SC1110 Sink and Source DC/DC Controller for Termination Power Supply Applications POWER MANAGEMENT Description Features 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 bi-directionally. The termination voltage can be tightly regulated to track the chipset voltage, i.e. to be exactly 50% of that at all times. Generates termination voltages for active termination schemes 1% set point accuracy For ±7A output current, transient regulation is 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 MOSFETs. The SC1110 operates at a fixed 250kHz, providing an optimum compromise between efficiency, transient performance, external component size, and cost. better than ±80mV VREFIN pin available for external 50% resistive divider to allow termination voltage track of the chip set voltage 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 performance Gate drive capable for 0.5A sourcing and sinking Applications For DDR memory systems For active termination schemes in high speed logic systems Typical Application Circuit +5Vcc REFOUT + R1 5k C1 0.01 R2 1.24k C2 0.1 R3 10 U1 SC1110 1 VCC 2 R4 1k REFOUT 14 SS/ENBL REFIN 13 3 OCSET SENSE 12 4 PWRGD COMP 11 C7 1.0 C4 0.022 C8,9 2 x 10uF C10,11 2 x 560uF Vin 2.5V _ SS/ENBL C3 0.1 R5 1k PWRGD C25 0.1 5 R6 4.7k C5 0.047 10 GND BSTL 6 PHASE BSTH 9 7 DL DH 8 D1 MBRM120 R7 2.2 R8 2.2 Q1 Si9426DY Q2 Si9426DY 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) Revision: July 20, 2004 1 C6 1.0 L1 800 nH + C12-14 3 x 560uF C15-24 10 x 10uF Vout = 1.25V @ 7A _ www.semtech.com SC1110 POWER MANAGEMENT Absolute Maximum Ratings Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Parameter Symbol Maximum Units VIN -0.5 to 14 V PGND to GND +0.5 V PHASE to GND -0.3 to 18 V BSTH to PHASE 14 V VCC, BSTL to GND Thermal Impedance Junction to Case θJC 45 °C/W Thermal Resistance Junction to Ambient θJ A 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 ESD Rating (Human Body Model) V ESD 2 kV 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 VCC 4.4 Typ Max Units 12.6 V 12 mA Pow er Supply Supply Voltage Supply Current Line Regulation 8 VO = 2.5V ± 0.5V, VO = VIN/2 @ 0A 0.5 % Turn-On Threshold 4.15 V Turn-Off Threshold 3.95 V Transconductance 2 mS Open Loop DC Gain 50 dB 500 kHz ± 250 µA Under Voltage Lockout Error Amplifier Bandwidth - 3dB (Unity gain crossover 70MHz) COMP Source Capability Input Bias 2 5 µA 275 kHz Oscillator Oscillator Frequency 225 250 Oscillator Max Duty Cycle 90 95 % 1 V Ramp Height 2004 Semtech Corp. 2 www.semtech.com SC1110 POWER MANAGEMENT Electrical Characteristics (Cont.) 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 Timing Minimum Off-Time Dead Time 200 ns Guaranteed by characterization 80 ns BSTH - DH = 4.5V, DH - PHASE = 3.0V DH - PHASE = 1.5V 0.5 A MOSFET Drivers Peak DH Sink/Source Current 0.1 Peak DL Sink/Source Current BSTL - DL = 4.5V, DL - GND = 3.0V DL - GND = 1.5V 0.5 A VOCSET = 2.2V 180 200 220 µA Charge Current VSS = 1.5V 8 10 12 µA Discharge Current VSS = 1.5V 1 2 3 µA 0.1 Protection Overcurrent Set Isource Soft Start Pow er Good Upper Threshold 112 % Lower Threshold 88 % PWRGD Voltage Low IPWRGD = 2mA 0.5 V Reference REFOUT Source Current Offset 3 REFIN = 1.25V -5 mA 5 mV 0.65 V Enable Threshold 2004 Semtech Corp. 0.55 3 0.60 www.semtech.com SC1110 POWER MANAGEMENT Timing Diagrams SIMULA TION W AVEF ORMS SIMULATION WA VEFORMS 2.5V and 1.25V ramp up Output current of the VTT supply 2004 Semtech Corp. 4 www.semtech.com SC1110 POWER MANAGEMENT Pin Configuration Ordering Information Device Package(1)(2) Temp Range (TJ) SC1110CSTRT SO-14 0° to 125°C SC1110TSTRT TSSOP-14 (1) Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free product. (14 Pin SOIC or TSSOP) Pin Descriptions Pin # Pin Name Pin Function 1 VC C 2 SS/ENBL 3 OCSET Current limit set point. 4 PWRGD Logic high indicates correct output. 5 GND 6 PHASE 7 DL Low side driver output. 8 DH High side driver output. 9 BSTH High side driver supply. 10 BSTL Low side driver supply. 11 COMP Error amplifier output, compensation. 12 SENSE Error amplifier negative input. 13 REFIN Error amplifier positive input. 14 REFOUT Chip Supply Voltage. Soft start/Enable. Ground. Phase node connection between MOSFETs. Buffered reference voltage. NOTE: (1) All logic level inputs and outputs are open collector TTL compatible. 2004 Semtech Corp. 5 www.semtech.com SC1110 POWER MANAGEMENT Block Diagram Applications Information fier. When the oscillator output voltage drops below the error amplifier output voltage, the comparator output goes high. This pulls DL low, turning off the low-side FET, and DH is pulled high, turning on the high-side 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). THEORY OF OPERATION Synchronous Buck Converter VTERMINATION power is provided by a synchronous, voltagemode 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 external resistive divider generates reference voltage for the error amplifier from the chipset voltage which is usually 2.5V. The inverting input of the error amplifier receives its voltage from the SENSE pin. 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. 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 ampli 2004 Semtech Corp. 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 4.1V. Normal operation resumes once VCC rises above 4.2V. 6 www.semtech.com SC1110 POWER MANAGEMENT Applications Information 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. 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 ramp-up of the output voltages. 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 soft-start 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. 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 off-voltage. When the voltage at PHASE is less than the voltage at OCSET, an overcurrent condition occurs and the soft start cycle is initiated. The 2004 Semtech Corp. 7 www.semtech.com SC1110 POWER MANAGEMENT Typical Characteristics CH1: Vout_ripple CH2: Phase node Vin = 2.5V Vout = 1.25V Iout = 7A 95% Efficiency 90% 85% 80% 75% 70% 65% 60% 0 1 2 3 4 5 6 7 8 9 8 9 10 11 12 Current, A 1.0% Regulation 0.5% 0.0% -0.5% -1.0% 0 1 2 3 4 5 6 7 10 11 12 Current, A 2004 Semtech Corp. 8 www.semtech.com SC1110 POWER MANAGEMENT Evaluation Board Top View Bottom View 2004 Semtech Corp. 9 www.semtech.com SC1110 POWER MANAGEMENT Evaluation Board (Cont.) 2004 Semtech Corp. Top Copper Bottom Copper Midlayer 1 Midlayer 2 10 www.semtech.com SC1110 POWER MANAGEMENT Outline Drawing - SO-14 Land Pattern - SO-14 2004 Semtech Corp. 11 www.semtech.com SC1110 POWER MANAGEMENT Outline Drawing - TSSOP-14 Land Pattern - TSSOP-14 Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804 2004 Semtech Corp. 12 www.semtech.com