Intersil ISL62392IRTZ-T High-efficiency, triple-output system power supply controller for notebook computer Datasheet

ISL62391, ISL62392
¬
Data Sheet
December 22, 2008
High-Efficiency, Triple-Output System
Power Supply Controller for Notebook
Computers
Features
• High Performance R3 Technology
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.
• 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)
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.
Applications
• Notebook and Sub-Notebook Computers
The ISL62391, ISL62392 is available in a 28 Ld 4x4 TQFN
package and operates over the extended temperature range
(-40°C to +100°C).
• PDAs and Mobile Communication Devices
• 3-Cell and 4-Cell Li+ Battery-Powered Devices
Pinout
Ordering Information
TEMP
RANGE
(°C)
ISL62391HRTZ-T* 623 91HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4
OCSET2
EN2
PHASE2
UGATE2
PKG.
DWG. #
ISEN2
PACKAGE
(Pb-Free)
VOUT2
PART
MARKING
ISL62391, ISL62392
(28 LD 4X4 TQFN)
TOP VIEW
FB2
PART
NUMBER
(Note)
FN6666.4
ISL62392HRTZ
28
27
26
25
24
23
22
ISL62391HRTZ
623 91HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4
623 92HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4
ISL62392HRTZ-T* 623 92HRTZ -10 to +100 28 Ld 4x4 TQFN L28.4x4
PGOOD
1
21
BOOT2
ISL62391IRTZ
623 91IRTZ
-40 to +100 28 Ld 4x4 TQFN L28.4x4
FSET2
2
20
LGATE2
ISL62391IRTZ-T*
623 91IRTZ
-40 to +100 28 Ld 4x4 TQFN L28.4x4
FCCM
3
19
PGND
ISL62392IRTZ
623 92IRTZ
-40 to +100 28 Ld 4x4 TQFN L28.4x4
VCC
4
18
PVCC
ISL62392IRTZ-T*
623 92IRTZ
-40 to +100 28 Ld 4x4 TQFN L28.4x4
LDO3EN
5
17
VIN
FSET1
6
16
LDO3
FB1
7
15
LGATE1
*Please refer to TB347 for details on reel specifications.
1
8
9
10
11
12
13
14
ISEN1
OCSET1
EN1
PHASE1
UGATE1
BOOT1
CENTER PAD:
GND
VOUT1
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.
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.
ISL62391, ISL62392
Absolute Maximum Ratings
Thermal Information
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, 10µJ) . . . . . . . . . . . . . . . . . . . . . . . . . -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, 20µJ) . . . . . . . . . . . . . . . . . . . . . . . . -4.0V
LGATE1,2 . . . . . . . . . . . . . . . . . . . (DC) -0.3V to GND, PVCC +0.3V
(<100ns Pulse Width, 4µJ) . . . . . . . . . . . . . . . . . . . . . . . . . . -2.0V
LDO3 Current (Internal Regulator) Continuous . . . . . . . . . +100mA
Thermal Resistance (Typical, Notes 1, 2) θJA (°C/W) θJC (°C/W)
TQFN Package . . . . . . . . . . . . . . . . . .
