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ISL62391, ISL62392
Data Sheet December 22, 2008 FN6666.4
High-Efficiency, Triple-Output System Power Supply Controller for Notebook Computers
The ISL62391, ISL62392 controller generates supply voltages for battery-powered systems. It includes two pulse-width modulation (PWM) controllers, adjustable from 0.6V to 5.5V, and a linear regulator (LDO3) that generates a fixed 3.3V and can deliver up to 100mA. The ISL62391, ISL62392 includes on-board power-up sequencing, a power-good (PGOOD) output, digital soft-start, and internal soft-stop output discharge that prevents negative voltages on shutdown. The patented R3 PWM control scheme provides a low jitter system with fast response to load transients. Light-load efficiency is improved with period-stretching discontinuous conduction mode (DCM) operation. To eliminate noise in audio frequency applications, an ultrasonic DCM mode is included, which limits the minimum switching frequency to 28kHz. The ISL62391 and ISL62392 are identical except for how their overvoltage protection is handled. The ISL62391 utilizes a tri-state overvoltage scheme, whereas the ISL62392 employs a soft-crowbar method. The ISL62391, ISL62392 is available in a 28 Ld 4x4 TQFN package and operates over the extended temperature range (-40C to +100C).
Features
* High Performance R3 Technology * Fast Transient Response * 1% Output Voltage Accuracy * 2 Fully Programmable Switch-Mode Power Supplies * Programmable Switching Frequency * Fixed 3.3V LDO Output * Internal Soft-Start and Soft-Stop Output Discharge * Wide Input Voltage Range: 5.5V to 25V * Full and Ultrasonic Pulse-Skipping Mode * Power-Good Indicator * Overvoltage, Undervoltage and Overcurrent Protection * Thermal Monitor and Protection * Pb-Free (RoHS Compliant)
Applications
* Notebook and Sub-Notebook Computers * PDAs and Mobile Communication Devices * 3-Cell and 4-Cell Li+ Battery-Powered Devices
Ordering Information
PART NUMBER (Note) ISL62391HRTZ PART MARKING TEMP RANGE (C) PACKAGE (Pb-Free) PKG. DWG. #
Pinout
ISL62391, ISL62392 (28 LD 4X4 TQFN) TOP VIEW
OCSET2 PHASE2 23 UGATE2 22 21 20 19 18 17 CENTER PAD: GND 16 15 12 PHASE1 13 UGATE1 14 BOOT1 BOOT2 LGATE2 PGND PVCC VIN LDO3 LGATE1 VOUT2
ISEN2
623 91HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4
FB2
ISL62391HRTZ-T* 623 91HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4 ISL62392HRTZ 623 92HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4
PGOOD FSET2 FCCM VCC LDO3EN FSET1 FB1 1 2 3 4 5 6 7
28
27
26
25
24
ISL62392HRTZ-T* 623 92HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4 ISL62391IRTZ ISL62391IRTZ-T* ISL62392IRTZ ISL62392IRTZ-T* 623 91IRTZ 623 91IRTZ 623 92IRTZ 623 92IRTZ -40 to +100 28 Ld 4x4 TQFN L28.4x4 -40 to +100 28 Ld 4x4 TQFN L28.4x4 -40 to +100 28 Ld 4x4 TQFN L28.4x4 -40 to +100 28 Ld 4x4 TQFN L28.4x4
*Please refer to TB347 for details on reel specifications. NOTE: These Intersil Pb-free plastic packaged products employ special Pb-free material sets, molding compounds/die attach materials, and 100% matte tin plate plus anneal (e3 termination finish, which is RoHS compliant and compatible with both SnPb and Pb-free soldering operations). Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
8 VOUT1
9 ISEN1
10 OCSET1
11 EN1
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2008. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
EN2
ISL62391, ISL62392
Absolute Maximum Ratings
VIN to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +28V VCC, PGOOD, PVCC to GND . . . . . . . . . . . . . . . . . . -0.3V to +7.0V EN1, 2, LDO3EN . . . . . . . . . . . . . . . . . . . -0.3V to GND, VCC +0.3V VOUT1,2, FB1,2, FSET1,2 . . . . . . . . . . . . -0.3V to GND, VCC +0.3V PHASE1,2 to GND . . . . . . . . . . . . . . . . . . . . . . . (DC) -0.3V to +28V (<100ns Pulse Width, 10J) . . . . . . . . . . . . . . . . . . . . . . . . . -5.0V BOOT1,2 to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +33V BOOT1,2 to PHASE1,2 . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +7V UGATE1,2 . . . . . . . . . . . . (DC) -0.3V to PHASE1,2, BOOT1,2 +0.3V (<200ns Pulse Width, 20J) . . . . . . . . . . . . . . . . . . . . . . . . -4.0V LGATE1,2 . . . . . . . . . . . . . . . . . . . (DC) -0.3V to GND, PVCC +0.3V (<100ns Pulse Width, 4J) . . . . . . . . . . . . . . . . . . . . . . . . . . -2.0V LDO3 Current (Internal Regulator) Continuous . . . . . . . . . +100mA
Thermal Information
Thermal Resistance (Typical, Notes 1, 2) JA (C/W) JC (C/W) TQFN Package . . . . . . . . . . . . . . . . . . 37 3.5 Junction Temperature Range. . . . . . . . . . . . . . . . . .-55C to +150C Operating Temp. Range (ISL62391(2)IRTZ) . . . . . .-40C to +100C Operating Temp. Range (ISL62391(2)HRTZ) . . . . .-10C to +100C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65C to +150C Pb-Free Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp
Recommended Operating Conditions
Ambient Temperature Range (ISL62391(2)IRTZ) . .-40C to +100C Ambient Temperature Range (ISL62391(2)HRTZ) .-10C to +100C Supply Voltage (VIN to GND) . . . . . . . . . . . . . . . . . . . . 5.5V to 25V
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and result in failures not covered by warranty.
NOTES: 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. 2. For JC, the "case temp" location is the center of the exposed metal pad on the package underside.
