Intersil ISL6569ACR Multi-phase pwm controller Datasheet

ISL6569A
®
Data Sheet
December 29, 2004
FN9092.2
Multi-Phase PWM Controller
Features
The ISL6569A provides core-voltage regulation by driving
two interleaved synchronous-rectified buck-converter
channels in parallel. Interleaving the channel timing results
in increased ripple frequency which reduces input and output
ripple currents. The reduction in ripple results in lower
component cost, reduced dissipation, and a smaller
implementation area.
• Multi-Phase Power Conversion
- 2 Phase Operation
The ISL6569A uses cost and space-saving rDS(ON) sensing
for channel current balance, active voltage positioning, and
over-current protection. Output voltage is monitored by an
internal differential remote sense amplifier. A high-bandwidth
error amplifier drives the output voltage to match the
programmed 5-bit DAC reference voltage. The resulting
compensation signal guides the creation of pulse width
modulated (PWM) signals to control companion Intersil
MOSFET drivers. The OFS pin allows direct offset of the
DAC voltage from 0V to 50mV using a single external
resistor. The reference and amplifiers are trimmed to ensure
a system accuracy of ±0.5% over temperature.
Outstanding features of this controller IC include
Dynamic VIDTM technology allowing seamless on-the-fly VID
changing without the need of any external components.
Output voltage “droop” or active voltage positioning is
optional. When employed, it allows the reduction in size and
cost of the output capacitors required to support load
transients. A threshold-sensitive enable input allows the use
of an external resistor divider for start-up coordination with
Intersil MOSFET drivers or any other devices powered from
a separate supply.
Superior over-voltage protection is achieved by gating on the
lower MOSFET of all phases to crowbar the output voltage.
An optional second crowbar on VIN, formed with an external
MOSFET or SCR gated by the OVP pin, is triggered when
an over-voltage condition is detected. Under-voltage
conditions are detected, but PWM operation is not disrupted.
Over-current conditions cause a hiccup-mode response as
the controller repeatedly tries to restart. After a set number
of failed startup attempts, the controller latches off. A power
good logic signal indicates when the converter output is
between the UV and OV thresholds.
• Active Channel Current Balancing
• Precision rDS(ON) Current Sharing
- Lossless
- Low Cost
• Input Voltage: 12V or 5V Bias
• Precision CORE Voltage Regulation
- ± 0.5% System Accuracy Over Temperature
- Differential Remote Output Voltage Sensing
- Programmable Reference Offset
• Microprocessor Voltage Identification Input
- 5-Bit VID Input
- 0.800V to 1.550V in 25mV Steps
- Dynamic VIDTM Technology
• Programmable Droop Voltage
• Fast Transient Recovery Time
• Over Current Protection
• Digital Soft Start
• Threshold Sensitive Enable Input
• High Ripple Frequency (160kHz to 2MHz)
• QFN Package:
- Compliant to JEDEC PUB95 MO-220
QFN - Quad Flat No Leads - Package Outline
- Near Chip Scale Package footprint, which improves
PCB efficiency and has a thinner profile
• Pb-Free Available (RoHS Compliant)
Applications
• AMD Hammer Family Processor Voltage Regulator
• Low Output Voltage, High Current DC-DC Converters
• Voltage Regulator Modules
Ordering Information
PART NUMBER
TEMP.
(oC)
PACKAGE
PKG.
DWG. #
ISL6569ACB
0 to 70
24 Ld SOIC
M24.3
ISL6569ACBZ (Note)
0 to 70
24 Ld SOIC (Pb-free)
M24.3
ISL6569ACR
0 to 85
32 Ld 5x5 QFN
L32.5x5
ISL6569ACRZ (Note) 0 to 85
32 Ld 5x5 QFN (Pb-free) L32.5x5
Add “-T” suffix for tape and reel.
NOTE: Intersil Pb-free products employ special Pb-free material sets; molding
compounds/die attach materials and 100% matte tin plate termination finish, which are
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.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2003, 2004. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL6569A
Pinouts
17 ISEN2
COMP 9
16 VCC
FB 10
15 GND
IOUT 11
14 RGND
VDIFF 12
13 VSEN
2
OVP
GND
EN
FS/DIS
PGOOD
28
27
26
25
VID2
1
24 NC
VID1
2
23 NC
VID0
3
22 ISEN1
NC
4
21 PWM1
OFS
5
20 PWM2
COMP
6
19 GND
FB
7
18 ISEN2
NC
8
17 NC
9
10
11
12
13
14
15
16
NC
18 GND
OFS 8
29
VCC
VID0 7
30
GND
19 PWM2
31
GND
20 PWM1
VID1 6
32
RGND
VID2 5
VID4
21 ISEN1
VSEN
22 PGOOD
VID3 4
NC
23 FS/DIS
VID4 3
VDIFF
24 EN
OVP 2
IOUT
GND 1
ISL6569ACR (32 LD 5x5 QFN)
TOP VIEW
VID3
ISL6569ACB (24 LD SOIC)
TOP VIEW
FN9092.2
December 29, 2004
ISL6569A
Block Diagram
PGOOD
VCC
FS
EN
1.23V
VID4
6V
OSCILLAT0R
AND
SAWTOOTH
VID3
DYNAMIC
VID2
POR
AND
SOFT START
VID
DAC
VID1
UV
PWM1
350mV
+
VID0
+
+
PWM2
-
+
e/a
FB
-
+
COMP
OFS
x0.1
100µA
OVP
VDIFF
OV
2.2V
VSEN
90µA
diff
OC
RGND
I1
ISEN1
IDROOP
+
AVERAGE
1/2
+
I2
CURRENT
SENSE
ISEN2
GND
3
FN9092.2
December 29, 2004
ISL6569A
Typical Application - 2 Phase Converter
+12V
+12V
+12V
300Ω
PVCC
BOOT
UGATE
VCC
VSEN
RGND
PHASE
VCC
DRIVER
HIP6601B
VDIFF
LGATE
PWM
PWM1
FB
IOUT
RISEN1
GND
VOUT
ISEN1
+12V
COMP
OFS
+12V
ISL6569A
PVCC
µP
LOAD
BOOT
FS/DIS
RT
VID4
UGATE
VCC
PHASE
VID3
DRIVER
HIP6601B
VID2
LGATE
VID1
PWM
PWM2
VID0
RISEN2
GND
PGOOD
ISEN2
+12V
EN
GND
4
FN9092.2
December 29, 2004
ISL6569A
Absolute Maximum Ratings
Thermal Information
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7V
Input, Output, or I/O Voltage . . . . . . . . . . . GND -0.3V to VCC + 0.3V
ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 3kV
Thermal Resistance (Typical, Note 1)
Operating Conditions
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +5V ±5%
Ambient Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 0oC to 70oC
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 0oC to 125oC
θJA (oC/W)
θJC (oC/W)
SOIC Package (Note 1) . . . . . . . . . . . .
63
N/A
QFN Package (Notes 2, 3) . . . . . . . . . .
32
4
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . .150oC
Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC
Maximum Lead Temperature . . . . . . . . . . . . . . . . . . . . . . . . . .300oC
(SOIC - Lead Tips Only)
CAUTION: Stress above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device
at these or any other conditions above those indicated in the operational section of this specification is not implied.
NOTES:
1. θJA is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
2. 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.
3. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
Operating Conditions: VCC = 5V, TA = 0o C to 70oC. Unless Otherwise Specified.
