ltc3850gn-2 Linear Technology Corporation, ltc3850gn-2 Datasheet

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ltc3850gn-2

Manufacturer Part Number
ltc3850gn-2
Description
Dual, 2-phase Synchronous Step-down Switching Controller
Manufacturer
Linear Technology Corporation
Datasheet

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Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LTC3850GN-2
Manufacturer:
LTNEAR
Quantity:
20 000
FEATURES
APPLICATIONS
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L, LT, LTC, LTM, OPTI-LOOP 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.
TYPICAL APPLICATION
V
OUT1
3.3V
5A
Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
High Effi ciency: Up to 95%
R
±1% 0.8V Output Voltage Accuracy
Phase-Lockable Fixed Frequency 250kHz to 780kHz
Supports Pre-Biased Output
Dual N-Channel MOSFET Synchronous Drive
Wide V
Adjustable Soft-Start Current Ramping or Tracking
Foldback Output Current Limiting
Output Overvoltage Protection
Power Good Output Voltage Monitor
28-Pin Narrow SSOP Package
Notebook and Palmtop Computers
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
SENSE
2.2μH
100μF
6V
2.2k
IN
or DCR Current Sensing
63.4k
Range: 4V to 30V Operation
High Effi ciency Dual 3.3V/2.5V Step-Down Converter
20k
0.1μF
0.1μF
15k
220pF
500kHz
0.1μF
TG1
BOOST1
SW1
BG1
MODE/PLLIN
EXT
SENSE1
RUN1
SENSE1
V
I
TH1
TK/SS1
FB1
VCC
V
IN
LTC3850-2
+
PGOOD INTV
SGND
FREQ/PLLFLTR
SENSE2
SENSE2
BOOST2
TK/SS2
PGND
RUN2
SW2
V
CC
BG2
I
TG2
TH2
FB2
+
0.1μF
10k
10nF
0.1μF
0.1μF
4.7μF
15k
220pF
DESCRIPTION
The LTC
step-down switching regulator controller that drives all
N-channel power MOSFET stages. A constant-frequency
current mode architecture allows a phase-lockable
frequency of up to 780kHz. Power loss and supply noise
are minimized by operating the two controller output
stages out of phase.
OPTI-LOOP
to be optimized over a wide range of output capacitance
and ESR values. The LTC3850-2 features a precision 0.8V
reference and a power good output indicator. A wide 4V
to 30V input supply range encompasses most battery
chemistries and intermediate bus voltages.
Independent TK/SS pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit condi-
tions. The MODE/PLLIN pin selects among Burst Mode
operation, pulse-skipping mode, or continuous inductor
current mode and allows the IC to be synchronized to an
external clock.
The LTC3850-2 is identical to the LTC3850-1, except they
have different pin assignments.
20k
43.2k
Synchronous Step-Down
2.2k
38502 TA01
2.2μH
22μF
50V
®
3850-2 is a high performance dual synchronous
®
V
7V TO
26V
IN
compensation allows the transient response
100μF
6V
Switching Controller
V
2.5V
5A
OUT2
100
95
90
85
80
75
70
65
60
55
50
10
Dual, 2-Phase
V
V
IN
OUT
= 12V
= 3.3V
LOAD CURRENT (mA)
100
Effi ciency
LTC3850-2
POWER LOSS
EFFICIENCY
1000
38502 TA01b
10000
10000
1000
100
10
38502f
1
®

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ltc3850gn-2 Summary of contents

Page 1

FEATURES n Dual, 180° Phased Controllers Reduce Required Input Capacitance and Power Supply Induced Noise n High Effi ciency 95 DCR Current Sensing SENSE ±1% 0.8V Output Voltage Accuracy n n Phase-Lockable Fixed Frequency 250kHz ...

Page 2

... For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: 2 PIN CONFIGURATION ) < 500ms, with , CC to –0.3V CC PART MARKING PACKAGE DESCRIPTION LTC3850GN-2 28-Lead Narrow Plastic SSOP http://www.linear.com/leadfree/ http://www.linear.com/tapeandreel/ TOP VIEW 1 28 FREQ/PLLFLTR RUN1 + 2 ...