Electrical Specifications
Circuit of Figure 1 and Figure 2, LDO3, OUT1, OUT2, and REF, VIN = 12V, EN = VCC, TA = -40C to +100C, unless otherwise noted. Typical values are at TA = +25C. Parameters with MIN and/or MAX limits are 100% tested at +25C, unless otherwise specified. Temperature limits established by characterization and are not production tested. CONDITIONS MIN TYP MAX UNITS
PARAMETER LINEAR REGULATOR VIN Power-on Reset Rising Threshold Hysteresis VIN Shutdown Supply Current VIN Standby Supply Current LDO3 Output Voltage
5.3 20
5.4 80 6 150
5.5 150 15 250 3.35 3.35
V mV A A V V mA
EN1 = EN2 = LDO3EN = 0 EN1 = EN2 = 0, LDO3EN = 1 I_LDO3 = 100mA (Note 3) I_LDO3 = 0mA 3.25 3.25
3.3 3.3 180
LDO3 Short-Circuit Current LDO3EN Input Voltage
LDO3 = GND (Note 3) Rising edge Falling edge 1.1 0.94 -1
2.5 1.06 1 36 4.2 60
V V A V
LDO3EN Input Leakage Current LDO3 Discharge ON-resistance PVCC POR Threshold (Note 3) SMPS2 to PVCC Switchover Threshold SMPS2 to PVCC Switchover Resistance (Note 3) MAIN SMPS CONTROLLERS VCC Input Bias Current VCC POR Threshold
LDO3EN = 0 or VCC LDO3EN = 0
4.63 VOUT2 to PVCC, VOUT2 = 5V
4.8 2.5
4.93 3.2
V
EN1 = EN2 = 1, FB1 = FB2 = 0.65V Rising Edge Rising Edge (ISL62391(2)HRTZ, TA = -10C to +100C) Falling Edge Falling Edge (ISL62391(2)HRTZ, TA = -10C to +100C) 4.33 4.35 4.08 4.10
2 4.50 4.50 4.20 4.20 0.6 4.55 4.55 4.30 4.30
mA V V V V V 1 %
Reference Voltage Regulation Accuracy VOUT regulated to 0.6V -1
2
FN6666.4 December 22, 2008
ISL62391, ISL62392
Electrical Specifications
Circuit of Figure 1 and Figure 2, LDO3, OUT1, OUT2, and REF, VIN = 12V, EN = VCC, TA = -40C to +100C, unless otherwise noted. Typical values are at TA = +25C. Parameters with MIN and/or MAX limits are 100% tested at +25C, unless otherwise specified. Temperature limits established by characterization and are not production tested. (Continued) CONDITIONS FB = 0.6V FB = 0.6V (ISL62391(2)HRTZ, TA = -10C to +100C) Frequency Range Frequency Set Accuracy VOUT Voltage Adjust Range VOUT Soft-discharge Resistance PGOOD Pull-down Impedance PGOOD Leakage Current Maximum PGOOD Sink Current PGOOD Soft-start Delay (From first EN = 1 to PGOOD = 1) (Note 3) PGOOD = VCC (Note 3) EN1 = EN2 = 1 EN1 = 1, EN2 = Floating or EN1 = Floating, EN2 =1 EN1 = 1, EN2 = Floating or EN1 = Floating, EN2 =1 (ISL62391(2)HRTZ, TA = -10C to +100C) UGATE Pull-up ON-resistance UGATE Source Current UGATE Pull-down ON-resistance UGATE Sink Current LGATE Pull-up ON-resistance LGATE Source Current LGATE Pull-down ON-resistance LGATE Sink Current UGATE to LGATE Deadtime LGATE to UGATE Deadtime Bootstrap Diode Forward Voltage Bootstrap Diode Reverse Leakage Current FCCM Input Voltage 200mA source current (Note 3) UGATE-PHASE = 2.5V (Note 3) 250mA source current (Note 3) UGATE-PHASE = 2.5V (Note 3) 250mA source current (Note 3) LGATE-PGND = 2.5V (Note 3) 250mA source current (Note 3) LGATE-PGND = 2.5V (Note 3) UG falling to LG rising, no load LG falling to UG rising, no load 2mA forward diode current VR = 25V Low Level (DCM enabled) Float Level (audio filter enabled) High Level (forced CCM) FCCM Input Leakage Current Audio Filter Switching Frequency EN Input Voltage FCCM = GND or VCC FCCM floating Low Level (Clear fault level/SMPS off) Float Level (Delayed start) High Level (SMPS on) EN Input Leakage Current ISEN Input Impedance ISEN Input Leakage Current OCSET Input Impedance OCSET Input Leakage Current OCSET Current Source EN = GND or VCC EN = VCC EN = GND EN = VCC EN = GND EN = VCC EN = VCC (ISL62391(2)HRTZ, TA = -10C to +100C) 8.7 9 1.9 2.4 -3.5 600 0.1 600 0.1 10.0 10.0 10.5 10.5 3.5 1.9 2.4 -2 28 0.8 2.1 2 2.20 4.50 4.50 FSW = 300kHz (Note 4) VIN 6V for VOUT = 5.5V MIN -12 -10 200 -12 0.6 14 32 0 5 2.75 5.60 5.60 1.0 2.0 1.0 2.0 1.0 2.0 0.5 4.0 21 21 0.58 0.2 1 0.8 2.1 0.9 1.5 1.5 3.70 7.60 7.50 1.5 TYP MAX 30 30 600 12 5.5 50 50 1 UNITS nA nA kHz % V A mA ms ms ms A A A A ns ns V A V V V A kHz V V V A k A k A A A
PARAMETER FB Input Bias Current
3
FN6666.4 December 22, 2008
ISL62391, ISL62392
Electrical Specifications
Circuit of Figure 1 and Figure 2, LDO3, OUT1, OUT2, and REF, VIN = 12V, EN = VCC, TA = -40C to +100C, unless otherwise noted. Typical values are at TA = +25C. Parameters with MIN and/or MAX limits are 100% tested at +25C, unless otherwise specified. Temperature limits established by characterization and are not production tested. (Continued) CONDITIONS MIN -1.75 Falling edge, referenced to FB Falling edge, referenced to FB (ISL62391(2)HRTZ, TA = -10C to +100C) OVP Threshold Rising edge, referenced to FB Falling edge, referenced to FB OTP Threshold Rising edge (Note 3) Falling edge (Note 3) NOTES: 3. Limits established by characterization and are not production tested. 4. FSW accuracy reflects IC tolerance only; it does not include frequency variation due to VIN, VOUT, LOUT, ESRCOUT, or other application specific parameters. 80.9 81 113 99.5 TYP 0.0 84 84 116 103 150 135 MAX 1.75 87 87 120 106 UNITS mV % % % % C
PARAMETER OCP (OCSET-ISEN) Threshold UVP Threshold
4
FN6666.4 December 22, 2008
ISL62391, ISL62392 Functional Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Bottom Pad NAME PGOOD FSET2 FCCM VCC LDO3EN FSET1 FB1 VOUT1 ISEN1 OCSET1 EN1 PHASE1 UGATE1 BOOT1 LGATE1 LDO3 VIN PVCC PGND LGATE2 BOOT2 UGATE2 PHASE2 EN2 OCSET2 ISEN2 VOUT2 FB2 GND FUNCTION Open-drain power-good status outputs. Connect to VCC through a 100k resistor. Output will be high when all outputs are within regulation with no faults detected. Frequency control input for SMPS2. Connect a resistor to ground to program the switching frequency. The pin output is a pulsed current and requires a decoupling capacitor to average the signal. Logic input to control efficiency mode. Logic high forces continuous conduction mode (CCM). Logic low allows full discontinuous conduction mode (DCM). Float this pin for ultrasonic DCM operation. Analog power supply input for reference voltages and currents. Bypass to ground with a 1F ceramic capacitor near the IC. Logic input for enabling and disabling the LDO3 linear regulator. Positive logic input. Frequency control input for SMPS1. Connect a resistor to ground to program the switching frequency. The pin output is a pulsed current and requires a decoupling capacitor to average the signal. SMPS1 feedback input used for output voltage programming and regulation. SMPS1 output voltage sense input. Used for soft-discharge. SMPS1 DCR current sense input. Used for overcurrent protection and R3 regulation. Input from DCR current-sensing network used to program the overcurrent shutdown threshold for SMPS1. Logic input to enable and disable SMPS1. A logic high will immediately enable SMPS1. Floating this pin will enable SMPS1 only after SMPS2 has been enabled and achieved regulation. A logic low disables SMPS1. SMPS1 switching node for high-side gate drive return and synthetic ripple modulation. Connect to the switching NMOS source, the synchronous NMOS drain, and the output inductor for SMPS1. High-side NMOS gate drive output for SMPS1. Connect to the gate of the SMPS1 switching FET. SMPS1 bootstrap input for the switching NMOS gate drivers. Connect to SMPS1 PHASE with a ceramic capacitor of 0.22F. Low-side NMOS gate drive output for SMPS1. Connect to the gate of the SMPS1 synchronous FET. 3.3V linear regulator output, capable of providing 100mA continuous current. Bypass to ground with a 4.7F ceramic capacitor. Feed-forward input for line voltage transient compensation. Connect to the power train input voltage. 5V power source for SMPS gate drive current. Bypass to ground with a 4.7F ceramic capacitor. Power ground for SMPS1 and SMPS2. This provides a return path for synchronous FET switching currents. Low-side NMOS gate drive output for SMPS2. Connect to the gate of the SMPS2 synchronous FET. SMPS2 bootstrap input for the switching NMOS gate drivers. Connect to SMPS2 PHASE with a ceramic capacitor of 0.22F. High-side NMOS gate drive output for SMPS2. Connect to the gate of the SMPS2 switching FET. SMPS2 switching node for high-side gate drive return and synthetic ripple modulation. Connect to the switching NMOS source, the synchronous NMOS drain, and the output inductor for SMPS2. Logic input to enable and disable SMPS2. A logic high will immediately enable SMPS2. Floating this pin will enable SMPS2 only after SMPS1 has been enabled and achieved regulation. A logic low disables SMPS2. Input from DCR current-sensing network used to program the overcurrent shutdown threshold for SMPS2. SMPS2 DCR current sense input. Used for overcurrent protection and R3 regulation. SMPS2 output voltage sense input. Used for soft-discharge and switchover for PVCC 5V LDO. SMPS2 feedback input used for output voltage programming and regulation. Analog ground for analog and logic signals.
