CS5165HGDWR16

CS5165H CS5165H Fast, Precise 5-Bit Synchronous Buck Controller for the Next Generation Low Voltage Pentium® II Processors Description The CS5165H synchronous 5-bit NFET buck controller is optimized to manage the power of the next generation Pentium®II processors. It’s V2™ control architecture delivers the fastest transient response (100ns), and best overall voltage regulation in the industry today. It’s feature rich design gives end users the maximum flexibility to implement the best price/performance solutions for their end products. The CS5165H has been carefully crafted to maximize performance and protect the processor during operation. It has a 5-bit DAC on board that holds a ±1% tolerance over temperature. Its on board programmable soft start insures a control start up, and the FET nonoverlap circuitry ensures that both FETs do not conduct simultaneously. The on board oscillator can be programmed up to 1MHz to give the designer maximum flexibility in choosing external components and setting systems costs. The CS5165H protects the processor during potentially catastrophic events like overvoltage (OVP) and short circuit. The OVP feature is part of the V2™ architecture and does not require any additional components. During short circuit, the controller pulses the MOSFETs in a “hiccup” mode (3% duty cycle) until the fault is removed. With this method, the MOSFETs do not overheat or self destruct. The CS5165H is designed for use in both single processor desktop and multiprocessor workstation and server applications. The IC can be powered from either single or dual 5V, 12V power supplies. The CS5165H’s current sharing capability allows the designer to build multiple parallel and redundant power solutions for multiprocessor systems. The CS5165H contains other control and protection features such as Power Good, ENABLE, and adaptive voltage positioning. It is available in a 16 lead SOIC wide body package. Features s s s s s s s s s s s s s s s s s s s V2™ Control Topology Dual N Channel Design 100ns Controller Transient Response Excess of 1Mhz Operation 5 Bit DAC with 1% Tolerance Power Good Output With Internal Delay Enable Input Provides Micropower Shutdown Mode Complete Pentium® II System Requires 18 Components 5V and 12V Operation Using Either Dual or Single Supplies Adaptive Voltage Positioning Remote Sense Capability Current Sharing Capability VCC Monitor Hiccup Mode Short Circuit Protection Overvoltage Protection (OVP) Programmable Soft Start 150ns PWM Blanking 65ns FET Non-Overlap 40ns Gate Rise and Fall Times (3.3nF load) Application Diagram 5V to 2.8V @ 14.2A for 300MHz Pentium®II 12V 1µF 5V 1200µF/10V x 3 SS VCC GATE(H) GATE(L) IRL3103 PCB 0.1µF 0.1 µF 330pF COMP 1.2µH trace 6mΩ 1200µF 10V x 5 IRL3103 VCC VSS Package Options 16 Lead SO WIDE Pentium® II System COFF VID4 CS5165H PGnd LGnd VID3 VID2 VID1 VID0 PWRGD ENABLE VID0 3.3K VFB PWRGD ENABLE VID1 VID0 VID1 VID2 VID3 SS 1 VFB COMP LGnd PWRGD GATE(L) PGnd GATE(H) VCC 1000pF VID2 VID3 VID4 VID4 COFF ENABLE V2 is a trademark of Switch Power, Inc. Pentium is a registered trademark of Intel Corporation. Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com Rev. 12/24/98 1 A ® Company CS5165H Absolute Maximum Ratings Operating Junction Temperature, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to 150°C Lead Temperature Soldering: Reflow (SMD styles only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60 Sec max. above 183°C, 230°C Peak Storage Temperature Range, TS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −65°C to 150°C ESD Susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2kV Pin Symbol Pin Name VMAX 20V 6V 6V 6V 6V 6V 20V 20V 6V 6V 0V 0V VMIN -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V 0V 0V ISOURCE N/A 200µA 10mA 10µA 1mA 1mA 1.5A Peak; 200mA DC 1.5A Peak; 200mA DC 100µA 10µA 1.5A Peak 200mA DC 100mA ISINK 1.5A Peak 200mA DC 10µA 1mA 10µA 50mA 10µA 1.5A Peak; 200mA DC 1.5A Peak; 200mA DC 1mA 30mA N/A N/A VCC SS COMP VFB COFF VID0-4 GATE(H) GATE(L) ENABLE PWRGD PGnd LGnd IC Power Input Soft Start Capacitor Compensation Capacitor Voltage Feedback Input Off-Time Capacitor Voltage ID DAC Inputs High-Side FET Driver Low-Side FET Driver Enable Input Power-Good Output Power Ground Logic Ground Package Pin Description PACKAGE PIN # PIN SYMBOL FUNCTION 1,2,3,4,6 VID0 -VID4 