37
3.5
Junction Temperature Range. . . . . . . . . . . . . . . . . .-55°C to +150°C
Operating Temp. Range (ISL62391(2)IRTZ) . . . . . .-40°C to +100°C
Operating Temp. Range (ISL62391(2)HRTZ) . . . . .-10°C to +100°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Pb-Free Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
Recommended Operating Conditions
Ambient Temperature Range (ISL62391(2)IRTZ) . .-40°C to +100°C
Ambient Temperature Range (ISL62391(2)HRTZ) .-10°C to +100°C
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. θJA 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 θJC, 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 = -40°C to +100°C,
unless otherwise noted. Typical values are at TA = +25°C. Parameters with MIN and/or MAX limits are 100%
tested at +25°C, unless otherwise specified. Temperature limits established by characterization and are not
production tested.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Rising Threshold
5.3
5.4
5.5
V
Hysteresis
20
80
150
mV
6
15
µA
LINEAR REGULATOR
VIN Power-on Reset
VIN Shutdown Supply Current
EN1 = EN2 = LDO3EN = 0
VIN Standby Supply Current
EN1 = EN2 = 0, LDO3EN = 1
150
250
µA
LDO3 Output Voltage
I_LDO3 = 100mA (Note 3)
3.25
3.3
3.35
V
I_LDO3 = 0mA
3.25
3.3
3.35
V
LDO3 Short-Circuit Current
LDO3 = GND (Note 3)
LDO3EN Input Voltage
Rising edge
1.1
2.5
V
Falling edge
0.94
1.06
V
-1
1
µA
60
Ω
LDO3EN Input Leakage Current
LDO3EN = 0 or VCC
LDO3 Discharge ON-resistance
LDO3EN = 0
180
36
PVCC POR Threshold (Note 3)
mA
4.2
SMPS2 to PVCC Switchover Threshold
SMPS2 to PVCC Switchover Resistance (Note 3)
4.63
VOUT2 to PVCC, VOUT2 = 5V
V
4.8
4.93
V
2.5
3.2
Ω
MAIN SMPS CONTROLLERS
VCC Input Bias Current
EN1 = EN2 = 1, FB1 = FB2 = 0.65V
2
mA
VCC POR Threshold
Rising Edge
4.33
4.50
4.55
V
Rising Edge (ISL62391(2)HRTZ, TA = -10°C to
+100°C)
4.35
4.50
4.55
V
Falling Edge
4.08
4.20
4.30
V
Falling Edge (ISL62391(2)HRTZ, TA = -10°C to
+100°C)
4.10
4.20
4.30
V
1
%
Reference Voltage
0.6
Regulation Accuracy
VOUT regulated to 0.6V
2
-1
V
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 = -40°C to +100°C,
unless otherwise noted. Typical values are at TA = +25°C. Parameters with MIN and/or MAX limits are 100%
tested at +25°C, unless otherwise specified. Temperature limits established by characterization and are not
production tested. (Continued)
PARAMETER
CONDITIONS
FB Input Bias Current
MIN
TYP
MAX
UNITS
FB = 0.6V
-12
30
nA
FB = 0.6V (ISL62391(2)HRTZ, TA = -10°C to
+100°C)
-10
30
nA
Frequency Range
200
600
kHz
Frequency Set Accuracy
FSW = 300kHz (Note 4)
-12
12
%
VOUT Voltage Adjust Range
VIN ≥ 6V for VOUT = 5.5V
0.6
5.5
V
14
50
Ω
VOUT Soft-discharge Resistance
PGOOD Pull-down Impedance
(Note 3)
32
50
Ω
PGOOD Leakage Current
PGOOD = VCC
0
1
µA
Maximum PGOOD Sink Current
(Note 3)
5
PGOOD Soft-start Delay
(From first EN = 1 to PGOOD = 1)
EN1 = EN2 = 1
2.20
2.75
3.70
ms
EN1 = 1, EN2 = Floating or EN1 = Floating, EN2 =1
4.50
5.60
7.60
ms
EN1 = 1, EN2 = Floating or EN1 = Floating, EN2 =1
(ISL62391(2)HRTZ, TA = -10°C to +100°C)
4.50
5.60
7.50
ms
1.5
Ω
UGATE Pull-up ON-resistance
200mA source current (Note 3)
1.0
UGATE Source Current
UGATE-PHASE = 2.5V (Note 3)
2.0
UGATE Pull-down ON-resistance
250mA source current (Note 3)