5
FN6666.4 December 22, 2008
ISL62391, ISL62392 Typical Application Circuits
The typical application circuits generate the 5V/8A and 3.3V/8A (system regulator), or 1.05V/15A and 1.5V/15A (chip set) supplies in a notebook computer. The input supply (VBAT) range is 5.5V to 25V.
VBAT
4x10F 0.22F
3 .3 V
BO OT1
V IN
BOO T2
0.22F IRF7821 4.7H
5V
4.7H
IRF7821
UGATE1 PHASE1
UGATE2 PHASE2
330F
0.022F 14k
LGATE1 LG ATE2
14k 0.022F IRF7832 14k
OCSET1 OCSET2 IS E N 2 VOUT2 FB2
330F
14k 750 45.3k 1200pF
IRF7832
750 68.1k 1200pF
IS E N 1 VOUT1 FB1
10k
ISL62391, ISL62392
100k
LDO3 PGOOD EN1 EN2 LD O 3EN PVCC FCCM FSET1 FSET2 PAD PVCC
9.09k
4.7F
1F 1F
VCC PGND
24.3k 19.6k 0.01F
0.01F
FIGURE 1. TYPICAL SYSTEM REGULATOR APPLICATION CIRCUIT WITH INDUCTOR DCR CURRENT SENSE
VBAT
4x10F
3 .3 V
BO OT1
V IN
BO O T2
0.22F 4.7H 0.001 1k 1k
IRF7821
UG ATE1 PHASE1 UG ATE2 PHASE2
IRF7821
0.22F 4.7H 0.001
5V
330F
IRF7832
LGATE1 LG ATE2
IRF7832 1k 1k
330F
750 1200pF 45.3k
750
OCSET1 IS E N 1 VO UT1 FB1 OCSET2 IS E N 2 VOUT2 FB2
68.1k
1200pF
9.09k 10k
ISL62391, ISL62392
100k
PGOOD 3 .3 V LDO 3 EN1 EN2 LDO 3EN FCCM FSET1 FSET2 GND PVCC
4.7F 1F 1F
PVCC VCC PGND
24.3k 19.6k 0.01F
0.01F
FIGURE 2. TYPICAL SYSTEM REGULATOR APPLICATION CIRCUIT WITH RESISTOR SENSE
6
FN6666.4 December 22, 2008
ISL62391, ISL62392 Typical Application Circuits (Continued)
VBAT
4x10F 0.22F
1 .0 5 V
BO O T1
V IN
BO O T2
0.22F IRF7821 2x 14k 2x IRF7832 2.2H 0.022F
1 .5 V
2.2H
IRF7821 2x
UG ATE1 PHASE1
UGATE2 PHASE2
2x330F
0.022F 14k
LGATE1 LGATE2
2x330F
14k 590 36.5k 1800pF
IRF7832 2x
OCSET1 IS E N 1 VO UT1 FB1 OCSET2 IS E N 2 VOUT2 FB2
14k 36.5k
590 1800pF
48.7k
ISL62391, ISL62392
100k
LDO3 PGOOD EN1 EN2 LDO 3EN PVCC FCCM FSET1 FSET2 PAD PVCC
24.3k
4.7F
1F 1F
VCC PGND
17.4k 14k 0.01F
0.01F
FIGURE 3. TYPICAL CHIP SET APPLICATION CIRCUIT WITH INDUCTOR DCR CURRENT SENSE
VBAT
4x10F 0.22F
1 .0 5 V
BO OT1
V IN
BO O T2
IRF7821 2x IRF7832 2x
LGATE1 LG ATE2 UG ATE1 PHASE1 UGATE2 PHASE2
IRF7821 2x IRF7832 2x
0.22F 2.2H 0.001
1 .5 V
2.2H 0.001 1k 1k
2x330F
2x330F 1k 1k 590
590 1800pF 36.5k
OCSET1 IS E N 1 VOUT1 FB1
OCSET2 IS E N 2 VOUT2 FB2
36.5k
1800pF
24.3k 48.7k
ISL62391, ISL62392
100k
PGOOD 3 .3 V LDO3 EN1 EN2 LDO 3EN FCCM FSET1 FSET2 GND PVCC
4.7F 1F 1F
PVCC VCC PGND
17.4k 14k 0.01F
0.01F
FIGURE 4. TYPICAL CHIP SET APPLICATION CIRCUIT WITH RESISTOR SENSE
7
FN6666.4 December 22, 2008
ISL62391, ISL62392 Block Diagram
VIN VOUT2*
FSET1/2 4.8V 5V LDO R3 MODULATOR VREF 0.6V BOOT1/2 FCCM VOUT1/2 PVCC
FB1/2
PWM
UGATE DRIVER
UGATE1/2
PHASE1/2
SOFT DISCHARGE LGATE DRIVER LGATE1/2
PGND EN1 EN2 LDO3EN
START-UP AND SHUTDOWN LOGIC
PGOOD
VCC
10A OCSET1/2 ISEN1/2 OCP PROTECTION LOGIC OVP/UVP/OCP/OTP
BIAS AND REFERENCE
T-PAD
VREF + 16%
UVP
PVCC
FB1/2 OVP VREF - 16% THERMAL MONITOR
3.3V LDO
LDO3
SOFT DISCHARGE
*In addition to being used for regulation, VOUT2 will also provide power for PVCC when it is programmed to 5V.
