IR3889
IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Features
Single 4.3 V to 17 V application or Wide Input Voltage Range from 2.0 V to 17 V with an External VCC
Precision Reference Voltage (0.8 V +/- 0.5%)
Enhanced Fast COT Engine Stable with Ceramic Output Capacitors
Optional Forced Continuous Conduction Mode and Diode Emulation for Enhanced Light Load Efficiency
Programmable Switching Frequency from 600 kHz to 2 MHz
Monotonic Start-Up with Four Selectable Soft-Start Time & Enhanced Pre-Bias Start-Up
Thermally Compensated Internal Over Current Protection with Four Selectable Settings
Enable input with Voltage Monitoring Capability & Power Good Output
Thermal Shut Down
Operating Temp: -40 °C < Tj < 125 °C
Small Size: 5 mm x 6 mm PQFN
Halogen-free and RoHS2 Compliant with Exemption 7a
Potential applications
Server Applications
Storage Applications
Telecom & Datacom Applications
Distributed Point of Load Power Architectures
Product validation
Qualified for industrial applications according to the relevant tests of JEDEC47/20/22
Description
The IR3889 is an easy-to-use, fully integrated dc - dc Buck regulator. The onboard PWM controller and OptiMOS™
FETs with integrated bootstrap diode make IR3889 a small footprint solution, providing high-efficient power
delivery. Furthermore, it uses a fast Constant On-Time (COT) control scheme, which simplifies the design efforts
and achieves fast control response.
The IR3889 has an internal low dropout voltage regulator, allowing operations with a single supply. It can also
operate with an external bias supply, with an extended operating input voltage (PVin) range from 2.0 V to 17 V.
The IR3889 is a versatile regulator, offering programmable switching frequency from 600 kHz to 2 MHz, four
selectable current limits, four selectable soft-start time, Forced Continuous Conduction Mode (FCCM) and Diode
Emulation Mode (DEM) operation.
It also features important protection functions, such as pre-bias start-up, thermally compensated current limit,
over voltage and under voltage protection, and thermal shutdown to give required system level security in the
event of fault conditions.
Final Datasheet
www.infineon.com
Please read the Important Notice and Warnings at the end of this document
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Table of contents
Table of contents
Features ........................................................................................................................................ 1
Potential applications ..................................................................................................................... 1
Product validation .......................................................................................................................... 1
Description .................................................................................................................................... 1
Table of contents ............................................................................................................................ 2
1
Ordering information ............................................................................................................. 4
2
Functional block diagram........................................................................................................ 5
3
Typical application diagram .................................................................................................... 6
4
Pin descriptions ..................................................................................................................... 7
5
Absolute maximum ratings ..................................................................................................... 9
6
6.1
Thermal Characteristics ......................................................................................................... 10
Thermal Characteristics ........................................................................................................................ 10
7
7.1
7.2
Electrical specifications ......................................................................................................... 11
Recommended operating conditions................................................................................................... 11
Electrical characteristics ....................................................................................................................... 12
8
8.1
8.2
8.3
8.4
Typical efficiency and power loss curves .................................................................................. 15
PVin = Vin = 12 V, fsw = 600 kHz ............................................................................................................. 15
PVin = Vin = 12 V, fsw = 800 kHz ............................................................................................................. 16
PVin = Vin = 12 V, fsw = 1000 kHz ........................................................................................................... 17
PVin = Vin = VCC = 5 V, fsw = 600 kHz..................................................................................................... 18
9
Thermal De-rating curves ....................................................................................................... 19
10
RDS(ON) of MOSFET Over Temperature ........................................................................................ 20
11
Typical operating characteristics (-40 °C ≤ Tj ≤ +125 °C) .............................................................. 21
12
Theory of operation ............................................................................................................... 24
12.1
Fast Constant On-Time Control ............................................................................................................ 24
12.2
Enable .................................................................................................................................................... 24
12.3
FCCM and DEM Operation ..................................................................................................................... 25
12.4
Pseudo Constant Switching Frequency................................................................................................ 25
12.5
Soft-start ................................................................................................................................................ 26
12.6
Pre-bias Start-up ................................................................................................................................... 27
12.7
Internal Low - Dropout (LDO) Regulator............................................................................................... 27
12.8
Over Current Protection (OCP) ............................................................................................................. 28
12.9
Under Voltage Protection (UVP) ........................................................................................................... 29
12.10
Over Voltage Protection (OVP) .............................................................................................................. 29
12.11
Over Temperature Protection (OTP) .................................................................................................... 30
12.12
Power Good (PGood) Output ................................................................................................................ 30
12.13
Minimum On - Time and Minimum Off - Time ...................................................................................... 31
12.14
Selection of Feedforward Capacitor and Feedback Resistors ............................................................. 31
12.15
Resistors for Configuration Pins ........................................................................................................... 32
13
Design example..................................................................................................................... 33
13.1
Enabling the IR3889............................................................................................................................... 33
13.2
Programming the Switching Frequency and Operation Mode ............................................................ 33
13.3
Selecting Input Capacitors .................................................................................................................... 33
13.4
Inductor Selection ................................................................................................................................. 34
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Table of contents
13.5
13.6
13.7
13.8
13.9
Output Capacitor Selection .................................................................................................................. 34
Output Voltage Programming............................................................................................................... 35
Feedforward Capacitor ......................................................................................................................... 35
Bootstrap Capacitor .............................................................................................................................. 35
Vin, VCC/LDO and VDRV bypass Capacitor ........................................................................................... 35
14
Application Information ......................................................................................................... 36
14.1
Application Diagram.............................................................................................................................. 36
14.2
Typical Operating Waveforms............................................................................................................... 36
15
Layout Recommendations...................................................................................................... 39
15.1
Solder Mask ........................................................................................................................................... 43
15.2
Stencil Design ........................................................................................................................................ 44
16
Package ............................................................................................................................... 45
16.1
Marking Information ............................................................................................................................. 45
16.2
Dimensions ............................................................................................................................................ 45
16.3
Tape and Reel Information ................................................................................................................... 47
17
Environmental Qualifications ................................................................................................. 48
18
Evaluation Boards and Support Documentation ....................................................................... 49
Revision history............................................................................................................................. 50
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Ordering information
1
Ordering information
1.
