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NS ES I G WD T NE M EN F OR DED EPLACE 04) EN R 20 MM Feb. ECO DataNDED OT R COMME Sheet ble ila N (Ava RE 232 I S L6
TM
ISL6235
June 2001 FN9029
Advanced Triple PWM Only Mode and Dual Linear Power Controller for Portable Applications
The ISL6235 provides a highly integrated power control and protection solution for five output voltages required in highperformance notebook PC applications. The IC integrates three fixed frequency pulse-width-modulation (PWM) controllers and two linear regulators along with monitoring and protection circuitry into a single 24 lead SSOP package. The two PWM controllers that regulate the system main 5V and 3.3V voltages are implemented with synchronousrectified buck converters. Synchronous rectification insures high efficiency over a wide range of input voltage and load variation. Efficiency is 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 third PWM controller is a boost converter that regulates a resistor selectable output voltage of nominally 12V. Two internal linear regulators provide +5V ALWAYS and +3.3V ALWAYS low current outputs required by the notebook system controller.
Features
* PWM Only Mode for Reduced Noise at Light Loads * Provides Five Regulated Voltages - +5V ALWAYS - +3.3V ALWAYS - +5V Main - +3.3V Main - +12V * High Efficiency Over Wide Line and Load Range - Synchronous Buck Converters on Main Outputs * No Current-Sense Resistor Required - Uses MOSFET's rDS(ON) - Optional Current-Sense Resistor for More Precision * Operates Directly From Battery 5.6 to 24V Input * Input Undervoltage Lock-Out (UVLO) * Excellent Dynamic Response - Voltage Feed-Forward and Current-Mode Control * Monitors Output Voltages * Synchronous Converters Operate Out of Phase * Separate Shut-Down Pins for Advanced Configuration and Power Interface (ACPI) Compatibility * 300kHz Fixed Switching Frequency on Main Outputs
Ordering Information
PART NUMBER ISL6235CA IPM6220EVAL1 TEMP. RANGE (oC) -10 to 85 PACKAGE 24 Ld SSOP PKG. NO. M24.15
* Thermal Shut-Down Protection
Applications
* Mobile PCs * Hand-Held Portable Instruments
Evaluation Board
Pinout
ISL6235 (SSOP) TOP VIEW
VBATT 1 3.3V ALWAYS 2 BOOT2 3 UGATE2 4 PHASE2 5 5V ALWAYS 6 LGATE2 7 PGND2 8 ISEN2 9 VSEN2 10 SDWN2 11 PGOOD 12 24 BOOT1 23 UGATE1 22 PHASE1 21 ISEN1 20 LGATE1 19 PGND1 18 VSEN1 17 SDWN1 16 GATE3 15 VSEN3 14 GND 13 SDWNALL
* LCD PCs * Cable Modems * DSL Modems * Set Top Box
Related Literature
* Application Note AN9915 (IPM6220)
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 trademark of Intersil Americas Inc. Copyright (c) Intersil Americas Inc. 2001, All Rights Reserved
Block Diagram
VSEN3
GATE3
VBATT UVFLT
GND GATE LOGIC 1 HI HGDR1
BOOT1 UGATE1 PHASE1
CLK1
BOOST CONTROLLER
RAMP 2
CLK 200ns CLK1
RAMP 1
POWER-ON RESET (POR) POR
SHUTOFF
CLK2 REF
LGATE2 PGND2 VSEN2
LO OVP2
PWM ON
QD R Q< +
VOLTSECOND CLAMP R1 = 20K
OC COMP2 2.8V REF VOLTSECOND CLAMP ISEN2 R1 = 20K + UVFLT LGATE2 OVP1 OVP2 LGATE2 OUTPUT VOLTAGE MONITOR PGOOD LDO2 REF 3.3V-ALWAYS 5V-ALWAYS 2.5V + + EA2 + + OC LOGIC2 VCC PWM LATCH 2 DQ R >Q SDWN LDO1 VCC SDWN VBATT VSEN1 LGATE1
