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ISL9440, ISL9440A, ISL9441
Data Sheet December 5, 2007 FN6383.1
Triple, 180 Out-of-Phase, Step-Down PWM and Single Linear Controller
The ISL9440, ISL9440A and ISL9441 are quad-output synchronous buck controllers that integrate 3 PWM controllers and 1 low drop-out linear regulator controller, which are full featured and designed to provide multi-rail power for use in products such as cable and satellite set-top boxes, VoIP gateways, cable modems, and other home connectivity products as well as a variety of industrial and general purpose applications. Each output is adjustable down to 0.8V. The PWMs are synchronized at 180 out of phase thus reducing the RMS input current and ripple voltage. The ISL9440, ISL9440A and ISL9441 offer internal soft-start, independent enable inputs for ease of supply rail sequencing, and integrated UV/OV/OC/OT protections in a space conscious 5mmx5mm QFN package. The ISL9440 and ISL9440A offer an early warning function to output a logic signal to warn the system to back up data when input voltage falls below a certain level. The ISL9440, ISL9440A and ISL9441 utilize internal loop compensation to keep minimum peripheral components for compact design and a low total solution cost. These devices are implemented with current mode control with feed forward to cover various applications even with fixed internal compensations. The table below shows the difference in terms of ISL9440, ISL9440A and ISL9441 features.
PART NUMBER ISL9440 ISL9440A ISL9441 EARLY WARNING YES YES NO SWITCHING FREQUENCY (kHz) 300 600 300
Features
* Three Integrated Synchronous Buck PWM Controllers - Internal Bootstrap Diodes - Internal Compensation - Internal Soft-Start * Independent Control for Each Regulator and Programmable Output Voltages; Independent Enable/Shutdown * Fixed Switching Frequency: 300kHz (ISL9440, ISL9441); 600kHz (ISL9440A) * Adaptive Shoot Through Protection on all Synchronous Buck Controllers * Independently Programmable Voltage Outputs * Out-of-Phase Switching to Reduce Input Capacitance (0/180/0) * No External Current Sense Resistor - Uses Lower MOSFET's rDS(ON) * Current Mode Controller with Voltage Feed Forward * Complete Protection - Overcurrent, Overvoltage, Undervoltage Lockout, Over-Temperature * Cycle by Cycle Current Limiting * Wide Input Voltage Range - Input Rail Powers VIN Pin: 5.6V to 24V - Input Rail Powers VCC_5V Pin (VIN tied to VCC_5V, for 5V input applications): 4.5V to 5.6V * Early Warning (ISL9440, ISL9440A) on Input Voltage Failure * Integrated Reset Function (ISL9440, ISL9440A) * Pb-free (RoHS compliant)
Applications
* Satellite and Cable Set-Top Boxes * Cable Modems * VoX Gateway Devices * NAS/SAN Devices
Related Literature
* Technical Brief TB389 "PCB Land Pattern Design and Surface Mount Guidelines for QFN (MLFP) Packages"
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. 2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
ISL9440, ISL9440A, ISL9441 Ordering Information
PART NUMBER (Note) ISL9440IRZ* PART MARKING ISL9440IRZ TEMP. RANGE (C) PACKAGE (Pb-Free) PKG. DWG. #
PHASE1
Pinout
ISL9440, ISL9440A, ISL9441 (32 LD 5X5 QFN) TOP VIEW
PHASE2 25 24 ISEN2 23 PGND 22 LGATE3 21 UGATE3 20 BOOT3 19 PHASE3 18 ISEN3 17 EN3 9 G4 10 LDOFB 11 SGND 12 OCSET2 13 FB2 14 EN2 15 OCSET3 16 FB3
FN6383.1 December 5, 2007
UGATE1
BOOT1
ISL9440AIRZ* 9440AIRZ ISL9441IRZ* ISL9441IRZ
-40 to +85 32 Ld 5x5 QFN L32.5x5B -40 to +85 32 Ld 5x5 QFN L32.5x5B
ISEN1 PGOOD VCC_5V VIN EN1 FB1 OCSET1 RST 1 2 3 4 5 6 7 8
32
31
30
29
28
27
26
*Add "-T" for tape and reel. 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.
2
BOOT2
-40 to +85 32 Ld 5x5 QFN L32.5x5B
UGATE2
LGATE1
LGATE2
Block Diagram
BOOT1 VCC_5V UGATE1 PHASE1 ADAPTIVE DEAD-TIME VCC_5V LGATE1 POR PGND ENABLE BIAS SUPPLIES 0.8V REFERENCE G4
gm*VE
PGOOD
RST
VCC_5V VIN PGND
EN1
EN2
EN3 VCC_5V
BOOT2 UGATE2 PHASE2 ADAPTIVE DEAD-TIME V/I SAMPLE TIMING VCC_5V LGATE2
V/I SAMPLE TIMING
3
FB4 FB1 180k + 0.8V REF ISEN1 CURRENT SAMPLE OCSET1
PGND BOOT3 VCC_5V UGATE3
+
VE
REFERENCE FAULT LATCH
+
SOFT-START EARLY WARNING (see note 6) ADAPTIVE DEAD-TIME V/I SAMPLE TIMING
PHASE3
VCC_5V LGATE3
1400k
18.5pF
OCP
PGOOD
PGND
16k
+
ERROR AMP 1
+
PWM1
OC1 OC2 OC3
UV/OV
UV PWM3 FB3
FB1 FB2 FB3 FB4
VIN
ISEN3
OCSET3 OC3 DUTY CYCLE RAMP GENERATOR PWM CHANNEL PHASE CONTROL PWM2 FB2
CHANNEL 3
+
CURRENT SAMPLE
+
1.75V REFERENCE
ISEN2
+
FN6383.1 December 5, 2007
OC1 SAME STATE FOR 2 CLOCK CYCLES REQUIRED TO LATCH OVERCURRENT FAULT
OC2
OCSET2
CHANNEL 2
VIN SGND VCC_5V
CHANNEL 1
ISL9440, ISL9440A, ISL9441 Typical Application - ISL9440, ISL9441
+12V + C2 4.7F C16 1F VIN 4 C3 10F C7 0.1F BOOT1 VCC_5V 3 C6 10F C8 0.1F C1 56F
31
26
BOOT2
UGATE1 30 PHASE1 32
27 25 24
UGATE2 PHASE2 ISEN2 R4 8.45k
VOUT1 +2.5V, 6A C9 330F + + C14 330F
L1 3.3H
R3 8.45k
ISEN1
L2 2.2H + C15 + C10 330F 330F
1
VOUT2 +1.5V, 6A R5 4.02k
LGATE1
R1 10.2k
Q1
IRF7907
29
28 LGATE2 13 FB2 Q2 IRF7907
FB1 R2 4.75k C11 0.01F
