LTC3720
Single Phase VRM8.5
Current Mode Step-Down Controller
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FEATURES
DESCRIPTIO
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5-Bit Programmable Output Voltage:
The LTC®3720 is a synchronous step-down switching
regulator controller for CPU power. An output voltage
between 1.05V and 1.825V is selected by a 5-bit code
(Intel VRM8.5 VID specification). The controller uses a
valley current control architecture to deliver very low duty
cycles without requiring a sense resistor. Operating fre-
quency is selected by an external resistor and is compen-
1.05V to 1.825V (VRM8.5)
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No Sense Resistor Required
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2% to 87% Duty Cycle at 200kHz
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tON(MIN) ≤ 100ns
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Supports Active Voltage Positioning
True Current Mode Control
Stable with Ceramic COUT
sated for variations in VIN and VOUT.
Dual N-Channel MOSFET Synchronous Drive
Power Good Output Voltage Monitor
Wide VIN Range: 4V to 36V
±1% 0.8V Reference
Adjustable Current Limit
Adjustable Switching Frequency
Forced Continuous Control Pin
Programmable Soft-Start
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Micropower Shutdown: IQ < 30µA
Available in 28-LUead Narrow SSOP Package
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling discontinuous mode
operation when the main output is lightly loaded.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and optional
short-circuitshutdowntimer.Soft-startcapabilityforsup-
ply sequencing is accomplished using an external timing
capacitor. The regulator current limit level is also user
programmable. Wide supply range allows operation from
4V to 36V at the input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
APPLICATIO S
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Power Supplies for Pentium® Processors
Notebook Computers and Servers
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TYPICAL APPLICATIO
LTC3720
PGOOD
330k
Efficiency vs Output Current
I
ON
100
V
IN
V
= 1.45V
OUT
L1 = 1µH
0.1µF
V
IN
5V TO 24V
95
90
85
80
75
70
65
60
55
10µF
×5
IRF7811W
RUN/SS
TG
×2
L1
470pF
1µH
V
= 5V
V
OUT
I
SW
IN
V
TH
1.05V TO 1.825V
20A
20k
0.33µF
C
OUT
SGND BOOST
+
= 15V
IN
270µF
2V
V
CMDSH-3
CC
INTV
CC
×4
UPS840
+
+
VID4
VID3
VID2
VID1
VID0
SENSE
BG
4.7µF
IRF7811W
×3
C
OUT
: CORNELL DUBILIER
ESRE271M02B
L1: SUMIDA CEP125-IROMC
5-BIT VID
PGND
SENSE¯
3720 F01a
V
OSENSE
0.01
1
10
100
0.1
OUTPUT CURRENT (A)
3720 F01b
Figure 1. High Efficiency Step-Down Converter
3720f
1