SS6577 SSC | Alldatasheet
Document overview
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Technical content
Rev.1.02 3/26/2004 External NMOS Step-Down PWM Controller
FEATURES
Operating input voltage from 4.5V to 24V Wide output Range : 0.8V to 20V Reference: ±1.5% 0.8V Reference Low dropout operation : 95% duty cycle Fixed constant frequency - 500kHz Low standby current, I Q typically 720µA Logic-control m icropower shutdown Output overvoltage protection Internal diode for bootstrapped gate drive Current-mode operation for excellent line and load transient response Available in 8-lead SO or MSOP packages
APPLICATIONS
Palmtop Computers, PDAs Wireless Modems On-Card Switching Regulators DC Power Distribution Systems
DESCRIPTION
The SS6577 is a current-mode switching regulator controller that drives an external N-channel power MOSFET using a fixed fre- quency architecture. It uses an external divider to adjust the output voltage from 0.8V to 20V with excellent line and load regulation. A maximum high duty-cycle limit of 95% provides low dropout operation which extends operating time in battery-operated systems. A constant switching frequency of 500KHz is used thus allowing smaller sized filter components. The operating current level is user-programmable via an external current sense resistor. It also provides output overvolt- age protection under fault conditions. A multifunction pin (I TH/RUN) allows external compensation for optimum load step re- sponse plus shutdown. Soft start can also be implemented with this pin to properly se- quence supplies. Packages available are SOP-8 and MSOP-8 for SMD. www.SiliconStandard.com 1 of 14
www.SiliconStandard.com 2 of 14 SS6577 Rev.1.02 3/26/2004 TYPICAL APPLICATION CIRCUIT VIN 6V~24V + CIN1 22µF RS 33m 0.1µF SL43 10µH VOUT 3.3V 3A C11000pF 330pF 24k R2 62k 20k VIN 8 ITH/RUN FB GND
4 SW 5
+ CIN2 22µF 0.1µF COUT 220µFC4 1nF 2.2µF CIN1, CIN2: HER-MEI 22µF/35V Electrolytic capacitors M1: N-MOSFET SSM6680M D1: GS SL43 L1: TDK SLF12555T-100M3R4 COUT: HER-MEI 220µF /16V Electrolytic capacitor C6: TAIYO YUDEN LMK212BJ225KG-T Ceramic capacitor ORDERING INFORMATION PIN CONFIGURATION SS6577C(X)XXX Packing type TB: Tube TR: Tape and reel Package outline S: SO-8 O: MSOP-8 G: Pb-free lead finish Example: SS6577COTR Æ in MSOP package shipped in tape and reel SS6577CGOTR Æ in MSOP package with Pb-free lead finish shipped in tape and reel TOP VIEW DRI VIN BOOST SW FB ITH/RUN GND CS 1
www.SiliconStandard.com 3 of 14 SS6577 Rev.1.02 3/26/2004 ABSOLUTE MAXIMUM RATINGS (Note 1) Thermal Resistance (θJA) (Assuming no ambient airflow, no heatsink) TEST CIRCUIT Refer to Typical Application Circuit. ELECTRICAL CHARACTERISTICS (TA=25°C, VIN=15V, unless otherwise noted.) PARAMETER TEST CONDITIONS MIN. TYP. MAX. UNIT Input Voltage 4.5 24 V Normal Mode (Note 2) 720 900 µA Input Supply Current Shutdown Mode, VITH/RUN=0V 16 20 µA Feedback Voltage 0.788 0.8 0.812 V ∆Output Overvoltage Lockout VFB connect to Vout, ∆VOVL=VOVL-VFB 20 55 90 mV Reference Voltage Line Regulation VIN= 4.5V to 20 V 0.002 0.015 %/V Output Voltage Load Regula- tion ITH Sinking 5µA ITH Sourcing 5µA 0.7 -0.4 1.1 -0.8 Run Threshold 0.6 0.8 0.9 V Maximum Current Sense Threshold VFB=0.72V 125 150 175 mV Oscillator Frequency 450 500 550 kHz