Electrical Specifications
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
VCC SUPPLY CURRENT
Nominal Supply
VCC = 5VDC; EN = 5VDC; RT = 100 kΩ ±1%
8.0
10.8
14.0
mA
Shutdown Supply
VCC = 5VDC; EN = 0VDC; RT = 100 kΩ ±1%
8.0
10.3
13.0
mA
VCC Voltage
VCC tied to 12VDC thru 300Ω resistor, RT = 100kΩ
5.63
5.8
5.97
V
VCC Sink Current
VCC tied to 12VDC thru 300Ω resistor, RT = 100kΩ
15
20
25
mA
VCC Rising
4.25
4.35
4.50
V
VCC Falling
3.75
3.85
4.00
V
EN Rising
1.205
1.23
1.255
V
Hysteresis
86
92
98
mV
0.792
0.8
0.808
V
-0.5
-
0.5
%VID
-
25
-
mV
VID Pull Up
-
-20
-
µA
VID Input Low Level
-
0.8
V
VID Input High Level
-
1.36
1.6
V
-
100
-
µA
47.0
50.0
53.0
mV
Accuracy
-10
-
10
%
Adjustment Range
0.08
-
1.0
MHz
SHUNT REGULATOR
POWER-ON RESET AND ENABLE
POR Threshold
ENABLE Threshold
REFERENCE VOLTAGE AND DAC
Reference Voltage
System Accuracy
(Note 4)
VID on Fly Step Size
RT = 100kΩ
PIN-ADJUSTABLE OFFSET
OFS Current
Offset Accuracy
ROFS = 5.00kΩ ±1%
OSCILLATOR
5
FN9092.2
December 29, 2004
ISL6569A
Operating Conditions: VCC = 5V, TA = 0o C to 70oC. Unless Otherwise Specified. (Continued)
Electrical Specifications
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
0.8
1.0
1.2
V
Sawtooth Amplitude
-
1.37
-
V
Max Duty Cycle
-
75
-
%
Disable Voltage
IFS/DIS = 1mA
ERROR AMPLIFIER
Open-Loop Gain
RL = 10kΩ to ground
-
72
-
dB
Open-Loop Bandwidth
CL = 100pF, RL = 10kΩ to ground
-
18
-
MHz
Slew Rate
CL = 100pF, Load = ±400mA
-
7.1
11
V/µs
Maximum Output Voltage
RL = 10kΩ to ground
3.6
4.5
-
V
Source Current
3.0
7.0
9.0
mA
Sink Current
1.6
3.0
5.4
mA
Input Impedance
-
80
-
kΩ
Bandwidth
-
20
-
MHz
Slew Rate
-
6
-
V/µs
-5
-
5
%
-
6
-
mV
72
90
108
µA
-
-
0.4
V
REMOTE-SENSE AMPLIFIER
SENSE CURRENT
ISEN1 = ISEN2 = 50µA
IOUT Accuracy
ISEN Offset Voltage
Over-Current Trip Level
POWER GOOD AND PROTECTION MONITORS
PGOOD Low Voltage
IPGOOD = 4mA
Under-Voltage Offset From VID
VSEN Falling
320
350
420
mV
Over-Voltage Threshold
VSEN Rising
2.08
2.13
2.20
V
OVP Voltage
IOVP = 100mA, VCC = 5V
2.2
3.28
4.0
V
NOTE:
4. These parts are designed and adjusted for accuracy within the system tolerance.
6
FN9092.2
December 29, 2004
ISL6569A
Functional Pin Description
ISL6569ACB
ISL6569ACR
24 LD SOIC
24 EN
VID3
NC
VID4
OVP
GND
EN
FS/DIS
PGOOD
32 LEAD QFN 5x5
GND 1
OVP 2
23 FS/DIS
VID4 3
22 PGOOD
VID3 4
VID2
VID1
VID0
19 PWM2
NC
18 GND
OFS
17 ISEN2 COMP
FB
16 VCC
NC
15 GND
VID1 6
VID0 7
OFS 8
COMP 9
FB 10
21 ISEN1
20 PWM1
IOUT 11
14 RGND
VDIFF 12
13 VSEN
GND
BOTTOM
SIDE PAD
NC
NC
ISEN1
PWM1
PWM2
GND
ISEN2
NC
IOUT
VDIFF
VSEN
RGND
GND
GND
VCC
NC
VID2 5
VCC
Supplies all the power necessary to operate the chip. The IC
starts to operate when the voltage on this pin exceeds the
rising POR threshold and shuts down when the voltage on
this pin drops below the falling POR threshold. Connect this
pin directly to a +5V supply or through a series 255Ω resistor
to a +12V supply.
ISEN1, ISEN2
Current sense inputs. A resistor connected between these
pins and their respective phase nodes sets a current
proportional to the current in the lower MOSFET during it’s
conduction interval. This current is used as a reference for
channel balancing, load sharing, protection, and load-line
droop.
PWM1, PWM2
GND
Bias and reference ground for the IC.
OVP
Over-voltage protection pin. This pin is pulled to VCC and is
latched when an over-voltage condition is detected. Connect
this pin to the gate of an SCR or MOSFET tied across VIN
and ground. A fuse must be placed upstream to open the
input supply rail and prevent damage to the load device.
VID4, VID3, VID2, VID1, VID0
The state of these five inputs program the internal DAC,
which provides the reference voltage for output regulation.
Connect these pins to either open-drain or active pull-up
type outputs. Pulling these pins above 2.9V can cause a
reference offset inaccuracy.
Pulse-width modulating outputs. Connect these pins to the
individual HIP660x driver PWM input pins. These logic
outputs command the driver IC(s) in switching the halfbridge configuration of MOSFETs.
PGOOD
Power good is an open-drain logic output that changes to a
logic low when the voltage at VDIFF is 350mV below the VID
setting or above 2.2V.
FS/DIS
A dual function pin for setting the switching frequency and
disabling the controller. Place a resistor from this pin to
ground to set the switching frequency between 25kHz and
1MHz. Pulling this pin below 0.8V disables the controller.
EN
OFS
Connecting a resistor between this pin and ground creates a
positive offset voltage which is added to the DAC voltage,
allowing easy implementation of load-line regulation. For no
offset, simply tie this pin to ground.
FB and COMP
The internal error amplifier inverting input and output
respectively. Connect the external R-C feedback
compensation network of the regulator to these pins.
IOUT
The current carried out of this pin is proportional to output
current and can be used to incorporate output voltage droop
and/or load sharing. The scale factor is set by the ratio of the
ISEN resistors and the lower MOSFET rDS(ON). If droop is
desired, connect this pin to FB. When not used for droop or
load sharing, simply leave this pin open.
VSEN, RGND, VDIFF
VSEN and RGND are the inputs to the differential remotesense amplifier. Connect these pins to the sense points of
the remote load. Connect an appropriately sized feedback
resistor, RFB, between VDIFF and FB.
7
Threshold sensitive enable input of the controller. Transition
this pin above 1.23V (typical enable threshold) to initiate a
soft-start cycle. Pull this pin below 1.14V, taking into account
the enable hysteresis, to disable the controller once in
operation. Connect a resistor divider to this pin to set the
power-on voltage level for proper coordination with Intersil
MOSFET drivers. If this function is not required, simply tie
this pin to VCC.
Multi-Phase Control
Microprocessor load current profiles have increased to the
point where the multi-phase power conversion advantage is
pronounced. The technical challenges associated with
producing a single-phase converter which is both costeffective and thermally viable have forced a change to the
cost-saving approach of multi-phase. The ISL6569A
controller helps reduce the complexity of implementation by
integrating vital functions and requiring minimal output
components. The block diagram in Figure 1 provides a top
level view of multi-phase power conversion using the
ISL6569A controller.
