SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS PRELIMINARY - October 9, 2000 SC1110 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com DESCRIPTION FEATURES •= Generates termination voltages for active termina- The SC1110 is a low-cost, full featured, synchronous voltage-mode controller designed to generate termination voltage in double data rate (DDR) memory systems and other applications where wide data bus need to be actively terminated. Synchronous control of the MOSFET half bridge allows power flowing bidirectionally. The termination voltage can be tightly regulated to track the chipset voltage, i.e. to be exactly 50% of that at all times. tion schemes •= 1% set point accuracy •= For ±7A output current, transient regulation is better than ±80mV •= VREFIN pin available •= Buffered VREFOUT for system usage •= RDSON sensing for over current protection in hiccup mode •= Soft start and logic input enabling •= 250kHz switching for best transient and efficiency The SC1110 is ideal for low cost implementation of termination voltage supplies. SC1110 features include temperature compensated voltage reference, triangle wave oscillator and current sense comparator circuitry, and allows the use of inexpensive N-channel power switches. performance •= Gate drive capable for 0.5A sourcing and sinking APPLICATIONS •= For DDR memory systems •= For active termination schemes in high speed logic The SC1110 operates at a fixed 250kHz, providing an optimum compromise between efficiency, transient performance, external component size, and cost. systems ORDERING INFORMATION (1) DEVICE PACKAGE TEMP. RANGE (TJ) SO-14 0 - 125°C SC1110CSTR Note: (1) Only available in tape and reel packaging. A reel contains 2500 devices. TYPICAL APPLICATION CIRCUIT REFOUT +5Vcc + R1 5k C1 0.01 R2 1.24k R3 10 U1 SC1110 C2 0.1 1 VCC R4 1k REFOUT C7 1.0 C4 0.022 C8,9 2 x 10uF C10,11 2 x 560uF Vin 2.5V _ 14 SS/ENBL 2 C3 0.1 SS/ENBL REFIN OCSET SENSE 13 R5 1k 3 12 PWRGD 4 PWRGD COMP 11 R6 4.7k C5 0.047 C25 0.1 5 GND BSTL PHASE BSTH 10 D1 MBRM120 6 7 DL DH 9 8 R7 2.2 R8 2.2 Q1 Si9426DY C6 1.0 L1 800 nH + Q2 Si9426DY C12-14 3 x 560uF C10-14: Sanyo, 4SP560M C8,9,15-24: TDK, CC3216AX5R0J106K L1: Panasonic, ETQP6F0R8L or Falco, QPIP1205-809-3 Q1,Q2 options: Si9426DY, FDS6890A, IRF7401 D1: ON Semi (Motorola) C15-24 10 x 10uF Vout = 1.25V @ 7A _ 1 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS SC1110 PRELIMINARY - October 9, 2000 ABSOLUTE MAXIMUM RATINGS Parameter Symbol Maximum Units VIN -0.5 to 14 V PGND to GND ± 0.5 V PHASE to GND -0.5 to 18 V BSTH to PHASE 14 V VCC, BSTL to GND Thermal Resistance Junction to Case θJC 45 °C/W Thermal Resistance Junction to Ambient θJA 115 °C/W Operating Temperature Range TA 0 to 70 °C Storage Temperature Range TSTG -65 to +150 °C Lead Temperature (Soldering) 10 sec TLEAD 300 °C ELECTRICAL CHARACTERISTICS Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25oC PARAMETER CONDITIONS MIN TYP MAX UNITS Supply Voltage VCC 4.4 12.6 V Supply Current EN = VCC 8 mA Line Regulation VIN = 2.5 ± 0.5V, VO = VIN/2 @ 0A 0.5 % POWER SUPPLY UNDER VOLTAGE LOCKOUT Turn-On Threshold TBD 4.2 TBD V Turn-Off Threshold TBD 4.0 TBD V ERROR AMPLIFIER Transconductance 2 mS Open Loop DC Gain 50 dB Bandwidth -3dB 500 kHz COMP Source Capability ±250 µA Input Bias 5 8 µA 275 kHz OSCILLATOR Oscillator Frequency 225 250 Oscillator Max Duty Cycle 90 95 % 1 V 100 ns Ramp Height TIMING Minimum Off-Time Dead Time 80 ns 2 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS SC1110 PRELIMINARY - October 9, 2000 ELECTRICAL CHARACTERISTICS Unless specified: VCC = 4.75V to 12.6V; GND = PGND = 0V; FB = VO; VBSTL = 12V; VBSTH-PHASE = 12V; TJ = 25oC PARAMETER CONDITIONS MIN BSTH - DH = 4.5V, DH - PHASE = 3.0V 0.5 DH - PHASE = 1.5V 0.1 BSTL - DL = 4.5V, DL - GND = 3.0V 0.5 DL - GND = 1.5V 0.1 VOCSET = 4.5V 180 TYP MAX UNITS MOSFET DRIVERS Peak DH Sink/Source Current Peak DL Sink/Source Current A A PROTECTION Over Current Set Isource 200 220 µA SOFT START Charge Current VSS = 1.5V 10 µA Discharge Current VSS = 1.5V 2 µA Upper Threshold 112 % Lower Threshold 88 % POWER GOOD PWRGD Voltage Low IPWRGD = 2mA 0.5 V REFERENCE REFOUT Source Current 3 Input Bias 5 mA 8 µA NOTE: (1) Specification refers to application circuit (Figure 1.). BLOCK DIAGRAM 3 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS SC1110 PRELIMINARY - October 9, 2000 PIN CONFIGURATION Top View (14-Pin SOIC) PIN DESCRIPTION Pin # Pin Name Pin Function 1 VCC Chip supply voltage. 2 SS/ENBL Soft start/Enable. 3 OCSET Current limit set point. 4 PWRGD Logic high indicates correct output. 5 GND Ground. 6 PHASE Phase node connection between MOSFET’s. 7 DL Low side driver output. 8 DH High side driver output. 9 BSTH High side drive supply. 10 BSTL Low side drive supply. 11 COMP Error amplifier output, compensation. 12 SENSE Error amplifier negative input. 13 REFIN Error amplifier positive input. 14 REFOUT Buffered reference voltage. NOTE: (1) All logic level inputs and outputs are open collector TTL compatible. 