SC1104A/B Simple, Synchronous Voltage Mode PWM Controller PRELIMINARY POWER MANAGEMENT Description Features K K K K K K K K The SC1104A/B is a versatile voltage-mode PWM controller designed for use in single ended DC/DC power supply applications. A simple, fixed frequency high efficiency buck regulator can be implemented using the SC1104A/B with a minimum of external components. Internal level shift and drive circuitry eliminates the need for an expensive P-channel, high-side switch. The small device footprint allows for compact circuit design. SC1104A/B features include temperature compensated voltage reference, triangle wave oscillator, current limit comparator and an externally compensated error amplifier. Current limit is implemented by sensing the voltage drop across the top FETs RDS(ON).. +5V or +12V operation High efficiency (>90%) 1% Reference voltage accuracy Hiccup mode over current protection Robust output drive RDS(ON) Current sensing Industrial temperature range SO-8 package Applications K K K K K The SC1104A/B operates at a fixed frequency of 300/ 600 kHz, providing an optimum compromise between efficiency, external component size, and cost. 600kHz switching frequency is typically reserved for the 5V operation only. Termination supplies Low cost microprocessor supplies Peripheral card supplies Industrial power supplies High density DC/DC conversion SC1104A/B has a thermal protection circuit, which is activated if the junction temperature exceeds 150°C. Typical Application Circuit Typical Distributed Power Supply R2 10 C1 220-680pF R1 2k + C3 0.1 C4 10.0 D1 MBRA130L C5 47/16V C6 47/16V C7 47/16V U1 SC1104A/B C2 0.01 Vin 5 to 12V _ R4 1 COMP/SS 2 GND SENSE 8 VCC 7 3 DL PHASE 6 4 DH BST 5 2.32k R3 1.00k R5 200-1k C8 0.1-0.22 R8 10 R6 1-5.1 Q1 Si4884DY C9 0.1 L1 1.5-3uH Q2 Si4874DY R7 1-5.1 + D2 (opt) C10 220/4V C11 220/4V C12 220/4V C13 220/4V C14-17 1.0 3.3V _ Figure 1 Revision 3, October 2001 1 www.semtech.com SC1104A/B PRELIMINARY POWER MANAGEMENT Absolute Maximum Ratings Parameter Symbol Maximum Units VCC to GND 15 V BST to PHASE 15 V PHASE to GND -1 to 15 V DH to PHASE 15 V DL to GND 15 V COMP/SS to GND 7 V SENSE to GND 7 V Thermal Resistance Junction to Case θJC 40 °C/W Thermal Resistance Junction to Ambient θJ A 160 °C/W Operating Temperature Range TA -40 to +85 °C Storage Temperature Range TSTG -65 to +150 °C Lead Temperature (Soldering) 10 Sec. TLead 300 °C Electrical Characteristics Unless specified: A: VCC = 12 ± 0.6V, VBST = 23 ± 1V, VOUT = 3.3V, TA = 25oC.B: VCC = 5 ± 0.25V, VBST = 12 ± 0.6V, VOUT = 2.0V, TA = 25oC Parameter Symbol Conditions Min Typ Max V CC FSW = 300kHz (nom.), (SC1104A) 4.2 12.6 V CC FSW = 600kHz (nom.), (SC1104B) 4.2 7 ICC VCOMP ≤ 0.4V Units Pow er Supply Supply Voltage V Supply Current 11 14 mA Error Amplifier E/A Transconductance gm 10 Input Bias Current IFB 1 Output Sink Current ISIK VSENSE ≥ 1.1V; VCOMP = 1.5V 0.7 Source Current ISC VSENSE ≥ 0.9V; VCOMP = 1.5V 1.1 FOSC VCC = 12V ± 0.6V 270 300 330 VCC = 5V ± 0.25V 540 600 660 mS 3 µA mA Oscillator Switching Frequency Ramp Peak Voltage © 2001 Semtech Corp. VP-K 4.75V ≤ VCC ≤ 12.6V 2 2.0 kHz V www.semtech.com SC1104A/B PRELIMINARY POWER MANAGEMENT Electrical Characteristics Unless specified: A: VCC = 12 ± 0.6V, VBST = 23 ± 1V, VOUT = 3.3V, TA = 25oC.B: VCC = 5 ± 0.25V, VBST = 12 ± 0.6V, VOUT = 2.0V, TA = 25oC Parameter Symbol Conditions Min Typ Max Units Ramp Valley Voltage VV 4.75V ≤ VCC ≤ 12.6V 1.0 V Maximum Duty Cycle dcMAX VCC = 12V (300kHz) 95 % VCC = 5V (600kHz) 90 MOSFET Drivers DH Sink/Source Current SC1104A IDH d.c. < 2%, tPW < 100µs VGS = 4.5V (src) 0.7 DL Sink/Source Current SC1104A IDL VGS = 2.5V (snk) 0.7 DH Sink/Source Current SC1104B IDH d.c. < 2%, tPW < 100µs VGS = 4.5V (src) 0.5 DL Sink/Source Current SC1104B IDL VGS = 2.5V (snk) 0.5 DH Rise/Fall Time tr, tf CL = 3000pF, See Fig. 2 50 DL Rise/Fall Time tr, tf CL = 4000pF, See Fig. 2 50 tdt S ee F i g. 2 80 tOFF 4.75V ≤ Vcc ≤ 12.6V 160 VREF 4.75V ≤ Vcc ≤ 12.6V 0.990 -40 < TA < 85°C -1 Vtrp 4.75V < Vcc < 12.6V Vtrp = Vcc - VPHASE 180 SS Source Current ISRC VCOMP < 2.5V 1.5 SS Sink Current ISNK VCOMP > 0.5V 1.5 Dead Time DH Minimum Off Time A A ns ns Reference Section Reference Voltage Reference Accuracy 1.000 1.010 V 1 % 220 mV Current Limit Trip Voltage 200 Soft-Start/Enable Enable Input Threshold µA 1 Enable Input Current VCOMP = 0.8V V 2 mA 4.5 V Under Voltage Lockout UVLO Threshold Vth -40< TA < 85°C 3.9 4.15 Thermal Shutdow n Over Temperature Trip Point TOTP 150 °C Note: 1. This device is ESD sensitive. Use of standard ESD handling precautions is required. © 2001 Semtech Corp. 3 www.semtech.com SC1104A/B PRELIMINARY POWER MANAGEMENT Electrical Characteristics Figure 2 Block Diagram Figure 3 © 2001 Semtech Corp. 4 www.semtech.com SC1104A/B PRELIMINARY POWER MANAGEMENT Pin Configuration Ordering Information Device Top View (2) SC1104XISTR (1) P ackag e Temp Range (TJ) SOIC-8 -40° to 125°C Note: (1) In place of “X”: A = 300kHz; B = 600kHz. (2) Only available in tape and reel packaging. A reel contains 2500 devices. (8-Pin SOIC) Pin Descriptions Pin # Pin Name 1 COMP/SS 2 GND 3 DL Low side driver output 4 DH High side driver output 5 BST Bootstrap, high side driver. 