-
2
BOOT2 UGATE2 PHASE2 HGDR2 HI VCC LGDR2
DEADTIME LGDR1 PWM ON GATE LOGIC 2 LO OVP1
VCC LGATE1 PGND1 VSEN1
SHUTOFF OC COMP1 DEADTIME PWM VCC LATCH 1 OC LOGIC1 + + EA1 + REF ISEN1 + LGATE1 POR SDWN1 REFERENCE AND SOFT START SDWN2 SDWNALL
ISL6235
ISL6235 Simplified Power System Diagram
VBATT VBATT Q1 3.3V ALWAYS LINEAR CONTROLLER LINEAR CONTROLLER PWM1 CONTROLLER Q2
5V MAIN
5V ALWAYS
ISL6235
VBATT Q1 PWM2 CONTROLLER Q2
VOLTAGE, CURRENT MONITORS
PGOOD
12V BOOST
3.3V MAIN
PWM3 CONTROLLER
Typical Application
+VBATT
PROCESSOR SDWN1 SDWN2 5V MAIN 3.3V MAIN 5V ALWAYS 3.3V ALWAYS 12V PCM CIA ENABLE C8051 VID CODE SDWN VI/O VCORE
P CORE
ISL6235
I/O CLOCK RESET
IPM6210
VCLOCK PGOOD PGOOD
SDWNALL ON/OFF
3
ISL6235
I
Absolute Maximum Ratings
Input Voltage, VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +27.0V Phase, ISEN and SDWNALL Pins . . . . . . . . . . . GND -0.3V to +27.0V Boot and UGATE Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +33.0V BOOT1, 2 with Respect to PHASE1, 2 . . . . . . . . . . . . . . . . . . . +6.5V All Other Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6.5V
Thermal Information
Thermal Resistance (Typical, Note 1) JA (oC/W) SSOP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Maximum Junction Temperature (Plastic Package) . . . . . . . .150oC Maximum Storage Temperature Range . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . .300oC (SSOP - Lead Tips Only)
Operating Conditions
Input Voltage, VBATT . . . . . . . . . . . . . . . . . . . . . . . . +5.6V to +24.0V Ambient Temperature Range . . . . . . . . . . . . . . . . . . . . -10oC to85oC 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 low effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
Electrical Specifications
PARAMETER Input Quiescent Current Stand-by Current Shut-down Current Input Undervoltage Lock Out Input Undervoltage Lock Out OSCILLATOR PWM1,2 Oscillator Frequency REFERENCE AND SOFT START Internal Reference Voltage Reference Voltage Accuracy
Recommended Operating Conditions, Unless Otherwise Noted. Refer to Block and Simplified Power System Diagrams, and Typical Application Schematic SYMBOL ICC ICCSB ICCSN UVLO UVLO TEST CONDITIONS SDWN1 = SDWN2 = 5V, SDWNALL = Vin, Outputs open circuited SDWN1 = SDWN2 = 0V, SDWNALL = Vin, Outputs open circuited SDWNALL = 0V Rising VBATT VBATT, Hysteresis MIN 4.3 TYP 1.4 300 <1.0 4.7 300 MAX 2.0 5.1 UNITS mA A A V mV
Fc1,2
255
300
345
kHz
VREF
-1.0
2.472 5
+1.0 -
V % A
SDWN1,SDWN2 Output Current During Start-up PWM1 CONVERTER, 5V Main Output Voltage Line and Load Regulation Undervoltage Shut-Down Level Current Limit Threshold Overvoltage Threshold Maximum Duty Cycle PWM2 CONVERTER, 3.3V Main Output Voltage Line and Load Regulation Undervoltage Shut-Down Level Current Limit Threshold Overvoltage Threshold Maximum Duty Cycle
ISS
-
VOUT1 0.0 < IVOUT1 < 5.0A; 5.6V < VBATT < 22.0V VUV1 IOC2 VOVP1 DCMAX 2s delay, % Feedback Voltage at VSNS1 Pin Current from ISNS1 Pin Through RSNS1 2s delay, % Feedback Voltage at VSNS1 Pin SDWN1>4.0V
-2 70 90 110 -
5.0 0.5 75 135 115 94
+2 80 180 120 -
