LTC3720_15 Datasheet, PDF (1/24 Pages) Linear Technology – Single Phase VRM8.5 Current Mode Step-Down Controller

LTC3720
Single Phase VRM8.5
Current Mode Step-Down Controller
FEATURES
s _{5-Bit Programmable Output Voltage:}
1.05V to 1.825V (VRM8.5)
s _{No Sense Resistor Required}
s _{2% to 87% Duty Cycle at 200kHz}
s _{tON(MIN) ≤ 100ns}
s _{Supports Active Voltage Positioning}
s _{True Current Mode Control}
s _{Stable with Ceramic COUT}
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Power Good Output Voltage Monitor}
s _{Wide VIN Range: 4V to 36V}
s _{±1% 0.8V Reference}
s _{Adjustable Current Limit}
s _{Adjustable Switching Frequency}
s _{Forced Continuous Control Pin}
s _{Programmable Soft-Start}
s _{Output Overvoltage Protection}
s _{Optional Short-Circuit Shutdown Timer}
s _{Micropower Shutdown: IQ < 30µA}
s _{Available in 28-Lead Narrow SSOP Package}
U
APPLICATIO S
s _{Power Supplies for Pentium}^® _Processors
s _{Notebook Computers and Servers}
DESCRIPTIO
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-
sated for variations in V_IN and V_OUT.
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-circuit shutdown timer. Soft-start capability for sup-
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 R_SENSE is a trademark of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
TYPICAL APPLICATIO
0.1µF
470pF
20k
5-BIT VID
LTC3720
PGOOD I_ON
V_IN
RUN/SS TG
I_TH
SW
SGND BOOST
VID4
VID3
VID2
VID1
VID0
V_CC
INTV_CC
SENSE⁺
BG
PGND
SENSE¯
V_OSENSE
330k
0.33µF
CMDSH-3
+
4.7µF
IRF7811W
×2
L1
1µH
IRF7811W
×3
UPS840
10µF
×5
V_IN
5V TO 24V
V_OUT
1.05V TO 1.825V
+ ^{COUT 20A}
270µF
2V
×4
C_OUT: CORNELL DUBILIER
ESRE271M02B
L1: SUMIDA CEP125-IROMC
3720 F01a
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Output Current
100
V_OUT = 1.45V
95 ^{L1 = 1µH}
90
V_IN = 5V
85
80
V_IN = 15V
75
70
65
60
55
0.01
0.1
1
10
OUTPUT CURRENT (A)
100
3720 F01b
3720f
1