6 +12V ISL9440/ISL9441 BOOT3 C81 0.1F C61 1F R6 4.53k
VOUT3 +5V
R12 100 VOUT4 +3.3V, 500mA C12 + 68F R10 15k Q4 IRF7404
G4
20 9 21 19
UGATE3 PHASE3 ISEN3 R41 2.8k
LDOFB
10 18
L3 15H + C13 330F R51 24.3k
VOUT3 +5V, 2A R52 100 C52 2.2nF
R11 4.75k OCSET1 7 OCSET2 12 OCSET3 15
22 LGATE3 16 FB3 V VCC_5V R91 10k 8 RST RST V VCC_5V R9 10K 2 5 14 17 23 11 PGOOD Q3 IRF7907
R71 301k R72 301k R73 261k
R61 4.53k
PGOOD
EN1 EN2 EN3
PGND SGND
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FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441 Typical Application - ISL9440A
+12V + C2 4.7F C16 1F VIN 4 C3 10F C7 0.1F BOOT1 VCC_5V 3 C6 10F C8 0.1F C1 56F
31
26
BOOT2
UGATE1 30 PHASE1 32
27 25 24
UGATE2 PHASE2 ISEN2 R4 8.45k
VOUT1 +2.5V, 6A C9 330F + C14 330F +
L1 1.8H
R3 8.45k
ISEN1 1
L2 1.2H + C15 + C10 330F 330F
VOUT2 +1.5V, 6A R5 4.02k
LGATE1
R1 10.2k
Q1
IRF7907
29
28 LGATE2 13 FB2 Q2 IRF7907
FB1 R2 4.75k C11 0.01F
6 +12V ISL9440A BOOT3 C81 0.1F C61 1F R6 4.53k
VOUT3 +5V
R12 100 VOUT4 +3.3V, 500mA C12 + 68F R10 15k Q4 IRF7404
G4
20 9 21 19
UGATE3 PHASE3 ISEN3 R41 2.8k
LDOFB
10 18
L3 8.2H + C13 330F R51 24.3k
VOUT3 +5V, 2A
R11 4.75k OCSET1 7 OCSET2 12 OCSET3 15
22 LGATE3 16 FB3 V VCC_5V R91 10k 8 RST RST V VCC_5V R9 10K 2 5 14 17 23 11 PGOOD Q3 IRF7907
R71 301k R72 301k R73 261k
R61 4.53k
PGOOD
EN1 EN2 EN3
PGND SGND
5
FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441
Absolute Maximum Ratings
VCC_5V to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V VCC_5V Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100mA VIN to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +28V BOOT/UGATE to PHASE . . . . . . . . . . . . . -0.3V to VCC_5V + 0.3V PHASE1,2,3 and ISEN1, 2,3, to GND . . . . . . . . . . . . . . . . . . . . .-5V (<100ns, 10J)/-0.3V (DC) to +28V EN1,EN2, EN3, FB1, FB2, FB3, to GND . . -0.3V to VCC_5V + 0.3V LDOFB, OCSET1, OCSET2, OCSET3, LGATE1, LGATE2, LGATE3, to GND. . . -0.3V to VCC_5V + 0.3V PGOOD, RST, G4 to GND . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V ESD Rating Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2000V Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .200V
Thermal Information
Thermal Resistance (Typical) JA(oC/W) JC(oC/W) 32 Ld QFN Package (Note 1). . . . . . . . 34 3.5 Maximum Junction Temperature . . . . . . . . . . . . . . .-55C to +150C Maximum Operating Temperature . . . . . . . . . . . . . . .-40C to +85C Maximum Storage Temperature. . . . . . . . . . . . . . . .-65C to +150C Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp
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.
NOTE: 1. JA is measured in free air with the component mounted on a high effective thermal conductivity test board with "direct attach" features. See Tech Brief TB379.
Electrical Specifications
Recommended operating conditions unless otherwise noted. Refer to Block Diagram and Typical Application Schematic. VIN = 5.6V to 24V, or VCC_5V = 5V 10%, C_VCC_5V = 4.7F, TA = -40C to +85C (Note 5), Typical values are at TA = +25C, unless otherwise specified. TEST CONDITIONS MIN TYP MAX UNITS
PARAMETER VIN SUPPLY Input Voltage Range Input Voltage Range VCC_5V SUPPLY (Note 2) Operation Voltage Internal LDO Output Voltage Maximum Supply Current of Internal LDO VIN SUPPLY CURRENT Shutdown Current (Note 3) Operating Current (Note 4) REFERENCE SECTION Internal Reference Voltage Reference Voltage Accuracy PWM CONTROLLER ERROR AMPLIFIERS DC Gain (Note 5) Gain-BW Product (Note 5) Slew Rate (Note 5) PWM REGULATOR Switching Frequency (ISL9440, ISL9441) Maximum Duty Cycle (ISL9440, ISL9441) Minimum Duty Cycle (ISL9440, ISL9441) Switching Frequency (ISL9440A) Maximum Duty Cycle (ISL9440A)
5.6 VIN = VCC_5V (Note 6) 4.5
12.0 5.0
24.0 5.6
V V
4.5 VIN > 5.6V, IL = 60mA VIN = 12V 4.5 60
5.0 5.0
5.6 5.5
V V mA
EN = EN2 = EN3 = 0, VIN =12V
50 3
100 5
A mA
Across specified temperature range Across specified temperature range -1
0.8 +1
V %
88 15 2.0
dB MHz V/s
260
300 93 3
340
kHz % %
522
600 86
678
kHz %
6
FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441
Electrical Specifications
Recommended operating conditions unless otherwise noted. Refer to Block Diagram and Typical Application Schematic. VIN = 5.6V to 24V, or VCC_5V = 5V 10%, C_VCC_5V = 4.7F, TA = -40C to +85C (Note 5), Typical values are at TA = +25C, unless otherwise specified. (Continued) TEST CONDITIONS MIN TYP 6 50 VIN = 12V VIN = 5.5V Ramp Offset Soft-start Period PWM GATE DRIVER CHANNEL 1, 2 (UGATE1, 2; LGATE 1, 2) (Note 5) Source Current Sink Current Upper Drive Pull-Up Upper Drive Pull-Down Lower Drive Pull-Up Lower Drive Pull-Down Rise Time Fall Time PWM GATE DRIVER CHANNEL 3 (UGATE3; LGATE 3) (Note 5) Sink/Source Current Upper Drive Pull-Up Upper Drive Pull-Down Lower Drive Pull-Up Lower Drive Pull-Down Rise Time Fall Time LOW DROP OUT CONTROLLER Drive Sink Current FB Threshold Voltage Amplifier Trans-conductance LDOFB Input Leakage Current (Note 5) ENABLE1, ENABLE2, ENABLE3 THRESHOLD Enable Pin Logic Input Low Enable Pin Logic Input High POWER GOOD MONITORS PGOOD Upper Threshold, PWM 1, 2 and 3 PGOOD Lower Threshold, PWM 1, 2 and 3 PGOOD for Linear Controller PGOOD Low Level Voltage PGOOD Leakage Current I_SINK = 4mA PGOOD = 5V 0.025 105.5 87 70 111 91 75 115.5 96 80 0.4 1 % % % V A 2.0 0.8 V V LDOFB = 0.8V LDOFB = 0.76V IG4 = 21mA 50 0.800 2 50 mA V A/V nA VCC_5V = 5.0V VCC_5V = 5.0V VCC_5V = 5.0V VCC_5V = 5.0V COUT = 1000pF COUT = 1000pF 400 8.0 3.2 8 1.8 18 18 12 6.0 12 3.5 mA ns ns VCC_5V = 5.0V VCC_5V = 5.0V VCC_5V = 5.0V VCC_5V = 5.0V COUT = 1000pF COUT = 1000pF 800 2000 4 1.6 4 0.9 18 18 8 3 8 2 mA mA ns ns 1.1 1.6 0.667 1 1.7 2.3 MAX UNITS % nA V V V ms
