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| (R) ISL6226 Data Sheet August 2002 FN9078.1 Advanced PWM and Linear Power Controller for Portable Applications The ISL6226 provides power control and protection for two user selected output voltages required in high-performance notebook PC applications. The IC integrates a fixed, selectable frequency pulse-width-modulation (PWM) controller and a 3A LDO linear regulator controller with monitoring and protection circuitry in a single 24 lead SSOP package. The PWM controller regulates the battery input voltage to a user selected output voltage. Synchronous converter and hysteretic operation at light loads contribute to a high efficiency over a wide range of input voltage and load variation. Efficiency can be further enhanced by using the lower MOSFET's rDS(ON) as the current sense element. Input voltage feed-forward ramp modulation, current-mode control, and internal feed-back compensation provide fast and stable handling of input voltage load transients encountered in advanced portable computer chip sets. The internal linear regulator controller provides a user selected high current output from an unregulated input with user selected current limit. Features * Provides Two Regulated Voltages - Linear Regulator, User Selected, Current Limited - High Efficiency PWM Over Wide Line and Load Range - Synchronous Buck Converter on PWM Output - Hysteretic Operation at Light Load * Dual Mode Operation: - Directly From Battery Input, VIN, of 5.6V to 24V or from VCC of 5V * PWM Output Adjustable From 0.9V to 0.93*VIN * Low Drop-Out (LDO) Linear Regulator Operates from Vout+0.5V to 24V * LDO Output Adjustable - From 0.8V to 3.8V at 0A to 3A for NPN Transistor - From 0.8V to 3.0V at 0A to 3A for N-MOSFET * 300/600kHz Switching Frequency Selectable * Forced PWM Mode Control Option * No Current-Sense Resistor Required on PWM Output - Uses MOSFET's rDS(ON) - Optional Current-Sense Resistor for More Precision * Separate Soft-Start For Both PWM and LDO Ordering Information PART NUMBER ISL6226CA ISL6226EVAL1 TEMP. RANGE (oC) -10 to 85 Evaluation Board PACKAGE 24 Ld SSOP PKG. NO. M24.15 * Separate Enable Pins for both PWM and LDO for Advanced Configuration and Power Interface (ACPI) Compatibility * Input Under voltage Lock-Out (UVLO) Protection * Excellent Dynamic Response Pinout ISL6226 (SSOP) TOP VIEW VIN 1 PGOODL 2 PWMEN 3 OCSET 4 LINEN 5 VCC 6 LINDR 7 LINCS1 8 LINCS2 9 SSLIN 10 LINVS 11 GND 12 24 VOUT 23 VSEN 22 FPWM 21 PGOODP 20 ISEN 19 BOOT 18 UGATE 17 PHASE 16 SSPWM 15 PVCC 14 LGATE 13 PGND - Input Voltage Feed-Forward and Current-Mode Control * Monitors Output Voltages and Provides PGOOD Status * Thermal Shut-Down Protection Applications * Mobile PCs * Hand-Held Portable Instruments * Other Devices and Appliances With up to 24V Input Related Literature * AN1013 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright (c) Intersil Americas Inc. 2002. All Rights Reserved ISL6226 Absolute Maximum Ratings Bias Voltage, Vcc. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to + 7V Input Voltage, VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +30.0V Phase and Isen Pins . . . . . . . . . . . . . . . . . . . . . GND-0.3V to +30.0V Boot and Ugate Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + 35.0V BOOT with respect to PHASE . . . . . . . . . . . . . . . . . . . . . . . . . .+ 7.0V Imax for LINDR Pin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70mA All other pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GND -0.3V to 7V ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 1 Thermal Information Thermal Resistance (Typical, Note 1) JA (oC/W) SSOP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Maximum Junction Temperature (Plastic Package) . . 150oC Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . .300oC (SSOP - Lead Tips Only) Recommended Operating Conditions Bias Voltage, Vcc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+ 5.0V 5 % Input Voltage, VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . +5.6V to +24.0V Ambient Temperature Range . . . . . . . . . . . . . . . . . . . -10oC to 85oC Junction Temperature Range. . . . . . . . . . . . . . . . . . -10oC 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 high effective thermal conductivity test board in free air. See Tech Brief TB379 for details. Electrical Specifications Operating Conditions: Vcc = 5V, TA = -10oC to 85oC, Unless Otherwise Noted. PARAMETER VCC SUPPLY Bias Current Bias Current Shut-down Current VCC UVLO Rising Vcc Threshold Falling Vcc Threshold Vcc Hysterises VIN Input Voltage Pin Current (Sink) Input Voltage Pin Current (Source) Shut-down Current OSCILLATOR PWM Oscillator Frequency PWM Oscillator Frequency Ramp Amplitude, pk-pk Ramp Amplitude, pk-pk Ramp Offset PWM CONTROLLER REFERENCE AND SOFT START PWM Internal