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HIP6014
Data Sheet March 2000 File Number 4420.2
Buck and Synchronous-Rectifier (PWM) Controller and Output Voltage Monitor
The HIP6014 provides complete control and protection for a DC-DC converter optimized for high-performance microprocessor applications. It is designed to drive two N-Channel MOSFETs in a synchronous-rectified buck topology. The HIP6014 integrates all of the control, output adjustment, monitoring and protection functions into a single package. The output voltage of the converter is easily adjusted and precisely regulated. The HIP6014 includes a fully TTLcompatible 5-input digital-to-analog converter (DAC) that adjusts the output voltage from 2.1VDC to 3.5VDC in 0.1V increments and from 1.8VDC to 2.05VDC in 0.05V steps. The precision reference and voltage-mode regulator hold the selected output voltage to within 1% over temperature and line voltage variations. The HIP6014 provides simple, single feedback loop, voltagemode control with fast transient response. It includes a 200kHz free-running triangle-wave oscillator that is adjustable from below 50kHz to over 1MHz. The error amplifier features a 15MHz gain-bandwidth product and 6V/s slew rate which enables high converter bandwidth for fast transient performance. The resulting PWM duty ratio ranges from 0% to 100%. The HIP6014 monitors the output voltage with a window comparator that tracks the DAC output and issues a Power Good signal when the output is within 10%. The HIP6014 protects against over-current and over-voltage conditions by inhibiting PWM operation. Additional built-in over-voltage protection triggers an external SCR to crowbar the input supply. The HIP6014 monitors the current by using the rDS(ON) of the upper MOSFET which eliminates the need for a current sensing resistor.
Features
* Drives Two N-Channel MOSFETs * Operates from +5V or +12V Input * Simple Single-Loop Control Design - Voltage-Mode PWM Control * Fast Transient Response - High-Bandwidth Error Amplifier - Full 0% to 100% Duty Ratio * Excellent Output Voltage Regulation - 1% Over Line Voltage and Temperature * TTL-Compatible 5-Bit Digital-to-Analog Output Voltage Selection - Wide Range . . . . . . . . . . . . . . . . . . . 1.8VDC to 3.5VDC - 0.1V Binary Steps . . . . . . . . . . . . . . . 2.1VDC to 3.5VDC - 0.05V Binary Steps . . . . . . . . . . . . . 1.8VDC to 2.05VDC * Power-Good Output Voltage Monitor * Over-Voltage and Over-Current Fault Monitors - Does Not Require Extra Current Sensing Element, Uses MOSFET's rDS(ON) * Small Converter Size - Constant Frequency Operation - 200kHz Free-Running Oscillator Programmable from 50kHz to over 1MHz
Applications
* Power Supply for Pentium(R), Pentium Pro, Pentium II, PowerPCTM, K6TM, 6X86TM and AlphaTM Microprocessors * High-Power 5V to 3.xV DC-DC Regulators * Low-Voltage Distributed Power Supplies
Pinout
HIP6014 (SOIC) TOP VIEW
VSEN OCSET SS VID0 VID1 VID2 VID3 VID4 COMP 1 2 3 4 5 6 7 8 9 20 RT 19 OVP 18 VCC 17 LGATE 16 PGND 15 BOOT 14 UGATE 13 PHASE 12 PGOOD 11 GND
Ordering Information
PART NUMBER HIP6014CB TEMP. RANGE (oC) 0 to 70 PACKAGE 20 Ld SOIC PKG. NO. M20.3
FB 10
6X86TM is a trademark of Cyrix Corporation. AlphaTM is a trademark of Digital Equipment Corporation. K6TM is a trademark of Advanced Micro Devices, Inc. Pentium(R) is a registered trademark of Intel Corporation. PowerPCTM is a trademark of IBM. CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Copyright (c) Intersil Corporation 2000
1
HIP6014 Typical Application
12V VCC PGOOD SS OVP RT VID0 VID1 VID2 VID3 VID4 FB MONITOR AND PROTECTION OCSET EN BOOT VIN = +5V OR +12V
OSC
UGATE PHASE +VOUT
HIP6014
D/A + +
-
LGATE PGND VSEN GND
-
COMP
Block Diagram
VCC VSEN 110% +
POWER-ON RESET (POR)
-
PGOOD
90% + 115% + SOFTSTART OVERCURRENT 4V OVERVOLTAGE 10A OVP SS BOOT UGATE PHASE VID0 VID1 VID2 VID3 VID4 FB COMP GND RT OSCILLATOR TTL D/A CONVERTER (DAC) DACOUT + PWM COMPARATOR GATE INHIBIT CONTROL LOGIC PWM LGATE PGND
+ OCSET 200A
REFERENCE
-
+
-
ERROR AMP
2
HIP6014
Absolute Maximum Ratings
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +15V Boot Voltage, VBOOT - VPHASE . . . . . . . . . . . . . . . . . . . . . . . . +15V Input, Output or I/O Voltage . . . . . . . . . . . .GND -0.3V to VCC +0.3V ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 2
Thermal Information
Thermal Resistance (Typical, Note 1) JA (oC/W) SOIC Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Maximum Junction Temperature (Plastic Package) . . . . . . . .150oC Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . .300oC (SOIC - Lead Tips Only)
Operating Conditions
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . +12V 10% Ambient Temperature Range . . . . . . . . . . . . . . . . . . . . . 0oC to 70oC Junction Temperature Range . . . . . . . . . . . . . . . . . . . . 0oC to 125oC
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE: 1. JA is measured with the component mounted on a low effective thermal conductivity test board in free air. See Tech Brief 379 for details.