PARAMETER Minimum Duty Cycle (ISL9440A) FB Bias Current (Note 5) Peak-to-Peak Saw-tooth Amplitude (Note 5)
7
FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441
Electrical Specifications
Recommended operating conditions unless otherwise noted. Refer to Block Diagram and Typical Application Schematic. VIN = 5.6V to 24V, or VCC_5V = 5V 10%, C_VCC_5V = 4.7F, TA = -40C to +85C (Note 5), Typical values are at TA = +25C, unless otherwise specified. (Continued) TEST CONDITIONS RPULLUP = 10k to 3.3V RPULLUP = 10k to 3.3V MIN TYP 0.05 0.05 MAX UNITS s s
PARAMETER PGOOD Rise Time PGOOD Fall Time EARLY WARNING FUNCTIONS Undervoltage Lockout Rising (VCC_5V Pin) Undervoltage Lockout Falling (VCC_5V Pin) Early Warning Voltage Rising (VIN Pin; ISL9440, ISL9440A only) Early Warning Voltage Falling (VIN Pin; ISL9440, ISL9440A only) RST RST Voltage Low RST Leakage Current RST Rise Time RST Fall Time PGOOD/RST TIMING RISING VIN/VOUT Rising Threshold to PGOOD High Rising PGOOD Rising to RST Rising PGOOD/RST TIMING FALLING VIN/VOUT Falling Threshold to PGOOD Falling PGOOD Falling to RST Falling OVER VOLTAGE PROTECTION OV Trip Point OVER CURRENT PROTECTION Overcurrent Threshold (OCSET_) (Note 5) Full Scale Input Current (ISEN_) (Note 5) Overcurrent Set Voltage (OCSET_) OVER-TEMPERATURE Over-Temperature Shutdown Over-Temperature Hysteresis NOTES:
4.25 3.95
4.45 4.20 5.75
4.50 4.40 5.90
V V V V
5.30
5.55
I_SINK = 4mA RST = 5V RPULLUP = 10k to 3.3V RPULLUP = 10k to 3.3V 0.025 0.05 0.05
0.4 1
V A s s
100
200 1.0
300
ms s
40 4.5
70 5.5
100 6.5
s s
118
%
ROCSET = 55k
32 15 1.70 1.75 1.80
A A V
150 20
C C
2. In normal operation, where the device is supplied with voltage on the VIN pin, the VCC_5V pin provides a 5V output capable of 60mA (min). When the VCC_5V pin is used as a 5V supply input, the internal LDO regulator is disabled and the VIN input pin must be connected to the VCC_5V pin. (Refer to the Pin Descriptions section for more details.) 3. This is the total shutdown current with VIN = 5.6 and 24V. 4. Operating current is the supply current consumed when the device is active but not switching. It does not include gate drive current. 5. Limits established by characterization and are not production tested. 6. Check Note 2 for VCC_5V and VIN configurations at 5V 10% input applications. ISL9440, ISL9440A's PGOOD signal will fall LOW when VIN pin voltage drops below 5.55V (TYP), which results from the early warning detection on VIN pin voltage. ISL9441 doesn't have an early warning function, so when VIN pin voltage is below 5.55V, PGOOD will not be pulled LOW; ISL9441's PGOOD only shows the output voltage regulation status.
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FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441 Pin Descriptions
BOOT3, BOOT2, BOOT1 (Pin 20, 26, 31)
These pins are bootstrap pins to provide bias for high side driver. The bootstrap diodes are integrated to help reduce total cost and reduce layout complexity.
VIN (Pin 4)
Use this pin to power the device with an external supply voltage with a range of 5.6V to 24V. For 5V 10% operation, connect this pin to VCC_5V. For ISL9440 and ISL9440A, the voltage on this pin is monitored for early warning function. If the voltage on this pin drop below 5.55V, the PGOOD will be pulled low. RST will be low after PGOOD toggles to low for 5.5s (TYP). Refer to Figure 1 for detailed time sequence. ISL9441 doesn't have early warning functions, which means the VIN pin voltage is not monitored.
UGATE3, UGATE2, UGATE1 (Pin 21, 27, 30)
These pins provide the gate drive for the upper MOSFETs.
PHASE3, PHASE2, PHASE1 (Pin 19, 25, 32)
These pins are connected to the junction of the upper MOSFET's source, output filter inductor, and lower MOSFET's drain.
VCC_5V (Pin 3)
This pin is the output of the internal 5V linear regulator. This output supplies the bias for the IC, the low side gate drivers, and the external boot circuitry for the high side gate drivers. The IC may be powered directly from a single 5V (10%) supply at this pin. When used as a 5V supply input, this pin must be externally connected to VIN. The VCC_5V pin must be always decoupled to power ground with a minimum of 4.7F ceramic capacitor, placed very close to the pin.
LGATE3, LGATE2, LGATE1 (Pin 22, 28, 29)
These pins provide the gate drive for the lower MOSFETs.