1.0
UGATE Sink Current
UGATE-PHASE = 2.5V (Note 3)
2.0
LGATE Pull-up ON-resistance
250mA source current (Note 3)
1.0
mA
A
1.5
Ω
A
1.5
Ω
0.9
Ω
LGATE Source Current
LGATE-PGND = 2.5V (Note 3)
2.0
LGATE Pull-down ON-resistance
250mA source current (Note 3)
0.5
LGATE Sink Current
LGATE-PGND = 2.5V (Note 3)
4.0
A
UGATE to LGATE Deadtime
UG falling to LG rising, no load
21
ns
LGATE to UGATE Deadtime
LG falling to UG rising, no load
21
ns
Bootstrap Diode Forward Voltage
2mA forward diode current
0.58
V
Bootstrap Diode Reverse Leakage Current
VR = 25V
0.2
FCCM Input Voltage
Low Level (DCM enabled)
Float Level (audio filter enabled)
1.9
High Level (forced CCM)
2.4
FCCM Input Leakage Current
FCCM = GND or VCC
-2
Audio Filter Switching Frequency
FCCM floating
EN Input Voltage
Low Level (Clear fault level/SMPS off)
Float Level (Delayed start)
A
1
µA
0.8
V
2.1
V
V
2
28
1.9
High Level (SMPS on)
2.4
EN Input Leakage Current
EN = GND or VCC
-3.5
ISEN Input Impedance
EN = VCC
µA
kHz
0.8
V
2.1
V
3.5
µA
V
600
kΩ
ISEN Input Leakage Current
EN = GND
0.1
µA
OCSET Input Impedance
EN = VCC
600
kΩ
OCSET Input Leakage Current
EN = GND
0.1
µA
OCSET Current Source
EN = VCC
EN = VCC (ISL62391(2)HRTZ, TA = -10°C to
+100°C)
3
8.7
10.0
10.5
µA
9
10.0
10.5
µA
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 = -40°C to +100°C,
unless otherwise noted. Typical values are at TA = +25°C. Parameters with MIN and/or MAX limits are 100%
tested at +25°C, unless otherwise specified. Temperature limits established by characterization and are not
production tested. (Continued)
PARAMETER
CONDITIONS
OCP (OCSET-ISEN) Threshold
UVP Threshold
Falling edge, referenced to FB
OVP Threshold
OTP Threshold
MIN
TYP
MAX
UNITS
-1.75
0.0
1.75
mV
80.9
84
87
%
Falling edge, referenced to FB (ISL62391(2)HRTZ,
TA = -10°C to +100°C)
81
84
87
%
Rising edge, referenced to FB
113
116
120
%
Falling edge, referenced to FB
99.5
103
106
%
Rising edge (Note 3)
150
Falling edge (Note 3)
135
°C
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.
4
FN6666.4
December 22, 2008
ISL62391, ISL62392
Functional Pin Description
PIN
NAME
FUNCTION
1
PGOOD
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.
2
FSET2
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.
3
FCCM
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.
4
VCC
5
LDO3EN
6
FSET1
7
FB1
8
VOUT1
SMPS1 output voltage sense input. Used for soft-discharge.
9
ISEN1
SMPS1 DCR current sense input. Used for overcurrent protection and R3 regulation.
10
OCSET1
11
EN1
12
PHASE1
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.
13
UGATE1
High-side NMOS gate drive output for SMPS1. Connect to the gate of the SMPS1 switching FET.
14
BOOT1
SMPS1 bootstrap input for the switching NMOS gate drivers. Connect to SMPS1 PHASE with a ceramic capacitor of 0.22µF.
15
LGATE1
Low-side NMOS gate drive output for SMPS1. Connect to the gate of the SMPS1 synchronous FET.
16
LDO3
17
VIN
18
PVCC
5V power source for SMPS gate drive current. Bypass to ground with a 4.7µF ceramic capacitor.
19
PGND
Power ground for SMPS1 and SMPS2. This provides a return path for synchronous FET switching currents.
20
LGATE2
Low-side NMOS gate drive output for SMPS2. Connect to the gate of the SMPS2 synchronous FET.