8
FN6666.4 December 22, 2008
ISL62391, ISL62392 Typical Performance Curves
100 95 90 EFFICIENCY (%) VIN = 19V EFFICIENCY (%) 85 80 75 70 65 60 55 50 0.10 1.00 IOUT (A) 10.00 VIN = 12V 100 VIN = 7V 95 90 85 80 75 70 65 60 55 50 0.01 0.10 IOUT (A) 1.00 10.00 VIN = 19V VIN = 12V VIN = 7V
FIGURE 5. CHANNEL 1 EFFICIENCY AT VO = 3.3V, DEM OPERATION. HIGH-SIDE 1xIRF7821, rDS(ON) = 9.1m; LOW-SIDE 1xIRF7832, rDS(ON) = 4m; L = 4.7H, DCR = 14.3m; CCM FSW = 270kHz
FIGURE 6. CHANNEL 2 EFFICIENCY AT VO = 5V, DEM OPERATION. HIGH-SIDE 1xIRF7821, rDS(ON) = 9.1m; LOW-SIDE 1xIRF7832, rDS(ON) = 4m; L = 4.7H, DCR = 14.3m; CCM FSW = 330kHz
VO1
VO1
FB1
FB1
PGOOD PGOOD PHASE1
PHASE1
FIGURE 7. POWER-ON, VIN = 12V, LOAD = 5A, VO = 3.3V
FIGURE 8. POWER-OFF, VIN = 12V, IO = 5A, VO = 3.3V
VO1
VO1
FB1
FB1
PGOOD
PGOOD
EN1 EN1
FIGURE 9. ENABLE CONTROL, EN1 = HIGH, VIN = 12V, VO = 3.3V, IO = 5A
FIGURE 10. ENABLE CONTROL, EN1 = LOW, VIN = 12V, VO = 3.3V, IO = 5A
9
FN6666.4 December 22, 2008
ISL62391, ISL62392 Typical Performance Curves (Continued)
VO1 PHASE1
VO1
PHASE1
VO2 PHASE2
VO2
PHASE2
FIGURE 11. CCM STEADY-STATE OPERATION, VIN = 12V, VO1 = 3.3V, IO1 = 5A, VO2 = 5V, IO2 = 5A
FIGURE 12. DCM STEADY-STATE OPERATION, VIN = 12V, VO1 = 3.3V, IO1 = 0. 2A, VO2 = 5V, IO2 = 0.2A
VO1
VO1
PHASE1 PHASE1 VO2 PHASE2
IO1
FIGURE 13. AUDIO FILTER OPERATION, VIN = 12V, VO1 = 3.3V, VO2 = 5V, NO LOAD
FIGURE 14. TRANSIENT RESPONSE, VIN = 12V, VO = 3.3V, IO = 0.1A/8.1A @ 2.5A/s
VO1 VO1
PHASE1
PHASE1
IO1
IO1
FIGURE 15. LOAD INSERTION RESPONSE, VIN = 12V, VO = 3.3V, IO = 0.1A/8.1A @ 2.5A/s
FIGURE 16. LOAD RELEASE RESPONSE, VIN = 12V, VO = 3.3V, IO = 0.1A/8.1A @ 2.5A/s
10
FN6666.4 December 22, 2008
ISL62391, ISL62392 Typical Performance Curves (Continued)
EN1 EN2
VO1
VO1
VO2 VO2
FIGURE 17. DELAYED START, VIN = 12V, VO1 = 3.3V, VO2 = 5V, EN2 = FLOAT, NO LOAD
FIGURE 18. DELAYED START, VIN = 12V, VO1 = 3.3V, VO2 = 5V, EN1 = FLOAT, NO LOAD
VO1
VO1
PGOOD
IO1 VO2 PGOOD
FIGURE 19. DELAYED START, VIN = 12V, VO1 = 3.3V, VO2 = 5V, EN1 = 1, EN2 = FLOAT, NO LOAD
FIGURE 20. OVERCURRENT PROTECTION, VIN = 12V, VO = 3.3V
VO1
VO1
UGATE1-PHASE1
UGATE1-PHASE1
LGATE1 LGATE1
PGOOD PGOOD
FIGURE 21. CROWBAR OVERVOLTAGE PROTECTION, VIN = 12V, VO = 3.3V, NO LOAD
FIGURE 22. TRI-STATE OVERVOLTAGE PROTECTION, VIN = 12V, VO = 3.3V, NO LOAD
11
FN6666.4 December 22, 2008
ISL62391, ISL62392 Theory of Operation
Three Output Controller
The ISL62391, ISL62392 generates three regulated output voltages. Two are produced with switch-mode power supplies (SMPS), and the third by a low dropout linear regulator (LDO). An additional 5V LDO (PVCC) is used to power the chip during operation, allowing the ISL62391, ISL62392 to regulate all outputs from a single power source (VIN) with no need for a separate quiescent supply. This makes the ISL62391, ISL62392 an ideal choice as system regulator for notebook PCs. Because the two SMPS channels are identical and almost entirely independent, all conclusions drawn apply to both channels unless otherwise noted. A window voltage VW is referenced with respect to the error amplifier output voltage VCOMP, creating an envelope into which the ripple voltage VR is compared. The amplitude of VW is set by a resistor, RW, connected across the FSET and GND pins. The VR, VCOMP, and VW signals feed into a window comparator in which VCOMP is the lower threshold voltage and VW is the higher threshold voltage. Figure 23 shows PWM pulses being generated as VR traverses the VW and VCOMP thresholds. The PWM switching frequency is proportional to the slew rates of the positive and negative slopes of VR; it is inversely proportional to the voltage between VW and VCOMP. Equation 3 illustrates how to calculate the window size based on output voltage and frequency set resistor.
V W = g m V OUT ( 1 - D ) R W (EQ. 3)
Modulator and Switching Frequency
The ISL62391, ISL62392 modulator features Intersil's R3 technology, a hybrid of fixed frequency PWM and variable frequency hysteretic control. Intersil's R3 technology can simultaneously affect the PWM switching frequency and PWM duty cycle in response to input voltage and output load transients. The R3 modulator synthesizes an AC signal, VR, which is an analog representation of the output inductor ripple current. The duty-cycle of VR is the result of charge and discharge current through a ripple capacitor, CR. The current through CR is provided by a transconductance amplifier that measures the VIN and VO pin voltages. The positive slope of VR can be written as Equation 1:
V RPOS = g m ( V IN - V OUT ) (EQ. 1)
The frequency can be expressed in Equation 4:
1 F SW = ----------------K RW (EQ. 4)
Inverting Equation 4 allows easy selection of RW for a desired FSW:
1 R W = -------------------K F SW (EQ. 5)
For Equations 3 through 5: gm = 1.66s K = 1.7 x 10-10 (20%) D = VOUT/VIN
The negative slope of VR can be written as Equation 2:
V RNEG = g m V OUT (EQ. 2)
Power-On Reset
The ISL62391, ISL62392 is disabled until the voltage at the VIN pin has increased above the rising power-on reset (POR) threshold. Conversely, the controller will be disabled when the voltage at the VIN pin decreases below the falling POR threshold. In addition to VIN POR, the PVCC pin is also monitored. If its voltage falls below 4.2V, the SMPS outputs will be shut down. This ensures that there is sufficient BOOT voltage to enhance the upper MOSFET.