V % % A % %
VOUT2 0.0 < IVOUT2 < 5.0A; 5.6V 4.0V
-2 70 90 110 -
3.3 0.5 75 135 115 94
+2 80 180 120 -
V % % A % %
4
ISL6235
Electrical Specifications
PARAMETER Internal Resistance to GND on VSNS2 Pin Recommended Operating Conditions, Unless Otherwise Noted. Refer to Block and Simplified Power System Diagrams, and Typical Application Schematic (Continued) SYMBOL RVSNS2 TEST CONDITIONS MIN TYP 66K MAX UNITS
PWM1 and PWM2 CONTROLLER GATE DRIVERS Upper Drive Pull-Up Resistance Upper Drive Pull-Down Resistance Lower Drive Pull-Up Resistance Lower Drive Pull-Down Resistance PWM 3 CONVERTER 12V Feedback Regulation Voltage 12V Feedback Regulation Voltage Input Current Line and Load Regulation Undervoltage Shut-Down Level Overvoltage Threshold PWM3 Oscillator Frequency Maximum Duty Cycle PWM 3 CONTROLLER GATE DRIVERS Pull-Up Resistance Pull-Down Resistance 5V AND 3.3V ALWAYS Linear Regulator Accuracy 5V ALWAYS Output Voltage Regulation Maximum Output Current Current Limit 5V ALWAYS Undervoltage Shut-Down Bypass Switch rDS(ON) POWER GOOD AND CONTROL FUNCTIONS Power Good Threshold for PWM1 and PWM2 Output Voltages PGOOD Leakage Current PGOOD Voltage Low PGOOD Minimum Pulse Width SDWN1, 2- Low (Off) SDWN1, 2, - High (On) SDWNALL - High (On) SDWNALL - Low (Off) Over-Temperature Shutdown Over-Temperature Hysteresis SDWNALL IPGLKG VPGOOD TPGmin VPULLUP = 5.0V IPGOOD = -4mA -14 -12 0.2 10 0.8 4.3 2.4 40 150 25 -10 1.0 0.5 % A V s V V V mV
oC oC
R2UGPUP R2UGPDN R2LGPUP R2LGPDN
-
5 4 6 5
12 10 9 8

VSEN3 IVSEN3 0.0 < IVOUT3 < 120mA, 4.9V < 5VMain < 5.1V VUV3 VOVP3 Fc3 2s Delay, % Feedback Voltage at VSNS3 Pin 2s Delay, % Feedback Voltage at VSNS3 Pin
-2 70 85 -
2.472 0.1 75 115 100 33
1.0 +2 80 120 115 -
V A % % % kHz %
R3GPUP R3GPDN
-
8 8
12 12

PWM1, 5V Output OFF (SDWN1 = 0V); 5.6V < VBATT < 22V; 0 < Iload < 50mA PWM1, 5V output ON (SDWN1 = 5V); 0 < Iload < 50mA Combined 5V ALWAYS and 3.3V ALWAYS Combined 5V ALWAYS and 3.3V ALWAYS
-2.0 -3.3 50 100 -
0.5 1.0 180 75 1.3
+2.0 +2.0 -
% % mA mA %
PWM1, 5V output ON (SDWN1 = 5V)
-
5
ISL6235 Functional Pin Descriptions
VBATT (Pin 1)
Supplies all the power necessary to operate the chip. The IC starts to operate when the voltage on this pin exceeds 4.7V and stops operating when the voltage on this pin drops below approximately 4.5V. Also provides battery voltage to the oscillator for feed-forward rejection to input voltage variations. controllers. The PGOOD, overvoltage protection (OVP) and undervoltage shutdown circuits use these signals to determine output voltage status and/or to initiate undervoltage shut down. The VSEN1 input is also switched internally to the 5V ALWAYS output if the +5V Main output is enabled.
SDWNALL (Pin 13)
This pin provides enable/disable function for all outputs. The chip is completely disabled when this pin is pulled to ground. When this pin is pulled high, the 5V ALWAYS and 3.3 ALWAYS outputs are on and the other outputs are enabled. The state of 5V Main and 3.3V Main outputs depend on the voltage on SDWN1 and SDWN2 respectively. See Table 1.
3.3V ALWAYS (Pin 2)
Output of 3.3V ALWAYS linear regulator.
5V ALWAYS (Pin 6)
Output of 5V ALWAYS linear regulator or the +5V Main output. If the +5V Main output is enabled, it is switched internally from the VSEN1 pin to the 5V ALWAYS output. This improves efficiency and reduces the power dissipation in the controller.
SDWN1 (Pin 17)
This pin provides enable/disable function and soft-start for the PWM1, 5V Main, output. The output is enabled when this pin is high and SDWNALL is also high. The 5V output is held off when the pin is pulled to the ground.
BOOT1, BOOT2 (Pins 24 and 3)
Power is supplied to the upper MOSFET drivers of PWM1 and PWM2 converters via the BOOT pins. Connect these pins to the respective junctions of bootstrap capacitors with the cathodes of the bootstrap diodes. Anodes of the bootstrap diodes are connected to pin 6, 5V ALWAYS.
SDWN2 (Pin 11)
This pin provides enable/disable function and soft-start for PWM2, 3.3V Main, output. The output is enabled when this pin is high and SDWNALL is also high. The 3.3V output is held off when the pin is pulled to the ground.
UGATE1, UGATE2 (Pins 23 and 4)
These pins provide the gate drive for the upper MOSFETs. Connect UGATE pins to the respective PWM converter's upper MOSFET gate.
VSEN3 (Pin 15)
This input pin is the voltage feedback signal for PWM3, the boost controller. The boost controller regulates this point to a voltage divided level of 2.472 VDC. The PGOOD, overvoltage protection (OVP) and undervoltage shutdown circuits use this signal to determine output-voltage status and/or to initiate undervoltage shut down. This pin can also be used to independently disable the PWM3 controller. Connect this pin to 5V ALWAYS if the boost converter is not populated in your design.
PHASE1, PHASE2 (Pins 22 and 5)
The phase nodes are the junctions of the upper MOSFET sources, output filter inductors, and lower MOSFET drains. Connect the PHASE pins directly to the respective PWM converter's lower MOSFET drain.
ISEN1, ISEN2 (Pins 21 and 9)
These pins are used to monitor the voltage drop across the lower MOSFETs for current feedback and current-limit protection. For more precise current detection, these inputs can be connected to optional current sense resistors placed in series with the sources of the lower MOSFETs.
GATE3 (Pin 16)
This pin drives the gate of the boost MOSFET.
PGOOD (Pin 12)
PGOOD is an open drain output used to indicate the status of the PWM converters' output voltages. This pin is pulled low when any of the outputs except PWM3 (12V) is not within -10% of respective nominal voltages, or when PWM3 (12V) is not within its undervoltage and overvoltage thresholds.
LGATE1, LGATE 2 (Pins 20 and 7)
These pins provide the gate drive for the lower MOSFETs. Connect the lower MOSFET gate of each converter to the corresponding pin.
PGND1, PGND2 (Pins 19 and 8)
These are the lower MOSFET gate drive return connection for PWM1 and PWM2 converters, respectively. Tie each lower MOSFET source directly to the corresponding pin.
GND (Pin 14)
Signal ground for the IC. All voltage levels are measured with respect to this pin.
VSEN1, VSEN2 (Pins 18, 10)
These pins are connected to the main outputs and provide the voltage feedback signal for the respective PWM
6
ISL6235 General Description
The ISL6235 addresses the system electronics power needs of modern notebook and LCD PCs that require a fixed frequency, PWM mode only, controller. The ISL6235 is similar to the IPM6220A but without the Hysteretic mode of operation. The IC integrates control circuits for two synchronous buck converters for 5V Main and 3.3V Main buses, two linear regulators for 3.3V ALWAYS and 5V ALWAYS, and a flexible boost converter, nominally 12V. The two synchronous converters operate out of phase to substantially reduce the input-current ripple, minimizing input filter requirements, minimizing battery heating and prolonging battery life. The 12V boost controller uses a 100kHz clock derived from the main clock. This controller uses leading edge modulation with the maximum duty cycle limited to 33%. The chip has three input control lines SDWN1, SDWN2 and SDWNALL. These are provided for Advanced Configuration and Power Interface (ACPI) compatibility. They turn on and off all outputs, as well as provide independent control of the 3.3V Main and +5V Main outputs. To maximize efficiency for the 5V Main and 3.3V Main outputs, the current-sense technique is based on the lower MOSFET rDS(ON).
