POWER LOSS (mW)
LTC3868-1
Low I , Dual
Q
2-Phase Synchronous
Step-Down Controller
FEATURES DESCRIPTION
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Low Operating I : 170A (One Channel On) The LTC 3868-1 is a high performance dual step-down
Q
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switching regulator controller that drives all N-channel
Wide Output Voltage Range: 0.8V V 14V
OUT
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synchronous power MOSFET stages. A constant frequency
Wide V Range: 4V to 24V
IN
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current mode architecture allows a phase-lockable fre-
R or DCR Current Sensing
SENSE
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quency of up to 850kHz. Power loss and noise due to the
Out-of-Phase Controllers Reduce Required Input
input capacitor ESR are minimized by operating the two
Capacitance and Power Supply Induced Noise
controller outputs out of phase.
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OPTI-LOOP Compensation Minimizes C
OUT
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Phase-Lockable Frequency (75kHz to 850kHz)
The 170A no-load quiescent current extends operating
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Programmable Fixed Frequency (50kHz to 900kHz)
life in battery powered systems. OPTI-LOOP compensation
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Selectable Continuous, Pulse-Skipping or
allows the transient response to be optimized over a wide
Burst Mode Operation at Light Loads
range of output capacitance and ESR values. The LTC3868-
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Very Low Dropout Operation: 99% Duty Cycle
1 features a precision 0.8V reference and a power good
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Adjustable Output Voltage Soft-Start
output indicator. A wide 4V to 24V input supply range
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Power Good Output Voltage Monitor
encompasses a wide range of intermediate bus voltages
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Output Overvoltage Protection
and battery chemistries.
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Output Latchoff Protection During Short Circuit
Independent soft-start pins for each controller ramp the
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Low Shutdown I : 8A
Q
output voltages during start-up. Current foldback limits
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Internal LDO Powers Gate Drive from V or EXTV
IN CC
MOSFET heat dissipation during short-circuit conditions.
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No Current Foldback During Start-Up
The output short-circuit latchoff feature further protects
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Small 4mm 5mm QFN and Narrow SSOP Packages
the circuit in short-circuit conditions.
For a leadless 32-pin QFN package with the additional fea-
APPLICATIONS
tures of adjustable current limit, clock out, phase modula-
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Notebook and Palmtop Computers
tion and two PGOOD outputs, see the LTC3868 data sheet.
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Portable Instruments
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Module, Linear Technology and the Linear logo
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Battery Operated Digital Devices
are registered trademarks and No R and UltraFast are trademarks of Linear Technology
SENSE
Corporation. All other trademarks are the property of their respective owners. Protected by U.S.
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Distributed DC Power Systems
Patents, including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
TYPICAL APPLICATION
High Ef ciency Dual 8.5V/3.3V Step-Down Converter
V
IN Ef ciency and Power Loss
9V TO 24V
22F
vs Load Current
4.7F
50V
V INTV 100 10000
IN CC
TG1 TG2
90
0.1F 0.1F
BOOST1 BOOST2
3.3H
7.2H 80 1000
SW1 SW2
70
EFFICIENCY
BG1 BG2
60 100
LTC3868-1
PGND 50
POWER LOSS
+ +
40 10
SENSE1 SENSE2
30
0.007 0.01
20 1
V
V SENSE1 SENSE2 OUT2
V = 12V
OUT1 IN
8.5V
3.3V V V
FB1 FB2 10 V = 3.3V
OUT
3.5A
5A 62.5k 193k
I I FIGURE 12 CIRCUIT
TH1 TH2
0 0.1
150F 680pF
680pF
150F
SS1 SGND SS2 0.0001 0.001 0.01 0.1 1 10
20k
20k 15k 15k OUTPUT CURRENT (A)
0.1F 0.1F
38681 TA01b
38681 TA01
38681fd
1
EFFICIENCY (%)LTC3868-1
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage (V ) ......................... 0.3V to 28V FREQ Voltages ..................................... 0.3V to INTV
CC
IN
Topside Driver Voltages EXTV ...................................................... 0.3V to 14V
CC
BOOST1, BOOST2 ................................. 0.3V to 34V I , I , V , V Voltages ..................... 0.3V to 6V
TH1 TH2 FB1 FB2
Switch Voltage (SW1, SW2) ........................ 5V to 28V PGOOD1 Voltage ......................................... 0.3V to 6V
PLLIN/MODE, SS1, SS2, INTV Voltages ......................... 0.3V to 6V
CC
(BOOST1-SW1), (BOOST2-SW2) ................ 0.3V to 6V Operating Temperature Range (Note 2).... 40C to 85C
RUN1, RUN2 ............................................... 0.3V to 8V Junction Temperature (Note 3) ............................. 125C
Maximum Current Sourced into Pin from Storage Temperature Range ................... 65C to 150C
Source >8V ......................................................100A Lead Temperature (Soldering, 10 sec)
+ +
SENSE1 , SENSE2 , SENSE1 SSOP ................................................................300C
SENSE2 Voltages ...................................... 0.3V to 16V
PIN CONFIGURATION
TOP VIEW
TOP VIEW
1 SS1
I 28
TH1
2 PGOOD1
V 27
FB1
+
3 TG1
28 27 26 25 24 23 SENSE1 26
+
SENSE1 1 22 BOOST1 4 SW1
SENSE1 25
SENSE1 2 21 BG1
5 BOOST1
FREQ 24
FREQ 3 20 V
IN 6 BG1
PLLIN/MODE 23
PLLIN/MODE 4 19 PGND
29
7 V
SGND 22
IN
SGND
SGND 5 18
EXTV
CC
8 PGND
RUN1 21
RUN1 6 17 INTV
CC
9 EXTV
RUN2 20
CC
RUN2 7 16 BG2
10 INTV
SENSE2 19
CC
SENSE2 8 15 BOOST2
+
11 BG2
SENSE2 18
9 10 11 12 13 14
12 BOOST2
V 17
FB2
13 SW2
I 16
TH2
14 TG2
SS2 15
UFD PACKAGE
28-LEAD (4mm s 5mm) PLASTIC QFN
GN PACKAGE
T = 125C, = 43C/W 28-LEAD PLASTIC SSOP
JMAX JA
EXPOSED PAD (PIN 29) IS SGND, MUST BE SOLDERED TO PCB
T = 125C, = 90C/W
JMAX JA
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3868EUFD-1#PBF LTC3868EUFD-1#TRPBF 38681 28-Lead (4mm 5mm) Plastic QFN 40C to 85C
LTC3868IUFD-1#PBF LTC3868IUFD-1#TRPBF 38681 28-Lead (4mm 5mm) Plastic QFN 40C to 85C
LTC3868EGN-1#PBF LTC3868EGN-1#TRPBF LTC3868GN-1 28-Lead Plastic SSOP 40C to 85C
LTC3868IGN-1#PBF LTC3868IGN-1#TRPBF LTC3868GN-1 28-Lead Plastic SSOP 40C to 85C
Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping
container.Consult LTC Marketing for information on non-standard lead based nish parts.
For more information on lead free part marking, go to: