ltc3853euj Linear Technology Corporation, ltc3853euj Datasheet

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ltc3853euj

Manufacturer Part Number
ltc3853euj
Description
Triple Output, Multiphase Synchronous Step-down Controller
Manufacturer
Linear Technology Corporation
Datasheet

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FEATURES
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TYPICAL APPLICATION
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
Triple, 120° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
Confi gurable as a 180° Dual Phase Controller Plus a
Single Phase Controller
The Third Phase Can Regulate Up to a 13.5V Output
High Effi ciency: Up to 92%
R
±0.75% 0.8V Output Voltage Accuracy
Phase-Lockable Fixed Frequency 250kHz to 750kHz
Supports Pre-Biased Outputs
Dual N-Channel MOSFET Synchronous Drive
Wide V
Adjustable Soft-Start Current Ramping or Tracking
Foldback Output Current Limiting
Output Overvoltage Protection
Dual Power Good Output Voltage Monitors
40-Lead 6mm × 6mm QFN Package
SENSE
V
OUT1
5V
5A
IN
or DCR Current Sensing
+
Range: 4.5V to 24V Operation (28V Abs Max)
100μF
10V
2.2μH
0.1μF
105k
2.2k
220pF
20k
15k
500kHz
1500pF
f
IN
4.7μF
High Effi ciency Triple 5V/3.3V/1.2V Step-Down Converter
TG1
PGOOD12
PGOOD3
SW1
BG1
MODE/PLLIN
I
SENSE1
SENSE1
V
I
V
SGND
LIM
TH1,2,3
FB1
FB3
V
IN
+
TK/SS1,2,3
LTC3853
FREQ/PLLFLTR
BOOST1,2,3
0.1μF
RUN1,2,3
INTV
SENSE2
SENSE2
SENSE3
SENSE3
PGND
SW2
V
SW3
CC
TG2
BG2
TG3
BG3
FB2
+
+
0.1μF
10k
SW1,2,3
10nF
DESCRIPTION
The LTC
down switching regulator controller that drives all N-chan-
nel synchronous power MOSFET stages. Power loss and
supply noise are minimized by operating the output stages
out of phase. The part can be confi gured as a dual phase
controller plus a single phase controller if needed. The
part can also be confi gured to provide a single 3-phase
output for even higher output currents.
A wide 4.5V to 24V (28V maximum) input voltage sup-
ply range encompasses most battery chemistries and
intermediate bus voltages. Phase 3 can regulate output
voltages up to 13.5V. A constant frequency current mode
architecture allows for a phase-lockable frequency up to
750kHz.
Independent TK/SS pins for each output ramps the output
voltages and can be confi gured for coincident or ratiometric
tracking. Current foldback limits MOSFET heat dissipation
during short-circuit conditions. The MODE/PLLIN pin
selects among Burst Mode
continuous inductor current modes.
Multiphase Synchronous
20k
®
63.4k
3853 is a high performance triple output step-
2.2k
Step-Down Controller
2.2μH
0.1μF
+
100μF
6V
V
3.3V
5A
OUT2
®
Triple Output,
operation, pulse-skipping or
1k
20k
0.1μF
22μF
50V
1μH
10k
V
7V TO 24V
IN
LTC3853
+
100μF
6V
V
1.2V
5A
OUT3
1
3853f

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ltc3853euj Summary of contents

Page 1

... Dual Power Good Output Voltage Monitors 40-Lead 6mm × 6mm QFN Package n L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258. ...

Page 2

... LTC3853IUJ#TRPBF LEAD BASED FINISH TAPE AND REEL LTC3853EUJ LTC3853EUJ#TR LTC3853IUJ LTC3853IUJ#TR Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi label on the shipping container For more information on lead free part marking, go to: For more information on tape and reel specifi ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T SYMBOL PARAMETER Main Control Loops V Regulated Feedback Voltage FB1,2,3 I Feedback Current FB1,2,3 V Reference Voltage Line Regulation REFLNREG V Output Voltage Load Regulation LOADREG g Transconductance Amplifi er ...

Page 4

... The LTC3853I is guaranteed over the full –40°C to 125°C operating temperature range. Note calculated from the ambient temperature T J dissipation P according to the following formulas: D LTC3853EUJ • 33°C/ The denotes the specifi ...

Page 5

TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency vs Output Current and Mode 100 BURST 60 50 DCM CCM 12V 1.8V OUT FIGURE 15 MODIFIED 10 WITH DCR SENSING 0 1.00E-02 1.00E-01 ...