Ordering Information
Sales Product Name
Package Type
IR3889MTRPBF
QFN 5 mm x 6 mm
Standard Pack Form and Qty
Tape and Reel
Orderable Part Number
5000
IR3889MTRPBFAUMA1
IR3889MTRPBF
A1
Designator
UM
SS/Latch
Yes
Yes
No
FB
Halogen Free
RoHS compliant
Total lead free
VSENM
330 mm
AGND
Packing size
NC
Dry
NC
Moisture
protection packing
NC
Tape & Reel
TON/MODE
A
Packing type
36
35
34
33
32
31
30
29
ILIM
1
28
NC
PGood
2
27
En
Vin
3
26
BOOT
VCC/LDO
4
25
PHASE
VDRV
5
GATEL
24
PVin
GATEL
6
37
23
PVin
PGND
7
22
PVin
PGND
8
21
PVin
PGND
9
20
PVin
PGND
10
19
PGND
11
12
13
14
15
16
17
18
SW SW SW SW SW SW SW SW
Figure 1 Package Top View
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Functional block diagram
Functional block diagram
2
AGND
PGood
VCC/LDO
Vin
VDRV
AGND
UVP
Threshold
POR
UVP OTP
+
-
LDO
EN
Fault
VCC
AGND
BOOT
OVP
+
-
Hysteresis
OVP
Threshold
Turn-on Delay
PVin
PGood
+
PGood
Threshold
-
Q
S
Prebias
Q
R
Fault
HDrVin
HDrv
Hysteresis
PHASE
POR
VCC
4.0V
+
POR
-
GATE
DRIVE
LOGIC
Hiccup
OVP
SW
VDRV
OTP
En
+
1.2V
Fault
-
LDrv
LDrVin
PWM
SOFT
START
SS/Latch
PWM
COMP
SS
+
+-
ADAPTIVE
ON-TIME
GENERATOR
SET
ZC
Zero Cross
DETECTION
PGND
PGND
SW
FB
-
TON/
MODE
Floor
GENERATOR
+
RAMP
GENERATOR
OCP
+
VSENM
GATEL
OVP
Latch Off
Hiccup
UVP
VREF
S
Q
R
SW
20ms
Delay
ILIM
Figure 2 Block diagram
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical application diagram
Typical application diagram
3
PVin
Enable
EN
Vin PVin
VCC/LDO
BOOT
PHASE
VDRV
Vo
SW
PGood
PGood
NC
IR3889
GATEL
SS/Latch
FB
TON/MODE
Cff
VSENM
ILIM
AGND
0.1uF
PGND
NC
NC
NC
RFB2
RFB1
Figure 3 IR3889 basic application circuit
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Pin descriptions
4
Pin descriptions
Note:
I = Input, O = Output
Pin#
Pin Name
I/O
Type
Pin Description
Connecting a resistor to a quiet ground to set the Over
Current Protection (OCP) limit. Four user selectable OCP
limits are available.
Power Good status output pin is open drain. Connect a pull
up resistor from this pin to VCC or to an external bias voltage,
e.g. 3.3 V.
Input voltage for an Internal LDO. A 4.7 µF capacitor should
be connected between this pin and PGND. If an external
supply is connected to VCC/LDO pin, this pin should be
shorted to VCC/LDO pin and a 10 µF ceramic capacitor can be
shared with Vin and VCC/LDO pin.
Output of the internal LDO or input for an external VCC
voltage. A 2.2 µF - 10 µF ceramic capacitor is recommended
to use between VCC, VDRV and the Power ground (PGND).
Input bias for the internal driver. It should be shorted to
VCC/LDO pin on the PCB. A 2.2 µF - 10 µF ceramic capacitor is
recommended to use between VDRV, VCC/LDO and the
Power ground (PGND).
Gate of Low-side FET. This pin can be used to monitor the
gate signal of LS FET. No external components should be
connected to it.
Power Ground. Must be connected to the system’s power
ground plane. PGND and AGND are internally connected via
the lead frame.
1
ILIM
I
Analog
2
PGood
O
Analog
3
Vin
I
Power
4
VCC/LDO
I/O
Power
5
VDRV
I
Power
6, 37
GATEL
I
Analog
7, 8, 9, 10,
19
PGND
-
Ground
11, 12, 13,
14, 15, 16,
17, 18
SW
O
Power
Switch Node. Connect these pins to an output inductor.
20, 21, 22,
23, 24
PVin
I
Power
Input supply for the power stage.
Source of High-side FET. Connect a bootstrap capacitor
between this pin and BOOT pin. A high temperature (x7R) 0.1
µF or greater value ceramic capacitor is recommended.
Supply voltage for the high side driver. Connect this pin to
the PHASE pin through a bootstrap capacitor. For PVin above
14 V, a resistor (e.g., 1 Ω~ Ω is recommended in series with
the bootstrap capacitor to control the slew rate of the SW
node rising edge.
25
PHASE
O
Analog
26
BOOT
I
Analog
27
En
I
Analog
Enable pin to turn the IC on and off.
Analog
Multi-function pin. Connect a resistor to a quiet ground to
select Soft-Start time from 4 options. This pin also selects
latched-off Over Voltage Protection (OVP) or non-latched
OVP.
29
Final Datasheet
SS/Latch
I
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Pin descriptions
Pin#
Pin Name
I/O
Type
30
FB
I
Analog
31
VSENM
-
Analog
32
AGND
-
Ground
36
TON/MODE
I
Analog
28, 33, 34,
35
NC
-
Final Datasheet
Pin Description
Output voltage feedback pin. Connect this pin to the output
of the regulator via a resistor divider to set the output
voltage.
This pin provides the return connection for a pseudo remote
voltage sensing. The feedback resistor divider should be
connected to this pin. It is also used as ground for the
internal reference voltage.
Signal ground for the internal circuitry except the internal
reference voltage.
Multi-function pin. Connect a resistor to a quiet ground to set
the switching frequency to 1 of 8 settings and sets the mode
of operation to FCCM or DEM.
Not
Not connected internally. They can be left floating on PCB.
connected
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Absolute maximum ratings
Absolute maximum ratings
5
Absolute maximum ratings
Description
PVin, Vin, En to PGND
Min
-0.3
Max
25
Unit
V
PVin to SW and PHASE
-0.3 V(dc) ,
below -5 V for 5 ns
-0.3
25 V(dc),
above 32 V for 2 ns
6
V
-0.3 V(dc),
below -0.3 V for 5 ns
-0.3 (dc),
below -5 V for 5 ns
-0.3
29
V
Note 1
Note 1
25 V(dc),
above 32 V for 2 ns
6 V(dc),
7 V for 5 ns
V
Note 1
-0.3
6
V
-0.3
0.3
V
VSENM to AGND
-0.3
0.3
V
Storage Temperature Range
Junction Temperature Range
-55
-40
150
°C
150
°C
VCC, VDRV to PGND
BOOT to PGND
SW and PHASE to PGND
BOOT to PHASE
ILIM, FB, PGood, TON/MODE,
GATEL and SS to AGND
PGND to AGND
V
Conditions
Note 1
V
Note 1
Note:
1.