Reference Voltage PWM Soft-Start Threshold Reference Voltage Accuracy VREF VSOFT -2.0 0.9 1.5 +2.0 V V % Fc1 Fc2 VR1 VR2 VROFF VIN=3.5V -- 24V VIN 0.5V VIN= 16V VIN5V 255 510 300 600 2 1.25 0.5 345 690 kHz kHz V V V IVIN IVIN IVIN VIN pin connected to the input voltage source VIN pin connected to ground 10 -7 20 -12 30 -17 1 A A A 4.30 4.1 30 4.65 4.45 500 V V mV ICC ICC ICCSN LGATE, UGATE Open, VSEN forced above regulation point (Fs = 300K Hz) LGATE, UGATE Open, VSEN forced above regulation point (Fs = 600K Hz) 1100 1100 5 25 A A A SYMBOL TEST CONDITIONS MIN TYP MAX UNITS 2 ISL6226 PARAMETER Soft-Start Current During Start-up PWM CONVERTER Load Regulation VSEN pin bias current VOUT pin input impedance Under-Voltage Shut-Down Level Under Voltage Delay Over-Voltage Protection Over Voltage Delay PWM CONTROLLER GATE DRIVER Upper Drive Pull-Up Resistance Upper Drive Pull-Down Resistance Lower Drive Pull-Up Resistance Lower Drive Pull-Down Resistance POWER GOOD AND CONTROL FUNCTIONS Power Good Lower Threshold Power Good Higher Threshold PGOOD Leakage Current PGOOD Voltage Low EN- Low (Off) EN - High (On) FCCM -Hysteretic Operation Enabled LOW DROP OUT CONTROLLER FUNTIONS Linear Input Voltage Linear Input Voltage Linear Output Voltage Output Drive Current for NPN OverCurrent Feedback Voltage Under-Voltage Shut-Down Level Under-Voltage Delay REFERENCE AND SOFT START LDO Internal Reference Voltage LDO Soft-Start Threshold Reference Voltage Accuracy Soft-Start Current During Start-up POWER GOOD AND CONTROL FUNTIONS Power Good Lower Threshold Power Good Higher Threshold PGOOD Leakage Current PGOOD Voltage Low LINEN-Low (OFF) VPGVPG+ IPGLKG VPGOOD Vo 3 ISL6226 PARAMETER LINEN-High (ON) Input Bias Current LINCS1 and LINCS2 Input Bias Current LINVS Ibias1 Ibias2 Vlincs = 0.8 V Vlinvs = 0.8 V SYMBOL TEST CONDITIONS MIN 2.0 TYP -80 -80 MAX UNITS V nA nA Functional Pin Descriptions VIN (Pin 1) Provides battery voltage to the oscillator for feed-forward rejection of the input voltage variation. Also, this pin programs frequency of the internal clock and gain of the ramp generator. PGOODL (Pin 2) PGOODL is an open drain output used to indicate the status of the LDO output voltages. This pin is pulled low when the output voltage is not within of its respective nominal voltage or over 120mV between pin 8 and 9. capacitor till it reaches the value of 0.8V. At this moment the output voltage starts to regulate and soft start continues to rise to 1.5V. At this time, the soft start is complete and the PGOODL will be high to indicate the output voltage within its respective nominal voltage. The further rise of soft start capacitor does not affect the output voltage. The soft-start time can be obtained from the following equation. 1.5VxCss Tsslin = --------------------------5A LINVS (Pin 11) Voltage regulation point (0.8V) for the linear output. PWMEN (Pin 3) This pin provides enable/disable function the PWM output. The output is enabled when this pin is high. The PWM output is held off when this pin is pulled to ground. Intersil recommends to use hysteresis mode when input voltage higher than 18V and output voltage is 1.25V or less. OCSET (Pin 4) A resistor on this pin to ground sets the over current threshold for the PWM controller. GND (Pin 12) Signal ground for the IC. All voltage levels are measured with respect to this pin. PGND (Pin 13) This is the lower MOSFET gate drive return connection for PWM converter. Tie the lower MOSFET source directly to this pin. LGATE (Pin 14) This pin provides the gate drive for the lower MOSFET. Connect the lower MOSFET gate to this pin. LINEN (Pin 5) This pin provides enable/disable function and soft-start for the LDO. The output is enabled when this pin is high. The LDO is held off when this pin is pulled to ground. PVCC (Pin 15) This pin powers the lower MOSFET gate driver. VCC (Pin 6) Input power for the controller and the upper MOSFET gate drive. The IC starts to operate when the voltage on this pin exceeds 4.3V and stops operating when the voltage on this pin drops below approximately 4.45V. SSPWM (Pin 16) This pin provides soft start of the PWM controller. This pin has the same function as SSLIN pin. When the EN pin is pulled high, the voltage on the capacitor connected to the soft start pin is rising linearly due to the 5 A pull-up current. The output voltage follows the voltage on the capacitor till it reaches the value of 0.9V. At this moment the output voltage starts to regulate and soft start continues to rise to 1.5V. At this time, the soft start is complete and the PGOODPWM will be high to indicate the output voltage within its respective nominal voltage. The further rise of soft start capacitor does not affect the output voltage. The soft-start time can be obtained from the following equitation. 