Page 6

LTC3853 TYPICAL PERFORMANCE CHARACTERISTICS Prebiased Output OUT 1V/DIV V TK/SS 500mV/DIV V FB 500mV/DIV 3853 G08 50ms/DIV Quiescent Current vs Input Voltage Without EXTV CC 6.0 5.5 5.0 4.5 4 INPUT VOLTAGE (V) ...

Page 7

TYPICAL PERFORMANCE CHARACTERISTICS TK/SS Pull-Up Current vs Temperature 1.75 1.65 1.55 1.45 1.35 1.25 –50 – 100 TEMPERATURE (°C) 3853 G17 Oscillator Frequency vs Temperature 900 V = INTV FREQ CC 800 700 600 V = ...

Page 8

LTC3853 PIN FUNCTIONS + + + SENSE1 , SENSE2 , SENSE3 (Pins 3, 5, 7): Current Sense Comparator Inputs. The (+) inputs to the current compara- tors are normally connected to DCR sensing networks or current sensing resistors. SENSE3 to ...

Page 9

PIN FUNCTIONS TG1, TG2, TG3 (Pins 32, 26, 19): Top Gate Driver Outputs. These are the outputs of fl oating drivers with a voltage swing equal to INTV superimposed on the switch nodes CC voltages. BOOST1, BOOST2, BOOST3 (Pins 33, ...

Page 10

LTC3853 FUNCTIONAL DIAGRAM FREQ/PLLFLTR MODE/PLLIN MODE/SYNC DETECT PLL-SYNC OSC – I CMP + – SLOPE I LIM COMPENSATION INTV CC UVLO 1 SLOPE RECOVERY ACTIVE CLAMP 51k I THB V SLEEP IN 0.8V REF EA – ...

Page 11

OPERATION Main Control Loop The LTC3853 is a constant-frequency, current mode step-down controller with three channels operating 120 degrees out-of-phase. During normal operation, each top MOSFET is turned on when the clock for that channel sets the RS latch, and ...

Page 12

LTC3853 OPERATION voltage below 0.8V (e.g., SGND). To select pulse skipping mode of operation, tie the MODE/PLLIN pin to INTV select Burst Mode operation, fl oat the MODE/PLLIN pin. When the controller is enabled for Burst Mode operation, the peak ...

Page 13

OPERATION Triple vs Dual ( Operation The LTC3853 can be used to regulate three different outputs. It can also be used as a dual output controller with a high current 2-phase output and a single phase output. Tying ...

Page 14

LTC3853 APPLICATIONS INFORMATION the information at the sense terminals and making the programmed current limit unpredictable. If DCR sensing is used (Figure 2b), sense resistor R1 should be placed close to the switching node, to prevent noise from coupling into ...

Page 15

APPLICATIONS INFORMATION superposition of a purely resistive component and a purely inductive component. It was measured using two scope probes and waveform math to obtain a differential measurement. Based on additional measurements of the inductor ripple current and the on-time ...

Page 16

LTC3853 APPLICATIONS INFORMATION To ensure that the application will deliver full load cur- rent over the full operating temperature range, choose the minimum value for the Maximum Current Sense Threshold ( the Electrical Characteristics SENSE(MAX) table (22mV, 42mV, ...

Page 17

APPLICATIONS INFORMATION Inductor Core Selection Once the inductance value is determined, the type of in- ductor must be selected. Core loss is independent of core size for a fi xed inductor value, but it is very dependent on inductance selected. ...

Page 18

LTC3853 APPLICATIONS INFORMATION The optional Schottky diodes conduct during the dead time between the conduction of the two power MOSFETs. These prevent the body diodes of the bottom MOSFETs from turn- ing on, storing charge during the dead time and ...

Page 19

APPLICATIONS INFORMATION TIME (5a) Coincident Tracking Figure 5. Two Different Modes of Output Voltage Tracking V OUT1 TK/SS2 PIN R4 R2 (6a) Coincident Tracking Setup Figure 6. Setup for Coincident and Ratiometric Tracking ...

Page 20

LTC3853 APPLICATIONS INFORMATION ceramic capacitor placed directly adjacent to the INTV and PGND pins is highly recommended. Good bypassing is needed to supply the high transient currents required by the MOSFET gate drivers and to prevent interaction between the channels. ...