FN9092.2
December 29, 2004
ISL6569A
OFS
VIN
100µA
COMP
PWM
CIRCUIT
+
PWM1
-
L1
HIP6601B
x0.1
VOUT
REFERENCE
&
DAC
PWM
CIRCUIT
+
ISEN1
RISEN1
-
CO
VIN
µP
LOAD
+
ERROR
AMPLIFIER
-
PWM2
AVERAGE
IOUT
L2
HIP6601B
+
FB
ISEN2
IOUT
RISEN2
+
VDIFF
x1
-
-
CURRENT
SENSE
-
CURRENT
SENSE
+
+
VSEN
RGND
FIGURE 1. SIMPLIFIED BLOCK DIAGRAM OF A ISL6569A CONVERTER
Interleaving
The switching of each channel in a multi-phase converter is
timed to be symmetrically out of phase with the other
channel. In a 2-phase converter, channel-2 switches half a
cycle after channel-1. As a result, the converter has a ripple
frequency twice that of either phase. Figure 2 illustrates the
multiplicative effect on output ripple frequency. The two
channel currents (IL1 and IL2), combine to form the AC
ripple current and the DC load current. The ripple
component has twice the ripple frequency of either channel
current. Each PWM pulse is terminated half of a cycle, or
2.0µs, after the PWM pulse of the previous phase. The peakto-peak current waveform for each phase is about 7A, and
the dc components of the inductor currents combine to feed
the load.
IL1 + IL2, 7A/DIV
IL2, 7A/DIV
PWM2, 5V/DIV
IL1, 7A/DIV
PWM1, 5V/DIV
1µs/DIV
FIGURE 2. PWM AND INDUCTOR-CURRENT WAVEFORMS
FOR 2-PHASE CONVERTER
8
FN9092.2
December 29, 2004
ISL6569A
In addition, the peak-to-peak amplitude of the combined
inductor currents is reduced in proportion to the number of
phases. To understand the reduction of ripple current
amplitude in the multi-phase circuit, examine the equation
representing an individual channel’s peak-to-peak inductor
current.
( V IN – V OUT ) V OUT
I PP = ----------------------------------------------------L fS V
(EQ. 1)
IN
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. In the case of multi-phase converters, the
capacitor current is the sum of the ripple currents from each
of the individual channels. Compare Equation 1 to the
expression for the peak-to-peak current after the summation
of two symmetrically phase-shifted inductor currents in
Equation 2.
INPUT-CAPACITOR CURRENT, 10A/DIV
CHANNEL 2
INPUT CURRENT
10A/DIV
CHANNEL 1
INPUT CURRENT
10A/DIV
1µs/DIV
FIGURE 3. CHANNEL INPUT CURRENTS AND INPUTCAPACITOR RMS CURRENT FOR 3-PHASE
CONVERTER
PWM Operation
( V IN – 2 V OUT ) V OUT
I C, PP = ---------------------------------------------------------L fS V
(EQ. 2)
IN
Peak-to-peak ripple current decreases by an amount
proportional to the number of channels. 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.
Increased ripple frequency and lower ripple amplitude mean
that the designer can use less per-channel inductance and
lower total output capacitance for any performance
specification.
Another benefit of interleaving is to reduce input ripple
current. Input capacitance is determined in part by the
maximum input ripple current. Multi-phase topologies can
improve overall system cost and size by lowering input ripple
current and allowing the designer to reduce the cost of input
capacitance. The example in Figure 3 illustrates input
currents from a two-phase converter combining to reduce
the total input ripple current.
The converter depicted in Figure 3 delivers 36A to a 1.5V
load from a 12V input. The RMS input capacitor current is
8.6A. Compare this to a single-phase converter also
stepping down 12V to 1.5V at 36A. The single-phase
converter has 11.9A RMS input capacitor current. The
single-phase converter input capacitor bank must support
38% more RMS current than an equivalent 2-phase
converter.
One switching cycle is defined as the time between PWM1
pulse termination signals. The pulse termination signal is
an internally generated clock signal which triggers the
falling edge of PWM1. The cycle time of the pulse
termination signal is the inverse of the switching frequency
set by the resistor between the FS/DIS pin and ground.
Each cycle begins when the clock signal commands the
channel-1 PWM output to go low. The PWM1 transition
signals the channel-1 MOSFET driver to turn off the
channel-1 upper MOSFET and turn on the channel-1
synchronous MOSFET. The PWM2 pulse terminates 1/2 of
a cycle after PWM1.
Once a PWM signal transitions low, it is held low for a
minimum of 1/4 cycle. This forced off time is required to
ensure an accurate current sample. Current sensing is
described in the next section. After the forced off time
expires, the PWM output is enabled. The PWM output state
is driven by the position of the error amplifier output signal,
VCOMP, minus the current correction signal relative to the
sawtooth ramp as illustrated in Figure 1. When the modified
VCOMP voltage crosses the sawtooth ramp, the PWM
output transitions high. The MOSFET driver detects the
change in state of the PWM signal and turns off the
synchronous MOSFET and turns on the upper MOSFET.
The PWM signal will remain high until the pulse termination
signal marks the beginning of the next cycle by triggering
the PWM signal low.
Figure 16 in the section entitled Input Capacitor Selection
can be used to determine the input-capacitor RMS current
based on load current, duty cycle. It is provided as an aid in
determining the optimal input capacitor solution.
9
FN9092.2
December 29, 2004
ISL6569A
.
SAMPLED
CURRENT
I1
I
channel current. Using Figures 4 and 6, the average current
is defined as:
VIN
r
DS ( ON )
SEN = I L1 ------------------------R
ISEN
CHANNEL 1
UPPER MOSFET
(EQ. 4)
I OUT r DS ( ON )
- ---------------------I AVG = -----------2
R ISEN
IL1
SAMPLE
&
HOLD
I1 + I2
I AVG = --------------2
RISEN
where IOUT is the total load current.
+
ISEN1
I L1 r DS ( ON )
+
CHANNEL 1
LOWER MOSFET
ISL6569A INTERNAL CIRCUIT
EXTERNAL CIRCUIT
FIGURE 4. CHANNEL 1 INTERNAL AND EXTERNAL
CURRENT-SENSING CIRCUITRY
Current Sensing
During the forced off time following a PWM transition low, the
controller senses channel load current by sampling the voltage
across the lower MOSFET rDS(ON). A ground-referenced
amplifier, internal to the ISL6569A, connects to the PHASE
node through a resistor, RISEN. The voltage across RISEN is
equivalent to the voltage drop across the rDS(ON) of the lower
MOSFET while it is conducting. The resulting current into the
ISEN pin is proportional to the channel current, IL. The ISEN
current is then sampled and held after sufficient settling time
every switching cycle. The sampled current is used for channelcurrent balance, load-line regulation, overcurrent protection,
and module current sharing.
The circuitry shown in Figure 4 represents channel-1 of a
two channel converter. This circuitry is repeated for
channel-2 of the converter. From Figure 4, the following
equation for channel-1 sampled current, I1, is derived
r DS ( ON )
I 1 = I L1 ---------------------R ISEN
(EQ. 3)
where IL1 is half of the total load current.
If rDS(ON) sensing is not desired, an independent currentsense resistor in series with the lower MOSFET source can
serve as a sense element.
The average current is then subtracted from the individual
channel sample currents. The resulting error current, IER, is
then filtered before it adjusts VCOMP. The modified VCOMP
signal is compared to a sawtooth ramp signal and produces
a pulse width which corrects for any unbalance and drives
the error current toward zero. Figure 6 illustrates Intersil’s
patented current balance method as implemented on one
channel of a multi-phase converter.
Two considerations designers face are MOSFET selection
and inductor design. Both are significantly improved when
channel currents track at any load level. The need for
complex drive schemes for multiple MOSFETs, exotic
magnetic materials, and expensive heat sinks is avoided.
Resulting in a cost-effective and easy to implement solution
relative to single-phase conversion. Channel current balance
insures the thermal advantage of multi-phase conversion is
realized. Heat dissipation is spread over multiple channels
and a greater area than single phase approaches.