Voltage ID DAC inputs. These pins are internally pulled up to 5V if left open. VID4 selects the DAC range. When VID4 is high (logic one), the Error Amp reference range is 2.14V to 3.54V with 100mV increments. When VID4 is low (logic zero), the Error amp reference voltage is 1.34V to 2.09V with 50mV increments. Soft Start Pin. A capacitor from this pin to LGnd sets the Soft Start and fault timing. Off-Time Capacitor Pin. A capacitor from this pin to LGnd sets both the normal and extended off time. Output Enable Input. This pin is internally pulled up to 1.8V. A logic Low ( < 0.8V) on this pin disables operation and places the CS5165H into a low current sleep mode. Input Power Supply Pin. High Side Switch FET driver pin. High Current ground for the GATE(H) and GATE(L) pins. Low Side Synchronous FET driver pin. Power Good Output. Open collector output drives low when VFB is out of regulation. Active when ENABLE input is low Reference ground. All control circuits are referenced to this pin. Error Amp output. PWM Comparator reference input. A capacitor to LGnd provides Error Amp compensation. Error Amp, PWM Comparator, and Low VFB Comparator feedback input. 5 7 8 SS COFF ENABLE 9 10 11 12 13 14 15 16 VCC GATE(H) PGnd GATE(L) PWRGD LGnd COMP VFB 2 Electrical Characteristics: 0˚C < TA < 70˚C; 0˚C < TJ < 125˚C; 8V < VCC < 20V; 2.8V DAC Code (VID4=VID2=VID1=VID0=1, VID3= 0), CGATE(H) = CGATE(L) = 3.3nF, COFF = 330pF, CSS= 0.1µF; Unless otherwise stated. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT CS5165H s VCC Supply Current Operating Sleep Mode s VCC Monitor Start Threshold Stop Threshold Hysteresis s Error Amplifier VFB Bias Current COMP Source Current COMP CLAMP Voltage COMP Clamp Current COMP Sink Current Open Loop Gain Unity Gain Bandwidth PSRR @ 1kHZ s GATE(H) and GATE(L) High Voltage at 100mA Low Voltage at 100mA Rise Time Fall Time GATE(H) to GATE(L) Delay GATE(L) to GATE(H) Delay GATE pull-down s Fault Protection SS Charge Time SS Pulse Period SS Duty Cycle SS Comp Clamp Voltage VFB Low Comparator 1V < VFB < VDAC (max on-time) No Loads on Gate(H) and Gate(L) ENABLE = 0V, 8V< VCC 2.5V Note 1 Note 1 Note 1 15 0.85 0.4 180 50 0.5 60 0.1 30 1.0 1.0 400 60 2 85 1.0 60 1.15 1.6 800 µA µA V mA µA dB MHz dB Measure VCC-GATE Measure GATE 1.6V < GATE < (VCC- 2.5V), 8V < VCC < 14V (VCC - 2.5V) > GATE > 1.6V, 8V < VCC < 14V GATE(H) < 2V, GATE(L) > 2V, 8V < VCC < 14V GATE(L) < 2V, GATE(H) > 2V, 8V < VCC < 14V Resistance to PGnd (note 1) 1.2 1.0 40 40 30 30 20 65 65 50 2.0 1.5 80 80 100 100 115 V V ns ns ns ns kΩ VFB = 0V VFB = 0V (Charge Time/Period) × 100 VFB = 2.7V, VSS = 0V Increase VFB till no SS pulsing and normal Off-time. 1.6 25 1.0 0.50 0.9 3.3 100 3.3 0.95 1.0 5.0 200 6.0 1.10 1.1 ms ms % V V s PWM Comparator Transient Response VFB = 1.2 to 5V 500ns after GATE(H) (after Blanking time) to GATE(H) = (VCC - 1V) to 1V, 8V < VCC < 14V 3 100 150 ns CS5165H Electrical Characteristics: 0˚C < TA < 70˚C; 0˚C < TJ < 125˚C; 8V < VCC < 20V; 2.8V DAC Code (VID4=VID2=VID1=VID0=1, VID3= 0), CGATE(H) = CGATE(L) = 3.3nF, COFF = 330pF, CSS= 0.1µF; Unless otherwise stated. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT s PWM Comparator: continued Minimum Pulse Width Drive VFB 1.2 to 5V upon (Blanking Time) GATE(H) rising edge (> VCC -1V), measure GATE(H ) pulse width, 8V < VCC < 14V s COFF Normal Off-Time Extended Off-Time s Time-Out Timer Time-Out Time Fault Duty Cycle s Enable Input ENABLE Threshold Shutdown delay (Note 1) Pull-up Current Pull-up Voltage Input Resistance 50 150 250 ns VFB = 2.7V VSS = VFB = 0V 1.0 5.0 1.6 8.0 2.3 12.0 µs µs VFB = 2.7V, Measure GATE(H ) Pulse Width VFB = 0V 10 30 30 50 50 70 µs % GATE(H) Switching ENABLE-to-GATE(H) < 2V ENABLE = 0V No load on ENABLE pin ENABLE = 5V, R = (5V-VPULLUP)/IENABLE 0.8 3 1.30 10 1.15 3 7 1.8 20 1.30 15 3 50 V µs µA V kΩ s Voltage Identification DAC Accuracy (all codes except 11111) VID4 VID3 VID2 VID1 VID0 10 0 0 0 10 0 0 1 10 0 1 0 10 0 1 1 10 1 0 0 10 1 0 1 10 1 1 0 10 1 1 1 11 0 0 0 11 0 0 1 11 0 1 0 11 0 1 1 11 1 0 0 11 1 0 1 11 1 1 0 00 0 0 0 00 0 0 1 00 0 1 0 00 0 1 1 00 1 0 0 00 1 0 1 00 1 1 0 00 1 1 1 01 0 0 0 01 0 0 1 Measure VFB = COMP (COFF = 0V) 25˚C ≤ TJ ≤ 125˚C; VCC = 12V -1 3.505 3.406 3.307 3.208 3.109 3.010 2.911 2.812 2.713 2.614 2.515 2.416 2.317 2.218 2.119 2.069 2.020 1.970 1.921 1.871 1.822 1.772 1.723 1.673 1.624 3.540 3.440 3.340 3.240 3.140 3.040 2.940 2.840 2.740 2.640 2.540 2.440 2.340 2.240 2.140 2.090 2.040 1.990 1.940 1.890 1.840 1.790 1.740 1.690 1.640 +1 3.575 3.474 3.373 3.272 3.171 3.070 2.969 2.868 2.767 2.666 2.565 2.464 2.363 2.262 2.161 2.111 2.060 2.010 1.959 1.909 1.858 1.808 1.757 1.707 1.656 % V V V V V V V V V V V V V V V V V V V V V V V V V 4 Electrical Characteristics: 0˚C < TA < 70˚C; 0˚C < TJ < 125˚C; 8V < VCC < 20V; 2.8V DAC Code (VID4=VID2=VID1=VID0=1, VID3= 0), CGATE(H) = CGATE(L) = 3.3nF, COFF = 330pF, CSS= 0.1µF; Unless otherwise stated. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT CS5165H VID4 VID3 VID2 VID1 VID0 01 0 1 0 01 0 1 1 01 1 0 0 01 1 0 1 01 1 1 0 01 1 1 1 11 1 1 1 Input Threshold Input Pull-up Resistance Input Pull-up Voltage s Power Good Output Low to High Delay High to Low Delay Output Low Voltage Sink Current Limit VID4, VID3, VID2, VID1, VID0 VID4, VID3, VID2, VID1, VID0 1.574 1.525 1.475 1.426 1.376 1.327 1.223 1.000 25 4.85 1.590 1.540 1.490 1.440 1.390 1.340 1.247 1.250 50 5.00 1.606 1.555 1.505 1.455 1.405 1.353 1.273 2.400 100 5.15 V V V V V V V V kΩ V VFB = (0.8 × VDAC) to VDAC VFB = VDAC to (0.8 × VDAC) VFB = 2.4V, IPWRGD = 500µA VFB = 2.4V, PWRGD = 1V LOWER THRESHOLD MIN TYP MAX 30 30 0.5 65 75 0.2 4.0 UPPER THRESHOLD 110 120 0.3 15.0 µs µs V mA THRESHOLD ACCURACY MIN TYP MAX UNIT % of Nominal DAC Output s DAC CODE VID4 VID3 VID2 VID1 VID0 1 0 0 0 0 1 0 0 0 1 1 0 0 1 0 1 0 0 1 1 1 0 1 0 0 1 0 1 0 1 1 0 1 1 0 1 0 1 1 1 1 1 0 0 0 1 1 0 0 1 1 1 0 1 0 1 1 0 1 1 1 1 1 0 0 1 1 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 1 1 0 0 0 1 1 1 -12 -8.5 -5 5 8.5 12 % 3.115 3.027 2.939 2.851 2.763 2.675 2.587 2.499 2.411 2.323 2.235 2.147 2.059 1.971 1.883 1.839 1.795 1.751 1.707 1.663 1.619 1.575 1.531 3.239 3.148 3.056 2.965 2.873 2.782 2.690 2.599 2.507 2.416 2.324 2.233 2.141 2.050 1.958 1.912 1.867 1.821 1.775 1.729 1.684 1.638 1.592 3.363 3.268 3.173 3.078 2.983 2.888 2.793 2.698 2.603 2.508 2.413 2.318 2.223 2.128 2.033 1.986 1.938 1.810 1.843 1.796 1.748 1.701 1.653 3.717 3.612 3.507 3.402 3.297 3.192 3.087 2.982 2.877 2.772 2.667 2.562 2.457 2.352 2.250 2.195 2.142 2.090 2.037 1.985 1.932 1.880 1.827 3.841 3.732 3.624 3.515 3.407 3.298 3.190 3.081 2.973 2.864 2.756 2.647 2.539 2.430 2.322 2.268 2.213 2.159 2.105 2.051 1.996 1.942 1.888 3.965 3.853 3.741 3.629 3.517 3.405 3.293 3.181 3.069 2.957 2.845 2.733 2.621 2.509 2.397 2.341 2.285 2.229 2.173 2.117 2.061 2.005 1.949 V V V V V V V V V V V V V V V V V V V V V V V 5 CS5165H Electrical Characteristics: 0˚C < TA < 70˚C; 0˚C < TJ < 125˚C; 8V < VCC < 20V; 2.8V DAC Code (VID4=VID2=VID1=VID0=1, VID3= 0), CGATE(H) = CGATE(L) = 3.3nF, COFF = 330pF, CSS= 0.1µF; Unless otherwise stated. THRESHOLD ACCURACY LOWER THRESHOLD MIN TYP MAX UPPER THRESHOLD MIN TYP MAX UNITS % of Nominal DAC Output s DAC CODE VID4 VID3 VID2 VID1 VID0 0 1 0 0 0 0 1 0 0 1 0 1 0 1 0 0 1 0 1 1 0 1 1 0 0 0 1 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1 1 1 1 -12 -8.5 -5 5 8.5 12 % 1.487 1.443 1.399 1.355 1.311 1.267 1.223 1.179 1.097 1.546 1.501 1.455 1.409 1.363 1.318 1.272 1.226 1.141 1.606 1.558 1.511 1.463 1.416 1.368 1.321 1.273 1.185 1.775 1.722 1.670 1.617 1.565 1.512 1.460 1.407 1.309 1.834 1.779 1.725 1.671 1.617 1.562 1.508 1.454 1.353 1.893 1.837 1.781 1.724 1.669 1.613 1.557 1.501 1.397 V V V V V V V V V Note 1: Guaranteed by design, not 100% tested in production. Block Diagram VCC - 7µA 20k VCC Monitor Circuit Bias + VCC 3.95V 3.87V ENABLE + VGATE(H) 5V 60µA 0.7V + S Q 1.25V Enable Comparator SS Low Comparator R Q FAULT FAULT PGnd SS 2µA 2.5V + - SS High Comparator FAULT Latch VCC VGATE(L) PGnd COMP VID0 VID1 Error Amplifier + VID2 VID3 VID4 -8.5% 5 BIT DAC - + PWM Comp Blanking Maximum On-Time Timeout R S Q Q GATE(H) = ON GATE(H) = OFF +8.5% - PWM Comparator + Normal Off-Time Extended Off-Time Timeout PWM Latch Off-Time Timeout COFF One Shot R S Q + COFF PWRGD 65µs Delay VFB + Time Out Timer (30µs) Edge Triggered LGnd 1V VFB Low Comparator 6 CS5165H Application Information Theory Of Operation V2™ Control Method The V2™ method of control uses a ramp signal that is generated by the ESR of the output capacitors. This ramp is proportional to the AC current through the main inductor and is offset by the value of the DC output voltage. This control scheme inherently compensates