Electrical Specifications
PARAMETER VCC SUPPLY CURRENT Nominal Supply POWER-ON RESET Rising VCC Threshold Falling VCC Threshold Rising VOCSET Threshold OSCILLATOR Free Running Frequency Total Variation Ramp Amplitude REFERENCE AND DAC
Recommended Operating Conditions, Unless Otherwise Noted SYMBOL TEST CONDITIONS MIN TYP MAX UNITS
ICC
UGATE and LGATE Open
-
5
-
mA
VOCSET = 4.5V VOCSET = 4.5V
8.2 -
1.26
10.4 -
V V V
RT = OPEN 6k < RT to GND < 200k VOSC RT = Open
185 -15 -
200 1.9
215 +15 -
kHz % VP-P V V %
DAC(VID0-VID4) Input Low Voltage DAC(VID0-VID4) Input High Voltage DACOUT Voltage Accuracy ERROR AMPLIFIER DC Gain Gain-Bandwidth Product Slew Rate GATE DRIVERS Upper Gate Source Upper Gate Sink Lower Gate Source Lower Gate Sink PROTECTION Over-Voltage Trip (VSEN/DACOUT) OCSET Current Source OVP Sourcing Current Soft Start Current POWER GOOD Upper Threshold (VSEN /DACOUT) Lower Threshold (VSEN /DACOUT) Hysteresis (VSEN /DACOUT) PGOOD Voltage Low VPGOOD VSEN Rising VSEN Falling Upper and Lower Threshold IPGOOD = -5mA IOCSET IOVP ISS VOCSET = 4.5VDC VSEN = 5.5V, VOVP = 0V IUGATE RUGATE ILGATE RLGATE VBOOT - VPHASE = 12V, VUGATE = 6V ILGATE = 0.3A VCC = 12V, VLGATE = 6V ILGATE = 0.3A GBW SR COMP = 10pF
2.0 -1.0
-
0.8 +1.0
-
88 15 6
-
dB MHz V/s
350 300 -
500 5.5 450 3.5
10 6.5
mA mA % A mA A % % % V
170 60 -
115 200 10
120 230 -
106 89 -
2 0.5
111 94 -
3
HIP6014 Typical Performance Curves
80 70 1000 RESISTANCE (k) RT PULLUP TO +12V ICC (mA) 60 CUPPER = CLOWER = CGATE 50 40 CGATE = 1000pF 30 10 RT PULLDOWN TO VSS 10 10 100 SWITCHING FREQUENCY (kHz) 1000 0 100 200 20 CGATE = 10pF CGATE = 3300pF
100
300 400 500 600 700 800 SWITCHING FREQUENCY (kHz)
900
1000
FIGURE 1. RT RESISTANCE vs FREQUENCY
FIGURE 2. BIAS SUPPLY CURRENT vs FREQUENCY
Functional Pin Description
VID0-4 (Pins 4-8)
VSEN OCSET SS VID0 VID1 VID2 VID3 VID4 COMP 1 2 3 4 5 6 7 8 9 20 RT 19 OVP 18 VCC 17 LGATE 16 PGND 15 BOOT 14 UGATE 13 PHASE 12 PGOOD 11 GND
VID0-4 are the input pins to the 5-bit DAC. The states of these five pins program the internal voltage reference (DACOUT). The level of DACOUT sets the converter output voltage. It also sets the PGOOD and OVP thresholds. Table 1 specifies DACOUT for the 32 combinations of DAC inputs.
