INTERSIL ISL6314

ISL6314
®
Data Sheet
October 8, 2009
Single-Phase Buck PWM Controller with
Integrated MOSFET Drivers for Intel VR11
and AMD Applications
The ISL6314 single-phase PWM control IC provides a
precision voltage regulation system for advanced
microprocessors. This controller IC maintains the same
features as the multi-phase product family, but reduces the
output to a single-phase, for lower current systems. By
reducing the number of external parts, this integration is
optimized for a cost and space saving power management
solution.
One outstanding feature of this controller IC is its
multi-processor compatibility, allowing it to work with both
Intel and AMD microprocessors. Included are programmable
VID codes for Intel VR11 as well as AMD 5-bit and 6-bit DAC
tables. A circuit is provided for remote voltage sensing,
compensating for any potential difference between remote
and local grounds. The output voltage can also be positively
or negatively offset through the use of a single external
resistor.
Another unique feature of the ISL6314 is the addition of a
circuit that allows optimizing compensation to be added for
flatter load transient response and well controlled dynamic
VID response.
The ISL6314 also includes advanced control loop features
for optimal transient response to load apply and removal.
One of these features is highly accurate, fully differential,
continuous DCR current sensing for load line programming.
Active Pulse Positioning (APP) and Adaptive Phase
Alignment (APA) are two other unique features, allowing for
quicker initial response to high di/dt load transients; the
number of output bulk capacitors can be reduced, helping to
reduce cost.
Protection features of this controller IC include a set of
sophisticated overvoltage, undervoltage, and overcurrent
protection. Furthermore, the ISL6314 includes protection
against an open circuit on the remote sensing inputs.
Combined, these features provide advanced protection for the
microprocessor and power system.
1
FN6455.2
Features
• Integrated-driver Single-Phase Power Conversion
• Precision Core Voltage Regulation
- Differential Remote Voltage Sensing
- ±0.5% System Accuracy Over-Temperature
- Adjustable Reference-Voltage Offset
• Optimal Transient Response
- Adaptive Phase Alignment (APA)
- Active Pulse Positioning (APP) Modulation
• Fully Differential, Continuous DCR Current Sensing
- Accurate Load Line Programming
• Variable Gate Drive Bias: 5V to 12V
• Multi-Processor Compatible
- Intel VR11 Mode of Operation
- AMD Mode of Operation
• Microprocessor Voltage Identification Inputs
- 8-Bit DAC
- Selectable Between Intel VR11, AMD 5-bit, and AMD
6-bit DAC Tables
- Dynamic VID Technology
• Overcurrent Protection
• Multi-tiered Overvoltage Protection
• Digital Soft-Start
• Selectable Operation Frequency up to 1.0MHz
• Pb-Free (RoHS compliant)
Ordering Information
PART
NUMBER
(Note)
PART
MARKING
ISL6314CRZ* ISL6314 CRZ
ISL6314IRZ*
ISL6314 IRZ
TEMP.
RANGE
(°C)
0 to +70
PACKAGE
(Pb-free)
PKG.
DWG. #
32 Ld 5x5 QFN L32.5x5B
-40 to +85 32 Ld 5x5 QFN L32.5x5B
*Add “-T” suffix 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.
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, 2009. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL6314
Pinout
VID7
VID0
VID1
VID2
VID3
VID4
VID5
VID6
ISL6314
(32 LD QFN)
TOP VIEW
32
31
30
29
28
27
26
25
PGOOD
1
24 PHASE
SS
2
23 UGATE
FS
3
22 BOOT
REF
4
OFS
5
APA
6
19 PVCC
COMP
7
18 VCC
DVC
8
17 EN
21 LGATE
33
GND
9
10
11
12
13
14
15
16
FB
VDIFF
RGND
VSEN
OCSET
ISENO
ISEN-
ISEN+
20 NC
ISL6314 Integrated Driver Block Diagram
PVCC
BOOT
UGATE
20kΩ
PWM
GATE
CONTROL
LOGIC
SOFT-START
AND
SHOOTPHASE
THROUGH
PROTECTION
10kΩ
FAULT LOGIC
LGATE
2
FN6455.2
October 8, 2009
ISL6314
Block Diagram
ISENO
OCSET
PGOOD
ISEN-
EN
100µA
ISEN+
ISEN AMP
OC
RGND
VSEN
x1
FSD
VDIFF
0.85V
OPEN SENSE
LINE DETECT
SOFT-START
UNDERVOLTAGE
DETECTION
LOGIC
AND
FAULT LOGIC
VCC
POWER-ON
RESET
OVERVOLTAGE
DETECTION
LOGIC
FS
PVCC
FSD
FS/DROOP
SELECT
BOOT
SS
MODE/DAC
SELECT
MOSFET
DRIVER
UGATE
PHASE
VID7
LGATE
VID6
VID5
VID4
VID3
DYNAMIC
VID
D/A
CLOCK AND
MODULATOR
WAVEFORM
GENERATOR
VID2
VID1
2kΩ
VID0
DVC
x2
100µA
REF
PWM
E/A
FB
COMP
ADAPTIVE PHASE
ALLIGNMENT
CIRCUITRY
APA
OFS
OFFSET
GND
3
FN6455.2
October 8, 2009
ISL6314
Typical Application - ISL6314
FB
DVC VDIFF VSEN
RGND
COMP
APA
Typical Applications
+5V
1. PVCC = 12V; VIN =12V;
VCC
2. PVCC = 5V; VIN = 19V;
other combinations are also possible
OFS
PVCC
VIN
FS
PVCC
REF
BOOT
SS
UGATE
PHASE
ISL6314
LGATE
LOAD
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
PGOOD
EN
GND
ISEN+ OCSET ISENO
ROCSET
ISEN-
CCOMP
Rs
RCOMP
4
FN6455.2
October 8, 2009
ISL6314
Typical Application - ISL6314 with NTC
Thermal Compensation
FB
DVC VDIFF VSEN
RGND
COMP
APA
+5V
VCC
OFS
+12V
FS
PVCC
REF
BOOT
SS
PLACE IN CLOSE
PROXIMITY
UGATE
PHASE
ISL6314
NTC
LGATE
LOAD
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
PGOOD
EN
GND
ISEN+ OCSET ISENO
ROCSET
ISEN-
CCOMP
Rs
RCOMP
5
FN6455.2
October 8, 2009
ISL6314
Absolute Maximum Ratings
Thermal Information
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
Supply Voltage, PVCC . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +15V
Absolute Boot Voltage, VBOOT . . . . . . . . GND - 0.3V to GND + 36V
Phase Voltage, VPHASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GND - 8V (<400ns, 20µJ) to 30V (<200ns, VBOOT-PHASE = 5V)
Upper Gate Voltage, VUGATE . . . . VPHASE - 0.3V to VBOOT + 0.3V
VPHASE - 3.5V (<100ns Pulse Width, 2µJ) to VBOOT + 0.3V
Lower Gate Voltage, VLGATE. . . . . . . . GND - 0.3V to PVCC + 0.3V
GND - 5V (<100ns Pulse Width, 2µJ) to PVCC+ 0.3V
Input, Output, or I/O Voltage . . . . . . . . . GND - 0.3V to VCC + 0.3V
Thermal Resistance
θJA (°C/W)
θJC (°C/W)
QFN Package (Notes 1, 2) . . . . . . . . . .
32
3.5
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +150°C
Maximum Storage Temperature Range . . . . . . . . . .-65°C to +150°C
Pb-Free Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
Recommended Operating Conditions
VCC Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+5V ±5%
PVCC Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . +5V to 12V ±5%
Ambient Temperature
ISL6314CRZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C
ISL6314IRZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-40°C to +85°C
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 in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See
Tech Brief TB379.
2. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications
Recommended Operating Conditions, Unless Otherwise Specified. 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
TEST CONDITIONS
MIN
TYP
MAX
UNITS
BIAS SUPPLIES
Input Bias Supply Current
IVCC; VCC = 5V; EN = high,
not switching;
9
11.4
16
mA
Gate Drive Bias Current - PVCC Pin
IPVCC; PVCC = 12V; EN = high,
high, not switching
1
2
4
mA
VCC POR (Power-On Reset) Threshold
VCC rising
4.25
4.38
4.50
V
VCC falling
3.75
3.88
4.00
V
PVCC rising
4.25
4.38
4.50
V
PVCC falling
3.75
3.88
4.00
V
Oscillator Frequency Accuracy, fSW
(ISL6314CRZ)
RT = 100kΩ (± 0.1%)
225
250
275
kHz
Oscillator Frequency Accuracy, fSW
(ISL6314IRZ)
RT = 100kΩ (± 0.1%)
215
250
280
kHz
Adjustment Range of Switching Frequency
(Note 3)
0.08
-
1.0
MHz
Oscillator Ramp Amplitude, VP-P
(Note 3)
-
1.50
-
V
0.84
0.86
0.88
V
-
110
-
mV
System Accuracy (1.000V to 1.600V)
-0.5
-
0.5
%
System Accuracy (0.600V to 1.000V)
-1.0
-
1.0
%
System Accuracy (0.375V to 0.600V)
-2.0
-
2.0
%
-
-
0.4
V
PVCC POR (Power-On Reset) Threshold
PWM MODULATOR
CONTROL THRESHOLDS
EN Rising Threshold
EN Hysteresis
REFERENCE AND DAC
VIDx Input Low Voltage (INTEL)
Pins VID0 to VID7
6
FN6455.2
October 8, 2009
ISL6314
Electrical Specifications
Recommended Operating Conditions, Unless Otherwise Specified. 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
TEST CONDITIONS
MIN
TYP
MAX
UNITS
VIDx Input High Voltage (INTEL)
Pins VID0 to VID7
0.8
-
-
V
VIDx Input Low Voltage (AMD)
Pins VID0 to VID7
-
-
0.8
V
VIDx Input High Voltage (AMD)
Pins VID0 to VID7
1.4
-
-
V
VIDx Pull-Up Current (INTEL)
Pins VID0 to VID7; VIDx = 0V
-
-40
-
µA
VIDx Pull-Down Current (AMD)
Pins VID0 to VID7; VIDx = 0.5V
-
20
-
µA
OFS Sink Current Accuracy (Negative Offset) ROFS = 32.4kΩ from OFS to
VCC
47.0
49.4
53.0
µA
ROFS = 6.04kΩ from OFS to
GND
47.0
49.7
53.0
µA
DC Gain
RL = 10k to ground, (Note 3)
-
96
-
dB
Gain-Bandwidth Product
CL = 100pF, RL = 10k to
ground, (Note 3)
-
40
-
MHz
Slew Rate
CL = 100pF, load = ±400µA,
(Note 3)
-
20
-
V/µs
Maximum Output Voltage
Load = 1mA
3.90
4.20
-
V
Minimum Output Voltage
Load = -1mA
-
1.20
1.4
V
VR11, RSS = 100kΩ
-
1.25
-
mV/µs
AMD, RSS = 100kΩ
-
1.25
-
mV/µs
0.156
-
6.25
mV/µs
OCSET Trip Current (ISL6314CRZ)
94
100
106
µA
OCSET Trip Current (ISL6314IRZ)
93
100
107
µA
-5
0
5
mV
-1.7
0
1.7
mV
PIN-ADJUSTABLE OFFSET
OFS Source Current Accuracy
(Positive Offset)
ERROR AMPLIFIER
SOFT-START RAMP
Soft-Start Ramp Rate
Adjustment Range of Soft-Start Ramp Rate
(Note 3)
OVERCURRENT PROTECTION
OCSET Accuracy
OCSET and ISUM Difference
ISENO Offset
PROTECTION
Undervoltage Threshold
VSEN falling
VDAC - 325
VDAC - 350mV
VDAC - 375
V
Undervoltage Hysteresis
VSEN rising
-
100
-
mV
Overvoltage Threshold During Soft-Start
VR11 and AMD
1.24
1.27
1.30
V
Overvoltage Threshold (Default)
VR11, VSEN rising
VDAC + 150mV
VDAC + 175mV
VDAC + 200mV
V
AMD, VSEN rising
VDAC + 200mV
VDAC + 225mV
VDAC + 250mV
V
Overvoltage Hysteresis
VSEN falling
-
100
-
mV
PGOOD Output Sink Current
PGOOD = 0.4V
-
7.5
-
mA
Thermal Shutdown Setpoint
-
160
-
°C
Thermal Recovery Setpoint
-
100
-
°C
OVER-TEMPERATURE SHUTDOWN (Note 3)
7
FN6455.2
October 8, 2009
ISL6314
Electrical Specifications
Recommended Operating Conditions, Unless Otherwise Specified. 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
TEST CONDITIONS
MIN
TYP
MAX
UNITS
SWITCHING TIME (Note 3)
UGATE Rise Time
tRUGATE; VPVCC = 12V, 3nF
load, 10% to 90%
-
26
-
ns
LGATE Rise Time
tRLGATE; VPVCC = 12V, 3nF
load, 10% to 90%
-
18
-
ns
UGATE Fall Time
tFUGATE; VPVCC = 12V, 3nF
load, 90% to 10%
-
18
-
ns
LGATE Fall Time
tFLGATE; VPVCC = 12V, 3nF
load, 90% to 10%
-
12
-
ns
UGATE Turn-On Non-Overlap
tPDHUGATE; VPVCC = 12V, 3nF
load, adaptive
-
10
-
ns
LGATE Turn-On Non-Overlap
tPDHLGATE; VPVCC = 12V, 3nF
load, adaptive
-
10
-
ns
GATE DRIVE RESISTANCE (Note 3)
Upper Drive Source Resistance
VPVCC = 12V, 15mA source
current
1.25
2.0
3.0
Ω
Upper Drive Sink Resistance
VPVCC = 12V, 15mA sink
current
0.9
1.65
3.0
Ω
Lower Drive Source Resistance
VPVCC = 12V, 15mA source
current
0.85
1.25
2.2
Ω
Lower Drive Sink Resistance
VPVCC = 12V, 15mA sink
current
0.60
0.80
1.35
Ω
NOTE:
3. Limits should be considered typical and are not production tested.
Timing Diagram
tPDHUGATE
tRUGATE
tFUGATE
UGATE
LGATE
tFLGATE
tRLGATE
tPDHLGATE
8
FN6455.2
October 8, 2009
ISL6314
Functional Pin Description
VCC (Pin 18)
VCC is the bias supply for the ICs small-signal circuitry.