21
BOOT2
SMPS2 bootstrap input for the switching NMOS gate drivers. Connect to SMPS2 PHASE with a ceramic capacitor of 0.22µF.
22
UGATE2
High-side NMOS gate drive output for SMPS2. Connect to the gate of the SMPS2 switching FET.
23
PHASE2
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.
24
EN2
25
OCSET2
26
ISEN2
SMPS2 DCR current sense input. Used for overcurrent protection and R3 regulation.
27
VOUT2
SMPS2 output voltage sense input. Used for soft-discharge and switchover for PVCC 5V LDO.
28
FB2
SMPS2 feedback input used for output voltage programming and regulation.
Bottom
Pad
GND
Analog ground for analog and logic signals.
Analog power supply input for reference voltages and currents. Bypass to ground with a 1µF 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.
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.
3.3V linear regulator output, capable of providing 100mA continuous current. Bypass to ground with a 4.7µF ceramic capacitor.
Feed-forward input for line voltage transient compensation. Connect to the power train input voltage.
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.
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
4x10µF
BO OT1
V IN
BOO T2
0.22µF
0.22µF
4.7µH
3 .3 V
330µF
IRF7821
UGATE1
UGATE2
PHASE1
PHASE2
LGATE1
LG ATE2
IRF7821
5V
330µF
14k 0.022µF
0.022µF 14k
IRF7832
IRF7832
14k
4.7µH
750
14k
45.3k
1200pF
750
OCSET2
OCSET1
IS E N 1
IS E N 2
VOUT1
VOUT2
68.1k
1200pF
FB2
FB1
9.09k
ISL62391, ISL62392
10k
100k
PGOOD
LDO3
4.7µF
PVCC
EN1
EN2
LD O 3EN
FCCM
FSET1
FSET2
PVCC
1µF
VCC
1µF
PGND
PAD
0.01µF
24.3k
19.6k
0.01µF
FIGURE 1. TYPICAL SYSTEM REGULATOR APPLICATION CIRCUIT WITH INDUCTOR DCR CURRENT SENSE
VBAT
BO OT1
4x10µF
0.22µF
4.7µH
3 .3 V
0.001
330µF
1k
V IN
BO O T2
IRF7821
IRF7821
UG ATE1
UG ATE2
PHASE1
PHASE2
LGATE1
LG ATE2
OCSET1
OCSET2
4.7µH
0.001
5V
IRF7832
IRF7832
1k
0.22µF
330µF
1k
1k
750
750
1200pF 45.3k
IS E N 1
IS E N 2
VO UT1
VOUT2
FB1
68.1k
1200pF
FB2
9.09k
ISL62391, ISL62392
10k
100k
PGOOD
PVCC
EN1
EN2
3 .3 V
LDO 3
LDO 3EN
4.7µF
FCCM
FSET1
FSET2
PVCC
1µF
1µF
VCC
PGND
GND
24.3k
19.6k
0.01µF
0.01µF
FIGURE 2. TYPICAL SYSTEM REGULATOR APPLICATION CIRCUIT WITH RESISTOR SENSE
6
FN6666.4
December 22, 2008
ISL62391, ISL62392
Typical Application Circuits (Continued)
VBAT
4x10µF
BO O T1
V IN
BO O T2
0.22µF
0.22µF
IRF7821
2x
2.2µH
1 .0 5 V
2x330µF
UG ATE1
UGATE2
PHASE1
PHASE2
LGATE1
LGATE2
OCSET1
OCSET2
IRF7821
2x
0.022µF 14k
14k
2x
IRF7832
IRF7832
2x
14k
2.2µH
1 .5 V
2x330µF
0.022µF
14k
590
590
36.5k
1800pF
IS E N 1
IS E N 2