4 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS SC1110 PRELIMINARY - October 9, 2000 THEORY OF OPERATION Synchronous Buck Converter VTERMINATION power is provided by a synchronous, voltage-mode pulse width modulated (PWM) controller. This section has all the features required to build a high efficiency synchronous buck converter for termination of power application. The output voltage of the synchronous converter is set and controlled by the output of the error amplifier. The resistive divider generates reference voltage for the error amplifier from an external chipset voltage which is usually 2.5V. The inverting input of the error amplifier receives its voltage from the SENSE pin. The internal oscillator uses an on-chip capacitor and trimmed precision current sources to set the oscillation frequency to 250kHz. The triangular output of the oscillator sets the reference voltage at the inverting input of the PWM comparator. The non-inverting input of the comparator receives it’s input voltage from the error amplifier. When the oscillator output voltage drops below the error amplifier output voltage, the comparator output goes high. This pulls DL low, turning off the lowside FET, and DH is pulled high, turning on the highside FET (once the cross-current control allows it). When the oscillator voltage rises back above the error amplifier output voltage, the comparator output goes low. This pulls DH low, turning off the high-side FET, and DL is pulled high, turning on the low-side FET (once the cross-current control allows it). As SENSE increases, the output voltage of the error amplifier decreases. This causes a reduction in the ontime of the high-side MOSFET connected to DH, hence lowering the output voltage. Under Voltage Lockout The under voltage lockout circuit of the SC1110 assures that both the high-side MOSFET driver outputs remain in the off state whenever the supply voltage drops below set parameters. Lockout occurs if VCC falls below 4.0V. Normal operation resumes once VCC rises above 4.2V. Soft Start Initially, SS/ENABLE sources 10µA of current to charge an external capacitor. The outputs of the error amplifiers are clamped to a voltage proportional to the voltage on SS/ENABLE. This limits the on-time of the high-side MOSFETs, thus leading to a controlled rampup of the output voltages. RDS(ON) Current Limiting The current limit threshold is set by connecting an external resistor from the VCC supply to OCSET. The voltage drop across this resistor is due to the 200µA internal sink sets the voltage at the pin. This voltage is compared to the voltage at the PHASE node. This comparison is made only when the high-side drive is high to avoid false current limit triggering due to uncontributing measurements from the MOSFET’s offvoltage. When the voltage at PHASE is less than the voltage at OCSET, an overcurrent condition occurs and the soft start cycle is initiated. The synchronous switcher turns off and SS/ENABLE starts to sink 2µA. When SS/ENABLE reaches 0.8V, it then starts to source 10µA and a new cycle begins. Hiccup Mode During power up, the SS/ENABLE pin is internally pulled low until VCC reaches the undervoltage lockout level of 4.2V. Once VCC has reached 4.2V, the SS/ENABLE pin is released and begins to source 10µA of current to the external soft-start capacitor. As the softstart voltage rises, the output of the internal error amplifier is clamped to this voltage. When the error signal reaches the level of the internal triangular oscillator, which swings from 1V to 2V at a fixed frequency of 250 kHz, switching occurs. As the error signal crosses over the oscillator signal, the duty cycle of the PWM signal continues to increase until the output comes into regulation. If an over-current condition has not occurred the soft-start voltage will continue to rise and level off at about 2.2V. An over-current condition occurs when the high-side drive is turned on, but the PHASE node does not reach the voltage level set at the OCSET pin. The PHASE node is sampled only once per cycle during the valley of the triangular oscillator. Once an over-current occurs, both the high-side and low-side drivers turn off and the SS/ENABLE pin begins to sink 2uA. The softstart voltage will begin to decrease as the 2uA of current discharges the external capacitor. When the softstart voltage reaches 0.8V, the SS/ENABLE pin will begin to source 10uA and begin to charge the external capacitor causing the soft-start voltage to rise again. Again, when the soft-start voltage reaches the level of the internal oscillator, switching will occur. If the over-current condition is no longer present, normal operation will continue. If the over-current condition is still present, the SS/ENABLE pin will again begin to sink 2uA. This cycle will continue indefinitely until the over-current condition is removed. 5 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS SC1110 PRELIMINARY - October 9, 2000 SIMULATION WAVEFORMS 2.5V and 1.25V ramp up Output current of the VTT supply 6 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 SINK AND SOURCE DC/DC CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS SC1110 PRELIMINARY - October 9, 2000 OUTLINE DRAWING SO-14 ECN00-1363 7 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320