Connect this pin to a +5V supply and decouple using a
quality 0.1µF ceramic capacitor.
FB and COMP (Pins 9, 7)
These pins are the internal error amplifier inverting input and
output respectively. The FB pin, COMP pin, and the VDIFF
pins are tied together through external R-C networks to
compensate the regulator.
DVC (Pin 8)
PVCC (Pin 19)
This pin is the power supply pin for the channel MOSFET
drivers, and can be connected to any voltage from +5V to
+12V depending on the desired MOSFET gate-drive level.
Decouple this pin with a quality 1.0µF ceramic capacitor.
GND (Pin 33 = Metal Pad)
GND is the bias and reference ground for the IC, connected
to the metal pad under the IC.
EN (Pin 17)
This pin is a threshold-sensitive (approximately 0.85V) enable
input for the controller. Held low, this pin disables controller
operation. Pulled high, the pin enables the controller for
operation.
FS (Pin 3)
A resistor, RT, tied to this pin sets the channel switching
frequency of the controller. Refer to Equation 42 for proper
resistor calculation.
The FS pin also controls whether the droop voltage (as
described under pins ISENO, ISEN-, ISEN+) is added to the
differential remote-sense amplifier’s output (VDIFF). Tying the
RT resistor to ground connects droop voltage, allowing the
converter to incorporate output voltage droop proportional to
the output current. Tying the RT resistor to VCC disconnects
the droop voltage.
VID0, VID1, VID2, VID3, VID4, VID5, VID6, and VID7
(Pins 31, 30, 29, 28, 27, 26, 25, 32)
These are the inputs for the internal DAC that provide the
reference voltage for output regulation. These pins respond to
TTL logic thresholds. These pins are internally pulled high, to
approximately 1.2V, by 40µA internal current sources for Intel
modes of operation, and pulled low by 20µA internal current
sources for AMD modes of operation. The internal pull-up
current decreases to 0 as the VID voltage approaches the
internal pull-up voltage. All VID pins are compatible with
external pull-up voltages not exceeding the IC’s bias voltage
(VCC).
VSEN (Pin 12)
This pin senses the microprocessor’s CORE voltage. Connect
this pin to the CORE voltage sense pin or point of the
microprocessor.
RGND (Pin 11)
This pin senses the local ground voltage of the
microprocessor. Connect this pin to the Ground sense pin or
point of the microprocessor.
9
A series resistor and capacitor can be connected from the
DVC pin to the FB pin to compensate and smooth dynamic
VID transitions.
OCSET (Pin 13)
This is the overcurrent set pin. Placing a resistor from
OCSET pin to ISENO allows a 100µA current to flow out of
this pin, producing a voltage reference. Internal circuitry
compares the voltage at OCSET to the voltage at ISEN-, and
if ISEN- ever exceeds OCSET, the overcurrent protection
activates.
APA (Pin 6)
This is the Adaptive Phase Alignment set pin. A 100µA
current flows out the APA pin and by tying a resistor from this
pin to COMP the trip level for the Adaptive Phase Alignment
circuitry can be set.
REF (Pin 4)
The REF input pin is the positive input of the error amplifier. It
is internally connected to the DAC output through a 2kΩ
resistor. A capacitor is used between the REF pin and ground
to smooth the voltage transition during soft-start and Dynamic
VID transitions. This pin can also be returned to RGND if
desired.
NC (Pin 20)
This pin is presently NC (No Connect), but is reserved for a
future function.
OFS (Pin 5)
The OFS pin provides a means to program a DC current for
generating an offset voltage across the resistor between FB
and VDIFF. The offset current is generated via an external
resistor and precision internal voltage references. The polarity
is selected by connecting the resistor to GND (for positive
offset) or to VCC (for negative offset). For no offset, the OFS
pin should be left unconnected.
UGATE (Pin 23)
Connect this pin to the corresponding upper MOSFET gate.
This pin is used to control the upper MOSFET and is
monitored for shoot-through prevention purposes.
BOOT (Pin 22)
This pin provides the bias voltage for the upper MOSFET
drive. Connect this pin to appropriately-chosen external
bootstrap capacitors. Internal bootstrap diodes connected to
the PVCC pin provides the necessary bootstrap charge.
FN6455.2
October 8, 2009
ISL6314
PHASE (Pin 24)
Operation
Connect this pin to the source of the upper MOSFET. This
pin is the return path for the upper MOSFET drive.
Power Conversion
LGATE (Pin 21)
This pin is used to control the lower MOSFET. Connect this
pin to the lower MOSFET gate.
SS (Pin 2)
A resistor, RSS, placed from SS to VCC or GND will set the
soft-start ramp slope. Refer to Equations 16 and 17 for
proper resistor calculation.
The ISL6314 controller helps simplify implementation by
integrating vital functions and requiring minimal external
components. The “Block Diagram” on page 3 provides a top
level view of the single-phase power conversion using the
ISL6314 controller.
IL, 7A/DIV
The state of the SS pin also selects which of the available DAC
tables will be used to decode the VID inputs and puts the
controller into the corresponding mode of operation. For Intel
VR11 mode of operation the RSS resistor should be tied to
GND. AMD compliance is selected if the RSS resistor is tied to
VCC (once in AMD mode, the VID7 bit selects 5-bit DAC if set
to a logic high, or 6-bit DAC if set to a logic low).
PGOOD (Pin 1)
PWM, 5V/DIV
For Intel mode of operation, PGOOD indicates whether VSEN
is within specified overvoltage and undervoltage limits after a
fixed delay from the end of soft-start. If VSEN exceeds these
limits, or if an overcurrent event occurs, or if the part is
disabled, PGOOD is pulled low. PGOOD is always low prior to
the end of soft-start.
For AMD modes of operation, PGOOD will always be high as
long as VSEN is within the specified undervoltage/overvoltage
window and soft-start has ended. PGOOD only goes low if
VSEN is outside this window.
ISENO, ISEN-, and ISEN+ (Pins 14, 15, 16)
ISEN-, ISEN+, and ISENO are the DCR current sense
amplifier’s negative input, positive input, and output
respectively. For accurate DCR current sensing, connect a
resistor from the phase node to ISEN- and connect ISEN+ to
the output inductor, roughly VOUT. A parallel R-C feedback
circuit connected between ISEN- and ISENO will then create
a voltage from ISEN+ to ISENO proportional to the voltage
drop across the inductor DCR. This voltage is referred to as
the droop voltage and is added to the differential
remote-sense amplifier’s output.
An optional 0.001µF to 0.01µF ceramic capacitor can be
placed from the ISEN+ pin to the ISEN- pin to help reduce
common mode noise that might be introduced by the layout.
1µs/DIV
FIGURE 1. PWM AND INDUCTOR-CURRENT WAVEFORMS
FOR 1-PHASE CONVERTER
Output Ripple
Figure 1 illustrates the output ripple. The PWM current forms
the AC ripple current and the DC load current. The
peak-to-peak current about 7A, and the DC components of
the inductor current feeds the load.
To understand the ripple current amplitude, examine
Equation 1 representing a single channel peak-to-peak
inductor current.
( V IN – V OUT ) ⋅ V OUT
I P-P = --------------------------------------------------------L ⋅ fS ⋅ V
In Equation 1, VIN and VOUT are the input and output
voltages respectively, L is the single-channel inductor value,
and fS is the switching frequency.
The output capacitors conduct the ripple component of the
inductor current. Output voltage ripple is a function of
capacitance, capacitor equivalent series resistance (ESR),
and inductor ripple current. Reducing the inductor ripple
current allows the designer to use fewer or less costly output
capacitors. Equation 2 shows the approximation for the
output voltage ripple.
V P-P = I P-P ⋅ ESR
VDIFF (Pin 10)
VDIFF is the output of the differential remote-sense amplifier.
The voltage on this pin is equal to the difference between
VSEN and RGND (VOUT) added to the difference between
ISEN+ and ISENO (droop). VDIFF therefore represents the
VOUT voltage plus the droop voltage. The state of the FS pin
determines whether the droop voltage is added or not.
10
(EQ. 1)
IN
(EQ. 2)
Adaptive Phase Alignment (APA)
To improve the transient response, the ISL6314 implements
Intersil’s proprietary Adaptive Phase Alignment (APA)
technique, which turns on the channel during large current
step transient events.
FN6455.2
October 8, 2009
ISL6314
EXTERNAL CIRCUIT
ISL6314 INTERNAL CIRCUIT
APA
100µA
CAPA
RAPA
+
APA
VAPA,TRIP
+
LOW
PASS
FILTER
COMP
TO APA
CIRCUITRY
+
-
ERROR
AMPLIFIER
FIGURE 2. ADAPTIVE PHASE ALIGNMENT DETECTION
As Figure 2 shows, the APA circuitry works by monitoring the
voltage on the APA pin and comparing it to a filtered copy of
the voltage on the COMP pin. The voltage on the APA pin is
a copy of the COMP pin voltage that has been negatively
offset. If the APA pin exceeds the filtered COMP pin voltage
an APA event occurs and the channel is forced on.
The APA trip level is the amount of DC offset between the
COMP pin and the APA pin. This is the voltage excursion
that the APA and COMP pin must have during a transient
event to activate the Adaptive Phase Alignment circuitry.
This APA trip level is set through a resistor, RAPA, that
connects from the APA pin to the COMP pin. A 100µA
current flows across RAPA into the APA pin to set the APA
trip level as described in Equation 3. An APA trip level of
500mV is recommended for most applications. A 1000pF
capacitor, CAPA, should also be placed across the RAPA
resistor to help with noise immunity.
V APA, TRIP = R APA ⋅ 100 × 10
–6
(EQ. 3)
Active Pulse Positioning (APP) Modulated PWM
Operation
The ISL6314 uses a proprietary Active Pulse Positioning
(APP) modulation scheme to control the internal PWM
signals that command each channel’s driver to turn their
upper and lower MOSFETs on and off. The time interval in
which a PWM signal can occur is generated by an internal
clock, whose cycle time is the inverse of the switching
frequency set by the resistor connected to the FS pin. The
advantage of Intersil’s proprietary Active Pulse Positioning
(APP) modulator is that the PWM signal has the ability to
turn on at any point during this PWM time interval, and turn
off immediately after the PWM signal has transitioned high.
This is important because is allows the controller to quickly
respond to output voltage drops associated with current load
spikes, while avoiding the ring back affects associated with
other modulation schemes.
11
The PWM output state is driven by the position of the error
amplifier output signal, VCOMP, as illustrated in Figure 3. At
the beginning of each PWM time interval, this VCOMP signal
is compared to the internal modulator waveform. As long as
the VCOMP voltage is lower then the modulator waveform
voltage, the PWM signal is commanded low. The internal
MOSFET driver detects the low state of the PWM signal and
turns off the upper MOSFET and turns on the lower
synchronous MOSFET. When the VCOMP voltage crosses
the modulator ramp, the PWM output transitions high,
turning off the synchronous MOSFET and turning on the
upper MOSFET. The PWM signal will remain high until the
VCOMP voltage crosses the modulator ramp again. When
this occurs, the PWM signal will transition low again.
During each PWM time interval, the PWM signal can only
transition high once. Once PWM transitions high, it can not
transition high again until the beginning of the next PWM
time interval. This prevents the occurrence of double PWM
pulses occurring during a single period.
