Features: No Current Sense Resistors Required
Out-of-Phase Controllers Reduce Required
Input Capacitance
VOUT2 Tracks 1/2 VREF
Symmetrical Source/Sink Output Current
Capability (VOUT2)
Spread Spectrum Operation (When Enabled)
Wide V IN Range: 2.75V to 9.8V
Constant Frequency Current Mode Operation
0.6V ±1.5% Voltage Reference (VOUT1)
Low Dropout Operation: 100% Duty Cycle
True PLL for Frequency Locking or Adjustment
Internal Soft-Start Circuitry
Power Good Output Voltage Monitor
Output Overvoltage Protection
Micropower Shutdown: IQ = 9 A
Tiny Low Profile (4mm 4mm) QFN and Narrow
SSOP Packages
ApplicationDDR, DDR II and QDR Memory
SSTL, HSTL Termination Supplies
Servers, RAID Systems
Distributed DC Power SystemsPinout
SpecificationsInput Supply Voltage (V IN) ........................ 0.3V to 10V
PLLLPF, RUN/SS, SYNC/SSEN,
V REF, SENSE1+ , SENSE2 +, V FB2
IPRG1, IPRG2 Voltages.................... 0.3V to (V IN + 0.3V)
V FB1, I TH1, ITH2 Voltages......................... 0.3V to 2.4V
SW1, SW2 Voltages................. 2VIN to V + 1V (10V Max)
PGOOD ........................................................ 0.3V to 10V
TG1, TG2, BG1, BG2 Peak Output Current (<10 s) ..... 1A
Operating Temperature Range (Note 2)...... 40C to 85
Storage Temperature Range .....................65 C to 125
Junction Temperature (Note 3) ................................ 125
Lead Temperature (Soldering, 10 sec)
(LTC3776EGN) ...........................................................300
Description
The LTC(R) 3776 is a 2-phase dual output synchronous step- down switching regulator controller for DDR/QDR memory termination applications. The second controller regulates its output voltage to 1/2 V while providing symmetrical REF source and sink output current capability.
The No RSENSE constant frequency current mode architec- SENSE ture eliminates the need for sense resistors and improves efficiency. Power loss and noise due to the ESR of the input capacitance are minimized by operating the two controllers out of phase.
The switching frequency can be programmed up to 750kHz, allowing the use of small surface mount inductors and ca- pacitors. For noise sensitive applications, the LTC3776 switching frequency can be externally synchronized from 250kHz to 850kHz, or can be enabled for spread spectrum operation. Forced continuous operation reduces noise and RF interference. Soft-start for VOUT1is provided internally and can be extended using an external capacitor. The LTC3776 is available in the tiny thermally enhanced (4mm 4mm) QFN package or 24-lead SSOP narrow package.
LTC3776 Data Sheet