1.5VxCss Tsspwm = --------------------------5A LINDR (Pin 7) Current output to drive the NPN transistor. LINCS1 (Pin 8) High side of current sense resistor. LINCS2 (Pin 9) Low side of current sense resistor. Current limit for the linear regulator is initiated when the voltage difference between LINCS1 and LINCS2 is 120mV. SSLIN (Pin 10) This pin provides soft start of the LDO controller. When the EN pin is pulled high, the voltage on the capacitor connected to the soft start pin is rising linearly due to the 5 A pull-up current. The output voltage follows the voltage on the PHASE (Pin17) The phase node is the junctions of the upper MOSFET source, output filter inductor, and lower MOSFET drain. Connect the PHASE pin directly to the PWM converter's lower MOSFET drain. 4 ISL6226 UGATE (Pin18) This pin provides the gate drive for the upper MOSFET. Connect UGATE pin to the PWM converter's upper MOSFET gate. PGOODP (Pin 21) PGOODP is an open drain output used to indicate the status of the PWM converter's output voltages. This pin is pulled low when the output is not within of their respective nominal voltage. BOOT (Pin 19) Power is supplied to the upper MOSFET driver of the PWM converter via the BOOT pin. Connect this pin to the junction the bootstrap capacitor with the cathode of the bootstrap diode. The anode of the bootstrap diode is connected to pin 6, VCC. FPWM (Pin 22) This pin when pulled to VCC restrains hysterectic operation in light loads. VSEN (Pin 23) This pin is connected to the PWM voltage divider to provide the voltage feedback signal for the PWM controller. The PGOODP, overvoltage protection (OVP) and undervoltage shutdown circuits use this signal to determine output voltage status and/or to initiate undervoltage shut down. ISEN (Pin 20) This pin is used to monitor the voltage drop across the lower MOSFET for current feedback control. For more precise current detection, this input can be connected to optional current sense resistors placed in series with the source of the lower MOSFET. VOUT (Pin 24) The output voltage is sensed on this pin to provide feedback during the PWM to Hysteretic mode transition. 5 VIN VCC GND FPWM BOOT HGDR1 FPWM HI UGATE PHASE GATE CONTROL LGDR LO OVP PGND HYST COMP1 + OC COMP1 + CLK1 FSET CLK RAMP POWER-ON RESET (POR) SHUTOFF GATE LOGIC CLK POR DEADT PWM/HYST PWM ON HYST ON PVCC REF S VOLTAGE CLAMP FFBK LGATE1 PGOODP PGOODL LINDR OUTPUT VOLTAGE MONITOR VSEN MODE CHANGE + COMP LGATE R1=20K + -+ 6 POR PWMEN SDWN LINEN SSPWM SSLIN REFERENCE AND SOFT START REF PWM LATCH 1 VCC QD R Q< OVP UVO + POR LINCS1 LINEAR LINCS2 CONTROLLER REF LINVS SDWN LGATE OC LOGIC1 VSEN EA + ISEN OCSET PWM/HYS LOGIC VOUT ISL6226 FIGURE 1. FUNCTIONAL BLOCK DIAGRAM ISL6226 +5.6-24 VIN C2, 3 2x10F GND 5V VIN LINDR LINCS1 1 7 8 18 LINCS2 9 17 20 LINVS VCC 6 19 BOOT D1 BAT54WT1 C4 1F UGATE PHASE ISEN R4 Vout = 0.8V - 4.5V 0A to 50mA + R2 C5 10F R1 Q2 1/2 FDS6982S L2 6.4H Q3 1/2 FDS6982S C5 0.15F ISL6226 11 14 13 200 1K LGATE PGND Vout = 0.9V - 0.93*VIN (3A) R5 + C6 1x330F R3 LINEN PWMEN FPWM 5 3 22 24 23 VOUT VSEN R7 C8 PVCC PGOODL PGOODP SSLIN C10 15 2 21 10 12 GND 16 SSPWM C11 4 OCSET R8 FIGURE 2. 0A to 50mA OUTPUT CURRENT LDO AND SYNCHORNOUS BUCK CONVERTER (Fs=300KHz) 7 ISL6226 +5.6-24 VIN C2, 3 2x10F 5V LINEAR INPUT Q1 LINDR LINCS1 R1 Vout = 0.8V - 3.0V 3A + C5 330F R2 LINVS ISL6226 11 14 13 LINCS2 9 VIN 1 7 8 18 17 20 VCC 6 19 BOOT D1 BAT54WT1 C4 1F UGATE PHASE ISEN R4 Q2 1/2 FDS6982S L2 6.4H Q3 1/2 FDS6982S C5 0.15F Vout = 0.9V - 0.93*VIN (3A) R5 + C6 1x330F 200 1K LGATE PGND R3 LINEN PWMEN FPWM 5 3 22 24 23 VOUT VSEN R7 C8 PVCC PGOODL PGOODP SSLIN C10 15 2 21 10 12 GND 16 SSPWM C11 4 OCSET R8 Figure 3. LDO WITH EXTERNAL N-MOSFET AND SYNCHORNOUS BUCK CONVERTER (Fs = 300KHz) 8 ISL6226 +5.6-24 VIN C2, 3 2x10F 5V LINEAR INPUT Q1 LINDR LINCS1 R1 Vout = 0.8V - 3.8V 3A + C5 330F R2 LINVS ISL6226 11 14 13 LINCS2 9 VIN 1 7 8 18 17 20 VCC 6 19 BOOT D1 BAT54WT1 C4 1F UGATE PHASE ISEN 200 R4 1K Q2 1/2 FDS6982S L2 6.4H Q3 1/2 FDS6982S C5 0.15F Vout = 0.9V - 0.93*VIN (3A) R5 + C6 1x330F LGATE PGND R3 LINEN PWMEN FPWM 5 3 22 24 23 VOUT VSEN R7 C8 PVCC PGOODL PGOODP SSLIN C10 15 2 21 10 12 GND 16 SSPWM C11 4 OCSET R8 FIGURE 4. LDO with External NPN and Synchornous Buck Converter (Fs = 300KHz) 9 ISL6226 5V C2 2 x10F 150K LINEAR INPUT Q1 LINDR LINCS1 R1 1 7 8 R6 VIN VCC 6 19 BOOT D1 BAT54WT1 18 LINCS2 9 17 20 LINVS UGATE PHASE ISEN 200 R4 1K Q2 1/2 FDS6982S L2 6.4H Q3 1/2 FDS6982S C5 0.15F Vout = 0.8V - 3.8V 3A + C5 330F R2 Vout = 0.9V - 0.93*VIN (2A) R5 + C6 1x330F ISL6226 11 14 13 LGATE PGND R3 LINEN PWMEN FPWM 5 3 22 24 23 VOUT VSEN R7 C8 PVCC PGOODL PGOODP SSLIN C10 15 2 21 10 12 GND 16 SSPWM C11 4 OCSET R8 FIGURE 5. APPLICATION CIRCUIT FOR TWO STEP 300 kHz CONVERSION (MODE 2) NOTE: Q1 can be either N-MOSFET, NPN or not use for 50 mA 10 ISL6226 5V C2 2 x10F D1 BAT54WT1 LINEAR INPUT Q1 LINDR LINCS1 R1 Vout = 0.8V - 3.8V 3A + C5 330F