VCOMP
+
MODULATOR
RAMP
WAVEFORM
PWM
TO GATE
CONTROL
LOGIC
-
FIGURE 3. CHANNEL PWM FUNCTION
Output Voltage Setting
The ISL6314 uses a digital to analog converter (DAC) to
generate a reference voltage based on the logic signals at
the VID pins. The DAC decodes the logic signals into one of
the discrete voltages shown in Tables 2, 3 or 4. In the Intel
VR11 mode of operation, each VID pin is pulled up to an
internal 1.2V voltage by a weak current source (40µA),
which decreases to 0A as the voltage at the VID pin varies
from 0 to the internal 1.2V pull-up voltage. In AMD modes of
operation, the VID pins are pulled low by a weak 20µA
current source. External pull-up resistors or active-high
output stages can augment the pull-up current sources, up to
a voltage of 5V.
The ISL6314 accommodates three different DAC ranges:
Intel VR11, AMD K8/K9 5-bit, and AMD 6-bit. The state of
the SS and VID7 pins decide which DAC version is active.
Refer to Table 1 for a description of how to select the desired
DAC version.
.
FN6455.2
October 8, 2009
ISL6314
TABLE 1. ISL6314 DAC SELECT AND FUNCTION TABLE
TABLE 2. VR11 VOLTAGE IDENTIFICATION CODES (Continued)
DAC VERSION
SS PIN
VID7 PIN
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
INTEL VR11
RSS resistor tied to
GND
-
0
0
0
1
1
0
1
1
1.44375
0
0
0
1
1
1
0
0
1.43750
AMD 5-BIT
RSS resistor tied to
VCC
high
0
0
0
1
1
1
0
1
1.43125
AMD 6-BIT
RSS resistor tied to
VCC
low
0
0
0
1
1
1
1
0
1.42500
0
0
0
1
1
1
1
1
1.41875
0
0
1
0
0
0
0
0
1.41250
TIE RESISTOR to
VCC
OPEN
TIE RESISTOR to
GND
0
0
1
0
0
0
0
1
1.40625
0
0
1
0
0
0
1
0
1.40000
RSS: AMD Tables
-
RSS: Intel Table
0
0
1
0
0
0
1
1
1.39375
ROFS: Negative
No Offset
ROFS: Positive
0
0
1
0
0
1
0
0
1.38750
RT: No Droop
-
RT: Droop
0
0
1
0
0
1
0
1
1.38125
0
0
1
0
0
1
1
0
1.37500
TABLE 2. VR11 VOLTAGE IDENTIFICATION CODES
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
0
0
1
0
0
1
1
1
1.36875
0
0
0
0
0
0
0
0
OFF
0
0
1
0
1
0
0
0
1.36250
0
0
0
0
0
0
0
1
OFF
0
0
1
0
1
0
0
1
1.35625
0
0
0
0
0
0
1
0
1.60000
0
0
1
0
1
0
1
0
1.35000
0
0
0
0
0
0
1
1
1.59375
0
0
1
0
1
0
1
1
1.34375
0
0
0
0
0
1
0
0
1.58750
0
0
1
0
1
1
0
0
1.33750
0
0
0
0
0
1
0
1
1.58125
0
0
1
0
1
1
0
1
1.33125
0
0
0
0
0
1
1
0
1.57500
0
0
1
0
1
1
1
0
1.32500
0
0
0
0
0
1
1
1
1.56875
0
0
1
0
1
1
1
1
1.31875
0
0
0
0
1
0
0
0
1.56250
0
0
1
1
0
0
0
0
1.31250
0
0
0
0
1
0
0
1
1.55625
0
0
1
1
0
0
0
1
1.30625
0
0
0
0
1
0
1
0
1.55000
0
0
1
1
0
0
1
0
1.30000
0
0
0
0
1
0
1
1
1.54375
0
0
1
1
0
0
1
1
1.29375
0
0
0
0
1
1
0
0
1.53750
0
0
1
1
0
1
0
0
1.28750
0
0
0
0
1
1
0
1
1.53125
0
0
1
1
0
1
0
1
1.28125
0
0
0
0
1
1
1
0
1.52500
0
0
1
1
0
1
1
0
1.27500
0
0
0
0
1
1
1
1
1.51875
0
0
1
1
0
1
1
1
1.26875
0
0
0
1
0
0
0
0
1.51250
0
0
1
1
1
0
0
0
1.26250
0
0
0
1
0
0
0
1
1.50625
0
0
1
1
1
0
0
1
1.25625
0
0
0
1
0
0
1
0
1.50000
0
0
1
1
1
0
1
0
1.25000
0
0
0
1
0
0
1
1
1.49375
0
0
1
1
1
0
1
1
1.24375
0
0
0
1
0
1
0
0
1.48750
0
0
1
1
1
1
0
0
1.23750
0
0
0
1
0
1
0
1
1.48125
0
0
1
1
1
1
0
1
1.23125
0
0
0
1
0
1
1
0
1.47500
0
0
1
1
1
1
1
0
1.22500
0
0
0
1
0
1
1
1
1.46875
0
0
1
1
1
1
1
1
1.21875
0
0
0
1
1
0
0
0
1.46250
0
1
0
0
0
0
0
0
1.21250
0
0
0
1
1
0
0
1
1.45625
0
1
0
0
0
0
0
1
1.20625
0
0
0
1
1
0
1
0
1.45000
0
1
0
0
0
0
1
0
1.20000
12
FN6455.2
October 8, 2009
ISL6314
TABLE 2. VR11 VOLTAGE IDENTIFICATION CODES (Continued)
TABLE 2. VR11 VOLTAGE IDENTIFICATION CODES (Continued)
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
0
1
0
0
0
0
1
1
1.19375
0
1
1
0
1
0
1
1
0.94375
0
1
0
0
0
1
0
0
1.18750
0
1
1
0
1
1
0
0
0.93750
0
1
0
0
0
1
0
1
1.18125
0
1
1
0
1
1
0
1
0.93125
0
1
0
0
0
1
1
0
1.17500
0
1
1
0
1
1
1
0
0.92500
0
1
0
0
0
1
1
1
1.16875
0
1
1
0
1
1
1
1
0.91875
0
1
0
0
1
0
0
0
1.16250
0
1
1
1
0
0
0
0
0.91250
0
1
0
0
1
0
0
1
1.15625
0
1
1
1
0
0
0
1
0.90625
0
1
0
0
1
0
1
0
1.15000
0
1
1
1
0
0
1
0
0.90000
0
1
0
0
1
0
1
1
1.14375
0
1
1
1
0
0
1
1
0.89375
0
1
0
0
1
1
0
0
1.13750
0
1
1
1
0
1
0
0
0.88750
0
1
0
0
1
1
0
1
1.13125
0
1
1
1
0
1
0
1
0.88125
0
1
0
0
1
1
1
0
1.12500
0
1
1
1
0
1
1
0
0.87500
0
1
0
0
1
1
1
1
1.11875
0
1
1
1
0
1
1
1
0.86875
0
1
0
1
0
0
0
0
1.11250
0
1
1
1
1
0
0
0
0.86250
0
1
0
1
0
0
0
1
1.10625
0
1
1
1
1
0
0
1
0.85625
0
1
0
1
0
0
1
0
1.10000
0
1
1
1
1
0
1
0
0.85000
0
1
0
1
0
0
1
1
1.09375
0
1
1
1
1
0
1
1
0.84375
0
1
0
1
0
1
0
0
1.08750
0
1
1
1
1
1
0
0
0.83750
0
1
0
1
0
1
0
1
1.08125
0
1
1
1
1
1
0
1
0.83125
0
1
0
1
0
1
1
0
1.07500
0
1
1
1
1
1
1
0
0.82500
0
1
0
1
0
1
1
1
1.06875
0
1
1
1
1
1
1
1
0.81875
0
1
0
1
1
0
0
0
1.06250
1
0
0
0
0
0
0
0
0.81250
0
1
0
1
1
0
0
1
1.05625
1
0
0
0
0
0
0
1
0.80625
0
1
0
1
1
0
1
0
1.05000
1
0
0
0
0
0
1
0
0.80000
0
1
0
1
1
0
1
1
1.04375
1
0
0
0
0
0
1
1
0.79375
0
1
0
1
1
1
0
0
1.03750
1
0
0
0
0
1
0
0
0.78750
0
1
0
1
1
1
0
1
1.03125
1
0
0
0
0
1
0
1
0.78125
0
1
0
1
1
1
1
0
1.02500
1
0
0
0
0
1
1
0
0.77500
0
1
0
1
1
1
1
1
1.01875
1
0
0
0
0
1
1
1
0.76875
0
1
1
0
0
0
0
0
1.01250
1
0
0
0
1
0
0
0
0.76250
0
1
1
0
0
0
0
1
1.00625
1
0
0
0
1
0
0
1
0.75625
0
1
1
0
0
0
1
0
1.00000
1
0
0
0
1
0
1
0
0.75000
0
1
1
0
0
0
1
1
0.99375
1
0
0
0
1
0
1
1
0.74375
0
1
1
0
0
1
0
0
0.98750
1
0
0
0
1
1
0
0
0.73750
0
1
1
0
0
1
0
1
0.98125
1
0
0
0
1
1
0
1
0.73125
0
1
1
0
0
1
1
0
0.97500
1
0
0
0
1
1
1
0
0.72500
0
1
1
0
0
1
1
1
0.96875
1
0
0
0
1
1
1
1
0.71875
0
1
1
0
1
0
0
0
0.96250
1
0
0
1
0
0
0
0
0.71250
0
1
1
0
1
0
0
1
0.95625
1
0
0
1
0
0
0
1
0.70625
0
1
1
0
1
0
1
0
0.95000
1
0
0
1
0
0
1
0
0.70000
13
FN6455.2
October 8, 2009
ISL6314
TABLE 2. VR11 VOLTAGE IDENTIFICATION CODES (Continued)
VID7
VID6
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
1
0
0
1
0
0
1
1
0.69375
1
0
0
1
0
1
0
0
0.68750
1
0
0
1
0
1
0
1
0.68125
1
0
0
1
0
1
1
0
0.67500
1
0
0
1
0
1
1
1
0.66875
1
0
0
1
1
0
0
0
0.66250
1
0
0
1
1
0
0
1
0.65625
1
0
0
1
1
0
1
0
0.65000
1
0
0
1
1
0
1
1
0.64375
1
0
0
1
1
1
0
0
0.63750
1
0
0
1
1
1
0
1
0.63125
1
0
0
1
1
1
1
0
0.62500
1
0
0
1
1
1
1
1
0.61875
1
0
1
0
0
0
0
0
0.61250
1
0
1
0
0
0
0
1
0.60625
1
0
1
0
0
0
1
0
0.60000
1
0
1
0
0
0
1
1
0.59375
1
0
1
0
0
1
0
0
0.58750
1
0
1
0
0
1
0
1
0.58125
1
0
1
0
0
1
1
0
0.57500
1
0
1
0
0
1
1
1
0.56875
1
0
1
0
1
0
0
0
0.56250
1
0
1
0
1
0
0
1
0.55625
1
0
1
0
1
0
1
0
0.55000
1
0
1
0
1
0
1
1
0.54375
1
0
1
0
1
1
0
0
0.53750
1
0
1
0
1
1
0
1
0.53125
1
0
1
0
1
1
1
0
0.52500
1
0
1
0
1
1
1
1
0.51875
1
0
1
1
0
0
0
0
0.51250
1
0
1
1
0
0
0
1
0.50625
1
0
1
1
0
0
1
0
0.50000
1
1
1
1
1
1
1
0
OFF
1
1
1
1
1
1
1
1
OFF
TABLE 3. AMD 5-BIT VOLTAGE IDENTIFICATION
CODES
VID4
VID3
VID2
VID1
VID0
VDAC
1
1
1
1
1
Off
1
1
1
1
0
0.800
1
1
1
0
1
0.825
14
TABLE 3. AMD 5-BIT VOLTAGE IDENTIFICATION
CODES (Continued)
VID4
VID3
VID2
VID1
VID0
VDAC
1
1
1
0
0
0.850
1
1
0
1
1
0.875
1
1
0
1
0
0.900
1
1
0
0
1
0.925
1
1
0
0
0
0.950
1
0
1
1
1
0.975
1
0
1
1
0
1.000
1
0
1
0
1
1.025
1
0
1
0
0
1.050
1
0
0
1
1
1.075
1
0
0
1
0
1.100
1
0
0
0
1
1.125
1
0
0
0
0
1.150
0
1
1
1
1
1.175
0
1
1
1
0
1.200
0
1
1
0
1
1.225
0
1
1
0
0
1.250
0
1
0
1
1
1.275
0
1
0
1
0
1.300
0
1
0
0
1
1.325
0
1
0
0
0
1.350
0
0
1
1
1
1.375
0
0
1
1
0
1.400
0
0
1
0
1
1.425
0
0
1
0
0
1.450
0
0
0
1
1
1.475
0
0
0
1
0
1.500
0
0
0
0
1
1.525
0
0
0
0
0
1.550
TABLE 4. AMD 6-BIT VOLTAGE IDENTIFICATION
CODES
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
0
0
0
0
0
0
1.5500
0
0
0
0
0
1
1.5250
0
0
0
0
1
0
1.5000
0
0
0
0
1
1
1.4750
0
0
0
1
0
0
1.4500
0
0
0
1
0
1
1.4250
0
0
0
1
1
0
1.4000
FN6455.2
October 8, 2009
ISL6314
TABLE 4. AMD 6-BIT VOLTAGE IDENTIFICATION
CODES (Continued)
TABLE 4. AMD 6-BIT VOLTAGE IDENTIFICATION
CODES (Continued)
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
VID5
VID4
VID3
VID2
VID1
VID0
VDAC
0
0
0
1
1
1
1.3750
1
0
1
1
1
0
0.5875
0
0
1
0
0
0
1.3500
1
0
1
1
1
1
0.5750
0
0
1
0
0
1
1.3250
1
1
0
0
0
0
0.5625
0
0
1
0
1
0
1.3000
1
1
0
0
0
1
0.5500
0
0
1
0
1
1
1.2750
1
1
0
0
1
0
0.5375
0
0
1
1
0
0
1.2500
1
1
0
0
1
1
0.5250
0
0
1
1
0
1
1.2250
1
1
0
1
0
0
0.5125
0
0
1
1
1
0
1.2000
1
1
0
1
0
1
0.5000
0
0
1
1
1
1
1.1750
1
1
0
1
1
0
0.4875
0
1
0
0
0
0
1.1500
1
1
0
1
1
1
0.4750
0
1
0
0
0
1
1.1250
1
1
1
0
0
0
0.4625
0
1
0
0
1
0
1.1000
1
1
1
0
0
1
0.4500
0
1
0
0
1
1
1.0750
1
1
1
0
1
0
0.4375
0
1
0
1
0
0
1.0500
1
1
1
0
1
1
0.4250
0
1
0
1
0
1
1.0250
1
1
1
1
0
0
0.4125
0
1
0
1
1
0
1.0000
1
1
1
1
0
1
0.4000
0
1
0
1
1
1
0.9750
1
1
1
1
1
0
0.3875
0
1
1
0
0
0
0.9500
1
1
1
1
1
1
0.3750
0
1
1
0
0
1
0.9250
0
1
1
0
1
0
0.9000
0
1
1
0
1
1
0.8750
0
1
1
1
0
0
0.8500
0
1
1
1
0
1
0.8250
0
1
1
1
1
0
0.8000
0
1
1
1
1
1
0.7750
1
0
0
0
0
0
0.7625
1
0
0
0
0
1
0.7500
1
0
0
0
1
0
0.7375
1
0
0
0
1
1
0.7250
1
0
0
1
0
0
0.7125
1
0
0
1
0
1
0.7000
1
0
0
1
1
0
0.6875
1
0
0
1
1
1
0.6750
1
0
1
0
0
0
0.6625
1
0
1
0
0
1
0.6500
1
0
1
0
1
0
0.6375
1
0
1
0
1
1
0.6250
1
0
1
1
0
0
0.6125
1
0
1
1
0
1
0.6000
15
Voltage Regulation
In order to regulate the output voltage to a specified level,
the ISL6314 uses the integrating compensation network
shown in Figure 4. This compensation network insures that
the steady-state error in the output voltage is limited only to
the error in the reference voltage (output of the DAC) and
offset errors in the OFS current source, remote-sense and
error amplifiers. Intersil specifies the guaranteed tolerance of
the ISL6314 to include the combined tolerances of each of
these elements.
