LTC3851A-1
1
3851a1fa
Typical applicaTion
FeaTures
applicaTions
DescripTion
Synchronous
Step-Down Switching
Regulator Controller
The LTC
®
3851A-1 is a high performance synchronous
step-down switching regulator controller that drives
an all N-channel synchronous power MOSFET stage. A
con stant frequency current mode architecture allows a
phase-lockable frequency of up to 750kHz.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The LTC3851A-1 features a precision 0.8V
reference and a power good indicator. A wide 4V to 38V
(40V absolute maximum) input supply range encompasses
most battery configurations and intermediate bus voltages.
The TK/SS pin ramps the output voltage during start-up and
shutdown with coincident or ratiometric tracking. Current
foldback limits MOSFET heat dissipation during short-
circuit conditions. The MODE/PLLIN pin selects among
Burst Mode operation, pulse-skipping mode or continu-
ous inductor current mode at light loads and allows the IC
to be synchronized to an external clock. The LTC3851A-1
contains an improved PLL compared to the LTC3851-1.
The LTC3851A-1 is identical to the LTC3851A except that
the I
LIM
pin is replaced by PGOOD.
High Efficiency Synchronous Step-Down Converter
n
Wide V
IN
Range: 4V to 38V Operation
n
R
SENSE
or DCR Current Sensing
n
±1% Output Voltage Accuracy
n
Power Good Output Voltage Monitor
n
Phase-Lockable Fixed Frequency: 250kHz to 750kHz
n
Dual N-Channel MOSFET Synchronous Drive
n
Very Low Dropout Operation: 99% Duty Cycle
n
Adjustable Output Voltage Soft-Start or Tracking
n
Output Current Foldback Limiting
n
Output Overvoltage Protection
n
OPTI-LOOP
®
Compensation Minimizes C
OUT
n
Selectable Continuous, Pulse-Skipping or
Burst Mode
®
Operation at Light Loads
n
Low Shutdown I
Q
: 20µA
n
V
OUT
Range: 0.8V to 5.5V
n
Thermally Enhanced 16-Lead MSOP
or 3mm × 3mm QFN Package
n
Automotive Systems
n
Telecom Systems
n
Industrial Equipment
n
Distributed DC Power Systems
Efficiency and Power Loss
vs Load Current
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are registered
trademarks and No R
SENSE
, UltraFast are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258, 6611131.
PGO0D
RUN
TK/SS
I
TH
FREQ/PLLFLTR
V
IN
INTV
CC
TG
SW
INTV
CC
MODE/PLLIN
BG
SENSE
+
SENSE
–
V
FB
GND
0.047µF
0.1µF
4.7µF
3.01k
LTC3851A-1
22µF
V
IN
4.5V TO 38V
V
OUT
3.3V
15A
3851A1 TA01a
0.68µH
330pF
2200pF
0.1µF
0.1µF
330µF
×2
BOOST
15k
154k
48.7k
30.1k
82.5k
100k
LOAD CURRENT (mA)
10
70
EFFICIENCY (%)
POWER LOSS (mW)
75
80
85
90
100 1000 10000 100000
3851A1 TA01b
65
60
55
50
95
100
1000
100
10
10000
V
IN
= 12V
V
OUT
= 3.3V
EFFICIENCY
POWER LOSS