PGND (Pin 23)
This pin provides the power ground connection for the lower gate drivers for all PWM1, PWM2 and PWM3. This pin should be connected to the sources of the lower MOSFETs and the (-) terminals of the external input capacitors.
FB3, FB2, FB1, LDOFB (Pin 16, 13, 6, 10)
These pins are connected to the feedback resistor divider and provide the voltage feedback signals for the respective controller. They set the output voltage of the converter. In addition, the PGOOD circuit uses these inputs to monitor the output voltage status.
EN3, EN2, EN1 (Pin 17, 14, 5)
These pins provide an enable/disable function for their respective PWM output. The output is enabled when this pin is floating or pulled HIGH, and disabled when the pin is pulled LOW.
ISEN3, ISEN2, ISEN1 (Pin 18, 24, 1)
These pins are used to monitor the voltage drop across the lower MOSFET for current loop feedback and overcurrent protection.
G4 (Pin 9)
This pin is the open drain output of the linear regulator controller.
OCSET3, OCSET2, OCSET1 (Pin 15, 12, 7)
A resistor from this pin to ground sets the overcurrent threshold for the respective PWM.
PGOOD (Pin 2)
This is an open drain logic output used to indicate the status of the output voltages AND input voltage (voltage on VIN pin; early warning for ISL9440 and ISL9440A). This pin is pulled low when either of the three PWM outputs is not within 10% of the respective nominal voltage, or if the linear controller output is less than 75% of it's nominal value, or VIN pin voltage drops below 5.55V. ISL9440 and ISL9440A's PGOOD pin also indicates the VIN pin status for early warning function. If the voltage on VIN pin drops below 5.55V, this pin will be pulled low.
RST (Pin 8)
Reset pulse output. This pin outputs a logic LOW signal after PGOOD toggles to low for 5.5s (TYP). It can be used to reset system. Refer to Figure 1 for detailed time sequence of ISL9440 and ISL9440A with early warning function. ISL9441 doesn't have early warning functions, which means the VIN pin voltage is not monitored. But RST still output LOW signal following PGOOD LOW.
SGND (Pin 11)
This is the small-signal ground, common to all 4 controllers, and are suggested to be routed separately from the high current ground (PGND). In case of one whole solid ground and no noisy current going through around chip, SGND and PGND can be tied to the same ground copper plane. All voltage levels are measured with respect to this pin. A small ceramic capacitor should be connected right next to this pin for noise decoupling.
9
FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441
8 7 6 VOLTAGE (V) 5 4 3 2 1 0 0 5 10 MAX = 6.5s TIME (NOT TO SCALE) MAX = 100s 2.4V MAX = 2s 0.4V 15 20 25 PGOOD VIN = 5.5V RISING/ VIN = 5.5V RISING/ VOUT 1-4 IN REGULATION VOUT 1-4 IN REGULATION TYP = 200ms RST
VIN = 5.5V FALLING/ VOUT 1-4 OUT OF REGULATION
VIN/VOUT
FIGURE 1. PGOOD AND RST TIMING
Typical Performance Curves
(Oscilloscope Plots are Taken Using the ISL9440EVAL1Z Evaluation Board, VIN = 12V Unless Otherwise Noted.)
2.55 2.54 OUTPUT VOLTAGE (V) 2.53 EFFICIENCY (%) 1.0 2.0 3.0 4.0 5.0 6.0 7.0 2.52 2.51 2.50 2.49 2.48 2.47 2.46 2.45 0.0 65 60 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 90 85 80 75 70 95
LOAD CURRENT (A)
LOAD CURRENT (A)
FIGURE 2. PWM1 LOAD REGULATION
FIGURE 3. PWM1 EFFICIENCY vs LOAD (VO = 2.5V), VIN = 12V, 1 DUAL SO-8 MOSFET (IRF7907) FOR UPPER AND LOWER MOSFETS
1.55 1.54 OUTPUT VOLTAGE (V) 1.53 EFFICIENCY (%) 1.0 2.0 3.0 4.0 5.0 6.0 7.0 1.52 1.51 1.50 1.49 1.48 1.47 1.46 1.45 0.0
90 85 80 75 70 65 60 0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
LOAD CURRENT (A)
LOAD CURRENT (A)
FIGURE 4. PWM2 LOAD REGULATION
FIGURE 5. PWM2 EFFICIENCY vs LOAD (VO = 1.5V), VIN = 12V, 1 DUAL SO-8 MOSFET (IRF7907) FOR UPPER AND LOWER MOSFETS
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FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441 Typical Performance Curves
5.10 5.10 OUTPUT VOLTAGE (V) 5.09 EFFICIENCY (%) 5.09 5.08 5.08 5.07 5.07 5.06 5.06 5.05 0.0 1.0 2.0 LOAD CURRENT (A) 3.0 4.0 65 60 0. 0 1.0 2.0 LOAD CURRENT (A) 3.0 4. 0
(Continued)
(Oscilloscope Plots are Taken Using the ISL9440EVAL1Z Evaluation Board, VIN = 12V Unless Otherwise Noted.)
100 95 90 85 80 75 70
FIGURE 6. PWM3 LOAD REGULATION
FIGURE 7. PWM3 EFFICIENCY vs LOAD (VO = 5V), VIN = 12V, 1 DUAL SO-8 MOSFET (IRF7907) FOR UPPER AND LOWER MOSFETS
VOUT1 50mV/DIV, AC COUPLED
VOUT3 1V/DIV
VOUT2 50mV/DIV, AC COUPLED
VOUT4 (LDO) 1V/DIV
VOUT3 50mV/DIV, AC COUPLED
VOUT1 1V/DIV
VOUT2 1V/DIV
VOUT4 50mV/DIV, AC COUPLED
0.2ms/DIV
5s/DIV
FIGURE 8. PWM SOFT-START WAVEFORMS
FIGURE 9. OUTPUT RIPPLE UNDER MAXIMUM LOAD (IO1 = IO1 = 6A, IO3 = 2A, IO4 = 0.5A)
VIN, 1V/DIV, CH1 VIN, 1V/DIV, CH1
RST, 5V/DIV, CH3 CH1 RST, 5V/DIV, CH3 CH3
CH3 PGOOD, 5V/DIV, CH4 CH4 CH4 100s/DIV CH1 10s/DIV
PGOOD, 5V/DIV, CH4
FIGURE 10. VIN FALLING TO PGOOD FALLING DELAY TIME
FIGURE 11. PGOOD FALLING TO RST FALLING
11
FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441 Typical Performance Curves
(Continued)
(Oscilloscope Plots are Taken Using the ISL9440EVAL1Z Evaluation Board, VIN = 12V Unless Otherwise Noted.)