www.SiliconStandard.com 4 of 14 SS6577 Rev.1.02 3/26/2004 ELECTRICAL CHARACTERISTICS (Continued) PARAMETER TEST CONDITIONS MIN. TYP. MAX. UNIT DRI Rise Time CLOAD = 3000PF 50 75 ns DRI Fall Time CLOAD = 3000PF 50 75 ns BOOST Voltage VIN=8V, IBOOST=5mA, SW=0V 4.9 5.3 5.7 V Maximum Duty Cycle 90 94 % Soft Start Time 5 7.5 ms Run Current Source VITH/RUN=0V, VFB=0V 1.0 2.3 4.0 µA Run Pullup Current VITH/RUN=1V 100 190 250 µA Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. TYPICAL PERFORMANCE CHARACTERISTICS 1 10 100 1000 10000 100 VIN=6V Efficiency (%) Load Current (mA) VIN=12V VIN=19V VOUT=3.3V Fig. 1 Efficiency vs Load Current (VOUT=3.3V) Efficiency (%) Load Current (mA) Fig. 2 Efficiency vs Load Current (VOUT=5.0V) 1 10 100 1000 10000 100 VOUT=5V VIN=6V VIN=12V VIN=19V
www.SiliconStandard.com 5 of 14 SS6577 Rev.1.02 3/26/2004 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Efficiency (%) Input Voltage (V) Fig. 3 Efficiency vs Input Voltage 0 5 10 15 20 25 30 100 VOUT=3.3V ILOAD=1A ILOAD=0.1 A Efficiency (%) Input Voltage (V) Fig. 4 Efficiency vs Input Voltage 0 5 10 15 20 25 30 100 VOUT=5V ILOAD=1A ILOAD=0.1A Supply Current (µA) Input Voltage (V) Fig. 5 Supply Current vs Input Voltage 0 5 10 15 20 25 30 500 600 700 800 900 Normal Mode Shutdown Boost Voltage (V) Boost Load Current (mA) Fig. 6 Boost Load Regulation VCC=5V VCC=15V VPHASE=0V 0 51 0 15 20 Boost Voltage (V) Input Voltage (V) Fig. 7 Boost Line Regulation IBOOST=2mA VPHASE=0V 0 5 10 15 20 25 30 VCC DOWN VCC UP Reference Voltage (V) Temperature (°C) Fig. 8 Reference Voltage vs Temperature -40 -20 0 20 40 60 80 100 120 1400.790 0.791 0.792 0.793 0.794 0.795 0.796 0.797 0.798 0.799 0.800 0.801 0.802 0.803 0.804 0.805
www.SiliconStandard.com 6 of 14 SS6577 Rev.1.02 3/26/2004 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Boost Voltage (V) Temperature (°C) Fig. 9 Boost Voltage vs Temperature -40 -20 0 20 40 60 80 100 120 140 4.0 4.5 5.0 5.5 6.0 IBOOST=1mA VPHASE=0V Frequency (KHz) Temperature (°C) Fig. 10 Operating Frequency vs Temperature -40 -20 0 20 40 60 80 100 120 140 400 420 440 460 480 500 Current Sense Threshold (mV) Temperature (°C) Fig. 11 Maximum Current Sense Threshold vs Temperature -40 -20 0 20 40 60 80 100 120 140 120 125 130 135 140 145 150 155 160
www.SiliconStandard.com 7 of 14 SS6577 Rev.1.02 3/26/2004 BLOCK DIAGRAM Dropout DET OSC VIN INTVCC 1_SHUT Q3 Q4SS REF 0.8V Thermal Driver Floating LEB Blank EA VINT VIN VINT VINT 0.8V 1.2V 2.4V 0.8V 1.33V 0.855V LC_COMP Burst_Mode SD OVDT R S Q 2.5µA + Buffer_ITH VINCS ITH SW DRI FB GND BOOST ICOMP VIN VIN VIN Slope SD Clock SD ITH ClockITH VINT SlopeFB 40mV Logic Switching
www.SiliconStandard.com 8 of 14 SS6577 Rev.1.02 3/26/2004 PIN DESCRIPTIONS PIN 1: CS - Current sense comparator invert- ing input, not to exceed V IN volt- age. Built in offsets between the CS and V IN pins in conjunction with R SENSE set the current trip thresholds. PIN 2: I TH/RUN -Combination of error amplifier compensation point and run con- trol inputs. The current compara- tor threshold increases with this control voltage. Forcing this pin below 0.8V causes the device to be shutdown. PIN 3: FB - Feedback error amplifier input, to compare the feedback voltage with the internal reference voltage. Connecting a resistor R2 to con- verter output node and a resistor R1 to ground yields the output voltage: V OUT=0.8 x (R1+R2)/ R1 PIN4: GND - Singal GND for IC. All voltage lev- els are measured with respect to this pin. PIN 5: SW - Switch node connection to induc- tor. In buck converter applications the voltage swing at this pin is from a schottky diode voltage drop below ground to V IN PIN 6: DRI - External high-side N-MOSFET gate drive pin. Connect DRI to gate of the external high-side N- MOSFET. PIN 7: BOOST - Supply to high-side floating driver. The bootstrap capacitor C3 is returned to this pin. PIN 8: VIN - The chip power supply pin. It also provides the gate bias charge for all the MOSFETs controlled by the IC. Recommend supply volt- age is 4.5V~24V.