COMP (Pin 9) and FB (Pin 10)
COMP and FB are the available external pins of the error amplifier. The FB pin is the inverting input of the error amplifier and the COMP pin is the error amplifier output. These pins are used to compensate the voltage-control feedback loop of the converter.
FB 10
VSEN (Pin 1)
This pin is connected to the converters output voltage. The PGOOD and OVP comparator circuits use this signal to report output voltage status and for overvoltage protection.
GND (Pin 11)
Signal ground for the IC. All voltage levels are measured with respect to this pin
PGOOD (Pin 12)
PGOOD is an open collector output used to indicate the status of the converter output voltage. This pin is pulled low when the converter output is not within 10% of the DACOUT reference voltage. Exception to this behavior are the cases where the VID pins combination yield a 0V converter output; in these cases PGOOD asserts a high level.
OCSET (Pin 2)
Connect a resistor (ROCSET) from this pin to the drain of the upper MOSFET. ROCSET, an internal 200A current source (IOCS), and the upper MOSFET on-resistance (rDS(ON)) set the converter over-current (OC) trip point according to the following equation:
I OCS * R OCSET I PEAK = ------------------------------------------r DS ( ON )
PHASE (Pin 13)
Connect the PHASE pin to the upper MOSFET source. This pin is used to monitor the voltage drop across the MOSFET for over-current protection. This pin also provides the return path for the upper gate drive.
An over-current trip cycles the soft-start function.
SS (Pin 3)
Connect a capacitor from this pin to ground. This capacitor, along with an internal 10A current source, sets the softstart interval of the converter.
UGATE (Pin 14)
Connect UGATE to the upper MOSFET gate. This pin provides the gate drive for the upper MOSFET.
4
HIP6014
BOOT (Pin 15)
This pin provides bias voltage to the upper MOSFET driver. A bootstrap circuit may be used to create a BOOT voltage suitable to drive a standard N-Channel MOSFET. (COMP pin) and reference input (+ terminal of error amp) to the SS pin voltage. Figure 3 shows the soft start interval with CSS = 0.1F. Initially the clamp on the error amplifier (COMP pin) controls the converter's output voltage. At t1 in Figure 3, the SS voltage reaches the valley of the oscillator's triangle wave. The oscillator's triangular waveform is compared to the ramping error amplifier voltage. This generates PHASE pulses of increasing width that charge the output capacitor(s). This interval of increasing pulse width continues to t2 . With sufficient output voltage, the clamp on the reference input controls the output voltage. This is the interval between t2 and t3 in Figure 3. At t3 the SS voltage exceeds the DACOUT voltage and the output voltage is in regulation. This method provides a rapid and controlled output voltage rise. The PGOOD signal toggles `high' when the output voltage (VSEN pin) is within 5% of DACOUT. The 2% hysteresis built into the power good comparators prevents PGOOD oscillation due to nominal output voltage ripple.
PGND (Pin 16)
This is the power ground connection. Tie the lower MOSFET source to this pin.
LGATE (Pin 17)
Connect LGATE to the lower MOSFET gate. This pin provides the gate drive for the lower MOSFET.
VCC (Pin 18)
Provide a 12V bias supply for the chip to this pin.
OVP (Pin 19)
The OVP pin can be used to drive an external SCR in the event of an overvoltage condition. Output rising 15% more than the DAC-set voltage triggers a high output on this pin and disables PWM gate drive circuitry.
RT (Pin 20)
This pin provides oscillator switching frequency adjustment. By placing a resistor (RT) from this pin to GND, the nominal 200kHz switching frequency is increased according to the following equation:
5 * 10 Fs 200kHz + -------------------R T ( k )
6 0V
PGOOD (2V/DIV.)
SOFT-START (1V/DIV.) OUTPUT VOLTAGE (1V/DIV.) 0V 0V t1 t2 TIME (5ms/DIV.) t3
(RT to GND)
Conversely, connecting a pull-up resistor (RT) from this pin to VCC reduces the switching frequency according to the following equation:
4 * 10 Fs 200kHz - -------------------R T ( k )
7
(RT to 12V)
FIGURE 3. SOFT START INTERVAL
Functional Description
Initialization
The HIP6014 automatically initializes upon receipt of power. Special sequencing of the input supplies is not necessary. The Power-On Reset (POR) function continually monitors the input supply voltages. The POR monitors the bias voltage at the VCC pin and the input voltage (VIN) on the OCSET pin. The level on OCSET is equal to VIN less a fixed voltage drop (see over-current protection). The POR function initiates soft start operation after both input supply voltages exceed their POR thresholds. For operation with a single +12V power source, VIN and VCC are equivalent and the +12V power source must exceed the rising VCC threshold before POR initiates operation.