for variation in either line or load conditions, since the ramp signal is generated from the output voltage itself. This control scheme differs from traditional techniques such as voltage mode, which generates an artificial ramp, and current mode, which generates a ramp from inductor current. PWM Comparator + GATE(H) C – GATE(L) improved, since the error amplifier bandwidth can be rolled off at a low frequency. Enhanced noise immunity improves remote sensing of the output voltage, since the noise associated with long feedback traces can be effectively filtered. Line and load regulation are drastically improved because there are two independent voltage loops. A voltage mode controller relies on a change in the error signal to compensate for a deviation in either line or load voltage. This change in the error signal causes the output voltage to change corresponding to the gain of the error amplifier, which is normally specified as line and load regulation. A current mode controller maintains fixed error signal under deviation in the line voltage, since the slope of the ramp signal changes, but still relies on a change in the error signal for a deviation in load. The V2™ method of control maintains a fixed error signal for both line and load variation, since the ramp signal is affected by both line and load. Constant Off-Time To maximize transient response, the CS5165H uses a Constant Off-Time method to control the rate of output pulses. During normal operation, the Off-Time of the high side switch is terminated after a fixed period, set by the COFF capacitor. To maintain regulation, the V2™ Control Loop varies switch On-Time. The PWM comparator monitors the output voltage ramp, and terminates the switch On-Time. Constant Off-Time provides a number of advantages. Switch duty Cycle can be adjusted from 0 to 100% on a pulse-by pulse basis when responding to transient conditions. Both 0% and 100% Duty Cycle operation can be maintained for extended periods of time in response to Load or Line transients. PWM Slope Compensation to avoid sub-harmonic oscillations at high duty cycles is avoided. Switch On-Time is limited by an internal 30µs (typical) timer, minimizing stress to the Power Components. Programmable Output The CS5165H is designed to provide two methods for programming the output voltage of the power supply. A five bit on board digital to analog converter (DAC) is used to program the output voltage within two different ranges. The first range is 2.14V to 3.54V in 100mV steps, the second is 1.34V to 2.09V in 50mV steps, depending on the digital input code. If all five bits are left open, the CS5165H enters adjust mode. In adjust mode, the designer can choose any output voltage by using resistor divider feedback to the VFB pin, as in traditional controllers. The CS5165H is specifically designed to meet or exceed Intel’s Pentium® II specifications. Start-up Until the voltage on the VCC Supply pin exceeds the 3.95V monitor threshold, the Soft Start and Gate pins are held low. The Fault latch is Reset (no Fault condition). The output of the Error Amp (COMP) is pulled up to 1V by the Comp Clamp. When the VCC pin exceeds the monitor 7 Ramp Signal Error Amplifier – Output Voltage Feedback COMP Error Signal E + Reference Voltage Figure 1: V2™ Control Diagram The V2™ control method is illustrated in Figure 1. The output voltage is used to generate both the error signal and the ramp signal. Since the ramp signal is simply the output voltage, it is affected by any change in the output regardless of the origin of that change. The ramp signal also contains the DC portion of the output voltage, which allows the control circuit to drive the main switch to 0% or 100% duty cycle as required. A change in line voltage changes the current ramp in the inductor, affecting the ramp signal, which causes the V2™ control scheme to compensate the duty cycle. Since the change in inductor current modifies the ramp signal, as in current mode control, the V2™ control scheme has the same advantages in line transient response. A change in load current will have an affect on the output voltage, altering the ramp signal. A load step immediately changes the state of the comparator output, which controls the main switch. Load transient response is determined only by the comparator response time and the transition