R2 LINVS R3 ISL6226 11 14 13 LINCS2 9 VIN 1 7 8 18 17 20 VCC 6 19 BOOT C5 0.15F UGATE PHASE ISEN 200 R4 1K Q2 1/2 FDS6982S L2 6.4H Q3 1/2 FDS6982S Vout = 0.9V - 0.93*VIN (2A) R5 + C6 1x330F LGATE PGND LINEN PWMEN FPWM 5 3 22 24 23 VOUT VSEN R7 C8 PVCC PGOODL PGOODP SSLIN C10 15 2 21 10 12 GND 16 SSPWM C11 4 OCSET R8 FIGURE 6. APPLICATION CIRCUIT FOR TWO STEP 600 kHz CONVERSION (MODE 3) NOTE: Q1 can be either N-MOSFET, NPN or not used for 50 mA 11 ISL6226 Description Of Operation The ISL6226 is a single channel PWM controller and linear regulator controller intended for chipset, DRAM, audio or other low voltage power needs of modern notebook and subnotebook PCs. The IC integrates control circuits for a single synchronous buck converter whose output voltage is set in the range of 0.9V to 0.93*Vin by an external resistive divider and a linear regulator controller which drives an external NMOSFET or NPN pass transistor whose output is set in the range of 0.8V to 3.8V by an external resistor divider. The synchronous buck converter can be operated in several modes to optimize the application. The 300kHz frequency operation is recommended when powered from the battery, which voltage varies from 5.6V to 24V. In this case the VIN pin is connected to the battery terminal and the ramp generator gain is dynamically adjusted according to the input voltage. The IC also can be optimized for a two stage power conversion configuration where the output voltage is derived from a 5V input in lieu of the raw battery. Two operating frequencies of 300kHz or 600kHz are available in this mode. If 300kHz operation is desired while operating from the 5V system bus, the VIN pin should be connected to ground via a 150K ohm resistor. The ramp generator gain is corrected for the lower input voltage. When powered from the system 5V rail, the converter can be configured to operate on increased frequency of 600kHz to minimize the output filter components. In this case, the VIN pin is connected to the ground. Table 1 summarizes the various modes of operation. Figure 7 below shows plots of the ramp speed compensation. Table 1. Configuration for Modes of Operation Operation One stage 300kHz Two stage 300kHz Two stage 600kHz Pin 1 connection VIN 150K-GND GND Pin 1 potential V1>5.6V 1V The PWM converter uses the lower MOSFET on-state resistance, rDS(ON), as the current-sensing element. This technique eliminates the need for a current sense resistor and the associated power losses. If more accurate current protection is desired, current sense resistors may be used in series with the lower MOSFETs' source. A current proportional signal is used to provide average current mode control and over-current protection. The gain in the current sense circuit is set by the resistor connected from ISEN pin to the switching node of buck converter. The value of this resistor can be estimated by the following expression: Iomax * Rdson Risen = ------------------------------------------ - 100 75A where Iomax is the maximum inductor current. The value of Risen should be specified for the expected maximum MOSFET operating temperature. The resulting current out of the ISEN pin through Risen, is used for current feedback and current limit protection. An over-current protection threshold is set by an external resistor connected from OCSET (pin 4) to ground. The value of this resistor can be obtained from the following expression: 9.6 * ( Risen - 100 ) Rocset = --------------------------------------------------Ioc * Rdson where Ioc is the value of over current. This is compared with an internal current limit threshold. When a sampled value of the output current is determined to be above the current limit threshold, the PWM drive is terminated and a counter is initiated. This limits the inductor current build-up and essentially switches the converter into current-limit mode. If an overcurrent is detected between 26s to 53s later, an overcurrent shutdown is initiated. If during the 26s to 53s period, an overcurrent is not detected, the counter is reset and sampling continues as normal. This current limit scheme has proven to be very robust in applications like portable computers where fast inductor current build-up is common due to a large difference between input and output voltages and a low value of the inductor. 