Over-Current Protection
The over-current function protects the converter from a shorted output by using the upper MOSFET's on-resistance, rDS(ON) to monitor the current. This method enhances the converter's efficiency and reduces cost by eliminating a current sensing resistor. The over-current function cycles the soft-start function in a hiccup mode to provide fault protection. A resistor (ROCSET) programs the over-current trip level. An internal 200A current sink develops a voltage across ROCSET that is referenced to VIN . When the voltage across the upper MOSFET (also referenced to VIN) exceeds the voltage across ROCSET, the over-current function initiates a soft-start sequence. The softstart function discharges CSS with a 10A current sink and inhibits PWM operation. The soft-start function recharges CSS, and PWM operation resumes with the error amplifier clamped to the SS voltage. Should an overload occur while recharging CSS, the soft start function inhibits PWM operation while fully charging CSS to 4V to complete its cycle. Figure 4 shows this
Soft Start
The POR function initiates the soft start sequence. An internal 10A current source charges an external capacitor (CSS) on the SS pin to 4V. Soft start clamps the error amplifier output 5
HIP6014
little power with this method. The measured input power for the conditions of Figure 4 is 2.5W.
4V 2V 0V OUTPUT INDUCTOR 15A 10A 5A 0A
SOFT-START
The over-current function will trip at a peak inductor current (IPEAK) determined by:
I OCSET * R OCSET I PEAK = -------------------------------------------------r DS ( ON )
where IOCSET is the internal OCSET current source (200A typical). The OC trip point varies mainly due to the MOSFET's rDS(ON) variations. To avoid over-current tripping in the normal operating load range, find the ROCSET resistor from the equation above with:
TIME (20ms/DIV.)
1. The maximum rDS(ON) at the highest junction temperature. 2. The minimum IOCSET from the specification table. 3. Determine IPEAK for I PEAK > I OUT ( MAX ) + ( I ) 2 , where I is the output inductor ripple current. For an equation for the ripple current see the section under component guidelines titled `Output Inductor Selection'.
FIGURE 4. OVER-CURRENT OPERATION
operation with an overload condition. Note that the inductor current increases to over 15A during the CSS charging interval and causes an over-current trip. The converter dissipates very
TABLE 1. OUTPUT VOLTAGE PROGRAM PIN NAME VID4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 VID3 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 VID2 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 VID1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 VID0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 NOMINAL OUTPUT VOLTAGE DACOUT 0 0 0 0 0 0 0 0 0 0 1.80 1.85 1.90 1.95 2.00 2.05 PIN NAME VID4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 VID3 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 VID2 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 VID1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 VID0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 NOMINAL OUTPUT VOLTAGE DACOUT 0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5
NOTE: 0 = connected to GND or VSS, 1 = connected to VDD through pull-up resistors
A small ceramic capacitor should be placed in parallel with ROCSET to smooth the voltage across ROCSET in the presence of switching noise on the input voltage.
Output Voltage Program
The output voltage of a HIP6014 converter is programmed to discrete levels between 1.8VDC and 3.5VDC . The
voltage identification (VID) pins program an internal voltage reference (DACOUT) with a TTL-compatible 5-bit digital-toanalog converter (DAC). The level of DACOUT also sets the PGOOD and OVP thresholds. Table 1 specifies the DACOUT voltage for the 32 different combinations of connections on the VID pins. The output voltage should not be adjusted while the converter is delivering power.
6
HIP6014
Remove input power before changing the output voltage. Adjusting the output voltage during operation could toggle the PGOOD signal and exercise the overvoltage protection. All VID pin combinations resulting in a 0V output setting activate the Power-On Reset function and disable the gate drive circuitry. For these specific VID combinations, though, PGOOD asserts a high level. This unusual behavior has been implemented in order to allow for operation in dualmicroprocessor systems by AND-ing the PGOOD signals from the two individual power converters. close to the SS pin because the internal current source is only 10A. Provide local VCC decoupling between VCC and GND pins. Locate the capacitor, CBOOT as close as practical to the BOOT and PHASE pins.