PGND, VSENM, and AGND pin are connected together
Attention:
Final Datasheet
Stresses beyond these listed under Absolute Maximum Ratings may cause permanent
damage to the device. These are stress ratings only and functional operation of the device at
these or any other conditions beyond those indicated in the operational sections of the
specifications are not implied.
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Thermal Characteristics
6
Thermal Characteristics
6.1
Thermal Characteristics
Description
Junction to Ambient Thermal Resistance
Junction to PCB Thermal Resistance
Junction to Case Top Thermal Resistance
Symbol
Values
Test Conditions
θJA
19 °C/W
Note 2
θJC-PCB
1.1 °C/W
Note 3
θJC
24 °C/W
Note:
2.
3.
Thermal resistance is measured with components mounted on a standard EVAL_3889_1Vout demo board in
free air.
Thermal resistance is based on the board temperature near the pin 22.
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Electrical specifications
7
Electrical specifications
7.1
Recommended operating conditions
Description
Min
Max
Unit
Note
PVin Voltage Range with External VCC
2
17
V
Note 4, Note 5
PVin Voltage Range with Internal LDO
4.5
17
V
Note 5, Note 6 & 10
VCC and VDRV Supply Voltage Range
4.3
5.5
V
Note 4, Note 7
Output Voltage Range
0.8
6
V
Note 8, Note 9
30
A
Note 9
Note 10
Continuous Output Current Range
Switching Frequency
600
2000
kHz
Operating Junction Temperature
-40
125
°C
Note:
4.
5.
Vin is shorted to VCC and use an external bias voltage.
A common practice is to have 20% margin on the maximum SW node voltage in the design. For applications
requiring PVin equal to or above 14 V, a small resistor in series with the Boot pin should be used to ensure the
maximum SW node spike voltage does not exceed 20 V. Alternatively, a RC snubber can be used at the SW node
to reduce the SW node spike.
6. Vin is connected to PVin and the internal LDO is used. For single-rail applications with the internal LDO and PVin
=Vin = 4.3 V-5.4 V, the internal LDO may enter dropout mode. OCP limits can be reduced due to the lower VCC
voltage. Please refer to Section 12.7 for more detailed design guidelines.
7. The IR3889 is designed to function with VCC down to 4.2 V, however, electrical specifications such as OCP limits
may be degraded.
8. The maximum output voltage is also limited by the minimum off-time. Please refer to Section 12.13 for details.
Also note that OCP limit may be degraded when off-time is close to the minimum off-time.
9. Refer to Section 9 for maximum output current rating at different ambient temperatures.
10. The maximum LDO output current must be limited within 50 mA for operations requiring full operating
temperature range of -40 °C TJ 125 °C. Figure 6 shows the maximum LDO output current capability over
junction temperature. Thermal de-rating may be needed at an elevated ambient temperature to ensure the
junction temperature within the recommended operating range.
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Electrical specifications
7.2
Electrical characteristics
Note:
Unless otherwise specified, the specifications apply over 4.5 V ≤ Vin = PVin ≤ 7 V, °C < TJ < 125 °C.
Typical values are specified at Ta = 25 °C.
Parameter
Symbol
Conditions
Min
Typ
Top Switch
Rds(on)_Top
VBoot – Vsw= 5.0 V, IO = 30 A, Tj =25 °C
2.4
Bottom Switch
Rds(on)_Bot
VCC = 5.0 V, Io = 30 A, Tj =25 °C
0.8
I(BOOT) = 25 mA
280
Max
Unit
Power Stage
Bootstrap Forward Voltage
SW float voltage
VSW
Tdb
600
En = 0 V
300
En = high, No Switching
300
SW node falling edge, Io = 30 A,
Internal LDO, Tj = 25 °C, Note 11
Dead Band Time
mΩ
SW node rising edge, Io = 30 A,
Internal LDO, Tj = 25 °C, Note 11
mV
mV
10
ns
5
ns
Supply Current
Vin Supply Current (standby)
Iin(Standby)
En = Low, No Switching
4
10
µA
Vin Supply Current (static)
Iin(Static)
En=2 V, No Switching
2.3
4
mA
Soft Start
Soft Start Ramp Rate
SS rate
SS/Latch = 0 kΩ, 4.53 kΩ,
10.5 kΩ, 18.7 kΩ;
0.4
0.8
1.12
SS/Latch =1.5 kΩ, 5.76 kΩ,
12.1 kΩ, 21.5 kΩ;
0.2
0.4
0.56
SS/Latch = 2.49 kΩ, 7.32 kΩ,
14 kΩ, 24.9 kΩ, Floating
0.1
0.2
0.28
0.05
0.1
0.145
SS/Latch = 3.48 kΩ, 8.87 kΩ,
. kΩ, . kΩ;
mV/s
Feedback Voltage
Feedback Voltage
Accuracy
VFB Input Current
0.8
VFB
IVFB
V
0°C < Tj < 85 °C
-0.5
+0.5
-40 °C < Tj < 125 °C, Note 12
-1
1
VFB=0.8 V, Tj=25 C
-150
0
+150
%
nA
On-Time Timer Control
Vin=12 V, Vo=1 V,
TON= kΩ or
. kΩ, Note 13
Vin=12 V, Vo=1 V,
On Time
Ton
TON= 1.5 kΩ or 12.1 kΩ, Note 13
Vin=12 V, Vo=1 V,
TON= 2.49 kΩ, or 14 kΩ, Note 13
Vin=12 V, Vo=1 V,
TON= 3.48 kΩ, or 16.2 kΩ, Note 13
Final Datasheet
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114
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Electrical specifications
Parameter
Symbol
Conditions
Min
Vin=12 V, Vo=1 V,
TON= .