VO UT1
VOUT2
1800pF
FB2
FB1
48.7k
36.5k
24.3k
ISL62391, ISL62392
100k
PGOOD
LDO3
4.7µF
PVCC
EN1
EN2
LDO 3EN
FCCM
FSET1
FSET2
PVCC
1µF
VCC
1µF
PGND
17.4k
PAD
14k
0.01µF
0.01µF
FIGURE 3. TYPICAL CHIP SET APPLICATION CIRCUIT WITH INDUCTOR DCR CURRENT SENSE
VBAT
BO OT1
4x10µF
2x
2.2µH
1 .0 5 V
0.001
2x330µF
1k
BO O T2
IRF7821
UG ATE1
UGATE2
PHASE1
PHASE2
LGATE1
LG ATE2
OCSET1
OCSET2
IRF7832
2x
1k
0.22µF
2x
2.2µH
0.001
1 .5 V
2x330µF
IRF7832
2x
1k
1k
590
590
1800pF
V IN
IRF7821
0.22µF
36.5k
IS E N 1
IS E N 2
VOUT1
VOUT2
FB1
36.5k
1800pF
FB2
24.3k
ISL62391, ISL62392
48.7k
100k
PGOOD
PVCC
EN1
EN2
3 .3 V
LDO3
LDO 3EN
4.7µF
FCCM
FSET1
FSET2
PVCC
1µF
1µF
VCC
PGND
GND
17.4k
14k
0.01µF
0.01µF
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
FB1/2
R3
MODULATOR
VREF
PVCC
0.6V
BOOT1/2
FCCM
PWM
VOUT1/2
UGATE
DRIVER
UGATE1/2
PHASE1/2
SOFT DISCHARGE
LGATE
DRIVER
LGATE1/2
PGND
EN1
PGOOD
START-UP
AND
SHUTDOWN
LOGIC
EN2
LDO3EN
VCC
BIAS AND
REFERENCE
10µA
OCSET1/2
OCP
T-PAD
PROTECTION LOGIC
OVP/UVP/OCP/OTP
ISEN1/2
VREF + 16%
PVCC
UVP
3.3V
LDO
FB1/2
LDO3
OVP
VREF - 16%
THERMAL
MONITOR
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
100
VIN = 7V
95
90
90
VIN = 12V
85
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 7V
VIN = 19V
80
75
70
65
80
70
65
60
55
55
1.00
10.00
VIN = 19V
75
60
50
0.10
VIN = 12V
85
50
0.01
0.10
1.00
IOUT (A)
FIGURE 5. CHANNEL 1 EFFICIENCY AT VO = 3.3V, DEM
OPERATION. HIGH-SIDE 1xIRF7821,
rDS(ON) = 9.1mΩ; LOW-SIDE 1xIRF7832,
rDS(ON) = 4mΩ; L = 4.7µH, DCR = 14.3mΩ; CCM
FSW = 270kHz
10.00
IOUT (A)
FIGURE 6. CHANNEL 2 EFFICIENCY AT VO = 5V, DEM
OPERATION. HIGH-SIDE 1xIRF7821,
rDS(ON) = 9.1mΩ; LOW-SIDE 1xIRF7832,
rDS(ON) = 4mΩ; L = 4.7µH, DCR = 14.3mΩ; CCM
FSW = 330kHz
VO1
VO1
FB1
FB1
PGOOD
PGOOD
PHASE1
FIGURE 7. POWER-ON, VIN = 12V, LOAD = 5A, VO = 3.3V
VO1
PHASE1
FIGURE 8. POWER-OFF, VIN = 12V, IO = 5A, VO = 3.3V
VO1
FB1
FB1
PGOOD
PGOOD
EN1
EN1
FIGURE 9. ENABLE CONTROL, EN1 = HIGH, VIN = 12V,
VO = 3.3V, IO = 5A
9
FIGURE 10. ENABLE CONTROL, EN1 = LOW, VIN = 12V,
VO = 3.3V, IO = 5A
FN6666.4
December 22, 2008
ISL62391, ISL62392
Typical Performance Curves (Continued)
VO1
PHASE1
VO2
PHASE2
FIGURE 11. CCM STEADY-STATE OPERATION, VIN = 12V,
VO1 = 3.3V, IO1 = 5A, VO2 = 5V, IO2 = 5A
VO1
VO1
PHASE1
VO2
PHASE2
FIGURE 12. DCM STEADY-STATE OPERATION, VIN = 12V,
VO1 = 3.3V, IO1 = 0. 2A, VO2 = 5V, IO2 = 0.2A
VO1
PHASE1
PHASE1
VO2
PHASE2
FIGURE 13. AUDIO FILTER OPERATION, VIN = 12V,
VO1 = 3.3V, VO2 = 5V, NO LOAD
IO1
FIGURE 14. TRANSIENT RESPONSE, VIN = 12V, VO = 3.3V,