Feedback Compensation
Figure 7 highlights the voltage-mode control loop for a synchronous-rectified buck converter. The output voltage (VOUT) is regulated to the Reference voltage level. The error amplifier (Error Amp) output (VE/A) is compared with the oscillator (OSC) triangular wave to provide a pulse-width modulated (PWM) wave with an amplitude of VIN at the PHASE node. The PWM wave is smoothed by the output filter (LO and CO).
BOOT CBOOT +VIN Q1 LO VOUT VCC LOAD VOUT CO
Application Guidelines
Layout Considerations
As in any high frequency switching converter, layout is very important. Switching current from one power device to another can generate voltage transients across the impedances of the interconnecting bond wires and circuit traces. These interconnecting impedances should be minimized by using wide, short printed circuit traces. The critical components should be located as close together as possible, using ground plane construction or single point grounding.
VIN
D1
HIP6014
SS
PHASE +12V Q2 CO
CSS GND
CVCC
HIP6014
FIGURE 6. PRINTED CIRCUIT BOARD SMALL SIGNAL LAYOUT GUIDELINES
UGATE PHASE Q2 D2 Q1 LO VOUT LOAD OSC PWM COMPARATOR DRIVER VIN LO DRIVER PHASE
LGATE PGND
CIN
CO
VOSC
RETURN
-
+
ZFB
ESR (PARASITIC)
FIGURE 5. PRINTED CIRCUIT BOARD POWER AND GROUND PLANES OR ISLANDS
VE/A +
-
ZIN REFERENCE
Figure 5 shows the critical power components of the converter. To minimize the voltage overshoot the interconnecting wires indicated by heavy lines should be part of ground or power plane in a printed circuit board. The components shown in Figure 5 should be located as close together as possible. Please note that the capacitors CIN and CO each represent numerous physical capacitors. Locate the HIP6014 within 3 inches of the MOSFETs, Q1 and Q2. The circuit traces for the MOSFETs' gate and source connections from the HIP6014 must be sized to handle up to 1A peak current. Figure 6 shows the circuit traces that require additional layout consideration. Use single point and ground plane construction for the circuits shown. Minimize any leakage current paths on the SS PIN and locate the capacitor, CSS
ERROR AMP
DETAILED COMPENSATION COMPONENTS C2 C1 R2 ZFB ZIN C3 R1 R3 VOUT
COMP
+
FB
HIP6014
DACOUT
FIGURE 7. VOLTAGE-MODE BUCK CONVERTER COMPENSATION DESIGN
7
HIP6014
The modulator transfer function is the small-signal transfer function of VOUT/VE/A. This function is dominated by a DC Gain and the output filter (LO and CO), with a double pole break frequency at FLC and a zero at FESR. The DC Gain of the modulator is simply the input voltage (VIN) divided by the peak-to-peak oscillator voltage VOSC .
100 80 60 GAIN (dB) 40 20 0 -20 -40 FLC -60 10 100 1K 10K FESR 100K 1M 10M 20LOG (R2/R1) MODULATOR GAIN OPEN LOOP ERROR AMP GAIN
FZ1 FZ2
FP1
FP2
Modulator Break Frequency Equations
1 F LC = --------------------------------------2 * L O * C O 1 F ESR = ---------------------------------------2 * ESR * C O
20LOG (VIN/VOSC) COMPENSATION GAIN CLOSED LOOP GAIN
The compensation network consists of the error amplifier (internal to the HIP6014) and the impedance networks ZIN and ZFB. The goal of the compensation network is to provide a closed loop transfer function with the highest 0dB crossing frequency (f0dB) and adequate phase margin. Phase margin is the difference between the closed loop phase at f0dB and 180 degrees. The equations below relate the compensation network's poles, zeros and gain to the components (R1 , R2 , R3 , C1 , C2 , and C3) in Figure 7. Use these guidelines for locating the poles and zeros of the compensation network: 1. Pick Gain (R2/R1) for desired converter bandwidth 2. Place 1ST Zero Below Filter's Double Pole (~75% FLC) 3. Place 2ND Zero at Filter's Double Pole 4. Place 1ST Pole at the ESR Zero 5. Place 2ND Pole at Half the Switching Frequency 6. Check Gain against Error Amplifier's Open-Loop Gain 7. Estimate Phase Margin - Repeat if Necessary
FREQUENCY (Hz)
FIGURE 8. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN
Component Selection Guidelines
Output Capacitor Selection
An output capacitor is required to filter the output and supply the load transient current. The filtering requirements are a function of the switching frequency and the ripple current. The load transient requirements are a function of the slew rate (di/dt) and the magnitude of the transient load current. These requirements are generally met with a mix of capacitors and careful layout. Modern microprocessors produce transient load rates above 1A/ns. High frequency capacitors initially supply the transient and slow the current load rate seen by the bulk capacitors. The bulk filter capacitor values are generally determined by the ESR (effective series resistance) and voltage rating requirements rather than actual capacitance requirements. High frequency decoupling capacitors should be placed as close to the power pins of the load as physically possible. Be careful not to add inductance in the circuit board wiring that could cancel the usefulness of these low inductance components. Consult with the manufacturer of the load on specific decoupling requirements. For example, Intel recommends that the high frequency decoupling for the Pentium Pro be composed of at least forty (40) 1F ceramic capacitors in the 1206 surface-mount package. Use only specialized low-ESR capacitors intended for switching-regulator applications for the bulk capacitors. The bulk capacitor's ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient. An aluminum electrolytic capacitor's ESR value is related to the case size with lower ESR available in larger case sizes. However, the equivalent series inductance (ESL) of these capacitors increases with case size and can reduce the usefulness of the capacitor to high slew-rate transient loading. Unfortunately, ESL is not a specified parameter. Work with your capacitor supplier and measure the capacitor's impedance with frequency to select a