Vin=12 V, Vo=1 V,
52
TON= 7.32 kΩ, or 24.9 kΩ, Note 13
Vin=12V , Vo=1 V,
TON= 8.
kΩ, or
Unit
58.5
TON= 5.76 kΩ, or 21.5 kΩ, Note 13
Ton
Max
66.5
kΩ, or 18.7 kΩ, Note 13
Vin=12 V, Vo=1 V,
On Time
Typ
ns
47
. kΩ, Note 13
Vin=12V, Vo=1.0V,
114
TON = Floating, Note 13
Minimum On-Time
Ton (Min)
Vin=12 V, Vo=0 V
23
32
ns
Minimum Off-Time
Toff (Min)
Tj=25 C, VFB=0 V
270
360
ns
5.0
5.3
V
300
mV
VCC LDO Output
Output Voltage
VCC Dropout
Short Circuit Current
VCC
VCC_drop
Ishort
5.5 V Vin 17 V,
when Icc =50 mA, Cload = 2.2 µF
4.7
Vin = 4.3 V, Icc=50 mA, Cload=2.2 µF
90
5.5 V Vin 17 V
mA
Under Voltage Lockout
VCC-Start Threshold
VCC_UVLO_Start
VCC Rising Trip Level
3.8
4.0
4.2
V
VCC-Stop Threshold
VCC_UVLO_Stop
VCC Falling Trip Level
3.6
3.8
4.0
V
Enable-Start-Threshold
En_UVLO_Start
ramping up
1.14
1.2
1.36
Enable-Stop-Threshold
En_UVLO_Stop
ramping down
0.9
1
1.06
500
1000
1500
Tj = 25 °C, int LDO, RILIM=24.9 kΩ
33.9
39
45.0
Tj = 25 °C, int LDO, RILIM=21.5 kΩ
28.3
32.5
37.4
Tj = 25 °C, int LDO, RILIM=16.2 kΩ
22.6
26
29.9
Tj = 25 °C, int LDO, RILIM= . kΩ
15.0
19.5
23.0
FB Rising
115
121
125
FB Falling, OVP hysteresis
110
115
120
Input Impedance
REN
V
k
Over Current Limit
Current Limit Threshold
(Valley current)
Ioc
A
Over Voltage Protection
OVP Trip Threshold
OVP_Vth
OVP Protection Delay
OVP_Tdly
Hiccup Blanking Time
Tblk_Hiccup
Unlatched OVP
% Vref
7
µs
20
ms
Under Voltage Protection
UVP Trip Threshold
UVP_Vth
FB Falling
65
70
75
% Vref
UVP Protection Delay
UVP_Tdly
5
µs
Hiccup Blanking Time
Tblk_Hiccup
20
ms
Power Good
PGood Turn on Threshold
Final Datasheet
VPG(upper)
FB Rising
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95
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Electrical specifications
Parameter
PGood Turn off Threshold
Symbol
VPG(lower)
PGood Sink Current
IPG
PGood Voltage Low
VPG(low)
PGood Turn on Delay
PGood Comparator Delay
PGood Open Drain Leakage
Current
VPG(on)_Dly
VPG(comp)_Dly
Conditions
Min
Typ
Max
FB Falling
80
84
90
PG = 0.5 V, En = 2 V
2.5
5
Vin = VCC =0 V, Rpull-up = 50 kΩ to
3.3 V
0.3
FB Rising, see VPG(upper)
2.5
VFB < VPG(lower) or
VFB > VPG(upper)
1
2
PG = 3.3 V
Unit
% Vref
mA
0.5
V
ms
3.5
µs
1
µA
Thermal Shutdown
Thermal Shutdown
Note 11
140
Hysteresis
Note 11
20
°C
Note:
11. Guaranteed by construction and not tested in production
12. Cold temperature performance is guaranteed via correlation using statistical quality control. Not tested in
production.
13. The Ton is trimmed so that the target switching frequency is achieved at around 10A load current using
EVAL_3889_1Vout demo board.
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical efficiency and power loss curves
8
Typical efficiency and power loss curves
8.1
PVin = Vin =
V, fsw =
kHz
PVin = Vin = 12 V, VCC = Internal LDO, Io = 0 A-30 A, fsw= 600 kHz, Room Temperature, No Air Flow. Note that the
efficiency and power loss curves include the losses of IR3889, the inductor losses, the losses of the input and
output capacitors, and PCB trace losses. The table below shows the inductors used for each of the output
voltages in the efficiency measurement.
Table 1
Vo (V)
Inductors for PVin = Vin = 12 V, fsw = 600 kHz
Lout (nH)
P/N
DCR (m)
Size (mm)
1.0
150
HCB138380D-151 (Delta)
0.15
12.4 x 8.3 x 8
1.2
150
HCB138380D-151 (Delta)
0.15
12.4 x 8.3 x 8
1.8
220
FP1008R5-R220-R (Cooper)
0.17
10.8 x 8 x 8
3.3
350
HCBD101195-351(Delta)
0.35
10.1 x 11.4 x 9.5
5
450
HCBD101195-451(Delta)
0.35
10.1 x 11.4 x 9.5
Final Datasheet
15 of 50
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical efficiency and power loss curves
8.2
PVin = Vin =
V, fsw =
kHz
PVin = Vin = 12 V, VCC = Internal LDO, Io = 0 A-30 A, fsw = 800 kHz, Room Temperature, No Air Flow. Note that the
efficiency and power loss curves include the losses of IR3889, the inductor losses, the losses of the input and
output capacitors, and PCB trace losses. The table below shows the inductors used for each of the output
voltages in the efficiency measurement.
Table 2
Vo (V)
Inductors for PVin = Vin =12 V, fsw = 800 kHz
Lout (nH)
P/N
DCR (m)
Size (mm)
1.0
150
HCB138380D-151 (Delta)
0.15
12.4 x 8.3 x 8
1.2
150
HCB138380D-151 (Delta)
0.15
12.4 x 8.3 x 8
1.8
150
HCB138380D-151 (Delta)
0.15
12.4 x 8.3 x 8
3.3
350
HCBD101195-351(Delta)
0.35
10.1 x 11.4 x 9.5
Final Datasheet
16 of 50
V2.7
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical efficiency and power loss curves
8.3
PVin = Vin =
V, fsw =
kHz
PVin = Vin = 12 V, VCC = Internal LDO, Io = 0 A-30 A, fsw = 1000 kHz, Room Temperature, No Air Flow. Note that
the efficiency and power loss curves include the losses of IR3889, the inductor losses, the losses of the input
and output capacitors, and PCB trace losses. The table below shows the inductors used for each of the output
voltages in the efficiency measurement.