IO = 0.1A/8.1A @ 2.5A/µs
VO1
VO1
PHASE1
IO1
FIGURE 15. LOAD INSERTION RESPONSE, VIN = 12V,
VO = 3.3V, IO = 0.1A/8.1A @ 2.5A/µs
10
PHASE1
IO1
FIGURE 16. LOAD RELEASE RESPONSE, VIN = 12V,
VO = 3.3V, IO = 0.1A/8.1A @ 2.5A/µs
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
VO1
FIGURE 18. DELAYED START, VIN = 12V, VO1 = 3.3V, VO2 = 5V,
EN1 = FLOAT, NO LOAD
VO1
PGOOD
IO1
VO2
PGOOD
FIGURE 19. DELAYED START, VIN = 12V, VO1 = 3.3V, VO2 = 5V,
EN1 = 1, EN2 = FLOAT, NO LOAD
VO1
FIGURE 20. OVERCURRENT PROTECTION, VIN = 12V,
VO = 3.3V
VO1
UGATE1-PHASE1
UGATE1-PHASE1
LGATE1
LGATE1
PGOOD
PGOOD
FIGURE 21. CROWBAR OVERVOLTAGE PROTECTION,
VIN = 12V, VO = 3.3V, NO LOAD
11
FIGURE 22. TRI-STATE OVERVOLTAGE PROTECTION,
VIN = 12V, VO = 3.3V, NO LOAD
FN6666.4
December 22, 2008
ISL62391, ISL62392
Theory of Operation
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.
Modulator and Switching Frequency
V W = g m ⋅ V OUT ⋅ ( 1 – D ) ⋅ R W
Three Output Controller
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)
(EQ. 3)
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 = 1.66µs
K = 1.7 x 10-10 (±20%)
D = VOUT/VIN
The negative slope of VR can be written as Equation 2:
Power-On Reset
V RNEG = g m ⋅ V OUT
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.
(EQ. 2)
Where gm is the gain of the transconductance amplifier.
WINDOW VOLTAGE VW
(WRT VCOMP)
RIPPLE CAPACITOR VOLTAGE CR
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.
EN, Soft-Start and PGOOD
ERROR AMPLIFIER
VOLTAGE VCOMP
PWM
FIGURE 23. MODULATOR WAVEFORMS DURING LOAD
TRANSIENT
12
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.
FN6666.4
December 22, 2008
ISL62391, ISL62392
1.5ms
VO
tSOFTSTART
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 32Ω. 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.
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.
tLGFUGR
tUGFLGR
50%
UGATE
LGATE
50%
TABLE 1. SMPS ENABLE SEQUENCE LOGIC
EN1
EN2
START-UP SEQUENCE
0
0
All SMPS outputs OFF
0
FLOAT
All SMPS outputs OFF
0
1
SMPS1 OFF, SMPS2 ON
FLOAT
0
All SMPS outputs OFF
FLOAT
FLOAT
All SMPS outputs OFF
FLOAT
1
SMPS1 enables after SMPS2 is in regulation
1
0
SMPS1 ON, SMPS2 OFF
1
FLOAT
1
1
SMPS2 enables after SMPS1 is in regulation
All SMPS outputs ON simultaneously
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
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,
FN6666.4
December 22, 2008
ISL62391, ISL62392
ISL62392 monitors the phase voltage when the low-side
MOSFET is conducting inductor current to determine its
direction.