In some circumstances, it may be necessary to deliberately
design some channel-current unbalance into the system. In
a highly compact design, one channel may be able to cool
more effectively than the other due to nearby air flow or heat
sinking components. The other channel may have more
difficulty cooling with comparatively less air flow and heat
sinking. The hotter channel may also be located close to
other heat-generating components tending to drive it’s
temperature even higher. In these cases, the proper
selection of the current sense resistors (RISEN in Figure 4)
introduces channel current unbalance into the system.
Increasing the value of RISEN in the cooler channel and
decreasing it in the hotter channel moves both channels into
thermal balance at the expense of current balance.
VCOMP
+
+
-
The sampled current from both channels, I1 and I2, is used
to gauge both overall load current and the relative channel
current carried in each leg of the converter. The individual
sample currents are averaged. The resulting average
current, IAVG, provides a measure of the total load current
demand on the converter and the appropriate level of
PWM1
-
Channel-Current Balance
SAWTOOTH SIGNAL
f(jω)
IER
IAVG
-
÷2
Σ
I2
+
I1
FIGURE 5. CHANNEL-1 PWM FUNCTION AND CURRENTBALANCE ADJUSTMENT
10
FN9092.2
December 29, 2004
ISL6569A
Voltage Regulation
The output of the error amplifier, VCOMP, is compared to the
sawtooth waveform to modulate the pulse width of the PWM
signals. The PWM signals control the timing of the Intersil
MOSFET drivers and regulate the converter output to the
specified reference voltage. Three distinct inputs to the error
amplifier determine the voltage level of VCOMP. The internal
and external circuitry which control voltage regulation is
illustrated in Figure 6.
EXTERNAL CIRCUIT
RC
CC
ISL6569A INTERNAL CIRCUIT
COMP
ERROR AMPLIFIER
FB
+
RFB
+
+
IAVG
IOUT
VCOMP
VDROOP
-
REFERENCE
VOLTAGE
VDIFF
VOUT
REMOTE
SENSE
POINTS
GND
The ISL6569A features a second non-inverting input to the
error amplifier which allows the user to directly offset the
DAC reference voltage in the positive direction only. The
offset voltage is created by an internal current source which
feeds out the OFS pin into a user selected external resistor
to ground. The resulting voltage across the resistor, VOFS, is
internally divided down by ten to create the offset voltage.
This method of offsetting the DAC voltage is more accurate
than external methods of level-shifting the FB pin.The
integrating compensation network shown in Figure 6 assures
that the steady-state error in the output voltage is limited to
the error in the reference voltage (output of the DAC) plus
offset errors in the OFS current source, remote-sense and
error amplifiers. Intersil specifies the guaranteed tolerance of
the ISL6569A to include all variations in current sources,
amplifiers and the reference so that the output voltage
remains within the specified system tolerance of ±0.5% over
temperature.
TABLE 1. VOLTAGE IDENTIFICATION CODES
VSEN
RGND
+
VID4
VID3
VID2
VID1
VID0
DAC
-
0
0
0
0
0
1.550
0
0
0
0
1
1.525
0
0
0
1
0
1.500
0
0
0
1
1
1.475
0
0
1
0
0
1.450
0
0
1
0
1
1.425
0
0
1
1
0
1.400
0
0
1
1
1
1.375
0
1
0
0
0
1.350
0
1
0
0
1
1.325
0
1
0
1
0
1.300
0
1
0
1
1
1.275
0
1
1
0
0
1.250
0
1
1
0
1
1.225
0
1
1
1
0
1.200
0
1
1
1
1
1.175
1
0
0
0
0
1.150
1
0
0
0
1
1.125
1
0
0
1
0
1.100
1
0
0
1
1
1.075
1
0
1
0
0
1.050
1
0
1
0
1
1.025
1
0
1
1
0
1.000
1
0
1
1
1
0.975
1
1
0
0
0
0.950
1
1
0
0
1
0.925
DIFFERENTIAL
REMOTE-SENSE
AMPLIFIER
OFS
ROFS
they are pulled above 2.9V. The DAC-selected reference
voltage is connected to the non-inverting input of the error
amplifier.
x0.1
+
VOFS
-
OFFSET
VOLTAGE
100µA
FIGURE 6. OUTPUT-VOLTAGE AND LOAD-LINE REGULATION
Most multi-phase controllers simply have the output voltage
fed back to the inverting input of the error amplifier through a
resistor. The ISL6569A features 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 local 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 remote-sense
amplifier output, VDIFF, is then tied through an external
resistor to the inverting input of the error amplifier.
A digital to analog converter (DAC) generates a reference
voltage based on the state of logic signals at pins VID4
through VID0. The DAC decodes the a 5-bit logic signal
(VID) into one of the discrete voltages shown in Table 1.
Each VID input offers a 20µA pull-up to an internal 2.5V
source for use with open-drain outputs. External pull-up
resistors or active-high output stages can augment the pullup current sources, but a slight accuracy error can occur if
11
FN9092.2
December 29, 2004
ISL6569A
TABLE 1. VOLTAGE IDENTIFICATION CODES (Continued)
VID4
VID3
VID2
VID1
VID0
DAC
1
1
0
1
0
0.900
1
1
0
1
1
0.875
1
1
1
0
0
0.850
1
1
1
0
1
0.825
1
1
1
1
0
0.800
1
1
1
1
1
Shutdown
LOAD-LINE REGULATION
Microprocessor load current demands change from near noload to full load often during operation. The resulting sizable
transient current slew rate causes an output voltage spike
since the converter is not able to respond fast enough to the
rapidly changing current demands. The magnitude of the
spike is dictated by the ESR and ESL of the output
capacitors selected. In order to drive the cost of the output
capacitor solution down, one commonly accepted approach
is active voltage positioning. By adding a well controlled
output impedance, the output voltage can effectively be level
shifted in a direction which works against the voltage spike.
The average current of all the active channels, IAVG, flows out
IOUT, see Figure 6. IOUT is connected to FB through a loadline regulation resistor, RFB. The resulting voltage drop across
RFB is proportional to the output current, effectively creating
an output voltage droop with a steady-state value defined as
V DROOP = I AVG R FB
(EQ. 5)
In most cases, each channel uses the same RISEN value to
sense current. A more complete expression for VDROOP is
derived by combining Equations 4 and 5.
I OUT r DS ( ON )
V DROOP = ---------------------------------- R FB
2
R ISEN
(EQ. 6)
DYNAMIC VID
Next generation microprocessors can change VID inputs at
any time while the regulator is in operation. The power
management solution is required to monitor the DAC inputs
and respond to VID voltage transitions, or ‘on-the-fly’ VID
changes, in a controlled manner. Supervising the safe output
voltage transition within the DAC range of the processor
without discontinuity or disruption.
The ISL6569A checks the five VID inputs at the beginning of
each channel-1 switching cycle. If the VID code has
changed, the controller waits one complete switching cycle
to validate the new code. If the VID code is stable for this
entire switching cycle, then the controller will begin executing
the output voltage change. The controller begins
incrementing the reference voltage by making 25mV steps
every two switching cycles until it reaches the new VID code.
The total time required for a VID change, tDV, is dependent
on the switching frequency (fS), the size of the change
(∆VID), and the time before the next switching cycle begins.
Since the ISL6569A recognizes VID-code changes only at
the beginning of switching cycles, up to one full cycle may
pass before a VID change registers. This is followed by a
one-cycle wait before the output voltage begins to change.
The one-cycle uncertainty in Equation 8 is due to the
possibility that the VID code change may occur up to one full
cycle before being recognized.