Table 3
Vo (V)
Inductors for PVin = Vin = 12 V, fsw = 1000 kHz
Lout (nH)
P/N
DCR (m)
Size (mm)
1.0
100
AH3740A-100K (ITG)
0.145
6.4 x 9.5 x 10
1.2
100
AH3740A-100K (ITG)
0.145
6.4 x 9.5 x 10
1.8
120
AH3740A-120K (ITG)
0.145
6.4 x 9.5 x 10
Final Datasheet
17 of 50
V2.7
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical efficiency and power loss curves
8.4
PVin = Vin = VCC = V, fsw =
kHz
PVin = Vin = VCC = 5.0 V, Io = 0 A – 30 A, fsw = 600 kHz, Room Temperature, No Air Flow. Note that the efficiency
and power loss curves include the losses of IR3889, the inductor losses, the losses of the input and output
capacitors and and PCB trace losses. The table below shows the inductors used for each of the output voltages
in the efficiency measurement.
Table 4
Inductors for PVin = Vin = VCC= 5 V, fsw = 600 kHz
Vo (V)
Lout (nH)
P/N
DCR (m)
Size (mm)
1.0
120
AH3740A-120K (ITG)
0.145
6.4 x 9.5 x 10
1.2
120
AH3740A-120K (ITG)
0.145
6.4 x 9.5 x 10
1.8
150
AH3740A-150K (ITG)
0.145
6.4 x 9.5 x 10
3.3
150
AH3740A-150K (ITG)
0.145
6.4 x 9.5 x 10
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Thermal De-rating curves
9
Thermal De-rating curves
Measurement is done on Evaluation board of EVAL_3889. PCB is a 6-layer board with 1.5 ounce Copper for top
and bottom layer and 2 z Copper for the inner layers, FR4 material, size . x .75 .
Figure 4 Thermal de-rating curves, PVin = 12 V, Vo = 1.0 V/3.3 V/5 V, Fsw = 800 kHz, VCC = Internal LDO
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
RDS(ON) of MOSFET Over Temperature
10
RDS ON of MOSFET Over Temperature
Figure 5 RDS(on) of MOSFETs over Junction Temperature
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical operating characteristics (-
11
C ≤ Tj ≤ +
C
Typical operating characteristics -
°C ≤ Tj ≤ +
°C
Figure 6 Typical operating characteristics (set 1 of 3)
Final Datasheet
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V2.7
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical operating characteristics (-
C ≤ Tj ≤ +
C
Figure 7 Typical operating characteristics (set 2 of 3)
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Typical operating characteristics (-
C ≤ Tj ≤ +
C
Figure 8 Typical operating characteristics (set 3 of 3)
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
Theory of operation
12
Fast Constant On-Time Control
12.1
The IR3889 features a proprietary Fast Constant On-Time (COT) Control, which can provide fast load transient
response, good output regulation and minimize the design effort. Fast COT control compares the output voltage,
Vo, to a floor voltage combined with an internal ramp signal. When Vo drops below that signal, a PWM signal is
initiated to turn on the high-side FET for a fixed on-time. The floor voltage is generated from an internal
compensated error amplifier, which compares the Vo with a reference voltage. Compared to the traditional COT
control, Fast COT control significantly improves the Vo regulation.
Enable
12.2
En pin controls the on/off of the IR3889. An internal Under Voltage Lock-Out (UVLO) circuit monitors the En
voltage. When the En voltage is above an internal threshold, the internal LDO starts to ramp up. When the
VCC/LDO voltage rises above the VCC_UVLO_Start threshold, the soft-start sequence starts. The En pin can be
configured in three ways, as shown in Figure 9. With configuration 2, the Enable signal is derived from the PVin
voltage by a set of resistive divider, REN1 and REN2. By selecting different divider ratios, users can program a
UVLO threshold voltage for the bus voltage. This is a very desirable feature because it prevents the IR3889 from
operating until PVin is higher than a desired voltage level. For some space constrained designs, the En pin can be
directly connected to PVin without using the external resistor dividers, as shown in Configuration 3. The En pin
should not be left floating. A pull down resistor in the range of tens of kilohms is recommended. Figure 10
illustrates the corresponding start-up sequences with three En configurations.
PVin
PVin
PVin
Vin
PVin
PVin
REN1
Vin
Vcc
En
Vcc
En
IR3889
En = an external logic signal
Configuration 1
PVin
Vcc
IR3889
En
REN2
En =
��
Vin
��
+ ��
×
Configuration 2
�
IR3889
PVin = Vin = En
Configuration 3
Figure 9 Enable Configurations
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
Pvin= Vin=12V
PVin= Vin=En=12V
Pvin = Vin = 12V
Vcc_ UVLO
Vcc
Vcc
En Threshold
Vcc_UVLO
0V
0V
0V
0V
En >1.2V
Fb
Pgood Turn-on
threshold
0V
2.5ms
0V
0V
En = REN2/(REN1+REN2)*PVin
En Threshold
PGood
0V
En = an external logic signal
Configuration 1
Fb
Pgood Turn-on
threshold
2.5ms
0V
Pgood stays at logic low
0V
Fb
Pgood Turn-on
threshold
0V
PGood
0V
Vcc
Vcc_ UVLO
2.5ms
0V
PGood
0V
Pgood stays at logic low
Pgood stays at logic low
En =
��
��
+ ��
×
Configuration 2
�
PVin = Vin = En
Configuration 3
Figure 10 Start-up sequence
12.3
FCCM and DEM Operation
The IR3889 offers two operation modes: Forced Continuous Conduction (FCCM) and Diode Emulation Mode
(DEM). With FCCM, the IR3889 always operates as a synchronous buck converter with a pseudo constant
switching frequency and therefore achieves small output voltage ripples. In DEM, the synchronous FET is turned
off when the inductor current is close to zero, which reduces the switching frequency and improves the efficiency
at light load. At heavy load, both FCCM and DEM operate in the same way. The operation mode can be selected
with TON/MODE pin, as shown in Table 5. It should be noted that the selection of the operation mode cannot be
changed on the fly. To load a new TON/MODE configuration, En or VCC voltage needs to be cycled.
12.4
Pseudo Constant Switching Frequency
The IR3889 offers eight programmable switching frequencies, fsw, from 600 kHz to 2 MHz, by connecting an
external resistor from TON/MODE pin to a quiet ground (AGND or PGND). Based on the selected fsw, the IR3889
generates the corresponding on-time of the Control FET for a given PVin and Vo, as shown by the formula below.
=
�
×
��
Where fsw is the desired switching frequency. During the operation, the IR3889 monitors PVin and Vo, and can
automatically adjust the on-time to maintain the pre-selected fsw. With the increase of the load, the switching
frequency can increase to compensate for the power losses. Therefore, the IR3889 has a pseudo constant
switching frequency.