speed of the main switch. The reaction time to an output load step has no relation to the crossover frequency of the error signal loop, as in traditional control methods. The error signal loop can have a low crossover frequency, since transient response is handled by the ramp signal loop. The main purpose of this “slow”feedback loop is to provide DC accuracy. Noise immunity is significantly CS5165H Application Information: continued threshold, the GateH output is activated, and the Soft Start Capacitor begins charging. The GateH output will remain on, enabling the NFET switch, until terminated by either the PWM Comparator, or the Maximum On-Time Timer. If the Maximum On-Time is exceeded before the regulator output voltage achieves the 1V level, the pulse is terminated. The GateH pin drives low, and the GateL pin drives high for the duration of the Extended Off-Time. This time is set by the Time-out Timer and is approximately equal to the Maximum On-Time, resulting in a 50% Duty Cycle. The GateL Pin will then drive low, the GateH pin will drive high, and the cycle repeats. When regulator output voltage achieves the 1V level present at the Comp pin, regulation has been achieved and normal Off-Time will ensue. The PWM comparator terminates the switch On-Time, with Off-Time set by the COFF Capacitor. The V2™ control loop will adjust switch Duty Cycle as required to ensure the regulator output voltage tracks the output of the Error Amp. The Soft Start and Comp capacitors will charge to their final levels, providing a controlled turn-on of the regulator output. Regulator turn-on time is determined by the Comp capacitor charging to its final value. Its voltage is limited by the Soft Start Comp clamp and the voltage on the Soft start pin. Power Supply Sequencing The CS5165H offers inherent protection from undefined start-up conditions, regardless of the 12V and 5V supply power-up sequencing. The turn-on slew rates of the 12V and 5V power supplies can be varied over wide ranges without affecting the output voltage or causing detrimental effects to the buck regulator. Trace 1 Soft Start pin (2V/div) Trace 2 COMP pin (error amplifier output) (1V/div) Trace 4 Regulator output voltage (1V/div) Figure 3: Demonstration board start up waveforms. Trace 1 - Regulator Output Voltage (1V/div.) Trace 2 - Inductor Switching Node (5V/div.) Figure 4: Demonstration board enable start up waveforms. Normal Operation During Normal operation, Switch Off-Time is constant and set by the COFF capacitor. Switch On-Time is adjusted by the V2™ Control loop to maintain regulation. This results in changes in regulator switching frequency, duty cycle, and output ripple in response to changes in load and line. Output voltage ripple will be determined by inductor ripple current and the ESR of the output capacitors (see figures 5 & 6 ). Trace 1 - Regulator Output Voltage (1V/div.) Trace 2 - Inductor Switching Node (2V/div.) Trace 3 - 12V input (VCC) (5V/div.) Trace 4 - 5V Input (1V/div.) Figure 2: Demonstration board start up in response to increasing 12V and 5V input voltages. Extended off time is followed by normal off time operation when output voltage achieves regulation to the error amplifier output. 8 CS5165H Application Information: continued Holding tolerance to 1% allows the error amplifiers reference voltage to be targeted +40mV high without compromising DC accuracy. A “Droop Resistor”, implemented through a PC board trace, connects the Error Amps feedback pin (VFB) to the output capacitors and load and carries the output current. With no load, there is no DC drop across this resistor, producing an output voltage tracking the Error amps, including the +40mV offset. When the full load current is delivered, an 80mV drop is developed across this resistor. This results in output voltage being offset -40mV low. The result of Adaptive Voltage Positioning is that additional margin is provided for a load transient before reaching the output voltage specification limits. When load current suddenly increases from its minimum level, the output capacitor is pre-positioned +40mV. Conversely, when load current suddenly decreases from its maximum level, the output capacitor is pre-positioned -40mV (see figures 7, 8, and 9). For best Transient Response, a combination of a number of high frequency and bulk output capacitors