The ISL6314 incorporates an internal differential
remote-sense amplifier in the feedback path. The amplifier
removes the voltage error encountered when measuring the
output voltage relative to the controller ground reference
point, resulting in a more accurate means of sensing output
voltage. Connect the microprocessor sense pins to the
non-inverting input, VSEN, and inverting input, RGND, of the
remote-sense amplifier. The droop voltage, VDROOP, also
feeds into the remote-sense amplifier. The remote-sense
output, VDIFF, is therefore equal to the sum of the output
voltage, VOUT, and the droop voltage. VDIFF is connected to
the inverting input of the error amplifier through an external
resistor.
V OUT = V REF – V OFS – V DROOP
(EQ. 4)
FN6455.2
October 8, 2009
ISL6314
+
VL(s)
L
PHASE
IOUT
DCR
VOUT
INDUCTOR
I
L
RS
COUT
ISEN-
ISL6314 INTERNAL CIRCUIT
-
+
EXTERNAL CIRCUIT
RC CC
COMP
.
-
The output of the error amplifier, VCOMP, is compared to the
sawtooth waveform to generate the PWM signal. The PWM
signal controls the timing of the Internal MOSFET drivers
and regulates the converter output so that the voltage at FB
is equal to the voltage at REF. This will regulate the output
voltage to be equal to Equation 4. The internal and external
circuitry that controls voltage regulation is illustrated in
Figure 4.
CCOMP
RCOMP
ISENO
VID DAC
VDROOP
+ ISEN+
2k
REF
CREF
+
-
FB
RFB
+
VOFS
-
IOFS
VDIFF
VSEN
+
+
VOUT
RGND
-
ISEN+
+
-
VDROOP
-
ISL6314
VCOMP
FIGURE 5. DCR SENSING CONFIGURATION
ERROR AMPLIFIER
+
-
(OPTIONAL)
ISENO
DIFFERENTIAL
REMOTE-SENSE
AMPLIFIER
FIGURE 4. OUTPUT VOLTAGE AND LOAD-LINE
REGULATION WITH OFFSET ADJUSTMENT
Load-Line (Droop) Regulation
Some microprocessor manufacturers require a
precisely-controlled output resistance. This dependence of
output voltage on load current is often termed “droop” or
“load line” regulation. By adding a well controlled output
impedance, the output voltage can effectively be level shifted
in a direction which works to achieve the load-line regulation
required by these manufacturers.
In other cases, the designer may determine that a more
cost-effective solution can be achieved by adding droop.
Droop can help to reduce the output-voltage spike that
results from fast load-current demand changes.
The magnitude of the spike is dictated by the ESR and ESL
of the output capacitors selected. By positioning the no-load
voltage level near the upper specification limit, a larger
negative spike can be sustained without crossing the lower
limit. By adding a well controlled output impedance, the
output voltage under load can effectively be level shifted
down so that a larger positive spike can be sustained without
crossing the upper specification limit.
16
As shown in Figure 5, a voltage, VDROOP, proportional to the
current in the channel, IOUT, feeds into the differential
remote-sense amplifier. The resulting voltage at the output of
the remote-sense amplifier is the sum of the output voltage
and the droop voltage. Equation 5 shows that feeding this
voltage into the compensation network causes the regulator
to adjust the output voltage so that it’s equal to the reference
voltage minus the droop voltage.
The droop voltage, VDROOP, is created by sensing the
current through the output inductors. This is accomplished
by using a continuous DCR current sensing method.
Inductor windings have a characteristic distributed
resistance or DCR (Direct Current Resistance). For
simplicity, the inductor DCR is considered as a separate
lumped quantity, as shown in Figure 5. The channel current,
IL, flowing through the inductor, passes through the DCR.
Equation 5 shows the S-domain equivalent voltage, VL,
across the inductor.
V L ( s ) = I L ⋅ ( s ⋅ L + DCR )
(EQ. 5)
The inductor DCR is important because the voltage dropped
across it is proportional to the channel current. By using a
simple R-C network and a current sense amplifier, as shown
in Figure 5, the voltage drop across the inductor’s DCR can
be extracted. The output of the current sense amplifier,
VDROOP, can be shown to be proportional to the channel
current IL, shown in Equation 6.
V
DROOP
s⋅L
⎛ ------------⎞
R
⎝ DCR + 1⎠
COMP
( s ) = -------------------------------------------------------------------------- ⋅ ----------------------- ⋅ ( I ) ⋅ DCR
L
(s ⋅ R
⋅C
+ 1)
R
COMP
COMP
S
(EQ. 6)
If the R-C network components are selected such that the
R-C time constant matches the inductor L/DCR time
constant, then VDROOP is equal to the voltage drop across
the DCR, multiplied by a gain. As Equation 7 shows,
VDROOP is therefore proportional to the total output current,
IOUT.
FN6455.2
October 8, 2009
ISL6314
.
R COMP
V DROOP = --------------------- ⋅ I OUT ⋅ DCR
RS
VDIFF
(EQ. 7)
By simply adjusting the value of RS, the load line can be set
to any level, giving the converter the right amount of droop at
all load currents. It may also be necessary to compensate for
any changes in DCR due to temperature. These changes
cause the load line to be skewed, and cause the R-C time
constant to not match the L/DCR time constant. If this
becomes a problem a simple negative temperature
coefficient resistor network can be used in the place of
RCOMP to compensate for the rise in DCR due to
temperature.
+
VOFS
-
RFB
E/A
FB
IOFS
-
Note: An optional 10nF ceramic capacitor from the ISEN+
pin to the ISEN- pin is recommended to help reduce any
noise affects on the current sense amplifier due to layout
OFS
ISL6314
The ISL6314 allows the designer to accurately adjust the
offset voltage by connecting a resistor, ROFS, from the OFS
pin to VCC or GND. When ROFS is connected between OFS
and VCC, the voltage across it is regulated to 1.6V. This
causes a proportional current (IOFS) to flow into the OFS pin
and out of the FB pin, providing a negative offset. If ROFS is
connected to ground, the voltage across it is regulated to
0.3V, and IOFS flows into the FB pin and out of the OFS pin,
providing a positive offset. The offset current flowing through
the resistor between VDIFF and FB will generate the desired
offset voltage which is equal to the product (IOFS x RFB).
These functions are shown in Figures 6 and 7.
-
1.6V
+
+
ROFS
Output-Voltage Offset Programming
VREF
0.3V
GND
VCC
GND
FIGURE 6. POSITIVE OFFSET OUTPUT VOLTAGE
PROGRAMMING
VDIFF
VOFS
+
RFB
VREF
E/A
FB
IOFS
Once the desired output offset voltage has been determined,
use the following formulas in Equations 8 and 9 to set ROFS:
For Negative Offset (connect ROFS to VCC):
1.6 ⋅ RFB
R OFS = -------------------------V OFFSET
(EQ. 8)
-
ROFS
For Positive Offset (connect ROFS to GND):
0.3 ⋅ RFB
R OFS = -------------------------V OFFSET
VCC
+
(EQ. 9)
OFS
ISL6314
-
1.6V
+
0.3V
GND
VCC
FIGURE 7. NEGATIVE OFFSET OUTPUT VOLTAGE
PROGRAMMING
17
FN6455.2
October 8, 2009
ISL6314
Dynamic VID
Compensating Dynamic VID Transitions
Modern microprocessors need to make changes to their core
voltage as part of normal operation. They direct the ISL6314
to do this by making changes to the VID inputs. The ISL6314
is required to monitor the DAC inputs and respond to
on-the-fly VID changes in a controlled manner, supervising a
safe output voltage transition without discontinuity or
disruption. The DAC mode, ISL6314 is operating in,
determines how the controller responds to a dynamic VID
change.
During a VID transition, the resulting change in voltage on
the FB pin and the COMP pin causes an AC current to flow
through the error amplifier compensation components from
the FB to the COMP pin. This current then flows through the
feedback resistor, RFB, and can cause the output voltage to
overshoot or undershoot at the end of the VID transition. In
order to ensure the smooth transition of the output voltage
during a VID change, a VID-on-the-fly compensation
network is required. This network is composed of a resistor
and capacitor in series, RDVC and CDVC, between the DVC
and the FB pin, as shown in Figure 8.
INTEL DYNAMIC VID TRANSITIONS
When in Intel VR11 mode the ISL6314 checks the VID inputs
on the positive edge of an internal 5.5MHz clock. If a new
code is established and it remains stable for three consecutive
readings (0.36µs to 0.54µs), the ISL6314 recognizes the new
code and changes the internal DAC reference directly to the
new level. The Intel processor controls the VID transitions and
is responsible for incrementing or decrementing one VID step
at a time. In VR11 mode, the ISL6314 will immediately change
the internal DAC reference to the new requested value as
soon as the request is validated, which means the fastest
recommended rate at which a bit change can occur is once
every 1µs. If the VID code is changed by more then one step
at a time, the DAC will try to track it at a 5.5MHz step rate.
This will likely cause an overcurrent or overvoltage fault.
When running in AMD 5-bit or 6-bit modes of operation, the
ISL6314 responds differently to a dynamic VID change. In the
AMD modes the ISL6314 still checks the VID inputs on the
positive edge of an internal 5.5MHz clock. In these modes the
VID code can be changed by more than a 1-bit step at a time. If
a new code is established and it remains stable for three
consecutive readings (0.36µs to 0.54µs), the ISL6314
recognizes the change and begins slewing the DAC in
6.25mV steps at a stepping frequency of 345kHz until the VID
and DAC are equal. Thus, the total time required for a VID
change, tDVID, is dependent only on the size of the VID change
(ΔVVID).
The time required for a ISL6314-based converter in AMD 5-bit
DAC configuration to make a 1.1V to 1.5V reference voltage
change is about 186µs, as calculated using Equation 10.