Table 5 lists the resistors for TON/MODE pin. In this table, E96 resistors with ±1% tolerance are used. If E12
resistor values are preferred, please refer to the Section 12.15. To load a new TON/MODE configuration, En or
VCC voltage needs to be cycled.
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
Table 5 Configuration Resistors for TON/MODE Pin
TON/MODE Resistor (kΩ
±1% Tolerance
Freq (kHz)
0
600
1.5
800
2.49
1000
3.48
1200
4.53
1400
5.76
1600
7.32
1800
8.87
2000
10.5
600
12.1
800
14
1000
16.2
1200
18.7
1400
21.5
1600
24.9
1800
28.7
2000
Ton = Floating
800
12.5
Mode
FCCM
DEM
FCCM
Soft-start
The IR3889 has an internal digital soft-start to control the output voltage rise and to limit the current surge at the
start-up. To ensure a correct start-up, the soft-start sequence initiates when the En and VCC voltages rise above
their respective thresholds. The internal soft-start signal linearly rises from 0 V to 0.8 V in a defined time duration.
The soft-start time does not change with the output voltage. During the soft-start, the IR3889 operates in DEM
until 1ms after the output voltage ramps above the PGood turn-on threshold. The IR3889 has four soft-start time
options selected by placing a resistor from SS/Latch pin to the ground. Table 6 lists the resistor values and its
corresponding soft-start time. In this table, E96 resistors with ±1% tolerance are used. If E12 resistor values are
preferred, please refer to the Section 12.15. For each soft-start time, there are two resistor options available.
Please note that SS/Latch pin is a multi-function pin, which is also used to select different responses for Over
Voltage Protection (OVP). Please note that to load a new SS/Latch selection, En or VCC voltage needs to be
cycled.
Final Datasheet
26 of 50
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
Table 6 Configuration Resistor for SS/Latch Pin
SS/Latch Resistor kΩ
±1% Tolerance
Soft-start Time
(ms)
0
1
4.53
1.5
2
5.76
Latch
2.49
4
7.32
3.48
8
8.87
10.5
1
18.7
12.1
2
21.5
No Latch
14
4
24.9
16.2
8
28.7
SS/Latch = Floating
12.6
OVP
4
Latch
Pre-bias Start-up
The IR3889 is able to start up into a pre-charged output without causing oscillations and disturbances of the
output voltage. When IR3889 starts up with a pre-biased output voltage, both control FET and Synch FET are
kept off till the internal soft-start signal exceeds the FB voltage.
12.7
Internal Low - Dropout LDO Regulator
The IR3889 has an integrated low-dropout LDO regulator, providing the bias voltage for the internal circuitry. To
minimize the standby current, the internal LDO is disabled when the En voltage is pulled low. Vin pin is the input
of the LDO. When using the internal LDO for a single rail operation, Vin pin should be connected to PVin pin. To
save the power losses on the LDO, an external bias voltage can be used by connecting Vin pin to the VCC/LDO
pin. VDRV provides the bias voltage for the internal driver circuitry and should be shorted to VCC/LDO on the PCB.
Figure 11 illustrates the configuration of VCC/LDO, VDRV and Vin pin.
Ext Vcc
PVin
PVin
4.7uF
PVin
Vin
VCC
VDRV
IR3889
PVin
2.2uF ~10uF
IR3889
PGND
Single rail operation with the internal LDO
Vin
VCC
VDRV
10uF
PGND
Use an external VCC
Figure 11 Configuration of Using the internal LDO or an external VCC.
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
Section 7.1 specified the recommended operating voltage range of Vin and VCC under different configurations.
Following design guidelines are recommended when configuring the VCC/LDO.
Place a bypass capacitor to minimize the disturbance on the VCC and VDRV pin. For a single rail operation
using the internal LDO, a 4.7 µF low ESR ceramic capacitor must be used between Vin pin and PGND and a 2.2
µF~10 µF low ESR ceramic capacitor is required to be placed close to the VCC/LDO and VDRV pin with reference
to PGND. 10 µF MLCC is recommended for VCC bypass capacitor when Vin is below 5.5 V. When using an
external VCC bias voltage, a 10 µF ceramic capacitor can be shared with Vin, VCC/LDO and VDRV pin.
When using the internal LDO with 5.5 V Vin 17 V, it is recommended to check the required VCC bias current
for the operation above 1.6 MHz, to ensure that it does not exceed the LDO output current capability as shown
in Figure 6. With the increase of fsw, the resulting ICC is also increased mainly due to the increase of the gate
charge that is proportional to fsw. In Figure 6, the typical ICC at PVin = Vin = 12 V and fsw = 800 kHz has been
provided, which can be used to estimate the ICC at other fsw.
Vin
. V, the LDO can be in the dropout mode. It is
important to ensure that the LDO voltage does not fall below the VCC UVLO threshold voltage. At Vin = 4.3 V,
ICC must not exceed 50 mA under all operating conditions such as during a step-up load transient, in which the
control loop may require the increase of fsw. OCP limits can be reduced due to the lower VCC voltage.
For applications using the internal LDO with 4.3 V
12.8
Over Current Protection OCP
The IR3889 offers cycle-by-cycle OCP response with four selectable current limits, which is set by the resistance
at ILIM pin. The selected OCP limit bank is loaded to the IC during the power up and cannot be changed on the
fly. To change the OCP limit, users must cycle En signal or VCC voltage. Cycle-by-cycle OCP response allows the
IR3889 to fulfill a brief high current demand, such as a high inrush current during the start-up. The detailed
operation is explained as follows.
The OCP is activated when En voltage is above its threshold. The OCP circuitry monitors the current of the
Synchronous MOSFET through its Rds(on). When a new PWM pulse is requested by the control loop, if the current
of Synchronous MOSFET exceeds the selected OCP limit, the IR3889 skips the PWM pulse and extends the ontime of Synchronous MOSFET till the current drops below the OCP limit. The OCP operation is also illustrated in
Figure 12. As can be seen, during OCP events, the valley of the inductor current is regulated around the OCP
limit. But during the first switching cycle when the OCP is tripped, the valley of the inductor current can drop
slightly below the OCP limit. It should be noted that OCP events do not pull the PGood signal low unless the Vo
drops below the PGood turn-off threshold. If the OCP event persists, the output voltage can eventually drop
below the Under Voltage Protection (UVP) threshold and trigger UVP. Then the IR3889 enters a hiccup mode.