Compensation Break Frequency Equations
1 F Z1 = -------------------------------2 * R 2 * C 1 1 F P1 = --------------------------------------------------- C1 * C2 2 * R 2 * -------------------- C 1 + C 2 1 F P2 = -------------------------------2 * R 3 * C 3
1 F Z2 = --------------------------------------------------2 * ( R 1 + R 3 ) * C 3
Figure 8 shows an asymptotic plot of the DC-DC converter's gain vs. frequency. The actual Modulator Gain has a high gain peak due to the high Q factor of the output filter and is not shown in Figure 8. Using the above guidelines should give a Compensation Gain similar to the curve plotted. The open loop error amplifier gain bounds the compensation gain. Check the compensation gain at FP2 with the capabilities of the error amplifier. The Closed Loop Gain is constructed on the log-log graph of Figure 8 by adding the Modulator Gain (in dB) to the Compensation Gain (in dB). This is equivalent to multiplying the modulator transfer function to the compensation transfer function and plotting the gain. The compensation gain uses external impedance networks ZFB and ZIN to provide a stable, high bandwidth (BW) overall loop. A stable control loop has a gain crossing with -20dB/decade slope and a phase margin greater than 45 degrees. Include worst case component variations when determining phase margin.
8
HIP6014
suitable component. In most cases, multiple electrolytic capacitors of small case size perform better than a single large case capacitor. The important parameters for the bulk input capacitor are the voltage rating and the RMS current rating. For reliable operation, select the bulk capacitor with voltage and current ratings above the maximum input voltage and largest RMS current required by the circuit. The capacitor voltage rating should be at least 1.25 times greater than the maximum input voltage and a voltage rating of 1.5 times is a conservative guideline. The RMS current rating requirement for the input capacitor of a buck regulator is approximately 1/2 the DC load current. For a through hole design, several electrolytic capacitors (Panasonic HFQ series or Nichicon PL series or Sanyo MVGX or equivalent) may be needed. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating. These capacitors must be capable of handling the surge-current at power-up. The TPS series available from AVX, and the 593D series from Sprague are both surge current tested.
Output Inductor Selection
The output inductor is selected to meet the output voltage ripple requirements and minimize the converter's response time to the load transient. The inductor value determines the converter's ripple current and the ripple voltage is a function of the ripple current. The ripple voltage and current are approximated by the following equations:
I = VIN - VOUT Fs x L * VOUT VIN VOUT = I x ESR
Increasing the value of inductance reduces the ripple current and voltage. However, the large inductance values reduce the converter's response time to a load transient. One of the parameters limiting the converter's response to a load transient is the time required to change the inductor current. Given a sufficiently fast control loop design, the HIP6014 will provide either 0% or 100% duty cycle in response to a load transient. The response time is the time required to slew the inductor current from an initial current value to the transient current level. During this interval the difference between the inductor current and the transient current level must be supplied by the output capacitor. Minimizing the response time can minimize the output capacitance required. The response time to a transient is different for the application of load and the removal of load. The following equations give the approximate response time interval for application and removal of a transient load:
tRISE = L x ITRAN VIN - VOUT tFALL = L x ITRAN VOUT
MOSFET Selection/Considerations
The HIP6014 requires 2 N-Channel power MOSFETs. These should be selected based upon rDS(ON) , gate supply requirements, and thermal management requirements. In high-current applications, the MOSFET power dissipation, package selection and heatsink are the dominant design factors. The power dissipation includes two loss components; conduction loss and switching loss. The conduction losses are the largest component of power dissipation for both the upper and the lower MOSFETs. These losses are distributed between the two MOSFETs according to duty factor (see the equations below). Only the upper MOSFET has switching losses, since the Schottky rectifier clamps the switching node before the synchronous rectifier turns on. These equations assume linear voltagecurrent transitions and do not adequately model power loss due the reverse-recovery of the lower MOSFET's body diode. The gate-charge losses are dissipated by the HIP6014 and don't heat the MOSFETs. However, large gatecharge increases the switching interval, tSW which increases the upper MOSFET switching losses. Ensure that both MOSFETs are within their maximum junction temperature at high ambient temperature by calculating the temperature rise according to package thermal-resistance specifications. A separate heatsink may be necessary depending upon MOSFET power, package type, ambient temperature and air flow.