(EQ. 10)
VID “OFF” DAC CODES
Both the Intel VR11 and the AMD 5-bit VID tables include “Off”
DAC codes, which indicate to the controller to disable all
regulation. Recognition of these codes is slightly different in that
they must be stable for four consecutive readings of a 5.5MHz
clock (0.54µs to 0.72µs) to be recognized. Once an “Off” code
is recognized the ISL6314 latches off, and must be reset by
dropping the EN pin.
18
IDVC = IC
IC
IDVC
CC
CDVC
RC
RDVC
DVC
COMP
FB
x2
REF
+
CREF
VDAC+RGND
ERROR
AMPLIFIER
ISL6314 INTERNAL CIRCUIT
FIGURE 8. VID-ON-THE-FLY COMPENSATION NETWORK
AMD DYNAMIC VID TRANSITIONS
ΔV VID
1
t DVID = -------------------------- ⋅ ⎛ ---------------------⎞
3 ⎝ 0.00625⎠
345 × 10
RFB
VDIFF
This VID-on-the-fly compensation network works by
sourcing AC current into the FB node to offset the effects of
the AC current flowing from the FB to the COMP pin during a
VID transition. To create this compensation current the
ISL6314 sets the voltage on the DVC pin to be 2x the voltage
on the REF pin. Since the error amplifier forces the voltage
on the FB pin and the REF pin to be equal, the resulting
voltage across the series RC between DVC and FB is equal
to the REF pin voltage. The RC compensation components,
RDVC and CDVC, can then be selected to create the desired
amount of compensation current.
The amount of compensation current required is dependant
on the modulator gain of the system, K1, and the error
amplifier R-C components, RC and CC, that are in series
between the FB and COMP pins. Use Equations 11, 12, and
13 to calculate the RC component values, RDVC and CDVC,
for the VID-on-the-fly compensation network. For these
equations: VIN is the input voltage for the power train; VP-P
is the oscillator ramp amplitude (1.5V); and RC and CC are
the error amplifier R-C components between the FB and
COMP pins.
V IN
K1 = ----------V PP
K1
A = ----------------K1 – 1
(EQ. 11)
FN6455.2
October 8, 2009
ISL6314
1.6
R DVC = A × R C
(EQ. 12)
1.4
CC
C DVC = -------A
(EQ. 13)
The integrated drivers incorporate a unique adaptive deadtime
control technique to minimize deadtime, resulting in high
efficiency from the reduced freewheeling time of the lower
MOSFET body-diode conduction, and to prevent the upper and
lower MOSFETs from conducting simultaneously. This is
accomplished by ensuring either rising gate turns on its
MOSFET with minimum and sufficient delay after the other has
turned off.
During turn-off of the lower MOSFET, the PHASE voltage is
monitored until it reaches a -0.3V/+0.8V (forward/reverse
inductor current). At this time the UGATE is released to rise. An
auto-zero comparator is used to correct the rDS(ON) drop in the
phase voltage preventing false detection of the -0.3V phase
level during rDS(ON) conduction period. In the case of zero
current, the UGATE is released after 35ns delay of the LGATE
dropping below 0.5V. When LGATE first begins to transition
low, this quick transition can disturb the PHASE node and
cause a false trip, so there is 20ns of blanking time once
LGATE falls until PHASE is monitored.
Once the PHASE is high, the advanced adaptive
shoot-through circuitry monitors the PHASE and UGATE
voltages during a PWM falling edge and the subsequent
UGATE turn-off. If either the UGATE falls to less than 1.75V
above the PHASE or the PHASE falls to less than +0.8V, the
LGATE is released to turn-on.
Internal Bootstrap Device
The integrated driver features an internal bootstrap schottky
diode. Simply adding an external capacitor across the BOOT
and PHASE pins completes the bootstrap circuit. The
bootstrap function is also designed to prevent the bootstrap
capacitor from overcharging due to the large negative swing
at the PHASE node. This reduces voltage stress on the boot
to phase pins.
19
CBOOT_CAP (µF)
Advanced Adaptive Zero Shoot-Through Deadtime
Control (Patent Pending)
1.2
1.0
0.8
0.6
QGATE = 100nC
0.4
50nC
0.2
20nC
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
ΔVBOOT_CAP (V)
FIGURE 9. BOOTSTRAP CAPACITANCE vs BOOT RIPPLE
VOLTAGE
The bootstrap capacitor must have a maximum voltage
rating above PVCC + 4V and its capacitance value can be
chosen from Equation 14: where QG1 is the amount of gate
charge per upper MOSFET at VGS1 gate-source voltage and
NQ1 is the number of control MOSFETs. The ΔVBOOT_CAP
term is defined as the allowable droop in the rail of the upper
gate drive. Typical curves are shown in Figure 9.
Q GATE
C BOOT_CAP ≥ -------------------------------------ΔV BOOT_CAP
(EQ. 14)
Q G1 ⋅ PVCC
Q GATE = ---------------------------------- ⋅ N Q1
V GS1
Gate Drive Voltage Versatility
The ISL6314 provides the user flexibility in choosing the
gate drive voltage for efficiency optimization. The controller
ties the upper and lower drive rails together. Simply applying
a voltage from 5V up to 12V on PVCC sets both gate drive
rail voltages simultaneously.
Initialization
Prior to initialization, proper conditions must exist on the EN,
VCC, PVCC and the VID pins. When the conditions are met,
the controller begins soft-start. Once the output voltage is
within the proper window of operation, the controller asserts
PGOOD.
FN6455.2
October 8, 2009
ISL6314
.
ISL6314 INTERNAL CIRCUIT
EXTERNAL CIRCUIT
VCC
PVCC
POR
CIRCUIT
+12V
Once all of these conditions are met the controller will begin
the soft-start sequence and will ramp the output voltage up
to the user designated level.
Intel Soft-Start
ENABLE
COMPARATOR
10.7kΩ
EN
+
4. The VID code must not be 11111 in AMD 5-bit mode. This
code signals the controller that no load is present. The
controller will not allow soft-start to begin if this VID code
is present on the VID pins.
1.40kΩ
The soft-start function allows the converter to bring up the
output voltage in a controlled fashion, resulting in a linear
ramp-up. The soft-start sequence for the Intel modes of
operation is slightly different than the AMD soft-start
sequence.
0.85V
SOFT-START
AND
FAULT LOGIC
VOUT, 500mV/DIV
FIGURE 10. POWER SEQUENCING USING
THRESHOLD-SENSITIVE ENABLE (EN)
FUNCTION
Enable and Disable
td1
td2
td3
td4
td5
EN
While in shutdown mode, the LGATE and UGATE signals
are held low to assure the MOSFETs remain off. The
following input conditions must be met, for both Intel and
AMD modes of operation, before the ISL6314 is released
from shutdown mode to begin the soft-start start-up
sequence:
1. The bias voltage applied at VCC must reach the internal
power-on reset (POR) rising threshold. Once this
threshold is reached, proper operation of all aspects of
the ISL6314 is guaranteed. Hysteresis between the rising
and falling thresholds assure that once enabled, the
ISL6314 will not inadvertently turn off unless the bias
voltage drops substantially (see “Electrical
Specifications” on page 6).
2. The voltage on EN must be above 0.85V. The EN input
allows for power sequencing between the controller bias
voltage and another voltage rail. The enable comparator
holds the ISL6314 in shutdown until the voltage at EN
rises above 0.85V. The enable comparator has 110mV of
hysteresis to prevent bounce.
3. The driver bias voltage applied at the PVCC pin must
reach the internal power-on reset (POR) rising threshold.
Hysteresis between the rising and falling thresholds
assure that once enabled, the ISL6314 will not
inadvertently turn off unless the PVCC bias voltage drops
substantially (see “Electrical Specifications” on page 6).
For Intel VR11 and AMD 6-bit modes of operation these are
the only conditions that must be met for the controller to
immediately begin the soft-start sequence, as shown in
Figure 10. If running in AMD 5-bit mode of operation there is
one more condition that must be met:
20
PGOOD
500µs/DIV
FIGURE 11. INTEL SOFT-START WAVEFORMS
For the Intel VR11 mode of operation, the soft-start
sequence is composed of four periods, as shown in
Figure 11. Once the ISL6314 is released from shutdown and
soft-start begins (as described in “Enable and Disable” on
page 20), the controller will have fixed delay period td1,
typically 1.1ms. After this delay period, the VR will begin first
soft-start ramp until the output voltage reaches 1.1V VBOOT
voltage. Then, the controller will regulate the VR voltage at
1.1V for another fixed period td3, typically 93µs. At the end of
td3 period, ISL6314 will read the VID signals. It is
recommended that the VID codes be set no later then 50µs
into period td3. If the VID code is valid, ISL6314 will initiate
the second soft-start ramp until the output voltage reaches
the VID voltage plus/minus any offset or droop voltage.
The soft-start time is the sum of the 4 periods as shown in
Equation 15.
t SS = t d1 + t d2 + t d3 + t d4
(EQ. 15)
During td2 and td4, ISL6314 digitally controls the DAC
voltage change at 6.25mV per step. The time for each step is
determined by the frequency of the soft-start oscillator which
is defined by the resistor RSS from SS pin to GND. The
second soft-start ramp time td2 and td4 can be calculated
based on Equations 16 and 17:
FN6455.2
October 8, 2009
ISL6314
t d2 = 1.1 ⋅ R SS ⋅ 8 ⋅ 10
–3
TABLE 5. ISL6314 SOFT_START TIMING SUMMARY
( μs )
(EQ. 16)
t d4 = V VID – 1.1 ⋅ R SS ⋅ 8 ⋅ 10
–3
( μs )
(EQ. 17)
For example, when VID is set to 1.5V and the RSS is set at
100kΩ, the first soft-start ramp time td2 will be 880µs and the
second soft-start ramp time td4 will be 320µs.
After the DAC voltage reaches the final VID setting, PGOOD
will be set to high with the fixed delay td5. The typical value
for td5 is 93µs.
AMD Soft-Start
MODE
TIME SLOT
TIME
VR11
td1
1.1ms
VR11
td2
Equation 16
VR11
td3
93µs
VR11
td4
Equation 17
VR11
td5
93µs
AMD
tdA
1.1ms
AMD
tdB
Equation 18
Pre-Biased Soft-Start
OUTPUT PRECHARGED
ABOVE DAC LEVEL
VOUT, 500mV/DIV
OUTPUT PRECHARGED
BELOW DAC LEVEL
tdB
tdA
GND>
VOUT (0.5V/DIV)
EN
GND>
EN (5V/DIV)
PGOOD
T1 T2
500µs/DIV
FIGURE 12. AMD SOFT-START WAVEFORMS
FIGURE 13. SOFT-START WAVEFORMS FOR ISL6314-BASED
CONVERTER
For the AMD 5-bit and 6-bit modes of operation, the
soft-start sequence is composed of two periods, as shown in
Figure 12. At the beginning of soft-start, the VID code is
immediately obtained from the VID pins, followed by a fixed
delay period tdA of typically 1.1ms. After this delay period the
ISL6314 will begin ramping the output voltage to the desired
DAC level at a fixed rate of 6.25mV per step. The time for
each step is determined by the frequency of the soft-start
oscillator which is defined by the resistor RSS on the SS pin.
The amount of time required to ramp the output voltage to
the final DAC voltage is referred to as tdB, and can be
calculated as shown in Equation 18.
⋅ 8 ⋅ 10
t dB = V VID ⋅ R
SS
–3
( μs )
(EQ. 18)
At the end of soft-start, PGOOD will immediately go high if
the VSEN voltage is within the undervoltage and overvoltage
limits.
Table 5 is a summary table of the typical soft-start timing for
both modes. The times listed are fixed delays; the variable
ones (defined by the equations) depend on the slope of the
ramp (1.25 mV/µs for a nominal 100kΩ RSS resistor), and
the amount of voltage excursion.
21
T3
The ISL6314 also has the ability to start up into a pre-charged
output, without causing any unnecessary disturbance. The FB
pin is monitored during soft-start, and should it be higher than
the equivalent internal ramping reference voltage, the output
drives hold both MOSFETs off. Once the internal ramping
reference exceeds the FB pin potential, the output drives are
enabled, allowing the output to ramp from the pre-charged
level to the final level dictated by the DAC setting. Should the
output be pre-charged to a level exceeding the DAC setting,
the output drives are enabled at the end of the soft-start
period, leading to an abrupt correction in the output voltage
down to the DAC-set level. See Figure 13.
Fault Monitoring and Protection
The ISL6314 actively monitors output voltage and current to
detect fault conditions. Fault monitors trigger protective
measures to prevent damage to a microprocessor load. One
common power good indicator is provided for linking to
external system monitors. The schematic in Figure 14
outlines the interaction between the fault monitors and the
power-good signal.
FN6455.2
October 8, 2009
ISL6314
.