300kHz CLOCK 600kHz CLOCK Vin t -------- --2T Vin t -------- --4T Vin t -------- --8T Light-Load (Hysteretic) Operation In the light-load (hysteretic) mode the output voltage is regulated by the hysteretic comparator which regulates the output voltage by maintaining the output voltage ripple as shown in Figure 8. In Hysteretic mode, the inductor current flows only when the output voltage reaches the lower limit of the hysteretic comparator and turns off at the upper limit. Hysteretic mode saves converter energy at light loads by supplying energy only at the time when the output voltage Figure 7. Ramp Speed Compensation Vo=2.5V 12 ISL6226 requires it. This mode conserves energy by reducing the power dissipation associated with continuous switching. During the time between inductor current pulses, both the upper and lower MOSFETs are turned off. This is referred to as `diode emulation mode' because the lower MOSFET performs the function of a diode. This diode emulation mode prevents the output capacitor from discharging through the lower MOSFET when the upper MOSFET is not conducting. NOTE: the FPWM operation can intentionally be forced by tying pin 22, FPWM, to Vcc. PWM on the next clock cycle. This insures the full power required by the increase in output current. Gate Control Logic The gate control logic translates generated PWM control signals into the MOSFET gate drive signals providing necessary amplification, level shifting and shoot-through protection. Also, it has functions that help optimize the IC performance over a wide range of operational conditions. Since MOSFET switching time can vary dramatically from type to type and with the input voltage, the gate control logic provides adaptive dead time by monitoring the gate-tosource voltages of both upper and lower MOSFETs. The lower MOSFET is not turned on until the gate-to-source voltage of the upper MOSFET has decreased to less than approximately 1 volt. Similarly, the upper MOSFET is not turned on until the gate-to-source voltage of the lower MOSFET has decreased to less than approximately 1 volt. This allows a wide variety of upper and lower MOSFETs to be used without a concern for simultaneous conduction, or shoot-through. Operation-Mode Control The mode-control circuit changes the converter's mode of operation based on the voltage polarity of the phase node when the lower MOSFET is conducting and just before the upper MOSFET turns on. For continuous inductor current, the phase node is negative when the lower MOSFET is conducting and the converter operates in fixed-frequency PWM mode as shown in Figure 9. When the load current decreases to the point where the inductor current flows through the lower MOSFET in the `reverse' direction, the phase node becomes positive, and the mode is changed to hysteretic. A phase comparator handles the timing of the phase node voltage sensing. A low level on the phase comparator output indicates a negative phase voltage during the conduction time of the lower MOSFET. A high level on the phase comparator output indicates a positive phase voltage. When the phase node is positive (phase comparator high), at the end of the lower MOSFET conduction time, for eight consecutive clock cycles, the mode is changed to hysteretic as shown in Figure 9. The dashed lines indicate when the phase node goes positive and the phase comparator output goes high. The solid vertical lines at 1,2,...8 indicate the sampling time, of the phase comparator, to determine the polarity (sign) of the phase node. At the transition between PWM and hysteretic mode both the upper and lower MOSFETs are turned off. The phase node will `ring' based on the output inductor and the parasitic capacitance on the phase node and settle out at the value of the output voltage. The mode change from hysteretic to PWM can be caused by one of two events. One event is the same mechanism that causes a PWM to hysteretic transition. But instead of looking for eight consecutive positive occurrences on the phase node, it is looking for eight consecutive negative occurrences on the phase node. The operation mode will be changed from hysteretic to PWM when these eight consecutive pulses occur. This transition technique prevents jitter of the operation mode at load levels close to boundary. The other mechanism for changing from hysteretic to PWM is due to a sudden increase in the output current. This step load causes an instantaneous decrease in the output voltage due to the voltage drop on the output capacitor ESR and ESL. If the decrease causes the output voltage to drop below the hysteretic regulation level, the mode is changed to 13 VOUT t IL PHASE COMP t 12345 678 PWM HYSTERETIC t MODE OF OPERATION t FIGURE 8. REGULATION IN HYSTERETIC MODE IL t PHASE t NODE PHASE COMP MODE OF OPERATION PWM 1 2 3 4 5 6 7 8 t HYSTERETIC t FIGURE 9. MODE CONTROL WAVEFORMS ISL6226 Feedback Loop Compensation To reduce the number of external components and remove the burden of determining compensation components from a system designer, PWM controller has internally compensated error amplifiers. To make internal compensation possible several design measures where taken. First, the ramp signal applied to the PWM comparator is proportional to the input voltage provided via the VIN pin as shown in Figure 7. Second, the load current proportional signal is derived from the voltage drop