PUPPER = Io2 x rDS(ON) x D + PLOWER = Io2 x rDS(ON) x (1 - D) Where: D is the duty cycle = VOUT / VIN , tSW is the switch ON time, and FS is the switching frequency. 1 Io x V x t IN SW x FS 2
where: ITRAN is the transient load current step, tRISE is the response time to the application of load, and tFALL is the response time to the removal of load. With a +5V input source, the worst case response time can be either at the application or removal of load and dependent upon the DACOUT setting. Be sure to check both of these equations at the minimum and maximum output levels for the worst case response time. With a +12V input, and output voltage level equal to DACOUT, tFALL is the longest response time.
Input Capacitor Selection
Use a mix of input bypass capacitors to control the voltage overshoot across the MOSFETs. Use small ceramic capacitors for high frequency decoupling and bulk capacitors to supply the current needed each time Q1 turns on. Place the small ceramic capacitors physically close to the MOSFETs and between the drain of Q1 and the source of Q2.
9
HIP6014
Standard-gate MOSFETs are normally recommended for use with the HIP6014. However, logic-level gate MOSFETs can be used under special circumstances. The input voltage, upper gate drive level, and the MOSFET's absolute gate-tosource voltage rating determine whether logic-level MOSFETs are appropriate. Figure 9 shows the upper gate drive (BOOT pin) supplied by a bootstrap circuit from VCC. The boot capacitor, CBOOT develops a floating supply voltage referenced to the PHASE pin. This supply is refreshed each cycle to a voltage of VCC less the boot diode drop (VD) when the lower MOSFET, Q2 turns on. Logic-level MOSFETs can only be used if the MOSFET's absolute gate-to-source voltage rating exceeds the maximum voltage applied to VCC .
+12V DBOOT + VD BOOT CBOOT UGATE PHASE Q1 NOTE: VG-S VCC -VD Q2 D2 NOTE: VG-S VCC +5V or +12V
Figure 10 shows the upper gate drive supplied by a direct connection to VCC . This option should only be used in converter systems where the main input voltage is +5VDC or less. The peak upper gate-to-source voltage is approximately VCC less the input supply. For +5V main power and +12VDC for the bias, the gate-to-source voltage of Q1 is 7V. A logiclevel MOSFET is a good choice for Q1 and a logic-level MOSFET can be used for Q2 if its absolute gate-to-source voltage rating exceeds the maximum voltage applied to VCC.
Schottky Selection
Rectifier D2 is a clamp that catches the negative inductor swing during the dead time between turning off the lower MOSFET and turning on the upper MOSFET. The diode must be a Schottky type to prevent the lossy parasitic MOSFET body diode from conducting. It is acceptable to omit the diode and let the body diode of the lower MOSFET clamp the negative inductor swing, but efficiency will drop one or two percent as a result. The diode's rated reverse breakdown voltage must be greater than the maximum input voltage.
VCC
HIP6014
+
-
LGATE PGND GND
FIGURE 9. UPPER GATE DRIVE - BOOTSTRAP OPTION
+12V +5V OR LESS
VCC
HIP6014
BOOT Q1 NOTE: VG-S VCC -5V Q2 D2 NOTE: VG-S VCC
UGATE PHASE
-
+
LGATE PGND GND
FIGURE 10. UPPER GATE DRIVE - DIRECT VCC DRIVE OPTION
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HIP6014 HIP6014 DC-DC Converter Application Circuit
Figure 11 shows an application circuit of a DC-DC Converter for an Intel Pentium Pro microprocessor. Detailed information on the circuit, including a complete Bill-ofMaterials and circuit board description, can be found in Application Note AN9672. Although the Application Note details the HIP6004, the same evaluation platform can be used to evaluate the HIP6014. Intersil AnswerFAX (321-7247800) doc. #99672.