ROCSET
-
ISENO
VOCSET
+
OCSET
ISEN+
Overvoltage Protection
+
ISEN
-
VDROOP
ISEN-
100µA
+
+1V
-
+
OC
+
VDIFF
VSEN is outside this window. Even if the controller is shut
down the PGOOD signal will still stay high until VSEN falls
below the undervoltage threshold.
-
VID + OFFSET mV
SOFT-START, FAULT
AND CONTROL LOGIC
VOVP
VSEN
+
+
OV
PGOOD
x1
RGND
+
UV
VID - OFFSET mV ISL6314 INTERNAL CIRCUITRY
FIGURE 14. POWER-GOOD AND PROTECTION CIRCUITRY
Power-Good Signal
The power-good pin (PGOOD) is an open-drain logic output
that signals whether or not the ISL6314 is regulating the
output voltage within the proper levels, and whether any fault
conditions exist. This pin should be tied through a resistor to
a voltage source that’s equal to or less than VCC.
For Intel mode of operation, PGOOD indicates whether VSEN
is within specified overvoltage and undervoltage limits after a
fixed delay from the end of soft-start. PGOOD transitions low
when an undervoltage, overvoltage, or overcurrent condition
is detected or when the controller is disabled by a reset from
EN, POR, or one of the no-CPU VID codes. In the event of
an overvoltage or overcurrent condition, or a no-CPU VID
code, the controller latches off and PGOOD will not return
high until EN is toggled and a successful soft-start is
completed. In the case of an undervoltage event, PGOOD
will return high when the output voltage rises above the
undervoltage hysteresis level. PGOOD is always low prior to
the end of soft-start.
For AMD modes of operation, PGOOD will always be high as
long as VSEN is within the specified undervoltage/overvoltage
window and soft-start has ended. PGOOD only goes low if
22
The ISL6314 constantly monitors the difference between the
VSEN and RGND voltages to detect if an overvoltage event
occurs. During soft-start, while the DAC is ramping up, the
overvoltage trip level is the higher of a fixed voltage 1.27V or
DAC + 175mV for Intel modes of operation and DAC + 225mV
for AMD modes of operation. Upon successful soft-start, the
overvoltage trip level is only DAC + 175mV or DAC + 225mV
depending on whether the controller is running in Intel or AMD
mode. When the output voltage rises above the OVP trip level
actions are taken by the ISL6314 to protect the microprocessor
load.
At the inception of an overvoltage event, LGATE is
commanded high and the PGOOD signal is driven low. This
turns on the lower MOSFETs and pulls the output voltage
below a level that might cause damage to the load. The
LGATE output remains high until VSEN falls 100mV below
the OVP threshold that tripped the overvoltage protection
circuitry. The ISL6314 will continue to protect the load in this
fashion as long as the overvoltage condition recurs. Once an
overvoltage condition ends, the ISL6314 latches off, and
must be reset by toggling EN, or through POR, before a
soft-start can be reinitiated.
There is an OVP condition that exists that will not latch off the
ISL6314. During a soft-start sequence, if the VSEN voltage is
above the OVP threshold an overvoltage event will occur, but
will be released once VSEN falls 100mV below the OVP
threshold. If VSEN then rises above the OVP trip threshold a
second time, the ISL6314 will be latched off and cannot be
restarted until the controller is reset.
Pre-POR Overvoltage Protection
Prior to PVCC and VCC exceeding their POR levels, the
ISL6314 is designed to protect the load from any overvoltage
events that may occur. This is accomplished by means of an
internal 10kΩ resistor tied from PHASE to LGATE, which
turns on the lower MOSFET to control the output voltage
until the overvoltage event ceases or the input power supply
cuts off. For complete protection, the low side MOSFET
should have a gate threshold well below the maximum
voltage rating of the load/microprocessor. In the event that
during normal operation the PVCC or VCC voltage falls back
below the POR threshold, the pre-POR overvoltage
protection circuitry reactivates to protect from any more
pre-POR overvoltage events.
Undervoltage Detection
The undervoltage threshold is set at DAC - 350mV of the
VID code. When the output voltage (VSEN - RGND) is below
the undervoltage threshold, PGOOD gets pulled low. No
other action is taken by the controller. PGOOD will return
high if the output voltage rises above DAC - 250mV.
FN6455.2
October 8, 2009
ISL6314
Open Sense Line Protection
In the case that either of the remote sense lines (VSEN or
RGND) become open, the ISL6314 is designed to prevent
the controller from regulating. This is accomplished by
means of a small 5µA pull-up current on VSEN, and a
pull-down current on RGND. If the sense lines are opened at
any time, the voltage difference between VSEN and RGND
will increase until an overvoltage event occurs, at which
point overvoltage protection activates and the controller
stops regulating. The ISL6314 will be latched off and cannot be
restarted until the controller is reset.
OUTPUT CURRENT, 25A/DIV
0A
OUTPUT VOLTAGE,
500mV/DIV
Overcurrent Protection
The ISL6314 detects overcurrent events by comparing the
droop voltage, VDROOP, to the OCSET voltage, VOCSET, as
shown in Figure 14. The droop voltage, set by the external
current sensing circuitry, is proportional to the output current
as shown in Equation 19. A constant 100µA flows through
ROCSET, creating the OCSET voltage. When the droop
voltage exceeds the OCSET voltage, the overcurrent
protection circuitry activates. Since the droop voltage is
proportional to the output current, the overcurrent trip level,
IMAX, can be set by selecting the proper value for ROCSET,
as shown in Equation 20.
R COMP
V DROOP = --------------------- ⋅ I OUT ⋅ DCR
RS
(EQ. 19)
I MAX ⋅ R COMP ⋅ DCR
R OCSET = ---------------------------------------------------------100μA ⋅ R S
(EQ. 20)
0V
1ms/DIV
FIGURE 15. OVERCURRENT BEHAVIOR IN HICCUP MODE
General Design Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to create a power converter.
It is assumed that the reader is familiar with many of the basic
skills and techniques referenced in the following. In addition to
this guide, Intersil provides complete reference designs that
include schematics, bills of materials, and example board
layouts for all common microprocessor applications.
Power Stage
Once the output current exceeds the overcurrent trip level,
VDROOP will exceed VOCSET, and a comparator will trigger
the converter to begin overcurrent protection procedures.
At the beginning of an overcurrent shutdown, the controller
turns off both upper and lower MOSFETs and lowers
PGOOD. The controller will then immediately attempt to
soft-start (which includes the 1.1ms delay of either td1 or
tdA). If the overcurrent fault remains, the trip-retry cycles will
continue until either the controller is disabled or the fault is
cleared. But if five overcurrent events occur without
successfully completing soft-start, the controller will latch off
after the fifth try and must be reset by toggling EN before a
soft-start can be reinitiated. Note that the energy delivered
during trip-retry cycling is much less than during full-load
operation, so there is no thermal hazard. Figure 15 shows an
example.
The first step in designing a power converter using the
ISL6314 is to determine if one phase is sufficient (if not,
Intersil offers other parts, such as the ISL6313, which has
two phases with similar features). This determination
depends heavily on the cost analysis which in turn depends
on system constraints that differ from one design to the next.
Principally, the designer will be concerned with whether
components can be mounted on both sides of the circuit
board, whether through-hole components are permitted, the
total board space available for power-supply circuitry, and
the maximum amount of load current. Generally speaking,
the most economical solutions are those in which the output
handles between 25A and 30A. All surface-mount designs
will tend toward the lower end of this current range. If
through-hole MOSFETs and inductors can be used, higher
currents are possible. In cases where board space is the
limiting constraint, current can be pushed as high as 40A,
but these designs require heat sinks and forced air to cool
the MOSFETs, inductors and heat-dissipating surfaces.
MOSFETS
The choice of MOSFETs depends on the current each
MOSFET will be required to conduct, the switching frequency,
the capability of the MOSFETs to dissipate heat, and the
availability and nature of heat sinking and air flow.
23
FN6455.2
October 8, 2009
ISL6314
LOWER MOSFET POWER CALCULATION
The calculation for power loss in the lower MOSFET is
simple, since virtually all of the loss in the lower MOSFET is
due to current conducted through the channel resistance
(rDS(ON)). In Equation 21, IM is the maximum continuous
output current, IPP is the peak-to-peak inductor current (see
Equation 1), and d is the duty cycle (VOUT/VIN).
I L ( P-P2) ⋅ ( 1 – d ) (EQ. 21)
⎛ I M⎞ 2
P LOW ( 1 ) = r DS ( ON ) ⋅ ⎜ -----⎟ ⋅ ( 1 – d ) + ---------------------------------------12
⎝ N⎠
An additional term can be added to the lower-MOSFET loss
equation to account for additional loss accrued during the dead
time when inductor current is flowing through the
lower-MOSFET body diode. This term is dependent on the
diode forward voltage at IM, VD(ON), the switching frequency,
fS, and the length of dead times, td1 and td2, at the beginning
and the end of the lower-MOSFET conduction interval
respectively. Note that the dead times td1 and td2 in
Equation 22 are NOT related to the soft-start timing delays.
⎛I
⎞
⎛I
⎞
⎟
M I P-P⎟ ⋅ t
M I----------P LOW ( 2 ) = V D ( ON ) ⋅ f S ⋅ ⎜ -----+ ⎜ -----+ ----------– P-P⎟ ⋅ t d2
d1
⎜
2
⎝N
⎠
2
⎝N
⎠
(EQ. 22)
The total maximum power dissipated in each lower MOSFET
is approximated by the summation of PLOW(1) and PLOW(2).
UPPER MOSFET POWER CALCULATION
In addition to rDS(ON) losses, a large portion of the
upper-MOSFET losses are due to currents conducted across
the input voltage (VIN) during switching. Since a substantially
higher portion of the upper-MOSFET losses are dependent on
switching frequency, the power calculation is more complex.
Upper MOSFET losses can be divided into separate
components involving the upper-MOSFET switching times,
the lower-MOSFET body-diode reverse-recovery charge, Qrr,
and the upper MOSFET rDS(ON) conduction loss.
When the upper MOSFET turns off, the lower MOSFET does
not conduct any portion of the inductor current until the
voltage at the phase node falls below ground. Once the
lower MOSFET begins conducting, the current in the upper
MOSFET falls to zero as the current in the lower MOSFET
ramps up to assume the full inductor current. In Equation 23,
the required time for this commutation is t1 and the
approximated associated power loss is PUP(1)..
I M I P-P⎞ ⎛ t 1 ⎞
P UP ( 1 ) ≈ V IN ⋅ ⎛ ----- ⋅ ⎜ ---- ⎟ ⋅ f
⎝ N- + --------2 ⎠ ⎝ 2⎠ S
(EQ. 23)
A third component involves the lower MOSFET
reverse-recovery charge, Qrr. Since the inductor current has
fully commutated to the upper MOSFET before the
lower-MOSFET body diode can recover all of Qrr, it is
conducted through the upper MOSFET across VIN. The
power dissipated as a result is PUP(3), as shown in Equation
P UP ( 3 ) = V IN ⋅ Q rr ⋅ f S
(EQ. 25)
25.
Finally, the resistive part of the upper MOSFET is given in
Equation 26 as PUP(4)..
2
⎛ I M⎞
I P-P2
P UP ( 4 ) ≈ r DS ( ON ) ⋅ d ⋅ ⎜ -----⎟ + ---------12
⎝ N⎠
(EQ. 26)
The total power dissipated by the upper MOSFET at full load
can now be approximated as the summation of the results
from Equations 23, 24, 25 and 26. Since the power
equations depend on MOSFET parameters, choosing the
correct MOSFETs can be an iterative process involving
repetitive solutions to the loss equations for different
MOSFETs and different switching frequencies.
Package Power Dissipation
When choosing MOSFETs it is important to consider the
amount of power being dissipated in the integrated drivers
located in the controller. Since there is one set of drivers in
the controller package, the total power dissipated by it must
be less than the maximum allowable power dissipation for
the QFN package.
Calculating the power dissipation in the drivers for a desired
application is critical to ensure safe operation. Exceeding the
maximum allowable power dissipation level will push the IC
beyond the maximum recommended operating junction
temperature of +125°C. The maximum allowable IC power
dissipation for the 5x5 QFN package is approximately 3W at
room temperature. See “Layout Considerations” on page 29
for thermal transfer improvement suggestions.
When designing the ISL6314 into an application, it is
recommended that the following calculation is used to
ensure safe operation at the desired frequency for the
selected MOSFETs. The total gate drive power losses,
PQg_TOT, due to the gate charge of MOSFETs and the
integrated driver’s internal circuitry and their corresponding
average driver current can be estimated with Equations 27
and 28, respectively.
At turn on, the upper MOSFET begins to conduct and this
transition occurs over a time t2. In Equation 24, the
approximate power loss is PUP(2)..
⎛ I M I P-P⎞ ⎛ t 2 ⎞
P UP ( 2 ) ≈ V IN ⋅ ⎜ ----- – ----------⎟ ⋅ ⎜ ---- ⎟ ⋅ f S
2 ⎠ ⎝ 2⎠
⎝N
24
(EQ. 24)
FN6455.2
October 8, 2009
ISL6314
.