VIN = 10.8V 5A 3.3V PHASE (10V/DIV.) IL3.3V (2A/DIV.)
0 A, V 5A IL5V (2A/DIV.)
0 A, V 5V PHASE (10V/DIV.) 1s/DIV.
FIGURE 1. OUT OF PHASE OPERATION
Current Sensing and Current Limit Protection
Both PWM converters use 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. To set the current limit, place a resistor, RSNS, between the ISEN inputs and the drain of the lower MOSFET (or optional current sense resistor). The required value of the RSNS resistor is determined from the following equation:
Rcs Vo RSNS = ----------------- Iocdc + ---------------------------------------- - 100 135A L x 2 x 300kHz (EQ. 1)
3.3V Main and 5V Main Architecture
These main outputs are generated from the unregulated battery input by two independent synchronous buck converters. The IC integrates all the components required for output voltage setpoint and feedback compensation, significantly reducing the number of external components, saving board space and parts cost. The buck PWM controllers employ a 300kHz fixed frequency current-mode control scheme with input voltage feedforward ramp programming for better rejection of input voltage variations. Figure 1 shows the out-of-phase operation for the 3.3V Main and 5V Main outputs. The phase node is the junction of the upper MOSFET, lower MOSFET and the output inductor. The phase node is high when the upper MOSFET is conducting and the inductor current rises accordingly. When the phase node is low, the lower MOSFET is conducting and the inductor current is ramping down as shown.
where Iocdc is the desired DC overcurrent limit; Rcs is either the rDS(ON) of the lower MOSFET, or the value of the optional current-sense resistor, Vo is the output voltage and L is the output inductor. Also, the value of Rcs should be specified for the expected maximum operating temperature. The sensed voltage, and the resulting current out of the ISEN pin through RSNS, is used for current feedback and current limit protection. 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.
7
ISL6235
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. Figure 2 shows the soft-start initiated by the SDWNALL pin being pulled high with the Vbatt input at 10.8V and the resulting 3.3V Main and 5V Main outputs.
VIN = 10.8V SDWNALL,10V/DIV.
SDWN2, 2V/DIV. 0V
3.3VOUT, 2V/DIV.
SDWN1, 2V/DIV.
0V
5VOUT, 2V/DIV.
3.3V Main and 5V Main Soft Start, Sequencing and Stand-by
See Table 1 for the output voltage control algorithm. The 5V Main and 3.3V Main converters are enabled if SDWN1 and SDWN2 are high and SDWNALL is also high. The stand-by mode is defined as a condition when SDWN1 and SDWN2 are low and the PWM converters are disabled but SDWNALL is high (3.3V ALWAYS and 5V ALWAYS outputs are enabled). In this power saving mode, only the low power micro-controller and keyboard may be powered.
TABLE 1. OUTPUT VOLTAGE CONTROL SDWNALL SDWN1 0 1 1 1 1 X 0 1 0 1 SDWN2 X 0 0 1 1 3V AND 5V ALWAYS 5V MAIN 3V MAIN OFF ON ON ON ON OFF OFF ON OFF ON OFF OFF OFF ON ON
T0 T1
T2
T3 4ms/DIV.
T4
FIGURE 2. SOFT START ON 3.3V AND 5V OUTPUTS
While the SDWNALL pin is held low, prior to T0, all outputs are off. Pulling SDWNALL high enables the 3.3V ALWAYS and 5V ALWAYS outputs. With the 3.3V Main and 5V Main outputs enabled, at T1, the internal 5mA current sources start charging the soft start capacitors on the SDWN1 and SDWN2 pins. At T2 the outputs begin to rise and because they both have the same value of soft-start capacitors, 0.022mF, they both reach regulation at the same time, T3. The soft-start capacitors continue to charge and are completely charged at T4.