1 ∆VID
1 2 ∆VID
-----  2
------------------ – 1 < t DV ≤ -----  ------------------
f S  0.025
f S 0.025
(EQ. 8)
The time required for a converter running with fS = 500kHz to
make a 1.2V to 1.4V reference-voltage change is between
30µs and 32µs as calculated using Equation 8. This example
is also illustrated in Figure 7.
Droop is an optional feature of the ISL6569A. If active voltage
positioning is not required, simply leave the IOUT pin open.
01110
00110
VID, 5V/DIV
VID CHANGE OCCURS
ANYWHERE HERE
REFERENCE OFFSET
Typical microprocessor tolerance windows are centered
around a nominal DAC set point. Implementing a load-line
requires offsetting the output voltage above this nominal
DAC set point; centering the load-line within the static
specification window. The ISL6569A features an internal
100µA current source which feeds out the OFS pin. Placing
a resistor from OFS and ground allows the user to set the
amount of positive offset desired directly to the reference
voltage. The voltage developed across the OFS resistor,
ROFS, is divided down internally by a factor of 10 and directly
counters the DAC voltage at the error amplifier non-inverting
input. Select the resistor value based on the voltage offset
desired, VOFS, using Equation 7
V OFS ⋅ 10
R OFS = -------------------------100µA
VREF, 100mV/DIV
1.2V
VOUT, 100mV/DIV
1.2V
5µs/DIV
FIGURE 7. DYNAMIC-VID WAVEFORMS FOR 500kHz ISL6569A
BASED MULTI-PHASE BUCK CONVERTER
(EQ. 7)
12
FN9092.2
December 29, 2004
ISL6569A
Operation Initialization
Before converter operation is initialized, proper conditions
must exist on the enable and disable inputs. Once these
conditions are met, the controller begins a soft-start interval.
Once the output voltage is within the proper window of
operation, the PGOOD output changes state to update an
external system monitor.
Enable and Disable
The PWM outputs are held in a high-impedance state to
assure the drivers remain off while in shutdown mode. Four
separate input conditions must be met before the ISL6569A
is released from shutdown mode.
First, the bias voltage applied at VCC must reach the internal
power-on reset (POR) circuit rising threshold. Once this
threshold is met, the EN input signal becomes the gate for
soft-start initialization. Hysteresis between the rising and
falling thresholds insures that once enabled, the ISL6569A
will not inadvertently turn off unless the bias voltage drops
substantially. See Electrical Specifications for specifics on
POR rising and falling thresholds.
ISL6569A INTERNAL CIRCUIT
EXTERNAL CIRCUIT
Finally, the 11111 VID code is reserved as a signal to the
controller that no load is present. The controller will enter
shutdown mode after receiving this code and will start up
upon receiving any other code.
To enable the controller, VCC must be greater than the POR
threshold; the voltage on EN must be greater than 1.23V;
FS/DIS must not be grounded; and VID cannot be equal to
11111. Once these conditions are true, the controller
immediately initiates a soft-start sequence.
Soft-Start
The soft-start time, tSS, is determined by an 11-bit counter
that increments with every pulse of the phase clock. For
example, a converter switching at 250kHz per phase has a
soft-start time of
2048
T SS = ------------- = 8.3ms
f SW
During the soft-start interval, the soft-start voltage, VRAMP,
increases linearly from zero to 140% of the programmed
DAC voltage. At the same time a current source, IRAMP, is
decreasing from 160µA down to zero. These signals are
connected as shown in Figure 9 (IOUT may or may not be
connected to FB depending on the particular application).
+5V
VCC
EXTERNAL CIRCUIT
+12V
RC
ISL6569A INTERNAL CIRCUIT
COMP
ERROR AMPLIFIER
FB
EN
OV LATCH
SIGNAL
CC
10.7kΩ
ENABLE
COMPARATOR
POR
CIRCUIT
(EQ. 9)
-
+
-
1.40kΩ
1.23V (± 2%)
RFB
VCOMP
+
IOUT
REFERENCE
VOLTAGE
IRAMP
VDIFF
VRAMP
FIGURE 8. POWER SEQUENCING USING THRESHOLDSENSITIVE ENABLE (EN) FUNCTION
Second, the ISL6569A features an enable input (EN) for
power sequencing between the controller bias voltage and
another voltage rail. The enable comparator holds the
ISL6569A in shutdown until the voltage at EN rises above
1.23V. The enable comparator has about 90mV of hysteresis
to prevent bounce. It is important that the driver ICs reach
their POR level before the ISL6569A becomes enabled. The
schematic in Figure 8 demonstrates sequencing the
ISL6569A with the HIP660X family of Intersil MOSFET
drivers which require 12V bias.
Third, the frequency select/disable input (FS/DIS) will
shutdown the converter when pulled to ground. Under this
condition, the internal oscillator is disabled. The oscillator
resumes operation upon release of FS/DIS and a soft-start
sequence is initiated.
13
IAVG
IDEAL DIODES
FIGURE 9. RAMP CURRENT AND VOLTAGE FOR
REGULATING SOFT-START SLOPE
AND DURATION
The ideal diodes in Figure 9 assure that the controller tries to
regulate its output to the lower of either the reference voltage
or VRAMP. Since IRAMP creates an initial offset across RFB
(RFB x 160µA), the first PWM pulse will not be seen until
VRAMP is greater than the RFB IRAMP offset. This produces a
delay after the ISL6569A enables before the output voltage
starts moving. For example, if VID = 1.5V, RFB = 1kΩ and TSS
= 8.3ms, the delay time can be expressed using Equation 10.
T SS
t DELAY = -------------------------------------------------- = 560µs
1.4 ( VID)
1 + ---------------------------------------–
6
R FB 160 × 10
(EQ. 10)
FN9092.2
December 29, 2004
ISL6569A
Following the delay, the soft start ramps linearly until VRAMP
reaches VID. For the system described above, this first linear
ramp will continue for approximately
T SS
t RAMP1 = ---------- – t DELAY
1.4
PGOOD
(EQ. 11)
+
The final portion of the soft-start sequence is the time
remaining after VRAMP reaches VID and before IRAMP gets to
zero. This is also characterized by a slight change in the slope
of the output voltage ramp which, for the current example,
exists for a time of
-
UV
= 5.27ms
+
350mV
-
+
(EQ. 12)
VOUT, 500mV/DIV
+
90µA
IAVG
OV
OVP
-
= 2.34ms
This behavior is seen in the example in Figure 10 of a converter
switching at 500kHz. For this converter, RFB is set to 2.67kΩ
leading to TSS = 4.0ms, tDELAY = 700ns, tRAMP1 = 2.23ms,
and tRAMP2 = 1.17ms.
OC
DAC
REFERENCE
VDIFF
t RAMP2 = T SS – t RAMP1 – t DELAY
POR
CIRCUIT
2.2V
FIGURE 11. POWER GOOD AND PROTECTION CIRCUITRY
conditions. PGOOD pulls low during shutdown and releases
high during soft-start once the output voltage exceeds the
UV threshold. Once high, PGOOD will only transition low
when the controller is disabled or a fault condition is
detected. It will return high under certain circumstances
once a fault clears.
Under-Voltage Protection
EN, 5V/DIV
tDELAY tRAMP1
tRAMP2
1ms/div
FIGURE 10. SOFT-START WAVEFORMS FOR ISL6569A
BASED MULTI-PHASE BUCK CONVERTER
NOTE: Switching frequency 500kHz and RFB = 2.67kΩ
Fault Monitoring and Protection
The ISL6569A actively monitors voltage and current
feedback to detect fault conditions. Fault monitors trigger
protective measures to prevent damage to a microprocessor
load. One common power good indication signal is provided
for linking to external system monitors. The schematic in
Figure 11 outlines the interaction between the fault monitors
and the power good signal.