The OCP limits are thermally compensated. Please refer to the typical performance of OCP limits in Figure 7and
Figure 8. The OCP limits specified in the Section 7.2 refer to the valley of the inductor current when OCP is
tripped. Therefore, the corresponding output DC current can be calculated as follows:
�
=�
_
�
+
∆�
Where: Iout_OCP = Output DC current when OCP is tripped. ILIM = OCP limit specified in the Section 7.2, which is the
valley of inductor current. ΔiL = Peak-peak inductor ripple current.
To avoid the inductor saturation during OCP events, the following criterion is recommended for the inductor
saturation current rating.
��
�
� _ �
+ ∆�
Where: Isat is the inductor saturation current and ILIM_max is the maximum spec of the OCP limit.
Final Datasheet
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
OCP Tripped
Inductor
Current
UVP Hiccup
Blanking
time
Pulse
skipped
Current
Limit
HDrv
LDrv
PGood
UVP
Threshold
Vo
PGood Turn-off
Threshold
Figure 12 Cycle-by-cycle OCP response
12.9
Under Voltage Protection UVP
Under Voltage Protection (UVP) provides additional protection during OCP fault or other faults. UVP is activated
when the soft-start voltage rises above 130 mV. UVP circuitry monitors the FB voltage. When it is below the UVP
threshold for 5 µs (typical), an under voltage trip signal asserts and both Control MOSFET and Synchronous
MOSFET are turned off. The IR3889 enters a hiccup mode with a blanking time of 20 ms, during which Control
MOSFET and Synchronous MOSFET remain off. After the completion of blanking time, the IR3889 attempts to
recover to the nominal output voltage with a soft-start, as shown in Figure 12. The IR3889 will repeat hiccup
mode and attempt to recover until UVP condition is removed.
12.10
Over Voltage Protection OVP
Over Voltage Protection (OVP) is achieved by comparing the FB voltage to an OVP threshold voltage. When the
FB voltage exceeds the OVP threshold, an over voltage trip signal asserts after 7 µs (typical) delay. Control
MOSFET is latched off immediately and PGood flags low. Synchronous MOSFET remains on to discharge the
output capacitor. When FB voltage drops below around 115% of the reference voltage, Synchronous MOSFET
turns off to prevent the complete depletion of the output capacitors. Figure 13 illustrates the OVP operation.
The OVP comparator becomes active when the En signal is above the start threshold.
With SS/Latch pin, two OVP responses can be selected: Latch or No Latch, as shown in Table 6. With a latched
OVP response, Control FET remains latched off until either VCC voltage or En signal is cycled. With an unlatched
OVP response, the IR3889 enters a hiccup mode. Control FET remains off for a blanking time of 20ms. After hiccup
blanking time expires, the IR3889 will try to restart with a soft-start. The IR3889 can stay in the hiccup mode
infinitely if over voltage fault persists.
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
HDrv
LDrv
121%Vref
115%Vref
Vref
OVP
VFB
91%Vref
84%Vref
91%Vref
PGood
Pgood turn-on
Pgood turn-on OVP delay =7us
delay =2.5ms
delay =2.5ms
Figure 13 Over voltage protection response and PGood behavior.
12.11
Over Temperature Protection OTP
Temperature of the controller is monitored internally. When the temperature exceeds the over temperature
threshold, OTP circuitry turns off both Control and Synchronous MOSFETs and resets the internal soft start.
Automatic restart is initiated when the sensed temperature drops back into the operating range. The thermal
shutdown threshold has a hysteresis of 20 °C.
12.12
Power Good PGood Output
The PGood pin is the open drain of an internal NFET, and needs to be externally pulled high through a pull-up
resistor. PGood signal is high when three criteria are satisfied.
1. En signal and VCC voltage are above their respective thresholds.
2. No over voltage and over temperature faults occur.
3. Vo is within the regulation.
In order to detect if Vo is in regulation, PGood comparator continuously monitors the FB voltage. When FB voltage
ramps up above the upper threshold, PGood signal is pulled high after 2.5 ms. When FB voltage drops below the
lower threshold, PGood signal is pulled low immediately. Figure 13 illustrates the PGood response.
During the start-up with a pre-biased voltage, PGood signal is held low before the first PWM is generated and is
then pulled high with 2.5 ms delay after FB voltage rises above the PGood threshold. IR3889 also integrates an
additional PFET in parallel to the PGood NFET, as shown in Figure 2. This PFET allows PGood signal to stay at
logic low when the VCC voltage is not present, and PGood pin is pulled up by an external bias voltage. Please
refer to Figure 10. Since PGood PFET has relatively higher on resistance, a 50 kΩ pull-up resistor is needed for a
PGood bias voltage of 3.3 V to maintain the PGood signal at logic low when PGood PFET is on.
Final Datasheet
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30 A single-voltage synchronous Buck regulator
Theory of operation
12.13
Minimum On - Time and Minimum Off - Time
The minimum on-time refers to the shortest time for Control MOSFET to be reliably turned on. The minimum offtime refers to the minimum time duration in which Synchronous FET stays on before a new PWM pulse is
generated. The minimum off-time is needed for IR3889 to charge the bootstrap capacitor, and to sense the
current of the Synchronous MOSFET for OCP.
For applications requiring a small duty cycle, it is important that the selected switching frequency results in an
on-time larger than the maximum spec of the minimum on-time in the Section 7.2. Otherwise the resulting
switching frequency may be lower than the desired target. Following formula could be used to check for the
minimum on-time requirement.
�
�
> max �
× ��
�
i
Where fsw is the desired switching frequency. k is the variation of the switching frequency. As a rule of thumb,
select k = 1.25 to ensure the design margin.
For applications requiring a high duty cycle, it is important to make sure a proper switching frequency is selected
so that the resulting off-time is longer than the maximum spec of the minimum off-time in the Section 7.2, which
can be calculated as shown below.
�� − �
> max �
�
× ��
�
i
Where fsw is the desired switching frequency. k is the variation of the switching frequency. As a rule of thumb,
select k = 1.25 to ensure the design margin.
The resulting maximum duty cycle is therefore determined by the selected on-time and minimum off-time.
�
12.14
=
+
i
Selection of Feedforward Capacitor and Feedback Resistors
Output voltage can be programmed with an external voltage divider. The FB voltage is compared to an internal
reference voltage of 0.8 V. The divider ratio is set to provide 0.8 V at the FB pin when the output is at its desired
value. The calculation of the feedback resistor divider is shown below.
� =�
×
+
Where RFB1 and RFB2 are the top and bottom feedback resistors.