12V Converter Architecture
The 12V boost converter generates its output voltage from the 5V Main output. An external MOSFET, inductor, diode and capacitor are required to complete the circuit. The output signal is fed back to the controller via an external resistive divider. The boost controller can be disabled by connecting the VSEN3 pin to 5V ALWAYS. The control circuit for the 12V converter consists of a 3:1 frequency divider which drives a ramp generator and resets a PWM latch as shown in Figure 3. The width of the CLK/3 pulses is equal to the period of the main clock, limiting the duty cycle to 33%. The output of a non-inverting error amplifier is compared with the rising ramp voltage. When the ramp voltage becomes higher than the error signal, the PWM comparator sets the latch and the output of the gate driver is pulled high providing leading edge, voltage mode PWM. The falling edge of the CLK/3 pulses resets the latch and pulls the output of the gate driver low.
Soft start of the 3.3V Main and 5V Main converters is accomplished by means of capacitors connected from pins SDWN1 and SDWN2 to ground. In conjunction with 5A internal current sources, they provide a controlled rise of the 3.3V Main and 5V Main output voltages. The value of the soft-start capacitors can be calculated from the following expression.
Css = 5A x Tss --------------------------3.5V (EQ. 2)
Where Tss is the desired soft-start time. By varying the values of the soft-start capacitors, it is possible to provide sequencing of the main outputs at start-up.
8
ISL6235
VSEN3 + EA3 GATE3 PWM PWM COMPARATOR LATCH 3 SQ RAMP RQ +
REF CLK/3 CLK DIVIDER 3:1
-
controller or other peripherals. The combined current capability of these outputs is 50mA. When the 5V Main output is greater than it's undervoltage level, it is switched to the 5V ALWAYS output via an internal 1.3 MOSFET switch. Simultaneously, the 5V ALWAYS linear regulator is disabled to prevent excessive power dissipation. The rise time of the 5V ALWAYS is determined by the value of the output capacitance on the 5V and 3.3V ALWAYS outputs. The internal regulator is current limited to about 180mA, so the start up time is approximately:
CLK/3
RAMP GENERATOR
CLK CLK/3 RAMP VEA3 GATE3
t
5V t = C OUT x ------------------180mA
(EQ. 4)
t t
Where COUT is the sum of the capacitances on the 5V and 3.3V ALWAYS outputs.
Power Good Status
t
FIGURE 3. 12V BOOST OPERATION
The 33% maximum duty cycle of the converter guarantees discontinuous inductor current and unconditional stability
over all operating conditions.
The boost converter with the limited duty cycle and discontinuous inductor current can deliver to the load a limited amount of power before the output voltage starts to drop. When the duty cycle has reached Dmax, the control loop is operating open circuit and the output voltage varies with the output load resistance, Ro, as given by:
Ro Vo = Vin x Dmax ------------------ 2 ( LxF ) (EQ. 3)
The ISL6235 monitors all the output voltages except for the 3.3V ALWAYS. A single power-good signal, PGOOD, is issued when soft-start is completed and all monitored outputs are within 10% of their respective set points. After the soft-start sequence is completed, undervoltage protection latches the chip off when any of the monitored outputs drop below 75% of its set point. A `soft-crowbar' function is implemented for an overvoltage on the 3.3V Main or 5V Main outputs. If the output voltage goes above 115% of their nominal output level, the upper MOSFET is turned off and the lower MOSFET is turned on. This `soft-crowbar' condition will be maintained until the output voltage returns to the regulation window and then normal operation will continue. This `soft-crowbar' and monitoring of the output, prevents the output voltage from ringing negative as the inductor current flows in the `reverse' direction through the lower MOSFET and output capacitors.
Where Vin is the 5V Main voltage, Dmax = 0.33, L is the value of the boost inductor, L3, and F = 100kHz. This provides automatic output current limiting. When the maximum duty cycle has been reached and for a given inductor, a further reduction in Ro by one-half will pull the output voltage down to 0.707 of nominal and cause an undervoltage condition. The 12V converter starts to operate at the same time as the 5V Main converter. The rising voltage on the 5V Main output and the 33% duty cycle limit provides a similar soft-start, as the 5V Main, for the 12V output.
Over-Temperature Protection
The IC incorporates an over-temperature protection circuit that shuts all the outputs down when the die temperature exceeds 150oC. Normal operation is automatically restored when the die temperature cools to 125oC.