Power Good Signal
The power good pin (PGOOD) is an open-drain logic output
which indicates that the converter is operating properly and
the output voltage is within a set window. The under-voltage
(UV) and over-voltage (OV) comparators create the output
voltage window. The controller also takes advantage of
current feedback to detect output over-current (OC)
14
The voltage on VDIFF is internally offset by 350mV before it
is compared with the DAC reference voltage. By positively
offsetting the output voltage, an UV threshold is created
which moves relative to the VID code. During soft-start, the
slow rising output voltage eventually exceeds the UV
threshold. Assuming the POR leg of the PGOOD NOR gate
has not detected an OC fault, the PGOOD signal will go
high.
If a fault condition arises during operation and the output
voltage drops below the UV threshold, PGOOD will
immediately pull low, but converter operation will continue.
PGOOD will return high once the output voltage surpasses
the UV threshold.
If the ISL6569A is disabled during operation, the PGOOD
signal will not pull low until the output voltage decays below
the UV threshold.
Over-Voltage Protection
When the output of the differential amplifier (VDIFF) reaches
2.2V, PGOOD immediately goes low indicating a fault. Two
protective actions are taken by the ISL6569A to protect the
microprocessor load.
First, all PWM outputs are commanded low. Directing the
Intersil drivers to turn on the lower MOSFETs; shunting the
output to ground preventing any further increase in output
voltage. The PWM outputs remain low until VDIFF falls to the
programmed DAC level at which time they go into a high-
FN9092.2
December 29, 2004
ISL6569A
impedance state. The Intersil drivers respond by turning off
both upper and lower MOSFETs. If the over-voltage condition
reoccurs, the ISL6569A will again command the lower
MOSFETs to turn on. The ISL6569A will continue to protect
the load in this fashion as long as the over-voltage repeats.
Second, the OVP pin pulls to VCC and can deliver 100mA
into the gate of either a MOSFET or SCR placed on the input
rail (VIN) or VOUT. Turning on the MOSFET or SCR
collapses the power rail and causes a fuse placed further up
stream to blow. The fuse must be sized such that the
MOSFET or SCR will not overheat before the fuse blows.
Once an over-voltage condition is detected, normal PWM
operation ceases and PGOOD remains low until the
ISL6569A is reset. Cycling the voltage on EN below 1.23V or
the bias to VCC below the POR-falling threshold will reset
the controller.
Over-Current Protection
blanking the OC comparator during the VID-on-the-fly
transition, nuisance tripping is avoided.
OUTPUT CURRENT, 20A/DIV
0A
OUTPUT VOLTAGE,
500mV/DIV
0V
5ms/DIV
FIGURE 12. OVERCURRENT BEHAVIOR IN HICCUP MODE
The ISL6569A takes advantage of the proportionality
between the load current and the average current, IAVG, to
detect an over-current condition. See the Channel-Current
Balance section for more detail on how the average current
is created. The average current is continually compared with
a constant 90µA reference current. Once the average
current exceeds the reference current, the comparator
triggers the converter to shutdown. The POR circuit places
all PWM signals in a high-impedance state which commands
the drivers to turn off both upper and lower MOSFETs.
PGOOD pulls low and the system remains in this state while
the controller counts 2048 phase clock cycles. This is
followed by a soft-start attempt (see Soft-Start).
During the soft-start interval, the over-current protection
circuitry remains active. As the output voltage ramps up, if an
over-current condition is detected, the ISL6569A
immediately places all PWM signals in a high-impedance
state. The ISL6569A repeats the 2048-cycle wait period and
follows with another soft-start attempt, as shown in
Figure 12. This hiccup mode of operation repeats up to
seven times. On the eighth soft-start attempt, the part
latches off. Once latched off, the ISL6559 can only be reset
when the voltage on EN is brought below 1.23V or VCC is
brought below the POR falling threshold. Upon completion of
a successful soft-start attempt, operation will continue as
normal, PGOOD will return high, and the over-current latch
counter will reset.
During VID-on-the-fly transitions, the OC comparator output
is blanked. The quality and mix of output capacitors used in
different applications leads to a wide output capacitance
range. Depending upon the magnitude and direction of the
VID change, the change in voltage across the output
capacitors could result in significant current flow. Summing
this instantaneous current with the load current already
present could drive the average current above the reference
current level and cause an OC trip during the transition. By
15
General Design Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to create a multi-phase
power converter. It is assumed that the reader is familiar with
many of the basic skills and techniques referenced below. 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 Stages
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; and
the total board space available for power-supply circuitry.
Generally speaking, the most economical solutions are
those where each phase handles between 15 and 20A. All
surface-mount designs will tend toward the lower end of this
current range and, if through-hole MOSFETs can be used,
higher per-phase currents are possible. In cases where
board space is the limiting constraint, current can be pushed
as high as 30A per phase, but these designs require heat
sinks and forced air to cool the MOSFETs.
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.
LOWER MOSFET POWER CALCULATION
The calculation for heat dissipated in the lower MOSFET is
simple, since virtually all of the heat loss in the lower
MOSFET is due to current conducted through the channel
resistance (rDS(ON)). In Equation 13, IM is the maximum
continuous output current; IPP is the peak-to-peak inductor
FN9092.2
December 29, 2004
ISL6569A
current (see Equation 1); d is the duty cycle (VOUT/VIN); and
L is the per-channel inductance.
through the upper MOSFET across VIN. The power
dissipated as a result is PUP,3 and is approximately
I L, 2PP ( 1 – d )
 I M 2
P L = r DS ( ON )  ----- ( 1 – d ) + -------------------------------12
 2
P UP,3 ≈ V IN Q rr f S
(EQ. 13)
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.
I

I M I PP
M I PP t
P D = V D ( ON ) f S  ----- t d1 +  ----- – --------- d2
 2- + -------2
2
2 
(EQ. 14)
Thus the total maximum power dissipated in each lower
MOSFET is approximated by the summation of PL and PD.
UPPER MOSFET POWER CALCULATION
In addition to rDS(ON) losses, a large portion of the upperMOSFET 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 reverserecovery 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 15,
the required time for this commutation is t1 and the
approximated associated power loss is PUP,1.
I M I PP  t 1 
P UP,1 ≈ V IN  -----  ----  f
 2- + -------2   2 S
(EQ. 15)
The upper MOSFET begins to conduct and this transition
occurs over a time t2. In Equation 16, the approximate power
loss is PUP,2.
 I M I PP  t 2 
P UP, 2 ≈ V IN  ----- – ---------  ----  f S
2  2
2
(EQ. 16)
A third component involves the lower MOSFET’s reverserecovery charge, Qrr. Since the inductor current has fully
commutated to the upper MOSFET before the lowerMOSFET’s body diode can draw all of Qrr, it is conducted
16
(EQ. 17)
Finally, the resistive part of the upper MOSFET’s dissipation
is given in Equation 18 as PUP,4.
2
I PP2
 I M
P UP,4 = r DS ( ON )  ----- d + ---------12
 2
(EQ. 18)
In this case, of course, rDS(ON) is the on resistance of the
upper MOSFET.
The total power dissipated by the upper MOSFET at full load
can now be approximated as the summation of the results
from Equations 15, 16, 17 and 18. Since the power
equations depend on MOSFET parameters, choosing the
correct MOSFETs can be an iterative process that involves
repetitively solving the loss equations for different MOSFETs
and different switching frequencies until converging upon the
best solution.