Where gm is the gain of the transconductance amplifier.
RIPPLE CAPACITOR VOLTAGE CR
WINDOW VOLTAGE VW (WRT VCOMP)
EN, Soft-Start and PGOOD
ERROR AMPLIFIER VOLTAGE VCOMP
PWM
FIGURE 23. MODULATOR WAVEFORMS DURING LOAD TRANSIENT
The ISL62391, ISL62392 uses a digital soft-start circuit to ramp the output voltage of each SMPS to the programmed regulation setpoint at a predictable slew rate. The slew rate of the soft-start sequence has been selected to limit the in-rush current through the output capacitors as they charge to the desired regulation voltage. When the EN pins are pulled above their rising thresholds, the PGOOD Soft-Start Delay, tSS, starts and the output voltage begins to rise. The FB pin ramps to 0.6V in approximately 1.5ms and the PGOOD pin goes to high impedance approximately 1.25ms after the FB pin voltage reaches 0.6V.
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because the gate charge of a low r DS(ON) MOSFET can be large. Adaptive shoot-through protection prevents a gate-driver output from turning on until the opposite gate-driver output has fallen below approximately 1V. The dead-time shown in Figure 25 is extended by the additional period that the falling gate voltage stays above the 1V threshold. The typical dead-time is 21ns. The high-side gate-driver output voltage is measured across the UGATE and PHASE pins while the low-side gatedriver output voltage is measured across the LGATE and PGND pins. The power for the LGATE gate-driver is sourced directly from the PVCC pin. The power for the UGATE gatedriver is sourced from a "boot" capacitor connected across the BOOT and PHASE pins. The boot capacitor is charged from the 5V PVCC supply through a "boot diode" each time the lowside MOSFET turns on, pulling the PHASE pin low. The ISL62391, ISL62392 has integrated boot diodes connected from the PVCC pins to BOOT pins.
tSOFTSTART
1.5ms
VO VCC AND PVCC EN FB PGOOD
2.75ms PGOOD DELAY
FIGURE 24. SOFT-START SEQUENCE FOR ONE SMPS
The PGOOD pin indicates when the converter is capable of supplying regulated voltage. It is an undefined impedance if VIN is not above the rising POR threshold or below the POR falling threshold. When a fault is detected, the ISL62391, ISL62392 will turn on the open-drain NMOS, which will pull PGOOD low with a nominal impedance of 32. This will flag the system that one of the output voltages is out of regulation. Separate enable pins allow for full soft-start sequencing. Because low shutdown quiescent current is necessary to prolong battery life in notebook applications, the PVCC 5V LDO is held off until any of the three enable signals (EN1, EN2 or LDO3EN) are pulled high. Soft-start of all outputs will only start until after PVCC is above the 4.2V POR threshold. In addition to user-programmable sequencing, the ISL62391, ISL62392 includes a pre-programmed sequential SMPS soft-start feature. Table 1 shows the SMPS enable truth table.
TABLE 1. SMPS ENABLE SEQUENCE LOGIC EN1 0 0 0 FLOAT FLOAT FLOAT 1 1 1 EN2 0 FLOAT 1 0 FLOAT 1 0 FLOAT 1 START-UP SEQUENCE All SMPS outputs OFF All SMPS outputs OFF SMPS1 OFF, SMPS2 ON All SMPS outputs OFF All SMPS outputs OFF SMPS1 enables after SMPS2 is in regulation SMPS1 ON, SMPS2 OFF SMPS2 enables after SMPS1 is in regulation All SMPS outputs ON simultaneously
tLGFUGR
tUGFLGR
50% UGATE LGATE 50%
FIGURE 25. LGATE AND UGATE DEAD-TIME
Diode Emulation
FCCM is a logic input that controls the power state of the ISL62391, ISL62392. If forced high, the ISL62391, ISL62392 will operate in forced continuous-conduction-mode (CCM) over the entire load range. This will produce the best transient response to all load conditions, but will have increased light-load power loss. If FCCM is forced low, the ISL62391, ISL62392 will automatically operate in Diode Emulation Mode (DEM) at light load to optimize efficiency in the entire load range. The transition is automatically achieved by detecting the load current and turning off LGATE when the inductor current reaches 0A. Positive-going inductor current flows from either the source of the high-side MOSFET, or the drain of the low-side MOSFET. Negative-going inductor current flows into the drain of the low-side MOSFET. When the low-side MOSFET conducts positive inductor current, the phase voltage will be negative with respect to the GND and PGND pins. Conversely, when the low-side MOSFET conducts negative inductor current, the phase voltage will be positive with respect to the GND and PGND pins. The ISL62391,
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MOSFET Gate-Drive Outputs LGATE and UGATE
The ISL62391, ISL62392 has internal gate-drivers for the high-side and low-side N-Channel MOSFETs. The low-side gate-drivers are optimized for low duty-cycle applications where the low-side MOSFET conduction losses are dominant, requiring a low r DS(ON) MOSFET. The LGATE pull-down resistance is small in order to clamp the gate of the MOSFET below the VGS(th) at turn-off. The current transient through the gate at turn-off can be considerable 13
ISL62391, ISL62392
ISL62392 monitors the phase voltage when the low-side MOSFET is conducting inductor current to determine its direction. When the output load current is greater than or equal to 1/2 the inductor ripple current, the inductor current is always positive, and the converter is always in CCM. The ISL62391, ISL62392 minimizes the conduction loss in this condition by forcing the low-side MOSFET to operate as a synchronous rectifier. When the output load current is less than 1/2 the inductor ripple current, negative inductor current occurs. Sinking negative inductor through the low-side MOSFET lowers efficiency through unnecessary conduction losses. The ISL62391, ISL62392 automatically enters DEM after the PHASE pin has detected positive voltage and LGATE was allowed to go high for 8 consecutive PWM switching cycles. The ISL62391, ISL62392 will turn off the low-side MOSFET once the phase voltage turns positive, indicating negative inductor current. The ISL62391, ISL62392 will return to CCM on the following cycle after the PHASE pin detects negative voltage, indicating that the body diode of the low-side MOSFET is conducting positive inductor current. Efficiency can be further improved with a reduction of unnecessary switching losses by reducing the PWM frequency. It is characteristic of the R3 architecture for the PWM frequency to decrease while in diode emulation. The extent of the frequency reduction is proportional to the reduction of load current. Upon entering DEM, the PWM frequency makes an initial step-reduction because of a 33% step-increase of the window voltage V W. Because the switching frequency in DEM is a function of load current, very light load conditions can produce frequencies well into the audio band. This can be problematic if audible noise is coupled into audio amplifier circuits. To prevent this from occurring, the ISL62391, ISL62392 allows the user to float the FCCM input. This will allow DEM at light loads, but will prevent the switching frequency from going below ~28kHz to prevent noise injection to the audio band. A timer is reset each PWM pulse. If the timer exceeds 30s, LGATE is turned on, causing the ramp voltage to reduce until another UGATE is commanded by the voltage loop.