Component Selection Guidelines
Output Capacitor Selection
The output capacitors for each output have unique requirements. In general, the output capacitors should be selected to meet the dynamic regulation requirements including ripple voltage and load transients.
3V ALWAYS, 5V ALWAYS Linear Regulators
The 3.3V ALWAYS and 5V ALWAYS outputs are derived from the battery voltage and are the first voltages available in the notebook when power on is initiated. The 5V ALWAYS output is generated directly from the battery voltage by a linear regulator. It is used to power the system microcontroller and to internally power the chip and the gate drivers. The 3.3V ALWAYS output is generated from the 5V ALWAYS output and may be used to power the keyboard 9
3.3V Main and 5V Main PWM Output Capacitors
Selection of the output capacitors is also dependent on the output inductor so some inductor analysis is required to select the output capacitors.
ISL6235
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 ISL6235 will provide either 0% or 94% 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:
I TRAN L O x I TRAN C OUT = --------------------------------------------- x -------------------( V IN - V OUT ) x 2 DV OUT (EQ. 5)
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 (EQ. 7)
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.
3.3V ALWAYS and 5V ALWAYS Output Capacitors
The output capacitors for the linear regulators insure stability and provide dynamic load current. The 3.3V ALWAYS and the 5V ALWAYS linear regulators should have, as a minimum, 10F capacitors on their outputs.
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 VOUT 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 (EQ. 6)
3.3V Main and 5V Main PWM Output Inductor Selection
The PWM converters require output inductors. 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 --------------V IN FS x L (EQ. 8)
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 as shown in Figure 4. 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). Figure 4 also shows the advantage of having the PWM converters operating out of phase. If the converters were operating in phase, the combined RMS current would be the algebraic sum, which is a much larger value as shown. The combined out-of-phase current is the square root of the sum of the square of the individual reflected currents and is significantly less than the combined in-phase current.
where, IL 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 1.2kHz and 30kHz. This range is set by an internal, single compensation zero at 6kHz. The ESR zero can be a factor of five on either
10
ISL6235
5 INPUT RMS CURRENT 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0 1 2 3 4 3.3V AND 5V LOAD CURRENT 5 5V
IN-PHASE OUT-OF-PHASE
The maximum value of the boost capacitor, Comax that will charge to 9V in the soft start time, TSS , is shown below, where L is the value of the boost inductor.
Tss Comax = --------- x 0.115F L (EQ. 11)
3.3V
The output capacitor ESR and the boost inductor ripple current determines the output voltage ripple. The ripple voltage is given by:
V RIPPLE = I L x ESR (EQ. 12)
INPUT CAPACITANCE RMS CURRENT AT VIN = 10.8V
and the maximum ripple current, IL, is given by:
5V I L = ------- x 3.3 L (EQ. 13)
FIGURE 4. INPUT RMS CURRENT VS LOAD
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-CONTM 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 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.
where L is the boost inductor calculated above, 5V is the boost input voltage and 3.3 is the maximum on time for the boost MOSFET.
MOSFET Considerations
The logic level MOSFETs are chosen for optimum efficiency given the potentially wide input voltage range and output power requirements. Two N-channel MOSFETs are used in each of the synchronous-rectified buck converters for the PWM1 and PWM2 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
+12V Boost Converter Inductor Selection
The inductor value is chosen to provide the required output power to the load.
Vinmin 2 x Dmax 2 x Ro Lmax = ---------------------------------------------------------------2 x Vo 2 x F (EQ. 9)
where, Vinmin is the minimum input voltage, 4.9V; Dmax = 1/3, the maximum duty cycle; Ro is the minimum load resistance; Vo is the nominal output voltage and F is the switching frequency, 100kHz. Or, for L in uH, the maximum output current is nominally:
13.88 Imax = ---------------L x Vo (EQ. 10)
(EQ. 14)
+12V Boost Converter Output Capacitor Selection
The total capacitance on the 12V output should be chosen appropriately, so that the output voltage will be higher than the undervoltage limit (9V) when the 5V Main soft-start time has elapsed. This will avoid triggering of the 12V undervoltage protection.
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 ISL6235 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.