VOUT1, 100mV/DIV, 0A to 6A, 1.6A/s
VIN, 1V/DIV, CH1
VOUT2, 100mV/DIV, 0A to 6A, 1.6A/s
CH3
RST, 1V/DIV, CH3
VOUT3, 100mV/DIV, 0A to 2A, 1A/s
PGOOD, 5V/DIV, CH4
VOUT4 (LDO), 100mV/DIV, 0A to 0.5A, 1A/s
CH4 CH1 500ns/DIV
500s/DIV
FIGURE 12. PGOOD RISING TO RST RISING
FIGURE 13. OUTPUT RIPPLE UNDER TRANSIENT LOAD
PWM1, 5V/DIV
Vo1, 1V/DIV
PWM2, 5V/DIV
Vo2, 1V/DIV
Vo3, 1V/DIV 5ms/DIV
PWM3, 5V/DIV 1s/DIV
FIGURE 14. THREE CHANNEL HARD-SHORT OCP AT THE SAME TIME
FIGURE 15. PHASE NODE PWM WAVEFORMS, VIN = 24V
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FN6383.1 December 5, 2007
ISL9440, ISL9440A, ISL9441 Functional Description
General Description
The ISL9440, ISL9440A and ISL9441 integrate control circuits for three synchronous buck converters and one linear controller. The three synchronous bucks operate out of phase to substantially reduce the input ripple and thus reduce the input filter requirements. The chip has 3 control lines (EN1, EN2 and EN3), which provide independent control for each of the synchronous buck outputs. The buck PWM controllers employ free-running frequency of 300kHz (ISL9440 and ISL9441) and 600kHz (ISL9440A). The current mode control scheme with an input voltage feedforward ramp input to the modulator provides an excellent rejection of input voltage variations and provides simplified loop compensations. The linear controller can drive either a PNP or PFET to provide ultra low-dropout regulation with programmable voltages. start is done and all the four outputs are up and in regulations.
Output Voltage Programming
The ISL9440, ISL9440A and ISL9441 use a precision internal reference voltage to set the output voltage. Based on this internal reference, the output voltage can thus be set from 0.8V up to a level determined by the input voltage, the maximum duty cycle, and the conversion efficiency of the circuit. A resistive divider from the output to ground sets the output voltage of either PWM channel. The center point of the divider shall be connected to FBx pin. The output voltage value is determined by Equation 1.
R1 + R2 V OUTx = 0.8V --------------------- R2 (EQ. 1)
where R1 is the top resistor of the feedback divider network and R2 is the resistor connected from FBx to ground.
Internal 5V Linear Regulator (VCC_5V)
All ISL9440, ISL9440A and ISL9441 functions are internally powered from an on-chip, low dropout 5V regulator. The maximum regulator input voltage is 24V. Bypass the regulator's output (VCC_5V) with a 4.7F capacitor to ground. The dropout voltage for this LDO is typically 600mV, so when VIN is greater than 5.6V, VCC_5V is typically 5V. The ISL9440, ISL9440A and ISL9441 also employ an undervoltage lockout circuit that disables both regulators when VCC_5V falls below 4.4V. The internal LDO can source over 60mA to supply the IC, power the low side gate drivers and charge the external boot capacitor. When driving large FETs especially at 300kHz (ISL9440, ISL9441)/600kHz (ISL9440A) frequency, little or no regulator current may be available for external loads. For example, a single large FET with 15nC total gate charge requires 15nC x 300kHz = 4.5mA (15nC x 600kHz = 9mA). Also, at higher input voltages with larger FETs, the power dissipation across the internal 5V will increase. Excessive dissipation across this regulator must be avoided to prevent junction temperature rise. Larger FETs can be used with 5V 10% input applications. The thermal overload protection circuit will be triggered, if the VCC_5V output is short-circuit. Connect VCC_5V to VIN for 5V 10% input applications.
Out-of-Phase Operation
To reduce input ripple current, Channel 1 and Channel 2 operate 180 out-of-phase, Channel 3 keeps 0 phase degree with Channel 1. Channel 1 and Channel 2 typically output higher load compared to Channel 3 because of their stronger drivers. This reduces the input capacitor ripple current requirements, reduces power supply-induced noise, and improves EMI. This effectively helps to lower component cost, save board space and reduce EMI. Triple PWMs typically operate in-phase and turn on both upper FETs at the same time. The input capacitor must then support the instantaneous current requirements of the three switching regulators simultaneously, resulting in increased ripple voltage and current. The higher RMS ripple current lowers the efficiency due to the power loss associated with the ESR of the input capacitor. This typically requires more low-ESR capacitors in parallel to minimize the input voltage ripple and ESR-related losses, or to meet the required ripple current rating. With synchronized out-of-phase operation, the high-side MOSFETs turn on 180 out-of-phase. The instantaneous input current peaks of both regulators no longer overlap, resulting in reduced RMS ripple current and input voltage ripple. This reduces the required input capacitor ripple current rating, allowing fewer or less expensive capacitors, and reducing the shielding requirements for EMI. The typical operating curves show the synchronized 180 out-of-phase operation.
Digital Enable Signals
The typical applications for the ISL9440, ISL9440A and ISL9441 are using digital sequencing controllers for the power rails. Using a digital enable rather than an analog softstart provides a well controlled method for sequencing up and down on the power rails.
Input Voltage Range
The ISL9440, ISL9440A and ISL9441 are designed to operate from input supplies ranging from 4.5V to 24V. For 5V 10% input applications, ISL9441 is suggested. The reason is that VIN and VCC_5V Pin should be tied together for this input application. The early warning function will pull PGOOD and RST low for ISL9440 and ISL9440A. ISL9441 has not been implemented with early warning function.
FN6383.1 December 5, 2007
Soft-Start Operation
The ISL9440, ISL9440A and ISL9441 have a fixed soft-start time, 1.7ms (TYP). PGOOD will not toggle to high until soft-
13
ISL9440, ISL9440A, ISL9441
The input voltage range can be effectively limited by the available maximum duty cycle (DMAX = 93% for ISL9440 and ISL9441, DMAX = 86% for ISL9440A).
V OUT + V d1 V IN ( min ) = -------------------------------- + V d2 - V d1 0.93 (EQ. 2)
BOOT UGATE PHASE
VCC_5V
VIN
where, Vd1 = Sum of the parasitic voltage drops in the inductor discharge path, including the lower FET, inductor and PC board. Vd2 = Sum of the voltage drops in the charging path, including the upper FET, inductor and PC board resistances. The maximum input voltage and minimum output voltage is limited by the minimum on-time (tON(min)).
