LTC3720

Features:

5-Bit Programmable Output Voltage:
1.05V to 1.825V (VRM8.5)
No Sense Resistor Required
2% to 87% Duty Cycle at 200kHz
tON(MIN) 100ns
Supports Active Voltage Positioning
True Current Mode Control
Stable with Ceramic C_OUT
Dual N-Channel MOSFET Synchronous Drive
Power Good Output Voltage Monitor
Wide V_IN 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-Lead Narrow SSOP Package

Application

Power Supplies for Pentium^®Processors
Notebook Computers and Servers


Pinout




Specifications

Input Supply Voltage
   V_IN, I_ON..................................................36V to 0.3V
Boosted Topside Driver Supply Voltage
   BOOST.................................................. 42V to 0.3V
SW, SENSE⁺ Voltages................................. 36V to 5V
EXTV_CC, (BOOST SW), RUN/SS, V_CC
VID0-VID4, PGOOD Voltages......................  7V to 0.3V
FCB, V_ON, V_RNG Voltages...........INTV_CC + 0.3V to 0.3V
I_TH, V_FB, V_OSENSE Voltages....................... 2.7V to 0.3V
TG, BG, INTV_CC, EXTV_CC Peak Currents..................... 2A
TG, BG, INTV_CC, EXTV_CC RMS Currents.................. 50mA
Operating Ambient Temperature Range
    LTC3720EGN (Note 2)...........................40°C to 85°C
Junction Temperature (Note 3)............................ 125°C
Storage Temperature Range.................65°C to 150°C
Lead Temperature (Soldering, 10 sec)..................300°C


Description

The LTC^®3720 is a synchronous step-down switching regulator controller for CPU power. An output voltage of LTC3720 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 frequency is selected by an external resistor and is compen-sated for variations in V_IN and V_OUT.
Discontinuous mode operation of LTC3720 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 supply sequencing is accomplished using an external timing capacitor. The regulator current limit level of LTC3720 is also user programmable. Wide supply range allows operation from