are usually used. If the Maximum On-Time is exceeded while responding to a sudden increase in Load current, a normal off-time occurs to prevent saturation of the output inductor. Trace 1 GATE (H) (10V/div) Trace 2 Inductor Switching Node (5V/div) Trace 3 Output Inductor Ripple Current (2A/div) Trace 4 VOUT ripple (20mV/div) Figure 5: Normal Operation showing Output Inductor Ripple Current and Output Voltage Ripple, 0.5A Load, VOUT = +2.84V (DAC = 10111) Trace 1 - GATE(H) (10/div) Trace 2 - Inductor Switching Node (5V/div) Trace 3 - Output Inductor Ripple Current (2A/div) Trace 4 - VOUT ripple (20mV/div) Figure 6: Normal Operation showing Output Inductor Ripple Current and Output Voltage Ripple, ILOAD = 14A, VOUT = +2.84V (DAC = 10111) Trace 3 -Load Current (5A/10mV/div) Trace 4 - VOUT (100mV/div) Transient Response The CS5165H V2™ Control Loop’s 100ns reaction time provides unprecedented transient response to changes in input voltage or output current. Pulse-by-pulse adjustment of duty cycle is provided to quickly ramp the inductor current to the required level. Since the inductor current cannot be changed instantaneously, regulation is maintained by the output capacitor(s) during the time required to slew the inductor current. Overall load transient response is further improved through a feature called “Adaptive Voltage Positioning”. This technique pre-positions the output capacitors voltage to reduce total output voltage excursions during changes in load. 9 Figure 7: Output Voltage Transient Response to a 14A load pulse, VOUT= +2.84V (DAC = 10111). CS5165H Application Information: continued threshold. If this happens the cycle will repeat itself until the short is removed. The Soft Start charge/discharge current ratio sets the duty cycle for the pulses (2µA/60µA = 3.3%), while actual duty cycle is half that due to the extended off time mode (1.65%). This protection feature results in less stress to the regulator components, input power supply, and PC board traces than occurs with constant current limit protection (see Figures 10 and 11). If the short circuit condition is removed, output voltage will rise above the 1V level, preventing the FAULT latch from being set, allowing normal operation to resume. Trace 1 - GATE(H) (10V/div) Trace 2 - Inductor Switching Node (5V/div) Trace 3 -Load Current (5A/div) Trace 4 - VOUT (100mV/div) Figure 8: Output Voltage Transient Response to a 14A load step, VOUT = +2.84V(DAC = 10111). Trace 4 - 5V Supply Voltage (2V/div.) Trace 3 - Soft Start Timing Capacitor (1V/div.) Trace 2 - Inductor Switching Node (2V/div.) Figure 10: Demonstration board hiccup mode short circuit protection. Gate pulses are delivered while the Soft Start capacitor charges, and cease during discharge. Trace 1 - GATE(H) (10V/div) Trace 2 - Inductor Switching Node (5V/div) Trace 3 -Load Current (5A/div) Trace 4 - VOUT(100mV/div) Figure 9: Output Voltage Transient Response to a 14A load turn-off, VOUT = +2.84V (DAC = 10111). Protection and Monitoring Features Short Circuit Protection A lossless hiccup mode short circuit protection feature is provided, requiring only the Soft Start capacitor to implement. If a short circuit condition occurs the VFB low comparator sets the FAULT latch. This causes the top FET to shut off, disconnecting the regulator from its input voltage. The Soft Start capacitor is then slowly discharged by a 2µA current source until it reaches its lower 0.7V threshold. The regulator will then attempt to restart normally, operating in its extended off time mode with a 50% duty cycle, while the Soft Start capacitor is charged with a 60µA charge current. If the short circuit condition persists, the regulator output will not achieve the 1V low VFB comparator threshold before the Soft Start capacitor is charged to its upper 2.5V 10 Trace 4 = 5V from PC Power Supply (2V/div.) Trace 2 = Inductor Switching Node (2V/div.) Figure 11: Demonstration board Start up with regulator output shorted to ground. CS5165H Application Information: continued Overvoltage Protection Overvoltage protection (OVP) is provided as result of the normal operation of the V2™ control topology and requires no additional external components. The control loop responds to an overvoltage condition within 100ns, causing the top MOSFET to shut off, disconnecting the regulator from its input