across the lower MOSFET during on time of lower MOSFET. This signal is added to the amplifier error signal on the comparator input. This effectively creates an internal current control loop. Because of current loop, a compensation network with one zero and two poles is usually sufficient. One pole is place at origin which has high DC gain. The zero is place around 9kHz, and another pole is around 137kHz. The zero-pole pair causes a flat gain region at frequencies in between the zero and the pole. This region is also make the phase bump or reduce phase shift. The amount of phase shift reduction depends on how wide the region of flat gain and has maximum value of 90o. pin minus the diode drop voltage of between the base and emitter of NPN transistor device and minus 100mV across pin 8 and 9. In the case of using MOSFET instead of NPN transistor, the maximum output voltage equals to the voltage at LINDR pin minus the gate threshold voltage of MOSFET and minus 100mV across pin 8 and 9. External IC Internal IC PMOS VCC VIN C B E LINDR LINCS1 Vout LINCS2 FIGURE 10. LDO Output Current The LDO controller is capable of sourcing 50mA out of LINDR pin. This amount of current is used to drive the NPN transistor or as load current up to 50mA. The output current of the system equals the current out of LINDR pin times the current gain of NPN transistor ( , Beta). Low Drop Out Linear Regulator The linear has separate Enable, Pgood and Soft Start pins from the PWM. The linear also has over current and under voltage protection features. The over current protection will shut down the LDO controller when the voltage between pin 8 and 9 is more 100mV. The LDO controller will automatic restart again when the voltage is less than 100mV. Intersil recommend to use this feature to protect the ISL6226 IC otherwise the IC will damage when over current happen. The under voltage protection will start when the output voltage is 26% lower than the nominal output voltage. The ISL6226 has an internal P-channel MOSFET pass transistor. This provides several advantages over PNP pass transistor. PNP regulator waste considerable amounts of current in dropout when the pass transistor saturates. The Pchannel MOSFET requires no base drive current which reduces quiescent current. Component Selection Guidelines LDO Device Considerations The NPN transistor or MOSFET should be chosen to carry the load current and power dissipation required by the conditions of the load current and voltage drop across the device. Output Capacitor Selection-LDO For stable operation, the output current up to 50mA or without the external device, a minimum output capacitor value of 4.7F is recommended. The design simulation results indicated that the phase margins vary from 70 degree to 90 degree while the output currents vary from 5A to 50mA, respectively. The higher output capacitance indicates the higher phase margin. For stable operation with the external device, a minimum output capacitor value of 220F is recommended. Larger capacitor values provide better transient response. A capacitor value of 330F, such as SANYO POSCAP 6TPB330M, will provide good phase margin and better transient response. Output Voltage Calculation Figure 10 describe the output voltage which relative to the bias voltage. Due to the over current protection circuitry works properly, the internal P-channel MOSFET has an approximate 0.5V drop cross it. Therefore, the maximum voltage at LINDR pin will be. VLINDR = VCC - 0.5V Output Capacitor Selection-PWM The output capacitors have unique requirements. In general, the output capacitors should be selected to meet the dynamic regulation requirements including ripple voltage and load transients. The maximum output voltage equals to the voltage at LINDR 14 ISL6226 Selection of the output capacitors is also dependent on the output inductor so some inductor analysis is required to select the output capacitors. One of the parameters limiting the converter's response to a load transient is the time required for the inductor current to slew to it's new level. Given a sufficiently fast control loop design, the ISL6226 will provide either 0% or 93% duty cycle in response to a load transient. The response time is the time interval required to slew the inductor current from an initial current value to the load current level. During this interval the difference between the inductor current and the transient current level must be supplied by the output capacitor(s). Minimizing the response time can minimize the output capacitance required. Also, if the load transient rise time is slower than the inductor response time, as in a hard drive or CD drive, this reduces the requirement on the output capacitor. The maximum capacitor value required to provide the full, rising step, transient load current during the response time of the inductor