6 PHASE 7 VC C 8 SENSE © 2001 Semtech Corp. Pin Function Error amplifier output. Compensation, soft start/enable. Ground. Input from the phase node between the MOSFETs. Chip bias supply voltage. Output voltage sense input. 5 www.semtech.com SC1104A/B PRELIMINARY POWER MANAGEMENT Theory of Operation The circuit will be in steady state when Vout =3.3V , Vsense = 1V, Icomp = 0 . The COMP voltage and duty cycle depend on Vin. Synchronous Buck Converter The output voltage of the synchronous converter is set and controlled by the output of the error amplifier. The inverting input of the error amplifier receives its voltage from the SENSE pin. Under Voltage Lockout The under voltage lockout circuit of the SC1104A/B assures that both high-side and low-side MOSFET driver outputs remain in the off state whenever the supply voltage drops below set parameters. Lockout occurs if VCC falls below 4.2V typ. The non-inverting input of the error amplifier is connected to an internal 1V reference. The error amplifier output is connected to the COMPensation pin. The error amplifier generates a current proportional to (Vsense 1V), which is the COMP pin output current (Transconductance ~ 10mS). The voltage on the COMP pin is the integral of the error amplifier current. The COMP voltage is the non-inverting input to the PWM comparator and controls the duty cycle of the MOSFET drivers. The size of capacitor Ccomp controls the stability and transient response of the regulator. The larger the capacitor, the slower the COMP voltage changes, and the slower the duty cycle changes. RDS(ON) Current Limiting In case of a short circuit or overload, the high-side (HS) FET will conduct large currents. To prevent damage, in this situation, large currents will generate a fault condition and begin a soft start cycle. While the HS driver is on, the phase voltage is compared to the Vcc pin voltage. If the phase voltage is 200mV lower than Vcc, a fault is latched and the soft start cycle begins. The inverting input voltage of the PWM comparator is the triangular output of the oscillator. The voltages are compared during the middle of the HS pulse, to prevent transients from affecting the accuracy. When the oscillator output voltage drops below the COMP voltage, the comparator output goes high. This pulls DL low, turning off the low-side FET. After a short delay (dead time), DH is pulled high, turning on the high-side FET. 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 after a dead time delay, DL is pulled high, turning on the lowside FET. The dead time delay is determined by a monostable on the chip. Soft Start The soft start (or hiccup) circuitry is activated when a fault occurs. Faults occur for three reasons: 1) Under voltage (VCC < 4.2V) 2) Over temperature (die temperature > 150°C) 3) Over current in high side FET. All faults are handled the same way. Both DH and DL are forced low. The error amplifier is turned off, but a 2µA current flows into the comp pin (soft start current). The sink current reduces the Comp voltage down to 0.6V over a period of a few milliseconds. When Vcomp ~ 0.6V, the fault is cleared and the DL goes high. Also, the soft start current changes polarity and begins to increase the voltage on the Comp capacitor. The DH remains low, because Vcomp is less than the lowest excursion of the oscillator ramp (1.0V). After a few ms, the Vcomp increases to about 1.0V and the DH will start to switch. The duty cycle will gradually increase, and Vsns will increase. When Vsns ~ 1.00V, the error amplifier turns on again. The circuit has now reached its operating point. If a fault occurs during the soft start, the cycle will begin again (drivers low, Vcomp decreasing down to 0.6V). The triangle wave minimum is about 1V, and the maximum is about 2V. Thus, if Vcomp = 0.9V, high side duty cycle is the minimum (~0%) , but if Vcomp is 2.0V, duty cycle is at maximum ( ~80%).The internal oscillator uses an on-chip capacitor and trimmed precision current sources to set the oscillation frequency to 300/600kHz. Figure 1 shows a 3.3V output converter. If the Vout <3.3V, then the SENSE voltage < 1V. In this case the error amplifier will be sourcing current into the COMP pin so that COMP voltage and duty cycle will gradually increase. If Vout > 3.3V, the error amplifier will sink current and reduce the COMP voltage, so that duty cycle will decrease. © 2001 Semtech Corp. 6 www.semtech.com SC1104A/B PRELIMINARY POWER MANAGEMENT Outline Drawing - SO-8 Land Pattern - SO-8 Contact Information Semtech Corporation Power Management Products Division 652 Mitchell Rd., Newbury Park, CA 91320 Phone: (805)498-2111 FAX (805)498-3804 © 2001 Semtech Corp. 7 www.semtech.com