voltage. The bottom MOSFET is then activated, resulting in a “crowbar” action to clamp the output voltage and prevent damage to the load (see Figures 12 and 13). The regulator will remain in this state until the overvoltage condition ceases or the input voltage is pulled low. The bottom FET and board trace must be properly designed to implement the OVP function. If a dedicated OVP output is required, it can be implemented using the circuit in figure 14. In this figure the OVP signal will go high (overvoltage condition), if the output voltage (VCORE) exceeds 20% of the voltage set by the particular DAC code and provided that PWRGD is low. It is also required that the overvoltage condition be present for at least the PWRGD delay time for the OVP signal to be activated. The resistor values shown in figure 14 are for VDAC = +2.8V (DAC = 10111). The VOVP (overvoltage trip-point) can be set using the following equation: Trace 4 = 5V from PC Power Supply (2V/div.) Trace 1 = Regulator Output Voltage (1V/div.) Figure 13: OVP response to an input-to-output short circuit by pulling the input voltage to ground. VCORE 15K VOVP = VBEQ3 ( 1+ R2 R1 ) +5V R1 Q3 2N3906 +5V 56K 5K R2 OVP 20K Q2 2N3904 10K 10K 10K CS5165H Q1 PWRGD 2N3906 Figure 14: Circuit to implement a dedicated OVP output using the CS5165H. Output Enable Circuit The Enable pin (pin 8) is used to enable or disable the regulator output voltage, and is consistent with TTL DC specifications. It is internally pulled-up. If pulled low (below 0.8V), the output voltage is disabled. At the same time the Power Good and Soft Start pins are pulled low, so that when normal operation resumes power-up of the CS5165H goes through the Soft Start sequence. Upon pulling the Enable pin low, the internal IC bias is completely shut off, resulting in total shutdown of the Controller IC. Power Good Circuit The Power Good pin (pin 13) is an open-collector signal consistent with TTL DC specifications. It is externally pulled -up, and is pulled low (below 0.3V) when the regulator output voltage typically exceeds ± 8.5% of the nominal output voltage. Maximum output voltage deviation before Power Good is pulled low is ± 12%. Trace 4 = 5V from PC Power Supply (5V/div.) Trace1 = Regulator Output Voltage (1V/div.) Trace 2 = Inductor Switching Node (5V/div.) Figure 12: OVP response to an input-to-output short circuit by immediately providing 0% duty cycle, crow-barring the input voltage to ground. 11 CS5165H Application Information: continued Trace 2 - PWRGD (2V/div) Trace 4 - VOUT (1V/div) Trace 1 PWRGD (2V/div) Trace 4 VFB (1V/div) Figure 15: PWRGD signal becomes logic high as VOUT enters -8.5% of lower PWRGD threshold, VOUT = +2.84V (DAC = 10111) Figure 17: Power Good is insensitive to out of regulation conditions that are present for a duration less than the built in delay. Selecting External Components The CS5165H buck regulator can be used with a wide range of external power components to optimize the cost and performance of a particular design. The following information can be used as general guidelines to assist in their selection. NFET Power Transistors Both logic level and standard FETs can be used. The reference designs derive gate drive from the 12V supply which is generally available in most computer systems and utilize logic level FETs. A charge pump may be easily implemented to permit use of standard FET’s or support 5V or 12V only systems (maximum of 20V). Multiple FET’s may be paralleled to reduce losses and improve efficiency and thermal management. Voltage applied to the FET gates depends on the application circuit used. Both upper and lower gate driver outputs are specified to drive to within 1.5V of ground when in the low state and to within 2V of their respective bias supplies when in the high state. In practice, the FET gates will be driven rail to rail due to overshoot caused by the capacitive load they present to the controller IC. For the typical application where VCC = 12V and 5V is used as the source for the regulator output current, the following gate drive is provided: VGS (TOP) = 12V - 5V = 7V, VGS(BOTTOM) = 12V (see Figure 18). Trace 1 PWRGD (2V/div) Trace 4 VFB (1V/div) Figure 16: Power Good response to an out of regulation condition. Figure 16 shows the relationship between the regulated output voltage VFB and the Power Good signal. To prevent Power Good from interrupting the CPU unnecessarily, the CS5165H has a built-in delay to prevent noise at the VFB pin from toggling Power Good. The internal time delay is designed to take about 75µs for Power Good to go low and 65µs for it to recover. This allows the Power Good signal to be completely insensitive to out of regulation conditions that are present for a duration less than the built in delay (see figure 17). It is therefore required that the output voltage attains an out of regulation or in regulation level for at least the builtin delay time duration before the Power Good signal can change state. 