P Qg_TOT = P Qg_Q1 + P Qg_Q2 + I Q ⋅ VCC
(EQ. 27)
3
P Qg_Q1 = --- ⋅ Q G1 ⋅ PVCC ⋅ F SW ⋅ N Q1
2
P DR = P DR_UP + P DR_LOW + P BOOT + ( I Q ⋅ VCC )
P Qg_Q2 = Q G2 ⋅ PVCC ⋅ F SW ⋅ N Q2
BOOT
D
CGD
G
RLO1
RG1
CDS
RGI1
R HI2
R LO2
⎛
⎞ P Qg_Q2
P DR_LOW = ⎜ -------------------------------------- + ----------------------------------------⎟ ⋅ --------------------2
⎝ R HI2 + R EXT2 R LO2 + R EXT2⎠
R GI1
R EXT1 = R G1 + ------------N
Q1
R GI2
R EXT2 = R G2 + ------------N
Q2
Inductor DCR Current Sensing Component
Selection
For accurate load line regulation, the ISL6314 senses the
total output current by detecting the voltage across the
output inductor DCR (as described in “Load-Line (Droop)
Regulation” on page 16). As Figure 18 illustrates, an R-C
network is required to accurately sense the inductor DCR
voltage and convert this information into a “droop” voltage,
which is proportional to the total output current.
+
UGATE
R HI1
R LO1
⎛
⎞ P Qg_Q1
P DR_UP = ⎜ -------------------------------------- + ----------------------------------------⎟ ⋅ --------------------R
+
R
R
+
R
3
⎝ HI1
EXT1
LO1
EXT1⎠
CGS
Q1
VL(s)
L
S
PHASE
-
(EQ. 28)
In Equations 27 and 28, PQg_Q1 is the total upper gate drive
power loss and PQg_Q2 is the total lower gate drive power
loss; the gate charge (QG1 and QG2) is defined at the
particular gate to source drive voltage PVCC in the
corresponding MOSFET data sheet; IQ is the driver total
quiescent current with no load at both drive outputs; NQ1 and
NQ2 are the number of upper and lower MOSFETs
respectively. The IQ*VCC product is the quiescent power of
the controller without capacitive load and is typically 75mW at
300kHz.
RHI1
(EQ. 29)
P Qg_Q1
P BOOT = --------------------3
3
+ Q G2 ⋅ N Q2⎞ ⋅ F SW + I Q
I DR = ⎛ --- ⋅ Q G1 ⋅ N
⎝2
⎠
Q1
PVCC
the MOSFETs. Figures 16 and 17 show the typical upper and
lower gate drives turn-on transition path. The total power
dissipation in the controller itself, PDR, can be roughly
estimated as shown in Equation 29:
IOUT
DCR
VOUT
INDUCTOR
I
L
PHASE
RS
FIGURE 16. TYPICAL UPPER-GATE DRIVE TURN-ON PATH
COUT
ISEN-
D
CCOMP
CGD
RHI2
RLO2
RG2
RCOMP
ISENO
G
LGATE
-
+
PVCC
CDS
RGI2
CGS
VDROOP
+ ISEN+
(OPTIONAL)
Q2
S
ISL6314
FIGURE 18. DCR SENSING CONFIGURATION
FIGURE 17. TYPICAL LOWER-GATE DRIVE TURN-ON PATH
The total gate drive power losses are dissipated among the
resistive components along the transition path and in the
bootstrap diode. The portion of the total power dissipated in
the controller itself is the power dissipated in the upper drive
path resistance, PDR_UP, the lower drive path resistance,
PDR_UP, and in the boot strap diode, PBOOT. The rest of the
power will be dissipated by the external gate resistors (RG1
and RG2) and the internal gate resistors (RGI1 and RGI2) of
25
Choosing the components for this current sense network is a
two step process. First, RCOMP and CCOMP must be
chosen so that the time constant of this RCOMP - CCOMP
network matches the time constant of the inductor L/DCR.
Then the resistor RS must be chosen to set the current
sense network gain, obtaining the desired full load droop
voltage. Follow the steps outlined in the following to choose
the component values for this R-C network.
FN6455.2
October 8, 2009
ISL6314
1. Choose an arbitrary value for CCOMP. The recommended
value is 0.01µF.
2. Plug the inductor L and DCR component values, and the
values for CCOMP chosen in Step 1, into Equation 30 to
calculate the value for RCOMP.
L
R COMP = --------------------------------------DCR ⋅ C COMP
(EQ. 30)
3. Use the new value for RCOMP obtained from
Equation 30, as well as the desired full load current, IFL,
full load droop voltage, VDROOP, and inductor DCR in
Equation 31 to calculate the value for RS.
I FL
R S = ------------------------- ⋅ R COMP ⋅ DCR
V DROOP
(EQ. 31)
Due to errors in the inductance or DCR it may be necessary
to adjust the value of R1 to match the time constants
correctly. The effects of time constant mismatch can be seen
in the form of droop overshoot or undershoot during the
initial load transient spike, as shown in Figure 19. Follow the
steps outlined in the following to ensure the R-C and
inductor L/DCR time constants are matched accurately.
1. Capture a transient event with the oscilloscope set to
about L/DCR/2 (sec/div). For example, with L = 1µH and
DCR = 1mΩ, set the oscilloscope to 500µs/div.
2. Record ΔV1 and ΔV2 as shown in Figure 19.
3. Select new values, R1,NEW, for the time constant resistor
based on the original value, R1,OLD, using Equation 32.
ΔV 1
R 1, NEW = R 1, OLD ⋅ ---------ΔV 2
(EQ. 32)
4. Replace R1 with the new value and check to see that the
error is corrected. Repeat the procedure if necessary.
Loadline Regulation Resistor
If loadline regulation is desired, the resistor on the FS pin,
RT, should be connected to Ground (the value of RT
separately selects the switching frequency, as per
Equation 42). The desired loadline, RLL, can be calculated
by Equation 33 where VDROOP is the desired droop voltage
at the full load current IFL.
V DROOP
R LL = -----------------------I FL
(EQ. 33)
Based on values for Equation 31, the desired loadline can
also be calculated from Equation 34.
R COMP ⋅ DCR
R LL = --------------------------------------RS
(EQ. 34)
If no loadline regulation is required, the resistor on the FS
pin, RT, should be connected to the VCC pin (the value of
RT separately selects the switching frequency, as per
Equation 42).
APA Pin Component Selection
A 100µA current flows out of the APA pin and across RAPA
to set the APA trip level. A 1000pF capacitor, CAPA, should
also be placed across the RAPA resistor to help with noise
immunity. An APA trip level of 500mV is recommended for
most applications. Use Equation 35 to set RAPA to get the
desired APA trip level.
V APA, TRIP
500mV
R APA = ------------------------------- = ----------------------------- = 5kΩ
100 × 10 – 6
100 × 10 – 6
(EQ. 35)
Compensation
ΔV2
ΔV1
VOUT
The two opposing goals of compensating the voltage
regulator are stability and speed. Depending on whether the
regulator employs the optional load-line regulation as
described in Load-Line Regulation, there are two distinct
methods for achieving these goals.
COMPENSATION WITH LOAD-LINE REGULATION
ITRAN
ΔI
FIGURE 19. TIME CONSTANT MISMATCH BEHAVIOR
26
The load-line regulated converter behaves in a similar
manner to a peak current mode controller because the two
poles at the output filter L-C resonant frequency split with the
introduction of current information into the control loop. The
final location of these poles is determined by the system
function, the gain of the current signal, and the value of the
compensation components, RC and CC, as shown in
Figure 20.
FN6455.2
October 8, 2009
ISL6314
C2 (OPTIONAL)
Case 1:
RC
CC
1
-------------------------------- > f 0
2⋅π⋅ L⋅C
2 ⋅ π ⋅ f 0 ⋅ V P-P ⋅ L ⋅ C
R C = R FB ⋅ ---------------------------------------------------------V
COMP
IN
V IN
C C = ----------------------------------------------------2 ⋅ π ⋅ V P-P ⋅ R FB ⋅ f 0
FB
ISL6314
RFB
VDIFF
Case 2:
V P-P ⋅ ( 2 ⋅ π ) 2 ⋅ f 02 ⋅ L ⋅ C
R C = R FB ⋅ -----------------------------------------------------------------V
FIGURE 20. COMPENSATION CONFIGURATION FOR
LOAD-LINE REGULATED ISL6314 CIRCUIT
Since the system poles and zero are affected by the values
of the components that are meant to compensate them, the
solution to the system equation becomes fairly complicated.
Fortunately, there is a simple approximation that comes very
close to an optimal solution. Treating the system as though it
were a voltage-mode regulator, by compensating the L-C
poles and the ESR zero of the voltage mode approximation,
yields a solution that is always stable with very close to ideal
transient performance.
Select a target bandwidth for the compensated system, f0.
The target bandwidth must be large enough to assure
adequate transient performance, but smaller than 1/3 of the
switching frequency. The values of the compensation
components depend on the relationships of f0 to the L-C
pole frequency and the ESR zero frequency. For each of the
following three, there is a separate set of equations for the
compensation components.
In Equation 36, L is the filter inductance; C is the sum total of
all output capacitors; ESR is the equivalent series resistance
of the bulk output filter capacitance; and VP-P is the
peak-to-peak sawtooth signal amplitude, as described in the
“Electrical Specifications” on page 6.
Once selected, the compensation values in Equation 36
assure a stable converter with reasonable transient
performance. In most cases, transient performance can be
improved by making adjustments to RC. Slowly increase the
value of RC while observing the transient performance on an
oscilloscope until no further improvement is noted. Normally,
CC will not need adjustment. Keep the value of CC from
Equation 36 unless some performance issue is noted.
27
1
1
-------------------------------- ≤ f 0 < -----------------------------------2 ⋅ π ⋅ C ⋅ ESR
2⋅π⋅ L⋅C
(EQ. 36)
IN
V IN
C C = -------------------------------------------------------------------------------------2
2
( 2 ⋅ π ) ⋅ f 0 ⋅ V P-P ⋅ R FB ⋅ L ⋅ C
Case 3:
1
f 0 > ------------------------------------2 ⋅ π ⋅ C ⋅ ESR
2 ⋅ π ⋅ f 0 ⋅ V P-P ⋅ L
R C = R FB ⋅ ---------------------------------------------V ⋅ ESR
IN
V IN ⋅ ESR ⋅ C
C C = ----------------------------------------------------------------2 ⋅ π ⋅ V P-P ⋅ R FB ⋅ f 0 ⋅ L
The optional capacitor C2, is sometimes needed to bypass
noise away from the PWM comparator (see Figure 20). Keep
a position available for C2, and be prepared to install a
high-frequency capacitor of between 22pF and 150pF in
case any leading edge jitter problem is noted. For the
solutions in Equation 36, RFB is selected arbitrarily, typically
in the 1kΩ to 5kΩ range.
COMPENSATION WITHOUT LOAD-LINE REGULATION
The non load-line regulated converter is accurately modeled
as a voltage-mode regulator with two poles at the L-C
resonant frequency and a zero at the ESR frequency. A
type III controller, as shown in Figure 21, provides the
necessary compensation.
The first step is to choose the desired bandwidth, f0, of the
compensated system. Choose a frequency high enough to
assure adequate transient performance but not higher than
1/3 of the switching frequency. The type-III compensator has
an extra high-frequency pole, fHF. This pole can be used for
added noise rejection or to assure adequate attenuation at
the error-amplifier high-order pole and zero frequencies. A
good general rule is to choose fHF = 10f0, but it can be
higher if desired. Choosing fHF to be lower than 10f0 can
cause problems with too much phase shift below the system
bandwidth.
FN6455.2
October 8, 2009
ISL6314
In high-speed converters, the output capacitor bank is usually
the most costly (and often the largest) part of the circuit.
Output filter design begins with minimizing the cost of this part
of the circuit. The critical load parameters in choosing the
output capacitors are the maximum size of the load step, ΔI,
the load-current slew rate, di/dt, and the maximum allowable
output-voltage deviation under transient loading, ΔVMAX.
Capacitors are characterized according to their capacitance,
ESR, and ESL (equivalent series inductance).
C2
RC
CC
COMP
FB
C1
ISL6314
RFB
R1
VDIFF
FIGURE 21. COMPENSATION CIRCUIT WITHOUT LOAD-LINE
REGULATION
.