Current Sensing
The ISEN pins are denoted ISEN1 and ISEN2. The resistors
connected between these pins and their respective phase
nodes determine the gain in the load-line regulation loop and
the channel-current balance loop. Select the values for these
resistors based on the room temperature rDS(ON) of the
lower MOSFETs; the full-load operating current, IFL;
according to Equation 19 (see also Figure 4).
r DS ( ON )
R ISEN = ---------------------50 ×10 – 6
I FL
------2
(EQ. 19)
In certain circumstances, it may be necessary to adjust the
value of one or both of the ISEN resistors. This can arise
when the components of one channel are inhibited from
dissipating their heat so that the affected channel runs hotter
than desired (see the section entitled Channel-Current
Balance). In this case, chose a new, smaller value of RISEN
for the affected phase. Choose RISEN,2 in proportion to the
desired decrease in temperature rise in order to cause
proportionally less current to flow in the hotter phase.
∆T
R ISEN ,2 = R ISEN ----------2
∆T 1
(EQ. 20)
In Equation 20, make sure that ∆T2 is the desired temperature
rise above the ambient temperature, and ∆T1 is the measured
temperature rise above the ambient temperature. While a
single adjustment according to Equation 20 is usually
sufficient, it may occasionally be necessary to adjust RISEN
two or more times to achieve perfect thermal balance between
both channels.
FN9092.2
December 29, 2004
ISL6569A
Load-Line Regulation Resistor
The load-line regulation resistor is labeled RFB in Figure 6.
Its value depends on the desired full-load droop voltage
(VDROOP in Figure 6). If Equation 19 is used to select each
ISEN resistor, the load-line regulation resistor is as shown
in Equation 21.
V DROOP
R FB = -----------------------–6
50 ×10
(EQ. 21)
If one or both of the ISEN resistors was adjusted for thermal
balance, as in Equation 20, the load-line regulation resistor
should be selected according to Equation 22. Where IFL is
the full-load operating current and RISEN(n) is the ISEN
resistor connected to the nth ISEN pin.
V DROOP
R FB = -------------------------------I FL r DS ( ON )
∑ RISEN ( n )
(EQ. 22)
n
Output Filter Design
The output inductors and the output capacitor bank
together form a low-pass filter responsible for smoothing
the pulsating voltage at the phase nodes. The output filter
also must provide the transient energy during the interval of
time after the beginning of the transient until the regulator
can respond. Because it has a low bandwidth compared to
the switching frequency, the output filter necessarily limits
the system transient response leaving the output capacitor
bank to supply or sink load current while the current in the
output inductors increases or decreases to meet the
demand.
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, ∆I; the load-current slew rate, di/dt; and the
maximum allowable output-voltage deviation under transient
loading, ∆VMAX. Capacitors are characterized according to
their capacitance, ESR, and ESL (equivalent series
inductance).
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, the output voltage initially deviates
by an amount
di
∆V ≈ ( ESL ) ----- + ( ESR ) ∆I
dt
The filter capacitor must have sufficiently low ESL and ESR
so that ∆V < ∆VMAX.
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 highfrequency 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 Interleaving and
Equation 2), a voltage develops across the bulk-capacitor
ESR equal to IC,PP (ESR). Thus, once the output capacitors
are selected, the maximum allowable ripple voltage,
VPP(MAX), determines the lower limit on the inductance.
 V – 2V

OUT V OUT
 IN
L ≥ ( ESR ) ---------------------------------------------------------f S V IN V PP( MAX )
(EQ. 24)
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 inductors must be capable of assuming the entire
load current before the output voltage decreases more than
∆VMAX. This places an upper limits on inductance.
4CVO
L ≤ ---------------∆V MAX – ∆I ( ESR )
( ∆I ) 2
( 2.5 ) C
L ≤ ----------------- ∆V MAX – ∆I ( ESR )  V IN – V O


( ∆I ) 2
(EQ. 25)
(EQ. 26)
Equation 26 gives the upper limit on L for the cases when the
trailing edge of the current transient causes a greater outputvoltage deviation than the leading edge. Equation 25
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 per-channel
inductance, and C is the total output capacitance.
Compensation
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.
(EQ. 23)
17
FN9092.2
December 29, 2004
ISL6569A
COMPENSATING LOAD-LINE REGULATED
CONVERTER
.
Case 1:
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.
Since the system poles and zero are effected 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.
The feedback resistor, RFB, has already been chosen as
outlined in Load-Line Regulation Resistor. 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 perchannel 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 three cases which follow, there is a separate set
of equations for the compensation components.
C2 (OPTIONAL)
CC
COMP
FB
+
RFB
IOUT
VDROOP
ISL6569A
RC
VDIFF
FIGURE 13. COMPENSATION CONFIGURATION FOR
LOAD-LINE REGULATED ISL6569A CIRCUIT
In Equations 27, L is the per-channel filter inductance
divided by 2 (the number of active channels); C is the sum
total of all output capacitors; ESR is the equivalent-series
resistance of the bulk output-filter capacitance; and VPP is
the peak-to-peak sawtooth signal amplitude as described in
Figure 6 and Electrical Specifications.
18
1
------------------- > f 0
2π LC
2πf 0 V pp LC
R C = R FB ----------------------------------0.75V
IN
0.75V IN
C C = ----------------------------------2πV PP R FB f 0
Case 2:
1
1
------------------- ≤ f 0 < ----------------------------2πC ( ESR )
2π LC
V PP ( 2π ) 2 f 02 LC
R C = R FB -------------------------------------------0.75 V
(EQ. 27)
IN
0.75V IN
C C = -----------------------------------------------------------2
( 2π ) f 02 V PP R FB LC
Case 3:
1
f 0 > -----------------------------2πC ( ESR )
2π f 0 V pp L
R C = R FB ----------------------------------------0.75 V IN ( ESR )
0.75V IN ( ESR ) C
C C = -----------------------------------------------2πV PP R FB f 0 L
Once selected, the compensation values in Equations 27
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
Equations 27 unless some performance issue is noted.
The optional capacitor C2, is sometimes needed to bypass
noise away from the PWM comparator (see Figure 13). Keep
a position available for C2, and be prepared to install a highfrequency capacitor of between 22pF and 150pF in case any
trailing edge jitter problem is noted.
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 typeIII controller, as shown in Figure 14, 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 chose fHF = 10 f0, but it can be higher
if desired. Choosing fHF to be lower than 10 f0 can cause
problems with too much phase shift below the system
bandwidth.
FN9092.2
December 29, 2004
ISL6569A
Switching Frequency
C2
CC
COMP
FB
C1
IOUT
RFB
R1
ISL6569A
RC
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, and they establish the upper limit for
the switching frequency. The lower limit is established by the
requirement for fast transient response and small outputvoltage ripple as outlined in Input Supply Voltage Selection.
Choose the lowest switching frequency that allows the
regulator to meet the transient-response requirements.
VDIFF
1000
In the solutions to the compensation equations, there is a
single degree of freedom. For the solutions presented in
Equations 28, RFB is selected arbitrarily. The remaining
compensation components are then selected according to
Equations 28.
C ( ESR )
R 1 = R FB ----------------------------------------LC – C ( ESR )
RT (kΩ)
FIGURE 14. COMPENSATION CIRCUIT FOR ISL6569A BASED
CONVERTER WITHOUT LOAD-LINE
REGULATION
100
10
10
LC – C ( ESR )
C 1 = ----------------------------------------R FB
100
1000
SWITCHING FREQUENCY (kHz)
10000
FIGURE 15. RT vs SWITCHING FREQUENCY
0.75V IN
C 2 = -----------------------------------------------------------------2
( 2π ) f 0 f HF LCR FB V PP
(EQ. 28)
2
V PP  2π f 0 f HF LCR FB
 
R C = -------------------------------------------------------------------2πf

0.75 V
 HF LC – 1
IN

0.75V IN 2πf
 HF LC – 1
C C = ------------------------------------------------------------------( 2π ) 2 f 0 f HF LCR FB V PP
In Equations 28, L is the per-channel filter inductance
divided by the number of active channels; C is the sum total
of all output capacitors; ESR is the equivalent-series
resistance of the bulk output-filter capacitance; and VPP is
the peak-to-peak sawtooth signal amplitude as described in
Figure 6 and Electrical Specifications.