L DCR PHASE1 + ISL62391, ISL62392 10 OCSET1 ROCSET + VROCSET RO OUT1 VDCR CSEN _ IL _ CO VO
FIGURE 26. OVERCURRENT-SET CIRCUIT
Figure 26 shows the overcurrent-set circuit for SMPS1. The inductor consists of inductance L and the DC resistance (DCR). The inductor DC current IL creates a voltage drop across DCR, which is given by Equation 6:
V DCR = I L * DCR (EQ. 6)
The ISL62391, ISL62392 sinks a 10A current into the OCSET1 pin, creating a DC voltage drop across the resistor ROCSET, which is given by Equation 7:
V ROCSET = 10A * R OCSET (EQ. 7)
Resistor RO is connected between the OUT1 pin and the actual output voltage of the converter. During normal operation, the OUT1 pin is a high impedance path, therefore there is no voltage drop across RO. The DC voltage difference between the OCSET1 pin and the OUT1 pin can be established using Equation 8:
V OCSET1 - V OUT1 = I L * DCR - 10A * R OCSET (EQ. 8)
The ISL62391, ISL62392 monitors the OCSET1 pin and the OUT1 pin voltages. Once the OCSET1 pin voltage is higher than the OUT1 pin voltage for more than 10s, the ISL62391, ISL62392 declares an OCP fault. The value of ROCSET is then written as Equation 9:
I OC * DCR R OCSET = -------------------------10A (EQ. 9)
Where: - ROCSET () is the resistor used to program the overcurrent setpoint - IOC is the output current threshold that will activate the OCP circuit - DCR is the inductor DC resistance For example, if IOC is 20A and DCR is 4.5m, the choice of ROCSET is ROCSET = 20A x 4.5m/10A = 9k. Resistor ROCSET and capacitor CSEN form an R-C network to sense the inductor current. To sense the inductor current correctly, not only in DC operation but also during dynamic operation, the R-C network time constant ROCSET-CSEN
Overcurrent Protection
The overcurrent protection (OCP) setpoint is programmed with resistor, ROCSET, that is connected across the OCSET and PHASE pins.
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needs to match the inductor time constant L/DCR. The value of CSEN is then written as Equation 10:
L C SEN = ----------------------------------------R OCSET * DCR (EQ. 10)
threshold for more than 2s. The falling overvoltage threshold is typically 106% of the reference voltage, or 1.06*0.6V = 0.636V. This soft-crowbar process repeats as long as the output voltage fault is present, allowing the ISL62392 to protect against persistent overvoltage conditions.
For example, if L is 1.5H, DCR is 4.5m, and ROCSET is 9k, the choice of CSEN = 1.5H/(9k x 4.5m) = 0.037F. Upon converter start-up, the CSEN capacitor bias is 0V. To prevent false OCP during this time, a 10A current source flows out of the OUT1 pin, generating a voltage drop on the RO resistor, which should be chosen to have the same resistance as ROCSET. When the PGOOD pin goes high, the OUT1 pin current source will be removed. When an OCP fault is declared, the PGOOD pin will pull-down to 32 and latch-off the converter. The fault will remain latched until the EN pin has been pulled below the falling EN threshold voltage, or until VIN has decayed below the falling POR threshold. When using a discrete current sense resistor, inductor time-constant matching is not required. Equation 7 remains unchanged, but Equation 8 is modified in Equation 11:
V OCSET1 - V OUT1 = I L * R SENSE - 10A * R OCSET (EQ. 11)
Undervoltage Protection
The UVP fault detection circuit triggers after the FB pin voltage is below the undervoltage threshold for more than 2s. The undervoltage threshold is typically 86% of the reference voltage, or 0.86*0.6V = 0.516V. If a UVP fault is declared, the PGOOD pin will pull-down with 32 and latch-off the converter. The fault will remain latched until the EN pin has been pulled below the falling enable threshold, or if VIN has decayed below the falling POR threshold.
Programming the Output Voltage
When the converter is in regulation, there will be 0.6V between the FB and GND pins. Connect a two-resistor voltage divider across the OUT and GND pins with the output node connected to the FB pin, as shown in Figure 27. Scale the voltage-divider network such that the FB pin is 0.6V with respect to the GND pin when the converter is regulating at the desired output voltage. The output voltage can be programmed from 0.6V to 5.5V. Programming the output voltage is written as Equation 13:
R TOP V OUT = V REF * 1 + ---------------------------- R BOTTOM
Furthermore, Equation 9 is changed in Equation 12:
I OC * R SENSE R OCSET = -----------------------------------10A (EQ. 12)
(EQ. 13)
Where RSENSE is the series power resistor for sensing inductor current. For example, with an RSENSE = 1m and an OCP target of 10A, ROCSET = 1k.
Where: - VOUT is the desired output voltage of the converter - The voltage to which the converter regulates the FB pin is the VREF (0.6V) - RTOP is the voltage-programming resistor that connects from the FB pin to the converter output. In addition to setting the output voltage, this resistor is part of the loop compensation network - RBOTTOM is the voltage-programming resistor that connects from the FB pin to the GND pin Choose RTOP first when compensating the control loop, and then calculate RBOTTOM according to Equation 14:
V REF * R TOP R BOTTOM = -----------------------------------V OUT - V REF (EQ. 14)
Overvoltage Protection
The OVP fault detection circuit triggers after the FB pin voltage is above the rising overvoltage threshold for more than 2s. The FB pin voltage is 0.6V in normal operation. The rising overvoltage threshold is typically 116% of that value, or 1.16*0.6V = 0.696V. For both the ISL62391 and ISL62392, when an OVP fault is declared, the PGOOD pin will pull-down with 32 and latch-off the converter. The OVP fault will remain latched until the EN pin has been pulled below the falling EN threshold voltage, or until VIN has decayed below the falling POR threshold. During the latch condition, the ISL62391 will tri-state the PHASE node by turning both UGATE and LGATE off until the latch is cleared. Although latched, the ISL62392 LGATE gate-driver output will retain the ability to toggle the low-side MOSFET on and off in response to the output voltage transversing the OVP rising and falling thresholds. The LGATE gate-driver will turn on the low-side MOSFET to discharge the output voltage, thus protecting the load from potentially damaging voltage levels. The LGATE gate-driver will turn off the low-side MOSFET once the FB pin voltage is lower than the falling overvoltage
Compensation Design
Figure 27 shows the recommended Type-II compensation circuit. The FB pin is the inverting input of the error amplifier. The COMP signal, the output of the error amplifier, is inside the chip and unavailable to users. CINT is a 100pF capacitor integrated inside the IC that connects across the FB pin and the COMP signal. RTOP, RFB, CFB and CINT form the Type-II compensator. The frequency domain transfer function is given by Equation 15:
1 + s * ( R TOP + R FB ) * C FB G COMP ( s ) = ------------------------------------------------------------------------------------------s * R TOP * C INT * ( 1 + s * R FB * C )
FB
(EQ. 15)
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Selecting the LC Output Filter
CINT = 100pF RFB CFB
RTOP EA COMP + REF ISL62391, ISL62392 RBOTTOM VO FB
The duty cycle of an ideal buck converter is a function of the input and the output voltage. This relationship is written as Equation 16:
VO D = --------V IN (EQ. 16)
The output inductor peak-to-peak ripple current is written as Equation 17:
VO * ( 1 - D ) I PP = ----------------------------f SW * L (EQ. 17)
FIGURE 27. COMPENSATION REFERENCE CIRCUIT
The LC output filter has a double pole at its resonant frequency that causes rapid phase change. The R3 modulator used in the ISL62391, ISL62392 makes the LC output filter resemble a first order system in which the closed loop stability can be achieved with the recommended Type-II compensation network. Intersil provides a PC-based tool (example page is shown later) that can be used to calculate compensation network component values and help simulate the loop frequency response.