C ⋅ ESR
R 1 = R FB ⋅ -------------------------------------------L ⋅ C – C ⋅ ESR
L ⋅ C – C ⋅ ESR
C 1 = -------------------------------------------R FB
di
ΔV ≈ ESL ⋅ ----- + ESR ⋅ ΔI
dt
V IN
C 2 = ---------------------------------------------------------------------------------------------------2
( 2 ⋅ π ) ⋅ f 0 ⋅ f HF ⋅ ( L ⋅ C ) ⋅ R FB ⋅ V P-P
(EQ. 37)
2
V PP ⋅ ⎛ 2π⎞ ⋅ f 0 ⋅ f HF ⋅ L ⋅ C ⋅ R FB
⎝ ⎠
R C = ---------------------------------------------------------------------------------------V ⋅ ( 2 ⋅ π ⋅ f HF ⋅ L ⋅ C – 1 )
IN
V IN ⋅ ( 2 ⋅ π ⋅ f HF ⋅ L ⋅ C – 1 )
C C = ---------------------------------------------------------------------------------------------------( 2 ⋅ π ) 2 ⋅ f 0 ⋅ f HF ⋅ ( L ⋅ C ) ⋅ R FB ⋅ V P-P
In the solutions to the compensation equations, there is a
single degree of freedom. For the solutions presented in
Equation 37, RFB is selected arbitrarily, typically in the 1kΩ
to 5kΩ range. The remaining compensation components are
then selected according to Equation 37.
In Equation 37, L is the filter inductance; C is the sum total of
all output capacitors; ESR is the equivalent-series resistance
of the bulk output-filter capacitance; and VP-P is the
peak-to-peak sawtooth signal amplitude as described in the
“Electrical Specifications” on page 6.
Output Filter Design
The output inductors and the output capacitor bank together
to form a low-pass filter responsible for smoothing the
pulsating voltage at the phase node. The output filter also
must provide the transient energy until the regulator can
respond. Because it has a low bandwidth compared to the
switching frequency, the output filter limits the system
transient response. The output capacitors must supply or
sink load current while the current in the output inductor
increases or decreases to meet the demand.
28
At the beginning of the load transient, the output capacitors
supply all of the transient current. The output voltage will
initially deviate by an amount approximated by the voltage
drop across the ESL. As the load current increases, the
voltage drop across the ESR increases linearly until the load
current reaches its final value. The capacitors selected must
have sufficiently low ESL and ESR so that the total
output-voltage deviation is less than the allowable maximum.
Neglecting the contribution of inductor current and regulator
response, Equation 38 shows the output voltage initially
deviates by an amount as expressed in Equation 38:
(EQ. 38)
The filter capacitor must have sufficiently low ESL and ESR
so that ΔV < ΔVMAX.
Most capacitor solutions rely on a mixture of high frequency
capacitors with relatively low capacitance in combination
with bulk capacitors having high capacitance but limited
high-frequency performance. Minimizing the ESL of the
high-frequency capacitors allows them to support the output
voltage as the current increases. Minimizing the ESR of the
bulk capacitors allows them to supply the increased current
with less output voltage deviation.
The ESR of the bulk capacitors also creates the majority of
the output-voltage ripple. As the bulk capacitors sink and
source the inductor AC ripple current (see “Output Ripple”
on page 10 and Equation 39), a voltage develops across the
bulk capacitor ESR equal to IC(P-P ) (ESR). Thus, once the
output capacitors are selected, the maximum allowable
ripple voltage, VP-P(MAX), determines the lower limit on the
inductance.
⎛V – V
⎞
OUT⎠ ⋅ V OUT
⎝ IN
L ≥ ESR ⋅ ---------------------------------------------------------f S ⋅ V IN ⋅ V P-P( MAX )
(EQ. 39)
Since the capacitors are supplying a decreasing portion of
the load current while the regulator recovers from the
transient, the capacitor voltage becomes slightly depleted.
The output inductor must be capable of assuming the entire
load current before the output voltage decreases more than
ΔVMAX. This places an upper limit on inductance.
Equation 40 gives the upper limit on L for the cases when
the trailing edge of the current transient causes a greater
output-voltage deviation than the leading edge. Equation 41
FN6455.2
October 8, 2009
ISL6314
2 ⋅ C ⋅ VO
L ≤ ------------------------- ⋅ ΔV MAX – ( ΔI ⋅ ESR )
( ΔI ) 2
(EQ. 40)
1.25 ⋅ C- ⋅ ΔV
⎛
⎞
L ≤ ------------------MAX – ( ΔI ⋅ ESR ) ⋅ ⎝ V IN – V O⎠
( ΔI ) 2
(EQ. 41)
Switching Frequency
There are a number of variables to consider when choosing
the switching frequency, as there are considerable effects on
the upper MOSFET loss calculation. These effects are
outlined in “MOSFETs” on page 23, and they establish the
upper limit for the switching frequency. The lower limit is
established by the requirement for fast transient response
and small output-voltage ripple. Choose the lowest switching
frequency that allows the regulator to meet the
transient-response requirements.
Switching frequency is determined by the selection of the
frequency-setting resistor, RT. Figure 22 and Equation 42
are provided to assist in selecting the correct value for RT.
R T = 10
[10.61 – ( 1.035 ⋅ log ( f S ) ) ]
(EQ. 42)
500
current rating which will minimize the total number of input
capacitors required to support the RMS current calculated.
The voltage rating of the capacitors should also be at least
1.25x greater than the maximum input voltage.
.
0.6
INPUT-CAPACITOR CURRENT (IRMS/IO)
addresses the leading edge. Normally, the trailing edge
dictates the selection of L because duty cycles are usually
less than 50%. Nevertheless, both inequalities should be
evaluated, and L should be selected based on the lower of
the two results. In each equation, L is the inductance, and C
is the total output capacitance.
0.4
0.2
IL(P-P) = 0
IL(P-P) = 0.5 IO
IL(P-P) = 0.75 IO
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE (VO/VIN)
FIGURE 23. NORMALIZED INPUT-CAPACITOR RMS
CURRENT FOR SINGLE-PHASE CONVERTER
Low capacitance, high-frequency ceramic capacitors are
needed in addition to the input bulk capacitors to suppress
leading and falling edge voltage spikes. The spikes result from
the high current slew rate produced by the upper MOSFET
turn on and off. Select low ESL ceramic capacitors and place
one as close as possible to each upper MOSFET drain to
minimize board parasitics and maximize suppression.
RT (kΩ)
Layout Considerations
100
10
50
100
1k
2k
SWITCHING FREQUENCY (kHz)
FIGURE 22. RT vs SWITCHING FREQUENCY
Input Capacitor Selection
The input capacitors are responsible for sourcing the AC
component of the input current flowing into the upper
MOSFETs. Their RMS current capacity must be sufficient to
handle the ac component of the current drawn by the upper
MOSFETs which is related to duty cycle and the number of
active phases.
Use Figure 23 to determine the input-capacitor RMS current
requirement set by the duty cycle, maximum sustained
output current (IO), and the ratio of the peak-to-peak inductor
current (IL(P-P)) to IO. Select a bulk capacitor with a ripple
29
MOSFETs switch very fast and efficiently. The speed with
which the current transitions from one device to another
causes voltage spikes across the interconnecting
impedances and parasitic circuit elements. These voltage
spikes can degrade efficiency, radiate noise into the circuit
and lead to device overvoltage stress. Careful component
selection, layout, and placement minimizes these voltage
spikes. Consider, as an example, the turnoff transition of the
upper PWM MOSFET. Prior to turn-off, the upper MOSFET
was carrying channel current. During the turn-off, current
stops flowing in the upper MOSFET and is picked up by the
lower MOSFET. Any inductance in the switched current path
generates a large voltage spike during the switching interval.
Careful component selection, tight layout of the critical
components, and short, wide circuit traces minimize the
magnitude of voltage spikes.
There are two sets of critical components in a DC/DC
converter using a ISL6314 controller. The power
components are the most critical because they switch large
amounts of energy. Next, are small signal components that
connect to sensitive nodes or supply critical bypassing
current and signal coupling.
FN6455.2
October 8, 2009
ISL6314
The power components should be placed first, which include
the MOSFETs, input and output capacitors, and the inductor.
Keep the gate drive traces short, resulting in low trace
impedances.
When placing the MOSFETs try to keep the source of the
upper FETs and the drain of the lower FETs as close as
thermally possible. Input Bulk capacitors should be placed
close to the drain of the upper FETs and the source of the lower
FETs. Locate the output inductor and output capacitors
between the MOSFETs and the load. The high-frequency input
and output decoupling capacitors (ceramic) should be placed
as close as practicable to the decoupling target, making use of
the shortest connection paths to any internal planes, such as
vias to GND next to, or on the capacitor solder pad.
The critical small components include the bypass capacitors
for VCC and PVCC, and many of the components
surrounding the controller including the feedback network
and current sense components. Locate the VCC and PVCC
bypass capacitors as close to the ISL6314 as possible. It is
especially important to locate the components associated
with the feedback circuit close to their respective controller
pins, since they belong to a high-impedance circuit loop,
sensitive to EMI pick-up.
A multi-layer printed circuit board is recommended. Figure 24
shows the connections of the critical components for the
converter. Note that capacitors CxxIN and CxxOUT could each
represent numerous physical capacitors. Dedicate one solid
layer, usually the one underneath the component side of the
board, for a ground plane and make all critical component
ground connections with vias to this layer.
Dedicate another solid layer as a power plane and break this
plane into smaller islands of common voltage levels. Keep the
metal runs from the PHASE terminal to output inductor short.
The power plane should support the input power and output
power nodes. Use copper filled polygons on the top and bottom
circuit layers for the phase node. Use the remaining printed
circuit layers for small signal wiring.
Routing UGATE, LGATE, and PHASE Traces
Great attention should be paid to routing the UGATE, LGATE,
and PHASE traces since they drive the power train MOSFETs
using short, high current pulses. It is important to size them as
large and as short as possible to reduce their overall
impedance and inductance. They should be sized to carry at
least one ampere of current (0.02” to 0.05”). Going between
layers with vias should also be avoided, but if so, use two vias
for interconnection when possible.
Extra care should be given to the LGATE traces in particular
since keeping their impedance and inductance low helps to
significantly reduce the possibility of shoot-through. It is also
important to route each channels UGATE and PHASE traces
in as close proximity as possible to reduce their inductances.
Current Sense Component Placement and Trace
Routing
One of the most critical aspects of the ISL6314 regulator
layout is the placement of the inductor DCR current sense
components and traces. The R-C current sense components
must be placed as close to their respective ISEN+ and
ISEN- pins on the ISL6314 as possible.
The sense traces that connect the R-C sense components to
each side of the output inductors should be routed on the
bottom of the board, away from the noisy switching
components located on the top of the board. These traces
should be routed side by side, and they should be very thin
traces. It’s important to route these traces as far away from
any other noisy traces or planes as possible. These traces
should pick up as little noise as possible.
Thermal Management
For maximum thermal performance in high current, high
switching frequency applications, connecting the thermal
GND pad of the ISL6314 to the ground plane with multiple
vias is recommended. This heat spreading allows the part to
achieve its full thermal potential. It is also recommended
that the controller be placed in a direct path of airflow if
possible to help thermally manage the part.
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
30
FN6455.2
October 8, 2009
ISL6314
RFB
C2
LOCATE CLOSE TO IC
(MINIMIZE CONNECTION PATH)
R2
RDVC
CDVC
FB
DVC VDIFF VSEN
RGND
KEY
HEAVY TRACE ON CIRCUIT PLANE LAYER
C1
ISLAND ON POWER PLANE LAYER
C3
R1
ISLAND ON CIRCUIT PLANE LAYER
VIA CONNECTION TO GROUND PLANE
COMP
CAPA
APA
RAPA
+5V
VCC
(CF1)
LOCATE NEAR SWITCHING TRANSISTORS;
(MINIMIZE CONNECTION PATH)
ROFS
OFS
+12V
FS
PVCC
REF
RT
(CF2)
CREF
CBOOT
BOOT
SS
UGATE
CBIN (CHFIN)
CBOUT(CHFOUT)
PHASE
RSS
ISL6314
LOAD
LGATE
VID7
VID6
VID5
VID4
VID3
LOCATE NEAR LOAD;
(MINIMIZE CONNECTION
PATH)
VID2
VID1
VID0
PGOOD
EN
GND
ISEN+ OCSET ISENO
ROCSET
ISEN-
CCOMP
RS
RCOMP
FIGURE 24. PRINTED CIRCUIT BOARD POWER PLANES AND ISLANDS
31
FN6455.2
October 8, 2009
ISL6314
Package Outline Drawing
L32.5x5B
32 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 2, 11/07
4X 3.5
5.00
28X 0.50
A
B
6
PIN 1
INDEX AREA
6
PIN #1 INDEX AREA
32
25
1
5.00
24
3 .30 ± 0 . 15
17
(4X)
8
0.15
9
16
TOP VIEW
0.10 M C A B
+ 0.07
32X 0.40 ± 0.10
4 32X 0.23 - 0.05
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
0 . 90 ± 0.1
C
BASE PLANE
SEATING PLANE
0.08 C
( 4. 80 TYP )
(
( 28X 0 . 5 )
SIDE VIEW
3. 30 )
(32X 0 . 23 )
C
0 . 2 REF
5
( 32X 0 . 60)
0 . 00 MIN.
0 . 05 MAX.
DETAIL "X"
TYPICAL RECOMMENDED LAND PATTERN
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.
32
FN6455.2
October 8, 2009