LTC3770 Datasheet, PDF (1/24 Pages) Linear Technology – Synchronous Controller with Margining, Tracking and PLL

FEATURES
■ _{Wide VIN Range: 4V to 32V}
■ _{±0.67% 0.6V Reference Voltage}
■ _{Output Voltage Tracking Capability}
■ _{Programmable Margining}
■ _{Sense Resistor Optional}
■ _{True Current Mode Control}
■ _{2% to 90% Duty Cycle at 200kHz}
■ _{tON(MIN) ≤ 100ns}
■ _{Phase Lock Loop Frequency Synchronization}
■ _{Powerful Dual N-Channel MOSFET Driver}
■ _{Adjustable Cycle-by-Cycle Current Limit}
■ _{Adjustable Switching Frequency}
■ _{Programmable Soft-Start}
■ _{Current Foldback Protection (Disabled at Start-Up)}
■ _{Output Overvoltage Protection}
■ _{Micropower Shutdown: IQ < 30µA}
■ _{Power Good Output Voltage Monitor}
Tracks the Reference Input Pin
■ _{Available in (5mm × 5mm) QFN and 28-Lead}
SSOP Packages
U
APPLICATIO S
■ _{Distributed Power Systems}
■ _{Server Power Supply}
LTC3770
Fast No R_SENSE^TM Step-Down
Synchronous Controller with
Margining, Tracking and PLL
DESCRIPTIO
The LTC^®3770 is a synchronous step-down switching
regulator controller with output voltage up/down tracking
capability and voltage margining. Its advanced functions
and high accuracy reference are ideal for powering
high performance server, ASIC and computer memory
systems.
The LTC3770 uses a constant on-time, valley current
mode control architecture to deliver very low duty factors
without requiring a sense resistor. The operating fre-
quency is selected by an external resistor and is compen-
sated for variations in input supply voltage. An internal
phase-lock loop allows the IC to be synchronized to an
external clock.
Fault protection is provided by an overvoltage comparator
and input undervoltage lockout. The regulator current limit
is user programmable. A wide supply range allows volt-
ages as high as 32V to be stepped down to as low as a 0.6V
output. Power supply sequencing is accomplished using
an external soft-start timing capacitor.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. No R_SENSE is a trademark of Linear
Technology Corporation. Protected by U.S. Patents including 5481178, 5487554, 6580258,
6304066, 6476589, 6774611.
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
0.01µF _10k
0.1µF
1000pF ^10k
V_OUT
10k
82k
PGOOD I_ON
MARGIN _VIN
PLLFLTR _TG
PLLIN
SW
TRACK/SS
I_TH
BOOST
LTC3770
SGND
RUN
V_ON
V_RNG
INTV_CC
DRV_CC
BG
SENSE⁺
V_{REFOUTSENSE–}
V_REFIN
MPGM
PGND
V_FB
68k
0.22µF
Si4884
1.8µH
CMDSH-3
Si4874
B340A
V_IN
5V TO 28V
10µF
35V
x3 VOUT
2.5V
+
10A
180µF
4V
x2
10µF
95.3k
30.1k
3770 TA01
Efficiency and Power Loss vs Load Current
100
V_IN = 5V
95 V_OUT = 2.5V
90
EFFICIENCY
85
80
75
70
POWER LOSS
65
60
55
50
0.01
0.1
1
LOAD CURRENT (A)
10
1
0.1
0.01
10
3770 TA01b
3770f
1