L
DCR
+
When the output load current is greater than or equal to ½
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 ½ 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 30µs, LGATE is turned on,
causing the ramp voltage to reduce until another UGATE is
commanded by the voltage loop.
Overcurrent Protection
The overcurrent protection (OCP) setpoint is programmed
with resistor, ROCSET, that is connected across the OCSET
and PHASE pins.
ROCSET
ISL62391,
ISL62392
10µ
OCSET1
+ VROCSET
VO
IL
PHASE1
VDCR
CSEN
_
CO
_
RO
OUT1
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 10µA current into the
OCSET1 pin, creating a DC voltage drop across the resistor
ROCSET, which is given by Equation 7:
V ROCSET = 10μA • 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 – 10μA • 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 10µs, the ISL62391,
ISL62392 declares an OCP fault. The value of ROCSET is
then written as Equation 9:
I OC • DCR
R OCSET = --------------------------10μA
(EQ. 9)
Where:
- ROCSET (Ω) 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 4.5mΩ, the choice of
ROCSET is ROCSET = 20A x 4.5mΩ/10µA = 9kΩ.
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
14
FN6666.4
December 22, 2008
ISL62391, ISL62392
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)
For example, if L is 1.5µH, DCR is 4.5mΩ, and ROCSET is
9kΩ, the choice of CSEN = 1.5µH/(9kΩ x 4.5mΩ) = 0.037µF.
Upon converter start-up, the CSEN capacitor bias is 0V. To
prevent false OCP during this time, a 10µA 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 32Ω 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 – 10μA • R OCSET
(EQ. 11)
(EQ. 12)
Where RSENSE is the series power resistor for sensing
inductor current. For example, with an RSENSE = 1mΩ and
an OCP target of 10A, ROCSET = 1kΩ.
Overvoltage Protection
The OVP fault detection circuit triggers after the FB pin
voltage is above the rising overvoltage threshold for more
than 2µs. 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 32Ω 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
15
Undervoltage Protection
The UVP fault detection circuit triggers after the FB pin
voltage is below the undervoltage threshold for more than
2µs. 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 32Ω 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:
Furthermore, Equation 9 is changed in Equation 12:
I OC • R SENSE
R OCSET = ------------------------------------10μA
threshold for more than 2µs. 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.
R TOP ⎞
⎛
V OUT = V REF • ⎜ 1 + -----------------------------⎟
R BOTTOM⎠
⎝
(EQ. 13)
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)
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 )
(EQ. 15)
FB
FN6666.4
December 22, 2008
ISL62391, ISL62392
Selecting the LC Output Filter
CINT = 100pF
CFB
RFB
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:
RTOP
-
VO
FB
EA
RBOTTOM
COMP
+
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
REF
ISL62391, ISL62392
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.
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 +150°C, all outputs will be turned off to
sharply curtail power dissipation. The outputs will remain off
until the junction temperature has fallen below +135°C.
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.
16
(EQ. 17)
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
•
(EQ. 18)
DCR
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:
ΔV ESR = I P-P • E SR
(EQ. 19)
and Equation 20:
I P-P
ΔV C = ----------------------------8 • CO • f
(EQ. 20)
SW
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.
FN6666.4
December 22, 2008
ISL62391, ISL62392
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:
2
I IN_RMS, NORMALIZED =
2
x
( D – D ) + ⎛ D ⋅ ------ ⎞
⎝ 12 ⎠
(EQ. 21)
For the low-side (LS) MOSFET, the power loss can be
assumed to be conductive only and is written as Equation 23:
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)
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
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.