11
ISL6235
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 overvoltage 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 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 ISL6235 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.
Small Components Signal Layout Considerations
1. The VSNS1 and VSNS2 inputs should be bypassed with a 1.0F capacitor close to their respective IC pins. 2. A `T' filter consisting of a `split' RSNS and a small, 100pF, capacitor as shown in Figure 5, may be helpful in reducing noise coupling into the ISEN input. For example, if the calculated value of RSNS1 is 2.2K, dividing it as shown with a 100pF capacitor provides filtering without changing the current limit set point. For any calculated value of RSNS, keep the value of the R9 portion to approximately 200, and the remainder of the resistance in the R19 position. The 200 resistor and 100pF capacitor provide effective filtering for noise above 8MHz. This filter configuration may be helpful on both the 3.3V and 5V Main outputs.
RSNS = R19 + R9 ISEN1 R19 2K R9 200 C12 100pF
FROM PHASE NODE
FIGURE 5. NOISE FILTER FOR ISEN1 INPUT
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 vias 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.
3. The bypass capacitors for VBATT and the soft-start capacitors, CSS1 and CSS2 should be located close to their connecting pins on the control IC. Minimize any leakage current paths from SDWN1 and SDWN2 nodes, since the internal current source is only 5mA. 4. Refer to the Application Note for a recommended component placement and interconnections. Figure 6 shows an application circuit of a power supply for a notebook PC microprocessor system. The power supply provides +5V ALWAYS, +3.3V ALWAYS, +5.0V, +3.3V, and 12V from +5.6-22VDC battery voltage. For detailed information on the circuit, including a Bill of Materials and circuit board description, see Application Note AN9915. Also see Intersil's web site (www.intersil.com) for the latest information.
12
ISL6235
+5.6-22VIN C4 56F C3, 6, 10 3x1F
GND
D2 BAT54WT1 VBATT +3.3V ALWAYS (50mA) + +5V ALWAYS (50mA) + C1 100F C2 10F 5V ALWAYS 23 6 22 21 BOOT2 C7 0.15F +3.3V (5A) + L1 8.2H C22 330F Q4 HUF76112SK8 Q2 HUF76112SK8 ISL6235 3 4 5 9 18 VSEN1 Q5 HUF76112SK8 20 19 LGATE1 PGND1 1 3.3V ALWAYS 2 24 BOOT1 C9 0.15F
UGATE1 PHASE1 ISEN1 R9, 19 2.2K
Q3 HUF76112SK8 L2 8.2H Q5 HUF76112SK8
D1 BAT54WT1
L4 2.7H + + C36 22F D3 + R14 97.6K L3 6.8H
+5V (5A) C21, 32 2x330F
UGATE2 PHASE2 R10, 11 ISEN2 2.2K LGATE2 PGND2 VSEN2 SDWN2 C16 0.022F PGOOD
7 8 10 11
16
GATE3
C24, 33 2x47F
15 17
VSEN3 SDWN1 C17 0.022F SDWNALL
R13 24.9K
12 14 GND
13
FIGURE 6. APPLICATIONS CIRCUIT
13
ISL6235 Shrink Small Outline Plastic Packages (SSOP)
N INDEX AREA E -B1 2 3 L SEATING PLANE -AD -CA 0.25 0.010 h x 45o GAUGE PLANE H 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 MIN 0.053 0.004 0.008 0.007 0.337 0.150 MAX 0.069 0.010 0.061 0.012 0.010 0.344 0.157 MILLIMETERS MIN 1.35 0.10 0.20 0.18 8.55 3.81 MAX 1.75 0.25 1.54 0.30 0.25 8.74 3.98 NOTES 9 3 4 5 6 7 8o Rev. 0 12/00
A1 0.10(0.004) A2 C
E e H h L N
e
B 0.17(0.007) M C AM BS
0.025 BSC 0.228 0.0099 0.016 24 0o 8o 0.244 0.0196 0.050
0.635 BSC 5.80 0.26 0.41 24 0o 6.19 0.49 1.27
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 products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation's quality certifications can be viewed at website www.intersil.com/design/quality
Intersil 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.
For information regarding Intersil Corporation and its products, see web site www.intersil.com 14

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