V OUT V IN ( max ) --------------------------------------------------t ON ( min ) x 300kHz (EQ. 3)
ISL9440, ISL9440A, ISL9441
FIGURE 16.
where, tON(min) = 30ns
Gate Control Logic
The gate control logic translates generated PWM signals into gate drive signals providing amplification, level shifting and shoot-through protection. The gate drivers have some circuitry that helps optimize the IC performance over a wide range of operational conditions. As MOSFET switching times can vary dramatically from type to type and with input voltage, the gate control logic provides adaptive dead time by monitoring real gate waveforms of both the upper and the lower MOSFETs. Shoot-through control logic provides a 20ns dead-time to ensure that both the upper and lower MOSFETs will not turn on simultaneously and cause a shoot-through condition.
At start-up, the low-side MOSFET turns on and forces PHASE to ground in order to charge the BOOT capacitor to 5V. After the low-side MOSFET turns off, the high-side MOSFET is turned on by closing an internal switch between BOOT and UGATE. This provides the necessary gate-tosource voltage to turn on the upper MOSFET, an action that boosts the 5V gate drive signal above VIN. The current required to drive the upper MOSFET is drawn from the internal 5V regulator.
Adaptive Dead Time
The ISL9440, ISL9440A and ISL9441 incorporate an adaptive dead time algorithm on the synchronous buck PWM controllers that optimizes operation with varying MOSFET conditions. This algorithm provides an approximately 20ns of dead time between switching the upper and lower MOSFET's. This dead time is adaptive and allows operation with different MOSFET's without having to externally adjust the dead time using a resistor or capacitor. During turn-off of the lower MOSFET, the LGATE voltage is monitored until it reaches a 1V threshold, at which time the UGATE is released to rise. Adaptive dead time circuitry monitors the upper MOSFET gate voltage during UGATE turn-off. Once the upper MOSFET gate-to-source voltage has dropped below a threshold of 1V, the LGATE is allowed to rise.
Gate Drivers
The low-side gate driver is supplied from VCC_5V and provides a peak sink current of 2A/2A/200mA and source current of 800mA/800mA/400mA for Channels 1/2/3 respectively. The high-side gate driver is also capable of delivering the same current as those in low-side gate driver. Gate-drive voltages for the upper N-Channel MOSFET are generated by the flying capacitor boot circuit. A boot capacitor connected from the BOOT pin to the PHASE node provides power to the high side MOSFET driver. To limit the peak current in the IC, an external resistor may be placed between the UGATE pin and the gate of the external MOSFET. This small series resistor also damps any oscillations caused by the resonant tank of the parasitic inductances in the traces of the board and the FET's input capacitance.
Internal Bootstrap Diode
The ISL9440, ISL9440A and ISL9441 have integrated bootstrap diodes to help reduce total cost and reduce layout complexity. Simply adding an external capacitor across the BOOT and PHASE pins completes the bootstrap circuit. The bootstrap capacitor must have a maximum voltage rating above the maximum battery voltage plus 5V. The bootstrap capacitor can be chosen from Equation 4.
Q GATE C BOOT ----------------------V BOOT (EQ. 4)
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Where QGATE is the amount of gate charge required to fully charge the gate of the upper MOSFET. The VBOOT term is defined as the allowable droop in the rail of the upper drive. As an example, suppose an upper MOSFET has a gate charge (QGATE) of 25nC at 5V and also assume the droop in the drive voltage over a PWM cycle is 200mV. One will find that a bootstrap capacitance of at least 0.125F is required. The next larger standard value capacitance is 0.22F. A good quality ceramic capacitor is recommended.
Overvoltage Protection
All switching controllers within the ISL9440, ISL9440A and ISL9441 have fixed overvoltage set points. The overvoltage set point is set at 118% of the output voltage set by the feedback resistors. In the case of an overvoltage event, the IC will attempt to bring the output voltage back into regulation by keeping the upper MOSFET turned off and modulating the lower MOSFET for 2 consecutive PWM cycles. If the overvoltage condition has not been corrected in 2 cycles, the ISL9440, ISL9440A and ISL9441 will turn on the lower MOSFET until the overvoltage has been cleared, or the power path is interrupted by opening a fuse.
Protection Circuits
The converter output is monitored and protected against overload, short circuit and undervoltage conditions. A sustained overload on the output sets the PGOOD low and initiates hiccup mode.
Over-Temperature Protection
The IC incorporates an over-temperature protection circuit that shuts the IC down when a die temperature of +150C is reached. Normal operation resumes when the die temperatures drops below +130C through the initiation of a full soft-start cycle.
Undervoltage Lockout
The ISL9440, ISL9440A and ISL9441 include UVLO protection that will keep the devices in a reset condition until a proper operating voltage is applied and that will also shut down the ISL9440, ISL9440A and ISL9441 if the operating voltage drops below a pre-defined value. All controllers are disabled when UVLO is asserted. When UVLO is asserted, PGOOD will be valid and de-asserted.
Feedback Loop Compensation
To reduce the number of external components and to simplify the process of determining compensation components, all PWM controllers have internally compensated error amplifiers. To make internal compensation possible several design measures were taken. First, the ramp signal applied to the PWM comparator is proportional to the input voltage provided via the VIN pin. This keeps the modulator gain constant with variation in the input voltage. Second, the load current proportional signal is derived from the voltage drop across the lower MOSFET during the PWM time interval and is subtracted from the amplified error signal on the comparator input. This creates an internal current control loop. The resistor connected to the ISEN pin sets the gain in the current feedback loop. The following expression estimates the required value of the current sense resistor depending on the maximum operating load current and the value of the MOSFET's rDS(ON).
( I MAX ) ( r DS ( ON ) ) R CS ---------------------------------------------15A (EQ. 6)
Overcurrent Protection
All the PWM controllers use the lower MOSFET's on-resistance, rDS(ON) , to monitor the current in the converter. The sensed voltage drop is compared with a threshold set by a resistor connected from the OCSETx pin to ground.
