LTC1709 Datasheet, PDF (1/28 Pages) Linear Technology – 2-Phase, 5-Bit Adjustable, High Efficiency, Synchronous Step-Down Switching Regulator

LTC1709
FEATURES
2-Phase, 5-Bit Adjustable,
High Efficiency, Synchronous Step-Down
Switching Regulator
DESCRIPTIO
s _{Two Ouput Stages Operate Antiphase Reducing}
Input Capacitance and Power Supply Noise
s _{5-Bit VID Control (VRM 8.4 Compliant)}
V_OUT: 1.3V to 3.5V in 50mV/100mV Steps
s _{Current Mode Control Ensures Current Sharing}
s _{True Remote Sensing Differential Amplifier}
s _OPTI-LOOP^TM _{Compensation Minimizes COUT}
s _{Programmable Fixed Frequency: 150kHz to}
300kHz—Effective 300kHz to 600kHz Switching
Frequency
s _{±1% Output Voltage Accuracy}
s _{Wide VIN Range: 4V to 36V Operation}
s _{Adjustable Soft-Start Current Ramping}
s _{Internal Current Foldback}
s _{Short-Circuit Shutdown Timer with Defeat Option}
s _{Overvoltage Soft-Latch Eliminates Nuisance Trips}
s _{Low Shutdown Current: 20µA}
s _{Small 36-Lead Narrow (0.209") SSOP Package}
U
APPLICATIO S
s _{Desktop Computers}
s _{Internet/Network Servers}
s _{Large Memory Arrays}
s _{DC Power Distribution Systems}
s _{Battery Chargers}
The LTC^®1709 is a 2-phase, VID programmable, synchro-
nous step-down switching regulator controller that drives
all N-channel external power MOSFET stages in a fixed
frequency architecture. The 2-phase controller drives its
two output stages out of phase at frequencies up to
300kHz to minimize the RMS ripple currents in both input
and output capacitors. The 2-phase technique effectively
multiplies the fundamental frequency by two, improving
transient response while operating each channel at a
optimum frequency for efficiency. Thermal design is also
simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required in high current applications.
The RUN/SS pin provides soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
dissipaton during short-circuit conditions when overcurrent
latchoff is disabled. OPTI-LOOP compensation allows the
transient response to be optimized for a wide range of
output capacitors and ESR values.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
15k ^1.2nF
5 VID BITS
V_IN
RUN/SS
TG1
BOOST 1
SW1
LTC1709
BG1
I_TH
SGND
VID0–VID4
PGND
SENSE1⁺
SENSE1^–
TG2
EAIN
BOOST2
FBOUT
SW2
SENSEIN
BG2
V_DIFFOUT
V_OS–
V_OS+
INTV_CC
SENSE 2⁺
SENSE 2^–
0.47µF
10µF ×4
Q1
35V
0.002Ω
1µH
Q2
Q3
0.47µF
Q4
10µF
0.002Ω
1µH
Q1–Q4 2× FAIRCHILD FDS7760A OR SILICONIX Si4874
Figure 1. High Current 2-Phase Step-Down Converter
V_IN
5V TO 28V
V_OUT
1.3V TO 3.5V
40A
+
C_OUT
1000µF
4V
×2
1709 TA01
Efficiency Curve
100
V_IN = 5V
V_OUT = 1.6V
90
f_S = 200kHz
80
70
60
50
0 5 10 15 20 25 30 35 40 45
LOAD CURRENTS (A)
1709 TA01a
1