12 CS5165H Application Information: continued Synchronous MOSFET: Power = ILOAD2 × RDSON × (1 - duty cycle) Duty Cycle = VOUT + (ILOAD × RDSON OF SYNCH FET) VIN + (ILOAD × RDSON OF SYNCH FET) - (ILOAD × RDSON OF SWITCH FET) Off Time Capacitor (COFF) The COFF timing capacitor sets the regulator off time: TOFF = COFF × 4848.5 Trace 3 = GATE(H) (10V/div.) Trace 1= GATE(H) - 5VIN Trace 4 = GATE(L) (10V/div.) Trace 2 = Inductor Switching Node (5V/div.) Figure 18: Gate drive waveforms depicting rail to rail swing. The preceding equation for Duty Cycle can also be used to calculate the regulator switching frequency and select the COFF timing capacitor: COFF = Period × (1-Duty Cycle) 4848.5 where period = 1 switching frequency Trace 1 - GATE(H) (5V/div) Trace 2 - GATE(L) (5V/div) Figure 19: Normal Operation showing the guaranteed Non-Overlap time between the High and Low - Side MOSFET Gate Drives, ILOAD = 14A. The CS5165H provides adaptive control of the external NFET conduction times by guaranteeing a typical 65ns non-overlap between the upper and lower MOSFET gate drive pulses. This feature eliminates the potentially catastrophic effect of “shoot-through current”, a condition during which both FETs conduct causing them to overheat, self-destruct, and possibly inflict irreversible damage to the processor. The most important aspect of FET performance is RDSON, which effects regulator efficiency and FET thermal management requirements. The power dissipated by the MOSFETs may be estimated as follows: Switching MOSFET: Power = ILOAD2 × RDSON × duty cycle Schottky Diode for Synchronous FET For synchronous operation, A Schottky diode may be placed in parallel with the synchronous FET to conduct the inductor current upon turn off of the switching FET to improve efficiency. The CS5165H reference circuit does not use this device due to its excellent design. Instead, the body diode of the synchronous FET is utilized to reduce cost and conducts the inductor current. For a design operating at 200kHz or so, the low non-overlap time combined with Schottky forward recovery time may make the benefits of this device not worth the additional expense. The power dissipation in the synchronous MOSFET due to body diode conduction can be estimated by the following equation: Power = Vbd × ILOAD × conduction time × switching frequency Where Vbd = the forward drop of the MOSFET body diode. For the CS5165H demonstration board: Power = 1.6V × 14.2A × 100ns × 200kHz = 0.45W This is only 1.1% of the 40W being delivered to the load. 13 CS5165H Application Information: continued “Droop” Resistor for Adaptive Voltage Positioning Adaptive voltage positioning is used to help keep the output voltage within specification during load transients. To implement adaptive voltage positioning a “Droop Resistor” must be connected between the output inductor and output capacitors and load. This resistor carries the full load current and should be chosen so that both DC and AC tolerance limits are met. An embedded PC trace resistor has the distinct advantage of near zero cost implementation. However, this droop resistor can vary due to three reasons: 1) the sheet resistivity variation causes the thickness of the PCB layer to vary. 2) the mismatch of L/W, and 3) temperature variation. 1) Sheet Resistivity In order to determine the droop resistor value the nominal voltage drop across it at full load has to be calculated. This voltage drop has to be such that the output voltage full load is above the minimum DC tolerance spec. VDROOP(TYP) = [VDAC(MIN)-VDC(MIN)] 1+RDROOP(TOLERANCE) Example: for a 300MHz Pentium®II, the DC accuracy spec is 2.74 < VCC(CORE) < 2.9V, and the AC accuracy spec is 2.67V < VCC(CORE)