( 7 ) ( R CS ) R OCSET = -----------------------------------------( I OC ) ( r DS ( ON ) ) (EQ. 5)
where, IOC is the desired overcurrent protection threshold, and RCS is a value of the current sense resistor connected to the ISENx pin. If an overcurrent is detected for 2 consecutive clock cycles then the IC enters a hiccup mode by turning off the gate drivers and entering into soft-start. The IC will cycle 4 times through soft-start before trying to restart. The IC will continue to cycle through soft-start until the overcurrent condition is removed. Hiccup mode is active during soft-start so care must be taken to ensure that the peak inductor current does not exceed the overcurrent threshold during soft-start. Because of the nature of this current sensing technique, and to accommodate a wide range of rDS(ON) variations, the value of the overcurrent threshold should represent an overload current about 150% to 180% of the maximum operating current. If more accurate current protection is desired, place a current sense resistor in series with the lower MOSFET source.
Choosing RCS to provide 15A of current to the current sample and hold circuitry is recommended but values down to 2A and up to 100A can be used. The higher sampling current will help to stabilize the loop. Due to the current loop feedback, the modulator has a single pole response with -20dB slope at a frequency determined by the load.
1 F PO = -------------------------------2 R O C O (EQ. 7)
where RO is load resistance and CO is load capacitance. For this type of modulator, a Type 2 compensation circuit is usually sufficient.
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Figure 17 shows a Type 2 amplifier and its response along with the responses of the current mode modulator and the converter. The Type 2 amplifier, in addition to the pole at origin, has a zero-pole pair that causes a flat gain region at frequencies in between the zero and the pole.
1 F Z = ------------------------------ = 6kHz 2 R 2 C 1 1 F P = ------------------------------ = 600kHz 2 R 1 C 2
C2 R2 CONVERTER R1 EA TYPE 2 EA GM = 17.5dB
MODULATOR
(EQ. 8)
input, the controller sinks 21mA of current. An external PNP transistor or PFET pass element can be used. The dominant pole for the loop can be placed at the base of the PNP (or gate of the PFET), as a capacitor from emitter to base (source to gate of a PFET). Better load transient response is achieved however, if the dominant pole is placed at the output, with a capacitor to ground at the output of the regulator. Under no-load conditions, leakage currents from the pass transistors supply the output capacitors, even when the transistor is off. Generally this is not a problem since the feedback resistor drains the excess charge. However, charge may build up on the output capacitor making VLDO rise above its set point. Care must be taken to insure that the feedback resistor's current exceeds the pass transistors leakage current over the entire temperature range. The linear regulator output can be supplied by the output of one of the PWMs. When using a PFET, the output of the linear regulator will track the PWM supply after the PWM output rises to a voltage greater than the threshold of the PFET pass device. The voltage differential between the PWM and the linear output will be the load current times the rDS(ON).
60
(EQ. 9)
C1
GEA = 18dB FZ FP FC
FPO
ERROR AMPLIFIER SINK CURRENT (mA)
FIGURE 17. FEEDBACK LOOP COMPENSATION
50 40 30 20 10 0 0.79
The zero frequency, the amplifier high-frequency gain, and the modulator gain are chosen to satisfy most typical applications. The crossover frequency will appear at the point where the modulator attenuation equals the amplifier high frequency gain. The only task that the system designer has to complete is to specify the output filter capacitors to position the load main pole somewhere within one decade lower than the amplifier zero frequency. With this type of compensation plenty of phase margin is easily achieved due to zero-pole pair phase `boost'. Conditional stability may occur only when the main load pole is positioned too much to the left side on the frequency axis due to excessive output filter capacitance. In this case, the ESR zero placed within the 1.2kHz to 30kHz range gives some additional phase `boost'. Some phase boost can also be achieved by connecting capacitor CZ in parallel with the upper resistor R1 of the divider that sets the output voltage value. Please refer to "Output Inductor Selection" on page 18 and "Input Capacitor Selection" on page 19 for further details.
0.8
0.82 0.83 0.81 FEEDBACK VOLTAGE (V)
0.84
0.85
FIGURE 18. LINEAR CONTROLLER GAIN
Base-Drive Noise Reduction
The high-impedance base driver is susceptible to system noise, especially when the linear regulator is lightly loaded. Capacitively coupled switching noise or inductively coupled EMI onto the base drive causes fluctuations in the base current, which appear as noise on the linear regulator's output. Keep the base drive traces away from the step-down converter, and as short as possible, to minimize noise coupling. A resistor in series with the gate drivers reduces the switching noise generated by PWM. Additionally, a bypass capacitor may be placed across the base-to-emitter resistor. This bypass capacitor, in addition to the transistor's input capacitor, could bring in a second pole that will destabilize the linear regulator. Therefore, the stability
Linear Regulator
The linear regulator controller is a trans-conductance amplifier with a nominal gain of 2A/V. The N-channel MOSFET output device can sink a minimum of 50mA. The reference voltage is 0.8V. With zero volts differential at it's
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requirements determine the maximum base-to-emitter capacitance. 8. The output capacitors should be placed as close to the load as possible. Use short wide copper regions to connect output capacitors to load to avoid inductance and resistances. 9. Use copper filled polygons or wide but short trace to connect the junction of upper FET, Lower FET and output inductor. Also keep the PHASE node connection to the IC short. Do not unnecessarily oversize the copper islands for PHASE node. 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. 10. Route all high speed switching nodes away from the control circuitry. 11. Create a separate small analog ground plane near the IC. Connect the SGND pin to this plane. All small signal grounding paths including feedback resistors, current limit setting resistors and ENx pull-down resistors should be connected to this SGND plane. 12. Ensure the feedback connection to the output capacitor is short and direct.
Layout Guidelines
Careful attention to layout requirements is necessary for successful implementation of an ISL9440, ISL9440A and ISL9441 based DC/DC converter. The ISL9440, ISL9440A and ISL9441 switch at a very high frequency and therefore the switching times are very short. At these switching frequencies, even the shortest trace has significant impedance. Also, the peak gate drive current rises significantly in extremely short time. Transition speed of the current from one device to another causes voltage spikes across the interconnecting impedances and parasitic circuit elements. These voltage spikes can degrade efficiency, generate EMI, increase device overvoltage stress and ringing. Careful component selection and proper PC board layout minimizes the magnitude of these voltage spikes. There are three sets of critical components in a DC/DC converter using the ISL9440, ISL9440A and ISL9441: The controller, the switching power components and the small signal components. The switching power components are the most critical from a layout point of view because they switch a large amount of energy so they tend to generate a large amount of noise. The critical small signal components are those connected to sensitive nodes or those supplying critical bias currents. A multi-layer printed circuit board is recommended.
Component Selection Guidelines
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 3 PWM 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. 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.