VIN =
+5V OR +12V
F 1
L1 - 1H
C1 5x 1000F
2N6394 +12V 2K D1
2x 1F
0.1F VCC 18 SS 3 0.1F VSEN 1 RT VID0 VID1 VID2 VID3 VID4 FB 20 4 5 6 7 8 10 OSC 1000pF OVP 19 2 OCSET 12 PGOOD 15 BOOT 0.1F Q1 L2 3H 1K
MONITOR AND PROTECTION
14 UGATE 13 PHASE
HIP6014
D/A
+VO
+
+ 9 11 COMP
17 LGATE 16 PGND GND
Q2
D2
-
CO 9x 1000F
2.2nF 8.2nF 0.1F 1.33K 15 20K
Component Selection Notes: C0 - C9 - Each 1000F 6.3W VDC, Sanyo MV-GX or Equivalent C1 - C5 - Each 330F 25W VDC, Sanyo MV-GX or Equivalent L2 - Core: Micrometals T50-52B; Each Winding: 10 Turns of 16AWG L1 - Core: Micrometals T50-52; Winding: 5 Turns of 18AWG D1 - 1N4148 or Equivalent D2 - 3A, 40V Schottky, Motorola MBR340 or Equivalent Q1 , Q2 - Intersil MOSFET; RFP70N03
FIGURE 11. PENTIUM PRO DC-DC CONVERTER
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HIP6014 Small Outline Plastic Packages (SOIC)
N INDEX AREA E -B1 2 3 SEATING PLANE -AD -CA h x 45o H 0.25(0.010) M BM
M20.3 (JEDEC MS-013-AC ISSUE C) 20 LEAD WIDE BODY SMALL OUTLINE PLASTIC PACKAGE
INCHES SYMBOL A
L
MILLIMETERS MIN 2.35 0.10 0.33 0.23 12.60 7.40 MAX 2.65 0.30 0.51 0.32 13.00 7.60 NOTES 9 3 4 5 6 7 8o Rev. 0 12/93
MIN 0.0926 0.0040 0.013 0.0091 0.4961 0.2914
MAX 0.1043 0.0118 0.0200 0.0125 0.5118 0.2992
A1 B C D E
A1 0.10(0.004) C
e H h L N
0.050 BSC 0.394 0.010 0.016 20 0o 8o 0.419 0.029 0.050
1.27 BSC 10.00 0.25 0.40 20 0o 10.65 0.75 1.27
e
B 0.25(0.010) M C AM BS
NOTES: 1. Symbols are defined in the "MO Series Symbol List" in Section 2.2 of Publication Number 95. 2. Dimensioning and tolerancing per ANSI Y14.5M-1982. 3. Dimension "D" does not include mold flash, protrusions or gate burrs. Mold flash, protrusion and gate burrs shall not exceed 0.15mm (0.006 inch) per side. 4. Dimension "E" does not include interlead flash or protrusions. Interlead flash and protrusions shall not exceed 0.25mm (0.010 inch) per side. 5. The chamfer on the body is optional. If it is not present, a visual index feature must be located within the crosshatched area. 6. "L" is the length of terminal for soldering to a substrate. 7. "N" is the number of terminal positions. 8. Terminal numbers are shown for reference only. 9. The lead width "B", as measured 0.36mm (0.014 inch) or greater above the seating plane, shall not exceed a maximum value of 0.61mm (0.024 inch) 10. Controlling dimension: MILLIMETER. Converted inch dimensions are not necessarily exact.
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Intersil semiconductor products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
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NORTH AMERICA Intersil Corporation P. O. Box 883, Mail Stop 53-204 Melbourne, FL 32902 TEL: (321) 724-7000 FAX: (321) 724-7240 EUROPE Intersil SA Mercure Center 100, Rue de la Fusee 1130 Brussels, Belgium TEL: (32) 2.724.2111 FAX: (32) 2.724.22.05 ASIA Intersil (Taiwan) Ltd. 7F-6, No. 101 Fu Hsing North Road Taipei, Taiwan Republic of China TEL: (886) 2 2716 9310 FAX: (886) 2 2715 3029
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