APPLICATION INFORMATION
The SS6577 is a current mode switching regulator controller that drives an external N-channel power MOSFET with constant frequency architecture. It uses an external divider to adjust output voltage with excellent line regulation and load regulation. A maximum high duty cycle limit of 95% provides low dropout operation, which extends operating time in battery-operated system. Wide input voltage ranges from 4.5V to 24V, and a switching frequency of 500KHz allows smaller sized filter components. The operating current level is user-programmable via an external current sense resistor and it automatically enters PFM operation at low output current to boost circuit efficiency. A multifunction pin (I TH/RUN) allows external com- pensation plus shutdown. A built-in soft start can properly provide sequenced supplies. Available packages are SOP8 and MSOP8 for SMD. Principle of Operation The SS6577 uses a current mode with a constant frequency architecture. Normally high-side MOSFET turns on each cycle when oscillator sets RS latch and it turns off when internal current comparator re- sets RS latch. Voltage on I TH/RUN pin, which is the output voltage of voltage error amplifier, will control peak inductor current. The output voltage feeds back to V FB pin so that the error amplifier receives a voltage through external resistor divider. When load current increases, it causes a slight decrease
www.SiliconStandard.com 9 of 14 SS6577 Rev.1.02 3/26/2004 MAXI 100mV SR = in the voltage of VFB pin. Thus the I TH/RUN voltage remains increasing until the average inductor cur- rent matches new load current. While the high-side MOSFET turns off, the low-side MOSFET is turned on to recharge bootstrap capacitor C3. Inductor Selection With the high operating frequency of 500KHz, smaller inductor values are possible. In general, operating at high frequency will cause low efficiency because of large MOSFET switching loss. Thus the effect of inductor value on ripple current and low current operation must be considered as well. Main control loop is shut down when I TH/RUN goes below 0.8V. When ITH/RUN pulled up to 0.8V or up by error amplifier, main control loop is enabled. Low Current Operation During heavy load current operation, the SS6577 op- erates in PWM mode with a frequency of 500KHz. Decreasing of the current will cause a drop in ITH/RUN below 1.33V so that the SS6577 enters PFM mode operation for better ef ficiency. If the voltage across R S does not exceed the of fset of current comparator within a cycle, then the high-side and internal MOSFETs will disable until ITH/RUN goes over 1.33V. The inductor value has a direct influence on ripple current ( ΔIL), which decreases with high induc- tance and increases with high VIN or VOUT: DVINV DVOUTV Lf OUTVINV L∆I VD is the drop voltage of the output Schottky diode. Accepting a large value of ΔIL allows the use of low inductance, but yields high output ripple volt age and large core loss. The inductor value also has an effect on low current operation. Low inductor value causes the PFM operation to begin at high load cur- rent. The ef ficiency of the circuit decreases at the beginning of low current operation. Generally speaking, low induct ance in PFM mode will cause the efficiency to decrease. Component Selection The SS6577 can be used in many switching regulator applications, s uch as step-down, s tep-up, SEPIC and positive-to-negative converters. Among these step-down converter is the most common applica- tion. External component selection, beginning with selecting R S, depends on load requirement of the application. Once R S is decided, the choice of in- ductor, which is followed by selecting power MOSFET and diode, can be easily chosen. Finally , CIN and COUT can be determined. Power MOSFET Selection For an application of SS65577, an external N- channel power MOSFET , used as the high-side switch, must be properly selected. T o prevent MOSFET damage during high input voltage operation, attention should be given to the BV DSS specification of the MOSFET. RS Selection The choice of R S has subst antial connection with required output current. The threshold volt age of current comp arator decides peak inductor current, which yields a maximum average output current (IMAX), and the peak current is less than half of the peak-to-peak ripple current, ΔIL. Other important selection criteria for the power MOSFET include the “ON” resistance RDS(ON), in- put voltage and maximum output current. Allowing a margin for variation of the SS6577, external components can be calculated as:
www.SiliconStandard.com 10 of 14 SS6577 Rev.1.02 3/26/2004 Output Diode Selection += 1R 2R1V8.0VOUT In order not to exceed the diode ratings, it is impor- tant to specify the diode peak current and average power dissipation. The feedback reference volt age 0.8V allows low output voltages from 0.8V to input volt age. A small capacitor at 1nF in p arallel to the upper feedback resistor is required for a stable feedback. CIN and COUT Selection To prevent the high voltage spike resulted from high frequency switching, a low ESR input cap acitor for the maximum RMS current must be used. Usually capacitors may be p aralleled to meet size or height requirements in the design. ITH/RUN Function The ITH/RUN pin, also as a dual-purpose pin, pro- vides loop compensation as well as shutdown func- tion. An internal current source at 2.5µA charges up the external cap acitor C5. When the voltage on ITH/RUN pin reaches 0.8V , the SS6577 begins to operate. The selection of C OUT depends on the required ef - fective series resistance (ESR). In general once the ESR requirement is met, the capacitance is suitable for filtering. The output ripple volt age ( ΔVOUT) is determined by: 330pF 24k LL4148 C7 1µF 1.2M VIN 4.5V~24V ITH/RUN +∆≈∆ OUT LOUT fC4 1ESRIV where f = operating frequency , COUT = output ca- pacitance and ΔIL = ripple current of the inductor . Once the ESR requirement for C OUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. Fig. 12 ITH/RUN pin interfacing Topside MOSFET Driver Supply (C3) External bootstrap cap acitor C3 connecting to BOOST pin supplies the gate drive voltage for high- side MOSFET. C3 is charged from INTVCC when SW pin is low . When the high-side MOSFET turns on, the driver places the C3 voltage across the gate to the source of MOSFET . It will enhance the MOSFET and turn on the high-side switch. Then the switch node voltage SW rises to V IN and BOOST pin rises to V IN + INTVCC. In general, 0.1µF is acceptable. Over Current Protection Over current protection occurs when the peak in- ductor current reaches maximum current sense threshold divided by sense resistor. The maximum current under over current protection can be calcu- lated by the following formula. SR threshold)sensecurrentmum150mV(Maxi MAXI = At the same time, the frequency of oscillator will be reduced to sixteenth of original value, 500kHz. This lower frequency allows the inductor current to safely discharge, thereby preventing current run- away. The frequency of oscillator will automatically Output Voltage Programming The typical SS6577 application circuit is shown in figure17. A resistive divider, as in the following for- mula, sets the output voltage.
www.SiliconStandard.com 11 of 14 SS6577 Rev.1.02 3/26/2004 return to its designed value when the peak inductor value no longer exceeds over current protection point. Over Voltage Protection Over voltage protection occurs when the FB pin voltage (the negative input of error amplifier) ex- ceeds 0.855V. The over voltage comparator will force driver to pull low until output over voltage is removed. PCB Layout Since operating at a high switching frequency, 500KHz, proper PCB layout and component place- ment may enhance the performance of the SS6577 application circuit. For a better efficiency, major loop from input terminal to output terminal should be as short as possible. In addition, in the case of a large current loop, the track wid th of each component in the loop should maintain as wide as possible. In order to prevent the effect from noise, the GND pin should be placed close to the ground. Also keep the IC’s GND pin and the ground leads in the short- est distance. Recommended layout diagrams and component placement are as shown as figures 13 to 16. No sensitive component s, which may cause noise interference to the circuit, should be allowed to be close to SW pin. Furthermore, the SS6577 is a current-mode controller. Keeping the sense resistor close to both VIN and CS pins is recommended for better efficiency and output performance. In addition, all filtering and de- coupling cap acitors, such as C1 and C2, should connect to the SS6577 as close as possible. Fig. 12 Top Layer Fig. 13 Bottom Layer
www.SiliconStandard.com 12 of 14 SS6577 Rev.1.02 3/26/2004 Fig. 14 Placement (Top Overlay) Fig. 15 Placement (Bottom Overlay) APPLICATION EXAMPLES VIN 6V~24V + CIN1 22µF RS 33m SSM6680MC3 0.1µF SL43 10µH VOUT 3.3V 3A C11000pF 330pF 24k R2 62k 20k VIN 8 ITH/RUN FB GND + CIN2 22µF 0.1µF COUT 220µFC4 1nF LL4148 1µF 1.2M VIN 6V~24V ** 2.2µF Fig. 16 3.3V Step-Down Converter with External Soft-Start Circuit
www.SiliconStandard.com 13 of 14 SS6577 Rev.1.02 3/26/2004 VIN 5V + CIN1 22µF RS 33m SSM6680MC3 LL4148 SL43 10µH VOUT 3.3V 3A C11000pF 330pF 24k R2 62k 20k VIN 8 ITH/RUN FB GND + CIN2 22µF 0.1µF COUT 220µFC4 1nF 2.2µF 1nF Fig. 17 5V to 3.3V Step-Down Converter
Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, expre ss or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties. www.SiliconStandard.com 14 of 14 SS6577 Rev.1.02 3/26/2004 MSOP 8 (CO) SYMBOL MIN MAX A 0.76 0.97 A1 -- 0.20 B 0.28 0.38 C 0.13 0.23 D 2.90 3.10 E 2.90 3.10 e 0.65 H 4.80 5.00 L 0.40 0.66 D H e A B C E L PHYSICAL DIMENSIONS (unit: mm)
8 LEAD PLASTIC SO (CS)
A 1.35 1.75 A1 0.10 0.25 B 0.33 0.51 C 0.19 0.25 D 4.80 5.00 E 3.80 4.00 e 1.27(TYP) H 5.80 6.20 L 0.40 1.27 D H e A B C E L