0.55
0.50
0.45
0.40
0.35
x=1
x = 0.75
x = 0.50
x = 0.25
x=0
0.25
0.20
0.15
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
DUTY CYCLE
FIGURE 28. NORMALIZED RMS INPUT CURRENT
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.
17
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)
Where:
The selection of the bootstrap capacitor is written as
Equation 26:
0.05
0.1
For the high-side (HS) MOSFET, the conduction loss is
written as Equation 24:
Selecting The Bootstrap Capacitor
0.10
0
0
(EQ. 23)
- 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
0.60
0.30
2
P CON_LS ≈ I LOAD ⋅ r DS ( ON )_LS • ( 1 – D )
Qg
C BOOT = -----------------------ΔV BOOT
(EQ. 26)
Where:
- Qg is the total gate charge required to turn on the
high-side MOSFET
- ΔVBOOT, is the maximum allowed voltage decay across
the boot capacitor each time the high-side MOSFET is
switched on
FN6666.4
December 22, 2008
ISL62391, ISL62392
As an example, suppose the high-side MOSFET has a total
gate charge Qg, of 25nC at VGS = 5V, and a ΔVBOOT of
200mV. The calculated bootstrap capacitance is 0.125µF; for
a comfortable margin, select a capacitor that is double the
calculated capacitance. In this example, 0.22µF will suffice.
Use an X7R or X5R ceramic capacitor.
Layout Considerations
VOUT
HIGH-SIDE
HIGH-SIDE
MOSFETS
MOSFETS
L2
L2 U2
ISL6239
Ci
Ci
L1 U1
PGND PLANE
PHASE PLANES
VOUT PLANES
VIN PLANE
L1
Co
FIGURE 30. SYMMETRIC LAYOUT GUIDE
GND
GND
PLANE
INDUCTOR
INDUCTOR
PIN 18 (PVCC)
PIN 4 (VCC)
LINE OF SYMMETRY
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
Co
PHASE
PHASE
NODE
NODE
VIN
VIN
OUTPUT
OUTPUT
CAPACITORS
CAPACITORS
SCHOTTKY
SCHOTTKY
DIODE
DIODE
VCC (Pin 4)
For best performance, place the decoupling capacitor very
close to the VCC and GND pins.
LOW-SIDE
LOW-SIDE
MOSFETS
MOSFETS
PVCC (Pin 18)
INPUT
INPUT
CAPACITORS
CAPACITORS
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.
FIGURE 29. TYPICAL POWER COMPONENT PLACEMENT
EN (Pins 11 and 24), and PGOOD (Pin 1)
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.
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)
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 VIN pin should be connected close to the drain of the
high-side MOSFET, using a low resistance and low
inductance path.
18
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
FN6666.4
December 22, 2008
ISL62391, ISL62392
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
A
4 . 00
2 . 50
PIN #1 INDEX AREA
CHAMFER 0 . 400 X 45¬
0 . 40
22
28
1
0 . 40
15
3 . 20
2 . 50
4 . 00
21
0 . 4 x 6 = 2.40 REF
B
PIN 1
INDEX AREA
7
0 . 10
2X
14
8
0 . 20 ±0 . 0
0 . 10 M C A B
0 . 4 x 6 = 2 . 40 REF
TOP VIEW
3 . 20
BOTTOM VIEW
SEE DETAIL X''
0 . 10 C
(3 . 20)
C
PACKAGE BOUNDARY
MAX. 0 . 80
SEATING PLANE
(28X 0 . 20)
0 . 00 - 0 . 05
0 . 08 C
0 . 20 REF
(3 . 20)
(2 . 50)
SIDE VIEW
(0 . 40)
C
(0 . 40)
0 . 20 REF
5
0 ~ 0 . 05
(2 . 50)
(28X 0 . 60)
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