LTC3879_15 Datasheet, PDF (1/28 Pages) Linear Technology – Fast, Wide Operating Range No RSENSE Step-Down Controller

FEATURES
n _{Wide VIN Range: 4V to 38V}
n _{±1% 0.6V Voltage Reference}
n _{Extremely Fast Transient Response}
n _{tON(MIN): 43ns}
n _{No RSENSE™ Valley Current Mode Control}
n _{Stable with Low ESR Ceramic COUT}
n _{Supports Smooth Start-Up in Pre-Biased Output}
n _{Optimized for High Step-Down Ratios}
n _{Adjustable Output Voltage Soft-Start or Tracking}
n _{Power Good Output Voltage Monitor}
n _{Dual N-Channel MOSFET Synchronous Drive}
n _{Adjustable Switching Frequency}
n _{Programmable Current Limit with Foldback}
n _{Output Overvoltage Protection}
n _{16-Pin MSOP and 3mm × 3mm QFN Packages}
APPLICATIONS
n _{Distributed Power Systems}
n _{Embedded Computing}
n _{Communications Infrastructure}
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066.
LTC3879
Fast, Wide Operating
Range No R_SENSE
Step-Down Controller
DESCRIPTION
The LTC^®3879 is a synchronous step-down switching
regulator controller optimized for high switching frequency
and fast transient response. The constant on-time valley
current mode architecture allows for a wide input range,
including very low duty factor operation. No external sense
resistor or slope compensation is required. System flex-
ibility is offered through a user-programmable soft-start pin
and independent RUN pin. The voltage ramping soft-start
function can be programmed with a capacitor or made to
track an external reference source.
Operating frequency is set by an external resistor and
compensated for variations in V_IN to offer excellent line
stability. Discontinuous mode operation provides high
efficiency during light load conditions. A forced continu-
ous control pin allows the user to reduce noise and RF
interference. Safety features include output overvoltage
protection and programmable current limit with foldback.
The current limit is user programmable.
The LTC3879 allows operation from 4V to 38V at the input
and from 0.6V to 90% V_IN at the output. The LTC3879 is
available in a small 16-pin thermally enhanced MSOP or
3mm × 3mm QFN packages.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
0.1μF
RUN
I_ON
TRACK/SS V_IN
220pF
27k
TG
LTC3879
I_TH
SW
SGND BOOST
MODE
INTV_CC
BG
PGOOD PGND
V_RNG
V_FB
432k
RJK0305
0.56μH
0.22μF
4.7μF
RJK0330
10k
V_IN
4.5V TO 28V
10μF
V_OUT
1.2V
15A
330μF
s2
10k
3879 TA01a
Efficiency vs Load Current
100
90 DISCONTINUOUS
MODE
80
70
60
CONTINUOUS
MODE
50
40
30
20
10
0
0.01
V_IN = 12V
V_OUT = 1.2V
SW FREQ = 400kHz
FIGURE 10 CIRCUIT
0.1
1
10
LOAD CURRENT (A)
100
3879 TA01b
3879f
1