is: L O x I TRAN I TRAN C OUT = --------------------------------------------- x -------------------( V IN - V OUT ) x 2 DV OUT zero at 9kHz. The ESR zero can be a factor of five on either side of the internal zero and still contribute to increased phase margin of the control loop. Therefore: 1 C OUT = ------------------------------------------2 x x ESR x f Z In conclusion, the output capacitors must meet three criteria: 1. They must have sufficient bulk capacitance to sustain the output voltage during a load transient while the output inductor current is slewing to the value of the load transient 2. The ESR must be sufficiently low to meet the desired output voltage ripple due to the output inductor current, and 3. The ESR zero should be placed, in a rather large range, to provide additional phase margin. Output Inductor Selection The output inductor is selected to meet the output voltage ripple requirements. The inductor value determines the converter's ripple current and the ripple voltage is a function of the ripple current and output capacitor(s) ESR. The ripple voltage expression is given in the capacitor selection section and the ripple current is approximated by the following equation: V IN - V OUT V OUT I L = ------------------------------- x --------------FS x L V IN Where: COUT is the output capacitor(s) required, LO is the output inductor, ITRAN is the transient load current step, VIN is the input voltage, VOUT is output voltage, and DVOUT is the drop in output voltage allowed during the load transient. High frequency capacitors initially supply the transient current and slow the load rate-of-change seen by the bulk capacitors. The bulk filter capacitor values are generally determined by the ESR (Equivalent Series Resistance) and voltage rating requirements as well as actual capacitance requirements. The output voltage ripple is due to the inductor ripple current and the ESR of the output capacitors as defined by: V RIPPLE = I L x ESR where Fs is the switching frequency. Input Capacitor Selection The important parameters for the bulk input capacitor(s) are the voltage rating and the RMS current rating. For reliable operation, select bulk input capacitors 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 1.5 times is a conservative guideline. The AC RMS input current varies with load. Depending on the specifics of the input power and it's impedance, most (or all) of this current is supplied by the input capacitor(s). Use a mix of input bypass capacitors to control the voltage ripple across the MOSFETs. Use ceramic capacitors for the high frequency decoupling and bulk capacitors to supply the RMS current. Small ceramic capacitors can be placed very close to the upper MOSFET to suppress the voltage induced in the parasitic circuit impedances. For board designs that allow through-hole components, the Sanyo OS-CON(R) series offer low ESR and good temperature performance. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the where, I L is calculated in the Inductor Selection section. 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 circuitry for specific decoupling requirements. Use only specialized low-ESR capacitors intended for switching-regulator applications, at 300kHz, for the bulk capacitors. In most cases, multiple electrolytic capacitors of small case size perform better than a single large case capacitor. The stability requirement on the selection of the output capacitor is that the `ESR zero', fZ, be between 1.8kHz and 45kHz. This range is set by an internal, single compensation 15 ISL6226 capacitor surge current rating. These capacitors must be capable of handling the surge-current at power-up. The TPS series available from AVX is surge current tested. AN1013 for the evaluation board component placement and the printed circuit board layout details. There are two sets of critical components in a DC-DC converter using an ISL6226 controller. The switching power components are the most critical because they switch large amounts of energy, and as such, they tend to generate equally large amounts of noise. The critical small signal components are those connected to sensitive nodes or those supplying critical bias currents. MOSFET Considerations The logic level MOSFETs are chosen for optimum efficiency given the potentially wide input voltage range and output power requirements. One dual N-Channel or Two N-channel MOSFETs are used in each of the synchronous-rectified buck converters for the outputs. These MOSFETs should be selected based upon rDS(ON) , gate supply requirements, and thermal management considerations. The power dissipation includes two loss components; conduction loss and switching loss. These losses are distributed between the upper and lower MOSFETs according to duty cycle (see the following equations). The conduction losses are the main