A typical step-down DC/DC converter will have an IP-P of 20% to 40% of the maximum DC output load current. The value of IP-P is selected based upon several criteria, such as MOSFET switching loss, inductor core loss, and the resistive loss of the inductor winding. The DC copper loss of the inductor can be estimated by Equation 18:
P COPPER = I LOAD
2
*
DCR
(EQ. 18)
Where ILOAD is the converter output DC current. The copper loss can be significant so attention has to be given to the DCR selection. Another factor to consider when choosing the inductor is its saturation characteristics at elevated temperature. A saturated inductor could cause destruction of circuit components, as well as nuisance OCP faults. A DC/DC buck regulator must have output capacitance CO into which ripple current IP-P can flow. Current IP-P develops a corresponding ripple voltage VP-P across CO, which is the sum of the voltage drop across the capacitor ESR and of the voltage change stemming from charge moved in and out of the capacitor. These two voltages are written as Equation 19:
V ESR = I P-P * E SR (EQ. 19)
3.3V Linear Regulator
In addition to the two SMPS outputs, the ISL62391, ISL62392 also provides a fixed 3.3V LDO output (LDO3) capable of sourcing 100mA continuous current. LDO3 draws its power from PVCC and can be independently enabled from both SMPS channels. LDO3 also has a current limit feature with a nominal level of 180mA. Currents in excess of the limit will cause the LDO3 voltage to drop dramatically, limiting the power dissipation.
Thermal Monitor and Protection
LDO3 and PVCC LDOs can dissipate non-trivial power inside the ISL62391, ISL62392 at high input-to-output voltage ratios and full load conditions. To protect the silicon, ISL62391, ISL62392 continually monitors the die temperature. If the temperature exceeds +150C, all outputs will be turned off to sharply curtail power dissipation. The outputs will remain off until the junction temperature has fallen below +135C.
and Equation 20:
I P-P V C = ----------------------------8 * CO * f
SW
(EQ. 20)
General Application Design Guide
This design guide is intended to provide a high-level explanation of the steps necessary to design a single-phase power converter. It is assumed that the reader is familiar with many of the basic skills and techniques referenced in the following section. In addition to this guide, Intersil provides complete reference designs that include schematics, bills of materials, and example board layouts.
If the output of the converter has to support a load with high pulsating current, several capacitors will need to be paralleled to reduce the total ESR until the required VP-P is achieved. The inductance of the capacitor can cause a brief voltage dip if the load transient has an extremely high slew rate. Low inductance capacitors should be considered in this scenario. A capacitor dissipates heat as a function of RMS current and frequency. Be sure that IP-P is shared by a sufficient quantity of paralleled capacitors so that they operate below the maximum rated RMS current at fSW. Take into account that the rated value of a capacitor can fade as much as 50% as the DC voltage across it increases.
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Selection of the Input Capacitor
The important parameters for the bulk input capacitance are the voltage rating and the RMS current rating. For reliable operation, select bulk capacitors with voltage and current ratings above the maximum input voltage and capable of supplying the RMS current required by the switching circuit. Their voltage rating should be at least 1.25x greater than the maximum input voltage, while a voltage rating of 1.5x is a preferred rating. Figure 28 is a graph of the input RMS ripple current (normalized relative to output load current) as a function of duty cycle and is adjusted for a converter efficiency of 80%. The ripple current calculation is written as Equation 21:
I IN_RMS, NORMALIZED =
2 x ( D - D ) + D ----- 12 2
(EQ. 21)
There are several power MOSFETs readily available that are optimized for DC/DC converter applications. The preferred high-side MOSFET emphasizes low gate charge so that the device spends the least amount of time dissipating power in the linear region. Unlike the low-side MOSFET, which has the drain-source voltage clamped by its body diode during turn off, the high-side MOSFET turns off with a VDS of approximately VIN - VOUT, plus the spike across it. The preferred low-side MOSFET emphasizes low r DS(ON) when fully saturated to minimize conduction loss. It should be noted that this is an optimal configuration of MOSFET selection for low duty cycle applications (D < 50%). For higher output, low input voltage solutions, a more balanced MOSFET selection for high- and low-side devices may be warranted. For the low-side (LS) MOSFET, the power loss can be assumed to be conductive only and is written as Equation 23:
P CON_LS I LOAD r DS ( ON )_LS * ( 1 - D )
2
Where: - IMAX is the maximum continuous ILOAD of the converter - x is a multiplier (0 to 1) corresponding to the inductor peak-to-peak ripple amplitude expressed as a percentage of IMAX (0% to 100%) - D is the duty cycle that is adjusted to take into account the efficiency of the converter which is written as Equation 22.
VO D = ------------------------V IN EFF (EQ. 22)
(EQ. 23)
For the high-side (HS) MOSFET, the conduction loss is written as Equation 24:
P CON_HS = I LOAD
2
*
r DS ( ON )_HS * D
(EQ. 24)
For the high-side MOSFET, the switching loss is written as Equation 25:
V IN * I VALLEY * t ON * f V IN * I PEAK * t OFF * f SW SW P SW_HS = ---------------------------------------------------------------- + -----------------------------------------------------------2 2 (EQ. 25)
In addition to the bulk capacitance, some low ESL ceramic capacitance is recommended to decouple between the drain of the high-side MOSFET and the source of the low-side MOSFET.
NORMALIZED INPUT RMS RIPPLE CURRENT 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 x=1 x = 0.75 x = 0.50 x = 0.25 x=0
Where: - IVALLEY is the difference of the DC component of the inductor current minus 1/2 of the inductor ripple current - IPEAK is the sum of the DC component of the inductor current plus 1/2 of the inductor ripple current - tON is the time required to drive the device into saturation - tOFF is the time required to drive the device into cut-off
Selecting The Bootstrap Capacitor
The selection of the bootstrap capacitor is written as Equation 26:
Qg C BOOT = ----------------------V BOOT (EQ. 26)
DUTY CYCLE
FIGURE 28. NORMALIZED RMS INPUT CURRENT
Where: - Qg is the total gate charge required to turn on the high-side MOSFET - VBOOT, is the maximum allowed voltage decay across the boot capacitor each time the high-side MOSFET is switched on
MOSFET Selection and Considerations
Typically, a MOSFET cannot tolerate even brief excursions beyond their maximum drain to source voltage rating. The MOSFETs used in the power stage of the converter should have a maximum VDS rating that exceeds the sum of the upper voltage tolerance of the input power source and the voltage spike that occurs when the MOSFET switches off.
