FEATURES
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LTC1709
2-Phase, 5-Bit Adjustable,
High Efficiency, Synchronous Step-Down
Switching Regulator
DESCRIPTIO
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.
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Two Ouput Stages Operate Antiphase Reducing
Input Capacitance and Power Supply Noise
5-Bit VID Control (VRM 8.4 Compliant)
V
OUT
: 1.3V to 3.5V in 50mV/100mV Steps
Current Mode Control Ensures Current Sharing
True Remote Sensing Differential Amplifier
OPTI-LOOP
TM
Compensation Minimizes C
OUT
Programmable Fixed Frequency: 150kHz to
300kHz—Effective 300kHz to 600kHz Switching
Frequency
±
1% Output Voltage Accuracy
Wide V
IN
Range: 4V to 36V Operation
Adjustable Soft-Start Current Ramping
Internal Current Foldback
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Soft-Latch Eliminates Nuisance Trips
Low Shutdown Current: 20µA
Small 36-Lead Narrow (0.209") SSOP Package
APPLICATIO S
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Desktop Computers
Internet/Network Servers
Large Memory Arrays
DC Power Distribution Systems
Battery Chargers
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
V
IN
RUN/SS
1.2nF
I
TH
S
TG1
BOOST 1
SW1
Q1
S
10µF
×4
35V
0.002Ω
1µH
V
IN
5V TO 28V
100
0.47µF
S
LTC1709
15k
BG1
PGND
Q2
EFFICIENCY (%)
SGND
5 VID BITS
VID0–VID4
EAIN
FBOUT
SENSEIN
V
DIFFOUT
V
OS –
V
OS +
SENSE1
+
SENSE1
–
TG2
BOOST2
SW2
BG2
INTV
CC
SENSE 2
+
SENSE 2
–
S
S
S
Q3
0.47µF
1µH
Q4
0.002Ω
V
OUT
1.3V TO 3.5V
40A
S
10µF
+
C
OUT
1000µF
4V
×2
1709 TA01
+
Q1–Q4 2× FAIRCHILD FDS7760A OR SILICONIX Si4874
Figure 1. High Current 2-Phase Step-Down Converter
U
U
U
Efficiency Curve
V
IN
= 5V
V
OUT
= 1.6V
f
S
= 200kHz
90
80
70
60
50
0
5
10
15 20 25 30 35
LOAD CURRENTS (A)
40
45
1709 TA01a
1
LINER [ LINEAR TECHNOLOGY ]