Page 3

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

Page 4

LTC3850-2 ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T SYMBOL PARAMETER Oscillator and Phase-Locked Loop f Nominal Frequency NOM f Lowest Frequency LOW f Highest Frequency HIGH R MODE/PLLIN Input Resistance MODE/PLLIN I Phase Detector Output Current FREQ ...

Page 5

TYPICAL PERFORMANCE CHARACTERISTICS Load Step (Burst Mode Operation) I LOAD 2A/DIV 200mA TO 2. 2A/DIV V OUT 100mV/DIV AC COUPLED 40μs/DIV CIRCUIT OF FIGURE 12V 1.8V IN OUT Load Step (Pulse-Skipping Mode) I ...

Page 6

LTC3850-2 TYPICAL PERFORMANCE CHARACTERISTICS Tracking Up and Down with External Ramp TK/SS1 TK/SS2 2V/DIV V OUT1 3.3V 3Ω LOAD 1V/DIV V OUT2 1.8V 1.5Ω LOAD 1V/DIV 38502 G10 10ms/DIV Current Sense Threshold vs I Voltage ...

Page 7

TYPICAL PERFORMANCE CHARACTERISTICS Shutdown (RUN) Threshold vs Temperature 1.5 1.4 1.3 ON 1.2 OFF 1.1 1.0 –50 – TEMPERATURE (°C) 38502 G18 Undervoltage Lockout Threshold (INTV ) vs Temperature RISING 3 FALLING 2 ...

Page 8

LTC3850-2 PIN FUNCTIONS RUN1, RUN2 (Pin 1, Pin 13): Run Control Inputs. A voltage above 1.2V on either pin turns on the IC. However, forcing either of these pins below 1.2V causes the IC to shut down that particular channel. ...

Page 9

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

Page 10

LTC3850-2 OPERATION Main Control Loop The LTC3850 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 for that channel sets the RS latch, ...

Page 11

OPERATION mode of operation, tie the MODE/PLLIN pin to INTV select Burst Mode operation, fl oat the MODE/PLLIN pin. When a controller is enabled for Burst Mode operation, the peak current in the inductor is set to approximately one-third of ...

Page 12

LTC3850-2 APPLICATIONS INFORMATION The Typical Application on the fi rst page is a basic LTC3850- 2 application circuit. LTC3850-2 can be confi gured to use either DCR (inductor resistance) sensing or low value resis- tor sensing. The choice between the ...

Page 13

APPLICATIONS INFORMATION sets the peak of the inductor current, yielding a maximum average output current I equal to the peak value less MAX half the peak-to-peak ripple current, ΔI sense resistor value, use the equation: V SENSE(MAX ΔI ...

Page 14

... RLC meter, but the DCR tolerance is not always the same and varies with temperature; consult the manufacturers’ datasheets for detailed information. Using the inductor ripple current value from the Inductor Value Calculation section, the target sense resistor value is: ...

Page 15

APPLICATIONS INFORMATION sense resistors. Light load power loss can be modestly higher with a DCR network than with a sense resistor, due to the extra switching losses incurred through R1. However, DCR sensing eliminates a sense resistor, reduces conduc- tion ...

Page 16

LTC3850-2 APPLICATIONS INFORMATION Selection criteria for the power MOSFETs include the on-resistance R , Miller capacitance C DS(ON) voltage and maximum output current. Miller capacitance can be approximated from the gate charge curve MILLER usually provided on the ...

Page 17

APPLICATIONS INFORMATION to TK/SS = 0.64V. Between TK/SS = 0.64V and 0.74V, it will operate in forced continuous mode and revert to the selected mode once TK/SS > 0.74V. The output ripple is minimized during the 100mV forced continuous mode ...

Page 18

LTC3850-2 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 18 V OUT1 ...