( I O ) ( r DS ( ON ) ) ( V OUT ) ( I O ) ( V IN ) ( t SW ) ( F SW ) P UPPER = -------------------------------------------------------------- + ----------------------------------------------------------V IN 2 (EQ. 10) ( I O ) ( r DS ( ON ) ) ( V IN - V OUT ) P LOWER = -----------------------------------------------------------------------------V IN
2 2
Layout Considerations
1. The Input capacitors, Upper FET, Lower FET, Inductor and Output capacitor should be placed first. Isolate these power components on the topside of the board with their ground terminals adjacent to one another. Place the input high frequency decoupling ceramic capacitor very close to the MOSFETs. 2. Use separate ground planes for power ground and small signal ground. Connect the SGND and PGND together close to the IC. Do not connect them together anywhere else. 3. The loop formed by Input capacitor, the top FET and the bottom FET must be kept as small as possible. 4. Ensure the current paths from the input capacitor to the MOSFET, to the output inductor and output capacitor are as short as possible with maximum allowable trace widths. 5. Place The PWM controller IC close to lower FET. The LGATE connection should be short and wide. The IC can be best placed over a quiet ground area. Avoid switching ground loop current in this area. 6. Place VCC_5V bypass capacitor very close to VCC_5V pin of the IC and connect its ground to the PGND plane. 7. Place the gate drive components BOOT diode and BOOT capacitors together near controller IC
(EQ. 11)
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.
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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. Selection of output capacitors is also dependent on the output inductor, so some inductor analysis is required to select the output capacitors. One of the parameters limiting the converter's response to a load transient is the time required for the inductor current to slew to it's new level. The ISL9440, ISL9440A and ISL9441 will provide either 0% or maximum 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, it reduces the requirement on the output capacitor. The maximum capacitor value required to provide the full, rising step, transient load current during the response time of the inductor is:
( L O ) ( I TRAN ) C OUT = ---------------------------------------------------------2 ( V IN - V O ) ( DV OUT )
2
(ISL9440/ISL9441)/600kHz (ISL9440A) for the bulk capacitors. In most cases, multiple small-case electrolytic capacitors perform better than a single large-case capacitor. The stability requirement on the selection of the output capacitor is that the `ESR zero' (f Z) 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 side of the internal zero and still contribute to increased phase margin of the control loop. Therefore:
1 C OUT = -----------------------------------2 ( ESR ) ( f Z ) (EQ. 14)
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. 3. The ESR zero should be placed, in a rather large range, to provide additional phase margin. The recommended output capacitor value for the ISL9440, ISL9440A and ISL9441 is between 150F to 680F, to meet stability criteria with external compensation. Use of aluminum electrolytic (POSCAP) or tantalum type capacitors is recommended. Use of low ESR ceramic capacitors is possible but would take more rigorous loop analysis to ensure stability.
(EQ. 12)
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, VO is output voltage, and DVOUT is the drop in output voltage allowed during the load transient. High frequency capacitors initially supply the transient current and slow the load rate-of-change seen by the bulk capacitors. The bulk filter capacitor values are generally determined by the ESR (Equivalent Series Resistance) and voltage rating requirements as well as actual capacitance requirements. The output voltage ripple is due to the inductor ripple current and the ESR of the output capacitors as defined by:
V RIPPLE = I L ( ESR ) (EQ. 13)
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 Equation 15:
( V IN - V OUT ) ( V OUT ) I L = --------------------------------------------------------( f S ) ( L ) ( V IN ) (EQ. 15)
where, IL is calculated in the "Output Inductor Selection" on page 18. 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 18
For the ISL9440, ISL9440A and ISL9441, inductor values between 1.2H to 10H are recommended when using the Typical Application Schematic. Other values can be used but a thorough stability study should be done. A smaller volume cap in combination with big inductor will be more prone to stability issues. One way to get more phase margin is to add a small cap (typically 1nF to 10nF) in parallel with the upper resistor of the voltage sense resistor divider. For example, in ISL9440, ISL9440A Application Schematic, the 5V output has a 15H inductor with which the system phase margin is less than 45. An resistor and capacitor are added with the upper resistor of the divider to get more phase margin.
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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 the load. The total RMS current supplied by the input capacitance is:
I RMS =
2 2 I RMS1 + I RMS2 5.0 4.5 4.0 INPUT RMS CURRENT 3.5 3.0 2.5 2.0 1.5 1.0 3.3V 5V OUT OF PHASE IN PHASE
(EQ. 16)
0.5 0 0 1 2 3 3.3V AND 5V LOAD CURRENT 4 5
where,
I RMSx = DC - DC I O
2
(EQ. 17) FIGURE 19. INPUT RMS CURRENT vs LOAD
DC is duty cycle of the respective PWM. Depending on the specifics of the input power and its impedance, most (or all) of this current is supplied by the input capacitor(s). Figure 19 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.
Use a mix of input bypass capacitors to control the voltage ripple across the MOSFETs. Use ceramic capacitors for the high frequency decoupling and bulk capacitors to supply the RMS current. Small ceramic capacitors can be placed very close to the upper MOSFET to suppress the voltage induced in the parasitic circuit impedances. For board designs that allow through-hole components, the Sanyo OS-CON(R) series offer low ESR and good temperature performance. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating. These capacitors must be capable of handling the surgecurrent at power-up. The TPS series available from AVX is surge current tested.
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
FN6383.1 December 5, 2007
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Package Outline Drawing
L32.5x5B
32 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE Rev 2, 11/07
4X 3.5 5.00 A B 6 PIN 1 INDEX AREA 28X 0.50 6 PIN #1 INDEX AREA
25 24
32 1
5.00
3 .30 0 . 15
17
(4X) 0.15 16 9
8
0.10 M C A B 4 32X 0.23 - 0.05
+ 0.07
32X 0.40 0.10
TOP VIEW
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
0 . 90 0.1
C
BASE PLANE
SEATING PLANE 0.08 C
( 4. 80 TYP ) ( 3. 30 )
( 28X 0 . 5 )
SIDE VIEW
(32X 0 . 23 )
C ( 32X 0 . 60)
0 . 2 REF
5
0 . 00 MIN. 0 . 05 MAX.
TYPICAL RECOMMENDED LAND PATTERN
DETAIL "X"
NOTES: 1. Dimensions are in millimeters. Dimensions in ( ) for Reference Only. 2. Dimensioning and tolerancing conform to AMSE Y14.5m-1994. 3. Unless otherwise specified, tolerance : Decimal 0.05 4. Dimension b applies to the metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip. 5. Tiebar shown (if present) is a non-functional feature. 6. The configuration of the pin #1 identifier is optional, but must be located within the zone indicated. The pin #1 identifier may be either a mold or mark feature.
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FN6383.1 December 5, 2007

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