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As an example, suppose the high-side MOSFET has a total gate charge Qg, of 25nC at VGS = 5V, and a VBOOT of 200mV. The calculated bootstrap capacitance is 0.125F; for a comfortable margin, select a capacitor that is double the calculated capacitance. In this example, 0.22F will suffice. Use an X7R or X5R ceramic capacitor.
C o
PIN 18 (PVCC) PIN 4 (VCC)
L2 U2
L2
ISL6239 LINE OF SYMMETRY
Layout Considerations
As a general rule, power should be on the bottom layer of the PCB and weak analog or logic signals are on the top layer of the PCB. The ground-plane layer should be adjacent to the top layer to provide shielding. The ground plane layer should have an island located under the IC, the compensation components, and the FSET components. The island should be connected to the rest of the ground plane layer at one point.
VIAS TO VIAS TO GROUND GROUND PLANE GND GND OUTPUT OUTPUT CAPACITORS CAPACITORS SCHOTTKY SCHOTTKY DIODE DIODE LOW-SIDE LOW-SIDE MOSFETS MOSFETS INPUT INPUT CAPACITORS CAPACITORS
Ci
Ci
L1 U1
PGND PLANE PHASE PLANES VOUT PLANES VIN PLANE
L1 C o
FIGURE 30. SYMMETRIC LAYOUT GUIDE
PLANE
VCC (Pin 4) For best performance, place the decoupling capacitor very close to the VCC and GND pins. PVCC (Pin 18) For best performance, place the decoupling capacitor very close to the PVCC and respective PGND pin, preferably on the same side of the PCB as the ISL62391, ISL62392 IC. EN (Pins 11 and 24), and PGOOD (Pin 1)
VOUT
INDUCTOR INDUCTOR HIGH-SIDE HIGH-SIDE MOSFETS MOSFETS PHASE PHASE NODE NODE
VIN VIN
FIGURE 29. TYPICAL POWER COMPONENT PLACEMENT
Because there are two SMPS outputs and only one PGND pin, the power train of both channels should be laid out symmetrically. The line of bilateral symmetry should be drawn through pins 4 and 18. This layout approach ensures that the controller does not favor one channel over another during critical switching decisions. Figure 29 illustrates one example of how to achieve proper bilateral symmetry.
These are logic signals that are referenced to the GND pin. Treat as a typical logic signal. OCSET (Pins 10 and 25) and ISEN (Pins 9 and 26) For DCR current sensing, the current-sense network, consisting of ROCSET and CSEN, needs to be connected to the inductor pads for accurate measurement. Connect ROCSET to the phase-node side pad of the inductor, and connect CSEN to the output side pad of the inductor. The ISEN resistor should also be connected to the output pad of the inductor with a separate trace. Connect the OCSET pin to the common node of node of ROCSET and CSEN. For resistive current sensing, connect ROCSET from the OCSET pin to the inductor side of the resistor pad. The ISEN resistor should be connected to the VOUT side of the resistor pad. In both current-sense configurations, the resistor and capacitor sensing elements, with the exclusion of the current sense power resistor, should be placed near the corresponding IC pin. The trace connections to the inductor or sensing resistor should be treated as Kelvin connections. FB (Pins 7 and 28), and VOUT (Pins 8 and 27) The VOUT pin is used to generate the R3 synthetic ramp voltage and for soft-discharge of the output voltage during shutdown events. This signal should be routed as close to the regulation point as possible. The input impedance of the FB pin is high, so place the voltage programming and loop
Signal Ground and Power Ground
The bottom of the ISL62391, ISL62392 TQFN package is the signal ground (GND) terminal for analog and logic signals of the IC. Connect the GND pad of the ISL62391, ISL62392 to the island of ground plane under the top layer using several vias for a robust thermal and electrical conduction path. Connect the input capacitors, the output capacitors, and the source of the lower MOSFETs to the power ground plane. PGND (Pin 19) This is the return path for the pull-down of the LGATE low-side MOSFET gate driver. Ideally, PGND should be connected to the source of the low-side MOSFET with a low-resistance, low-inductance path. VIN (Pin 17) The VIN pin should be connected close to the drain of the high-side MOSFET, using a low resistance and low inductance path.
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compensation components close to the VOUT, FB, and GND pins, keeping the high impedance trace short. FSET (Pins 2 and 6) This pin requires a quiet environment. The resistor RFSET and capacitor CFSET should be placed directly adjacent to this pin. Keep fast moving nodes away from this pin. LGATE (Pins 15 and 20) The signal going through this trace is both high dv/dt and high di/dt, with high peak charging and discharging current. Route this trace in parallel with the trace from the PGND pin. These two traces should be short, wide, and away from other traces. There should be no other weak signal traces in proximity with these traces on any layer. BOOT (Pins 14 and 21), UGATE (Pins 13 and 22), and PHASE (Pins 12 and 23) The signals going through these traces are both high dv/dt and high di/dt, with high peak charging and discharging current. Route the UGATE and PHASE pins in parallel with short and wide traces. There should be no other weak signal traces in proximity with these traces on any layer.
Copper Size for the Phase Node
The parasitic capacitance and parasitic inductance of the phase node should be kept very low to minimize ringing. It is best to limit the size of the PHASE node copper in strict accordance with the current and thermal management of the application. An MLCC should be connected directly across the drain of the upper MOSFET and the source of the lower MOSFET to suppress the turn-off voltage spike.
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 19
FN6666.4 December 22, 2008
ISL62391, ISL62392
Package Outline Drawing
L28.4x4
28 LEAD THIN QUAD FLAT NO-LEAD PLASTIC PACKAGE Rev 0, 9/06
4 . 00 PIN 1 INDEX AREA A 2 . 50 B 0 . 40 22 21 28 PIN #1 INDEX AREA CHAMFER 0 . 400 X 45
1 0 . 4 x 6 = 2.40 REF
4 . 00
2 . 50
0 . 40
15 0 . 10 2X 14 8
7
0 . 20 0 . 0
TOP VIEW
0 . 4 x 6 = 2 . 40 REF 3 . 20
0 . 10 M C A B
BOTTOM VIEW
SEE DETAIL X'' (3 . 20) PACKAGE BOUNDARY MAX. 0 . 80 SEATING PLANE (28X 0 . 20) 0 . 00 - 0 . 05 0 . 20 REF 0 . 08 C 0 . 10 C C
SIDE VIEW
(2 . 50) (3 . 20)
(0 . 40) C
0 . 20 REF
5
(0 . 40) (2 . 50) (28X 0 . 60)
0 ~ 0 . 05
DETAIL "X" TYPICAL RECOMMENDED LAND PATTERN
NOTES: 1. Controlling dimensions are in mm. Dimensions in ( ) for reference only. 2. Unless otherwise specified, tolerance : Decimal 0.05 Angular 2 3. Dimensioning and tolerancing conform to AMSE Y14.5M-1994. 4. Bottom side Pin#1 ID is diepad chamfer as shown. 5. Tiebar shown (if present) is a non-functional feature.
20
FN6666.4 December 22, 2008
3 . 20

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