Page 19

APPLICATIONS INFORMATION High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maxi- mum junction temperature rating for the LTC3850 exceeded. The INTV current, which is dominated CC by the gate ...

Page 20

LTC3850-2 APPLICATIONS INFORMATION Topside MOSFET Driver Supply (C External bootstrap capacitors C 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 DB ...

Page 21

APPLICATIONS INFORMATION both controllers are 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 above for the worst-case controller is adequate for the dual controller design. ...

Page 22

LTC3850-2 APPLICATIONS INFORMATION of controller 2’s top MOSFET is thus 180 degrees out- of-phase with the external clock. The phase detector is an edge sensitive digital type that provides zero degrees phase shift between the external and internal oscillators. This ...

Page 23

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

Page 24

LTC3850-2 APPLICATIONS INFORMATION a minimum of 20μF to 40μF of capacitance having a maximum of 20mΩ to 50mΩ of ESR. The LTC3850-2 2-phase architecture typically halves this input capacitance requirement over competing solutions. Other losses including Schottky conduction losses during ...

Page 25

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. These items are also illustrated graphically in the layout diagram of Figure 12. Figure ...

Page 26

LTC3850-2 APPLICATIONS INFORMATION f IN Figure 12. Recommended Printed Circuit Layout Diagram BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. 26 TK/SS1 R PU2 V PULL-UP I PGOOD PGOOD TH1 ...

Page 27

APPLICATIONS INFORMATION 4.7μF M1 0.1μF L1 3.3μH 6.19k 1% 1.33k 1% 33pF V OUT1 3.3V 5A 63.4k 1800pF 1% C OUT1 20k 4.75k 100μ L1, L2: COILTRONICS HCP0703 M1, M2: VISHAY SILICONIX Si4816BDY ...

Page 28

LTC3850-2 APPLICATIONS INFORMATION Design Example As a design example for a two channel medium current regu- lator, assume V = 12V(nominal 3.3V 1.8V, I OUT1 OUT2 MAX1,2 (see Figure 14). The regulated output voltages ...

Page 29

APPLICATIONS INFORMATION The power loss the maximum input voltage is: − • V IN(MAX) OUT P R1= LOSS R1 (20V − 3.3V) • 3.3V = 9mW 6.19k The respective values for Channel 2 are ...

Page 30

LTC3850-2 TYPICAL APPLICATIONS 4.7μ 2.2μH 6mΩ 15pF V OUT1 3.3V 5A 63.4k 1% 1000pF + 20k C 10k OUT1 1% 1% 220μF L1: TDK RLF 7030T-2R2M5R4 L2: TDK ULF10045T-3R3N6R9 C : SANYO 4TPE220MF OUT1 C : SANYO 6TPE150MI ...

Page 31

TYPICAL APPLICATIONS LTC3850-2 38502f 31 ...

Page 32

LTC3850-2 TYPICAL APPLICATIONS 32 38502f ...

Page 33

TYPICAL APPLICATIONS 4.7μF M1 0.1μF L1 0.75μH 1.2k 1% 2.94k 1% 47pF V OUT1 1.8V 5A 25.5k 2200pF 1% C 20k 14k OUT1 100μ L1, L2: TOKO FDV0630 0.75μH M1, M2: VISHAY SILICONIX Si4816BDY ...

Page 34

LTC3850-2 TYPICAL APPLICATIONS 2.2Ω V IN1 12V 4.7μF 4.7μF M1 0.1μF L1 2.2μH 3.74k 1% 1.40k 1% 47pF V OUT1 2.5V 5A 43.2k 2200pF 1% C OUT1 20k 10k 100μ L1: TOKO FDV0630 2.2μH L2: TOKO FDV0630 ...

Page 35

... FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 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

... LT3845 Low I , High Voltage Single Output Synchronous Step-Down Q DC/DC Controller LTC3851 High Effi ciency Synchronous Step-Down Switching Regulator Controller 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 ● 10k RUN 0.1μ ...

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