Input Supply Voltage Selection
The VCC input of the ISL6569A can be connected to either a
+5V supply directly or through a current limiting resistor to a
+12V supply. An integrated 5.8V shunt regulator maintains
the voltage on the VCC pin when a +12V supply is used. A
300Ω resistor is suggested for limiting the current into the
VCC pin to approximately 20mA.
19
Switching frequency is determined by the selection of the
frequency-setting resistor, RT (see the figure Typical
Application on page 4). Figure 15 and Equation 29 are
provided to assist in the selecting the correct value for RT.
R T = 10
[11.09 – 1.13 log ( f S ) ]
(EQ. 29)
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.
For a two phase design, use Figure 16 to determine the
input-capacitor RMS current requirement given the duty
cycle, maximum sustained output current (IO), and the ratio
of the combined peak-to-peak inductor current (IC,PP) to IO.
Select a bulk capacitor with a ripple 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 1.25 times greater
than the maximum input voltage.
FN9092.2
December 29, 2004
ISL6569A
Next, place the input and output capacitors. Position one
high-frequency ceramic input capacitor next to each upper
MOSFET drain. Place the bulk input capacitors as close to
the upper MOSFET drains as dictated by the component
size and dimensions. Long distances between input
capacitors and MOSFET drains results in too much trace
inductance and a reduction in capacitor performance. Locate
the output capacitors between the inductors and the load,
while keeping them in close proximity around the
microprocessor socket.
INPUT-CAPACITOR CURRENT (IRMS / IO)
0.3
0.2
0.1
IC,PP = 0
IC,PP = 0.5 IO
IC,PP = 0.75 IO
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE (VIN / VO)
FIGURE 16. NORMALIZED INPUT-CAPACITOR RMS CURRENT
vs DUTY CYCLE FOR 2-PHASE CONVERTER
Layout Considerations
The following multi-layer printed circuit board layout
strategies minimize the impact of board parasitics on
converter performance. The following sections highlight
some important practices which should not be overlooked
during the layout process.
Component Placement
Within the allotted implementation area, orient the switching
components first. The switching components are the most
critical because they switch large amounts of energy and
tend to generate large amounts of noise. How the switching
components are placed should also take into account power
dissipation. Align the output inductors and MOSFETs such
that space between the components is minimized while
creating the PHASE plane. Place the Intersil HIP660X
drivers as close as possible to the MOSFETs they control to
reduce the parasitics due to trace length between critical
driver input and output signals. If possible, duplicate the
same placement of switching components for each phase.
20
The ISL6569A can be placed off to one side or centered
relative to the individual phase switching components.
Routing of sense lines and PWM signals will guide final
placement. Critical small signal components to place close
to the controller include the ISEN resistors, RT resistor,
feedback resistor, and compensation components.
Bypass capacitors for the ISL6569A and HIP660X driver
bias supplies must be placed next to their respective pins.
Stray trace parasitics will reduce their effectiveness.
Plane Allocation and Routing
Dedicate one solid layer, usually a middle layer, for a ground
plane. Make all critical component ground connections with
vias to this plane. Dedicate one additional layer for power
planes; breaking the plane up into smaller islands of
common voltage. Use the remaining layers for small signal
wiring.
Route PHASE planes of copper filled polygons on the top
and bottom once the switching component placement is set.
Size the trace width between the driver gate pins and the
MOSFET gates to carry 1A of current. When routing
components in the switching path, use short wide traces to
reduce the associated parasitics.
FN9092.2
December 29, 2004
ISL6569A
Small Outline Plastic Packages (SOIC)
M24.3 (JEDEC MS-013-AD ISSUE C)
N
24 LEAD WIDE BODY SMALL OUTLINE PLASTIC PACKAGE
INDEX
AREA
0.25(0.010) M
H
B M
INCHES
E
-B1
2
3
L
SEATING PLANE
-A-
h x 45o
A
D
-C-
e
A1
B
0.25(0.010) M
C
0.10(0.004)
C A M
SYMBOL
MIN
MAX
MIN
MAX
NOTES
A
0.0926
0.1043
2.35
2.65
-
A1
0.0040
0.0118
0.10
0.30
-
B
0.013
0.020
0.33
0.51
9
C
0.0091
0.0125
0.23
0.32
-
D
0.5985
0.6141
15.20
15.60
3
E
0.2914
0.2992
7.40
7.60
4
e
µα
B S
1. Symbols are defined in the “MO Series Symbol List” in Section 2.2 of
Publication Number 95.
0.05 BSC
1.27 BSC
-
H
0.394
0.419
10.00
10.65
-
h
0.010
0.029
0.25
0.75
5
L
0.016
0.050
0.40
N
α
NOTES:
MILLIMETERS
24
0o
1.27
24
8o
0o
6
7
8o
Rev. 0 12/93
2. Dimensioning and tolerancing per ANSI Y14.5M-1982.
3. Dimension “D” does not include mold flash, protrusions or gate burrs.
Mold flash, protrusion and gate burrs shall not exceed 0.15mm
(0.006 inch) per side.
4. Dimension “E” does not include interlead flash or protrusions. Interlead flash and protrusions shall not exceed 0.25mm (0.010 inch) per
side.
5. The chamfer on the body is optional. If it is not present, a visual index
feature must be located within the crosshatched area.
6. “L” is the length of terminal for soldering to a substrate.
7. “N” is the number of terminal positions.
8. Terminal numbers are shown for reference only.
9. The lead width “B”, as measured 0.36mm (0.014 inch) or greater
above the seating plane, shall not exceed a maximum value of
0.61mm (0.024 inch)
10. Controlling dimension: MILLIMETER. Converted inch dimensions
are not necessarily exact.
21
FN9092.2
December 29, 2004
ISL6569A
Quad Flat No-Lead Plastic Package (QFN)
Micro Lead Frame Plastic Package (MLFP)
L32.5x5
32 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
(COMPLIANT TO JEDEC MO-220VHHD-2 ISSUE C
MILLIMETERS
SYMBOL
MIN
NOMINAL
MAX
NOTES
A
0.80
0.90
1.00
-
A1
-
-
0.05
-
A2
-
-
1.00
9
A3
b
0.20 REF
0.18
D
0.30
5,8
5.00 BSC
D1
D2
0.23
9
-
4.75 BSC
2.95
3.10
9
3.25
7,8
E
5.00 BSC
-
E1
4.75 BSC
9
E2
2.95
e
3.10
3.25
7,8
0.50 BSC
-
k
0.25
-
-
-
L
0.30
0.40
0.50
8
L1
-
-
0.15
10
N
Nd
32
2
8
3
Ne
8
8
3
P
-
-
0.60
9
θ
-
-
12
9
Rev. 1 10/02
NOTES:
1. Dimensioning and tolerancing conform to ASME Y14.5-1994.
2. N is the number of terminals.
3. Nd and Ne refer to the number of terminals on each D and E.
4. All dimensions are in millimeters. Angles are in degrees.
5. Dimension b applies to the metallized terminal and is measured
between 0.15mm and 0.30mm from the terminal tip.
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.
7. Dimensions D2 and E2 are for the exposed pads which provide
improved electrical and thermal performance.
8. Nominal dimensions are provided to assist with PCB Land Pattern
Design efforts, see Intersil Technical Brief TB389.
9. Features and dimensions A2, A3, D1, E1, P & θ are present when
Anvil singulation method is used and not present for saw
singulation.
10. Depending on the method of lead termination at the edge of the
package, a maximum 0.15mm pull back (L1) maybe present. L
minus L1 to be equal to or greater than 0.3mm.
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
22
FN9092.2
December 29, 2004
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