component of power dissipation for the lower MOSFETs. Only the upper MOSFET has significant switching losses, since the lower device turns on and off into near zero voltage. I O x r DS ( ON ) x V OUT I O x V IN x t SW x F S P UPPER = ----------------------------------------------------------- + ---------------------------------------------------V IN 2 I O x r DS ( ON ) x ( V IN - V OUT ) P LOWER = -------------------------------------------------------------------------------V IN 2 2 Power Components Layout Considerations The power components and the controller IC should be placed first. Locate the input capacitors, especially the highfrequency ceramic decoupling capacitors, close to the power MOSFETs. Locate the output inductor and output capacitors between the MOSFETs and the load. Locate the PWM controller close to the MOSFETs. Insure the current paths from the input capacitors to the MOSFETs, to the output inductors and output capacitors are as short as possible with maximum allowable trace widths. A multi-layer printed circuit board is recommended. Dedicate one solid layer for a ground plane and make all critical component ground connections with via to this layer. Dedicate another solid layer as a power plane and break this plane into smaller islands of common voltage levels. The power plane should support the input power and output power nodes. Use copper filled polygons on the top and bottom circuit layers for the phase nodes, but do not unnecessarily oversize these particular islands. Since the phase nodes are subjected to very high dV/dt voltages, the stray capacitor formed between these islands and the surrounding circuitry will tend to couple switching noise. Use the remaining printed circuit layers for small signal wiring. The wiring traces from the control IC to the MOSFET gate and source should be sized to carry 2A peak currents. The equations assume linear voltage-current transitions and do not model power loss due to the reverse-recovery of the lower MOSFET's body diode. The gate-charge losses are dissipated by the ISL6226 and do not heat the MOSFETs. However, a large gate-charge increases the switching time, 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. Small Components Signal Layout Considerations The Vin pin 1 input should be bypassed with a 1.0uF capacitor. The bypass capacitors for Vin and the soft-start capacitor, should be located close to their connecting pins on the control IC. Refer to the Application Note AN1013 for a recommended component placement and interconnections. Layout Considerations MOSFETs switch very fast and efficiently. The speed with which the current transitions from one device to another causes voltage spikes across the interconnecting impedances and parasitic circuit elements. The voltage spikes can degrade efficiency, radiate noise into the circuit, and lead to device over voltage stress. Careful component layout and printed circuit design minimizes the voltage spikes in the converter. Consider, as an example, the turn-off transition of one of the upper PWM MOSFETs. Prior to turn-off, the upper MOSFET is carrying the full load current. During the turn-off, current stops flowing in the upper MOSFET and is picked up by the lower MOSFET. Any inductance in the switched current path generates a voltage spike during the switching interval. Careful component selection, tight layout of the critical components, and short, wide circuit traces minimize the magnitude of voltage spikes. See the Application Note 16 ISL6226 Plastic Packages for Integrated Circuits Plastic Packages for Integrated Circuits Shrink Small Outline Plastic Packages (SSOP) N INDEX AREA H E -B1 2 3 SEATING PLANE -AD -CA 0.25 0.010 h x 45o L GAUGE PLANE 0.25(0.010) M BM M24.15 24 LEAD THIN SHRINK NARROW BODY SMALL OUTLINE PLASTIC PACKAGE INCHES SYMBOL A A1 A2 B C D E C 0.10(0.004) C AM BS MILLIMETERS MIN 1.35 0.10 0.20 0.18 8.55 3.81 5.80 0.26 0.41 24 0o MAX 1.75 0.25 1.54 0.30 0.25 8.74 3.98 6.19 0.49 1.27 8o NOTES 9 3 4 5 6 7 Rev. 0 12/00 MIN 0.053 0.004 0.008 0.007 0.337 0.150 0.228 0.0099 0.016 24 0o MAX 0.069 0.010 0.061 0.012 0.010 0.344 0.157 0.244 0.0196 0.050 8o e B 0.17(0.007) M A1 A2 e H h L N 0.025 BSC 0.635 BSC 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. Dimension "B" does not include dambar protrusion. Allowable dambar protrusion shall be 0.10mm (0.004 inch) total in excess of "B" dimension at maximum material condition. 10. Controlling dimension: INCHES. Converted millimeter dimensions are not necessarily exact. All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation's quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software 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. For information regarding Intersil Corporation and its products, see www.intersil.com 17 |
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