Page 21

APPLICATIONS INFORMATION Topside MOSFET Driver Supply (C External bootstrap capacitors connected to the BOOST B pins supply the gate drive voltages for the topside MOSFETs. Capacitor C in the Functional Diagram is charged though B external diode, D ...

Page 22

LTC3853 APPLICATIONS INFORMATION time. The total RMS power lost is lower when more than one controller is operating due to the reduced overlap of current pulses required through the input capacitor’s ESR. This is why the input capacitor’s requirement calculated ...

Page 23

APPLICATIONS INFORMATION controller locked to the rising edge of an external clock signal applied to the MODE/PLLIN pin. The phase detector is an edge sensitive digital type that provides zero degrees phase shift between the external and ...

Page 24

LTC3853 APPLICATIONS INFORMATION on the current sense signal. The minimum on-time can be affected by PCB switching noise in the voltage and current loop. However, as the peak sense voltage decreases the minimum on-time gradually increases to 130ns. This is ...

Page 25

APPLICATIONS INFORMATION minimum of 20μF to 40μF of capacitance having a maxi- mum of 20mΩ to 50mΩ of ESR. The LTC3853 3-phase architecture reduces this input capacitance requirement up to 66% over competing solutions. Other losses including Schottky conduction losses ...

Page 26

LTC3853 APPLICATIONS INFORMATION PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the IC. Figure 12 illustrates the current waveforms pres- ent in the various branches of ...

Page 27

APPLICATIONS INFORMATION BOLD LINES INDICATE HIGH SWITCHING CURRENTS. KEEP LINES TO A MINIMUM LENGTH. SW1 L1 R SENSE1 C D1 OUT1 SW2 L2 R SENSE2 C D2 OUT2 SW3 L3 R SENSE3 C ...

Page 28

LTC3853 APPLICATIONS INFORMATION PC Board Layout Debugging Start with one controller at a time helpful to use a DC-50MHz current probe to monitor the current in the inductor while testing the circuit. Monitor the output switching node (SW ...

Page 29

APPLICATIONS INFORMATION 4.7μF M1 3.3μH 4.75k 0.1μF 1430Ω V OUT1 5V 5A 105k 1% R ITH1,2,3 10pF C P1,2,3 + 330μF 20k C ITH1,2,3 10V 1% M1, M2, M3: Si4816BDY CHANNEL 15k 1.5nF ...

Page 30

LTC3853 APPLICATIONS INFORMATION For channel 1, the DCR fi lter/divider values are: SENSE Ω 1100 = = ≅ • ...

Page 31

APPLICATIONS INFORMATION 4.7μF M1 1.5μH 10Ω* 0.008Ω 1000pF* 5% 10Ω* V OUT1 2.5V 5A 43. 10pF ITH1,2,3 C P1,2 ITH1,2,3 220μF 20k 4V 1% M1, M2, M3: Si4816BDY CHANNEL 18k 1500pF, ...

Page 32

LTC3853 TYPICAL APPLICATIONS Triple 3.3V/2.5V/12V, 5A Step-Down Converter with R 4.7μF M1 3.3μH 10Ω* 0.008Ω PLLIN 1000pF* 5% 400kHz 10Ω* V OUT1 3.3V 5A 63. 10pF ITH1,2,3 C P1,2 ITH1,2,3 220μF 20k 4V 1% M1, M2, ...

Page 33

TYPICAL APPLICATIONS Dual 1.2V/2.5V High Current Step-Down Converter with R 4.7μF 0.47μH 100Ω* 0.002Ω 1000pF* 5% 100Ω* V OUT1 1.2V 30A 10k 1% R 47pF ITH1 ITH1,3 660μF 20k 2. CHANNEL ...

Page 34

LTC3853 TYPICAL APPLICATIONS Three Phase 2.5V Output High Current Step-Down Converter with R 4.7μF 0.78μH 100Ω* 0.002Ω 1000pF* 5% 100Ω* V OUT1 2.5V 40A 43.2k 1% 47pF R C ITH1 P1 + 660μF 20k C ITH1 ...

Page 35

... SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 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 36

... Q DC/DC Controller LTC3850 Dual 2-Phase Synchrounous Controller LTC3851 No R Wide Input Range Step-Down Controller SENSE PolyPhase is a registered trademark of Linear Technology Corporation Linear Technology Corporation 36 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● COMMENTS 97% Effi ciency, 99% Duty Cycle Output Fault Protection, 16-Pin SSOP Up to 97% Effi ...

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