capacitor Instantaneous Current (Figure 13 2A/DIV V IN 200mV/DIV V SW1 10V/DIV V SW2 10V/DIV 3728L1 G22 V = 15V 1μs/DIV 5V 3.3V OUT1 OUT2 PLLFLTR ...
Page 8
LTC3728L-1 PIN FUNCTIONS Error Amplifi er Feedback Input. OSENSE1 OSENSE2 Receives the remotely-sensed feedback voltage for each controller from an external resistive divider across the output. PLLFLTR: Filter Connection for Phase-Locked Loop. Alter- natively, this pin ...
Page 9
FUNCTIONAL DIAGRAM PLLIN F PHASE DET IN 50k PLLFLTR CLK1 R LP OSCILLATOR CLK2 C LP – 0.86V + V OSENSE1 PGOOD – + 0.74V 0.86V – OSENSE2 – + 0.74V INTV CC 3V – 4.5V 0.18μA BINH ...
Page 10
LTC3728L-1 OPERATION (Refer to Functional Diagram) Main Control Loop The LTC3728L constant frequency, current mode step-down controller with two channels operating 180 degrees out of phase. During normal operation, each top MOSFET is turned on when the clock ...
Page 11
OPERATION (Refer to Functional Diagram) as Burst Mode operation, but does provide a lower noise, constant frequency operating mode down to approximately 1% of the designed maximum output current. Continuous Current (PWM) Operation Tying the FCB pin to ground will ...
Page 12
LTC3728L-1 OPERATION (Refer to Functional Diagram 2.53A IN(MEAS) (a) Figure 3. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for Dual Switching Regulators Converting 12V to 5V and 3. Each. The Reduced Input Ripple with ...
Page 13
APPLICATIONS INFORMATION Figure 1 on the fi rst page is a basic LTC3728L-1 applica- tion circuit. External component selection is driven by the load requirement, and begins with the selection of R and the inductor value. Next, the power MOSFETs ...
Page 14
LTC3728L-1 APPLICATIONS INFORMATION 25% of the current limit determined by R inductor values (higher ΔI ) will cause this to occur at L lower load currents, which can cause a dip in effi ciency in the upper range of low ...
Page 15
APPLICATIONS INFORMATION where δ is the temperature dependency (approximately 4Ω) is the effective driver resistance DR at the MOSFET’s Miller threshold voltage. V typical MOSFET minimum threshold voltage. 2 Both MOSFETs have I R losses while the ...
Page 16
LTC3728L-1 APPLICATIONS INFORMATION This formula has a maximum /2. This simple worst case condition is commonly OUT used for design because even signifi cant deviations do not offer much relief. Note that capacitor manufacturer’s ripple ...
Page 17
APPLICATIONS INFORMATION in cost-driven applications providing that consideration is given to ripple current ratings, temperature and long term reliability. A typical application will require several to many aluminum electrolytic capacitors in parallel. A combination of the above mentioned capacitors will ...
Page 18
LTC3728L-1 APPLICATIONS INFORMATION 2. EXTV Connected directly OUT connection for a 5V regulator and provides the highest effi ciency. 3. EXTV Connected to an External supply external CC supply is available in the 5V to ...
Page 19
APPLICATIONS INFORMATION stage is biased with internal resistors from an internal 2.4V source as shown in the Functional Diagram. This requires that current either be sourced or sunk from the SENSE pins depending on the output voltage. If the output ...
Page 20
LTC3728L-1 APPLICATIONS INFORMATION ent temperature, conditions that cause the highest power dissipation in the top MOSFET. Each controller includes current foldback to help further limit load current when the output is shorted to ground. The foldback circuit is active even ...
Page 21
APPLICATIONS INFORMATION pulling up the PLLFLTR pin. When the external frequency is less than f , current is sunk continuously, pulling down 0SC the PLLFLTR pin. If the external and internal frequencies are the same but exhibit a phase difference, ...
Page 22
LTC3728L-1 APPLICATIONS INFORMATION If V drops below this level, the FCB voltage forces SEC temporary continuous switching operation until V again above its minimum. In order to prevent erratic operation if no external connec- tions are made to the FCB ...
Page 23
APPLICATIONS INFORMATION 2. INTV current is the sum of the MOSFET driver and CC control currents. The MOSFET driver current results from switching the gate capacitance of the power MOSFETs. Each time a MOSFET gate is switched from low to ...
Page 24
LTC3728L-1 APPLICATIONS INFORMATION at this test point truly refl ects the closed loop response. Assuming a predominantly second order system, phase margin and/or damping factor can be estimated using the percentage of overshoot seen at this pin. The bandwidth can ...
Page 25
APPLICATIONS INFORMATION Design Example As a design example for one channel, assume V 12V(nominal 22V(max OUT and f = 300kHz. The inductance value is chosen fi rst based on a 30% ripple current assumption. The highest ...
Page 26
LTC3728L-1 APPLICATIONS INFORMATION maximum input voltage. The output voltage ripple due to ESR is approximately (Δ 0.02Ω(1.67A) = 33mV ORIPPLE ESR L PC Board Layout Checklist When laying out the printed circuit board, the following ...
Page 27
APPLICATIONS INFORMATION BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. be connected between the (+) terminal of C ground. The R2 and R4 connections should not be along the ...
Page 28
LTC3728L-1 APPLICATIONS INFORMATION 7. Use a modifi ed “star ground” technique: a low imped- ance, large copper area central grounding point on the same side of the PC board as the input and output capacitors with tie-ins for the bottom ...
Page 29
TYPICAL APPLICATIONS 59k RUN/SS1 0.1μF SENSE1 180pF 1000pF SENSE1 105k, 1% 20k 1% V OSENSE1 PLLFLTR PLLIN 33pF FCB LTC3728L-1 I TH1 15k 1000pF SGND 33pF 3.3V 3.3V OUT I TH2 15k 1000pF V OSENSE2 20k 1% SENSE2 63.4k 1000pF ...
Page 30
LTC3728L-1 TYPICAL APPLICATIONS RUN/SS1 0.1μF SENSE1 180pF 1000pF 105k SENSE1 1% 20k 1% V 0.01μF PLLFLTR 10k 1000pF f PLLIN SYNC 100pF FCB I 8.06k 1500pF SGND 100pF 3.3V 3.3V I 4.75k 1000pF V 20k 1% SENSE2 63.4k 1000pF 1% ...
Page 31
... APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...
Page 32
... PolyPhase Synchronous Controller Expandable from 2-Phase to 12-Phase, Uses all Surface Mount LTC3731 3- to 12-Phase Step-Down Synchronous Controller LTC3802 No R 2-Phase Dual Synchronous Step-Down SENSE Controller No R and PolyPhase are trademarks of Linear Technology Corporation. SENSE Linear Technology Corporation 32 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● I ...