A small MLCC capacitor, Cff, is preferred in parallel with the top feedback resistor, RFB1, to provide extra phase
boost and to improve the transient load response, as shown in Figure 14. Following formula can be used to help
select Cff and RFB1. The value of Cff is recommended to be 100 pF or higher to minimize the impact of circuit
parasitic capacitance. Table 7 lists the suggested m for some common outputs. Cff and RFB1 may be further
optimized based on the transient load tests. Where Lo and Co are the output LC filter of the buck regulator.
=
Final Datasheet
√�
�× .
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Theory of operation
Vo
RFB1
FB
Cff
RFB2
Figure 14 Configuration of feedforward capacitor, Cff.
Table 7 Selection of m
Vo
m
V Vo
V
0.4
1.2 V < Vo < 3 V
Vo
0.6
. V
0.8
Resistors for Configuration Pins
12.15
To properly configure SS/LATCH pin, MODE/TON pin and ILIM pin, E96 resistors with ±1% tolerance must be
used per Table 5, Table 6 and Section 7.2. If E12 resistor values are preferred, the E96 resistors can be replaced
with two or three E12 resistors in series, as shown in Table 8. Note that the tolerance of E12 resistors must be
±0.1%.
Table 8 Replacement of E96 configuration resistors with E12 resistors in series
E96 ±1%
E12 ±0.1% (R = RS1 + RS2 or RS1 + RS2 + RS3)
R kΩ
RS1 kΩ
RS2 kΩ
RS3 kΩ
4.53
2.7
1.8
N/A
1.50
1.5
0
N/A
5.76
5.6
0.15
N/A
2.49
1.8
0.68
N/A
7.32
6.8
0.56
N/A
3.45
3.3
0.15
N/A
8.87
8.2
0.68
N/A
10.5
10
0.47
N/A
12.1
12
0.1
N/A
21.5
18
3.3
N/A
14
10
3.9
N/A
24.9
22
2.7
N/A
16.2
15
1.2
N/A
28.7
27
1.8
N/A
21.5
18
3.3
0.18
24.9
22
2.7
0.18
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Design example
13
Design example
In this section, an example is used to explain how to design a buck regulator with the IR3889. The application
circuit is shown in Figure 15. The design specifications are given below.
PVin = 12 V (±10%)
Vo = 1.0 V
Io = 30 A
Vo ripple voltage = ±1% of Vo
Load transient response = ± 3% of Vo with a step load current = 9 A and slew rate = 30 A/µs
13.1
Enabling the IR
The IR3889 has a precise En threshold voltage, which can be used to implement a UVLO of the input bus voltage
by connecting the En pin to PVin with a resistor divider, as shown in Configuration 2 of Figure 9. The En resistor
divider, REN1 and REN2, can be calculated as follows.
��
i
×
×
+
�
��
i
�
ax
−�
ax
ax
Where VEN(max) is the maximum spec of the En-start-threshold as defined in Section 7.2. For PVin (min) =10.8 V,
select REN1=49.9 kΩ and REN2=7.5 kΩ.
13.2
Programming the Switching Frequency and Operation Mode
The IR3889 has very good efficiency performance and is suitable for high switching frequency operation. In this
case, 800 kHz is selected to achieve a good compromise between the efficiency, passive component size and
dynamic response. In addition, FCCM operation is selected to ensure a small output ripple voltage over the entire
load range. To select
kHz and FCCM operation, the TON/MODE pin can be left floating or connect a . kΩ
resistor to a quiet ground (AGND or PGND) per Table 5.
13.3
Selecting Input Capacitors
Without input capacitors, the pulse current of Control MOSFET is directly from the input supply power. Due to
the impedance on the cable, the pulse current can cause disturbance on the input voltage and potential EMI
issues. The input capacitors filter the pulse current, resulting in almost constant current from the input supply.
The input capacitors should be selected to tolerate the input pulse current, and to reduce the input voltage
ripple. The RMS value of the input ripple current can be expressed by:
�
=� ×√ ×
=
�
��
−
Where IRMS is the RMS value of the input capacitor current. Io is the output current and D is the Duty Cycle. For Io
= 30A and D(max) = 0.09, the resulting RMS current flowing into the input capacitor is Irms = 8.7 A.
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Design example
To meet the requirement of the input ripple voltage, the minimum input capacitance can be calculated as
follows.
�
i
� × −
×
× ∆ �� −
×� ×
>
−
Where ∆PVin is the maximum allowable peak-to-peak input ripple voltage, and ESR is the equivalent series
resistor of the input capacitors. Ceramic capacitors are recommended due to low ESR, ESL and high RMS current
capability. For Io = 30 A, fsw =
kHz, ESR = mΩ, and ∆PVin = 240 mV, Cin(min) > 18 µF. To account for the derating of ceramic capacitors under a bias voltage, 10 x 22 µF/0805/25V MLCC are used for the input capacitors. In
addition, a bulk capacitor is recommended if the input supply is not located close to the voltage regulator.
13.4
Inductor Selection
The inductor is selected based on output power, operating frequency and efficiency requirements. A low inductor
value results in a large ripple current, lower efficiency and high output noise, but helps with size reduction and
transient load response. Generally, the desired peak-to-peak ripple current in the inductor ∆i is found between
20% and 50% of the output current.
The inductor saturation current must be higher than the maximum spec of the OCP limit plus the peak-to-peak
inductor ripple current. For some core material, inductor saturation current may decrease as the increase of
temperature. So it is important to check the inductor saturation current at the maximum operating temperature.
The inductor value for the desired operating ripple current can be determined using the following relation:
�=
��
��
ax
�
−� ×
=
�
��
�
∆�
ax
+ ∆�
ax
�
×
ax
Where: PVin(max) = Maximum input voltage; ∆iLmax = Maximum peak-to-peak inductor ripple current; OCPmax =
maximum spec of the OCP limit as defined in Section 7.2; and Isat = inductor saturation current. In this case,
select inductor L =150 nH to achieve ∆iLmax = 25% of Iomax. The Isat should be no less than 53 A.
13.5
Output Capacitor Selection
The output capacitor selection is mainly determined by the output voltage ripple and transient requirements.
To satisfy the Vo ripple requirement, Co should satisfy the following criterion.
>
∆� �
8 × ∆� ×
Where ∆Vor is the desired peak-to-peak output ripple voltage. For ∆iLmax= 7.5 A, ∆Vor =20 mV, fsw = 800 kHz, Co
must be larger than 59 µF. The ESR and ESL of the output capacitors, as well as the parasitic resistance or
inductance due to PCB layout, can also contribute to the output voltage ripple. It is suggested to use MultiLayer Ceramic Capacitor (MLCC) for their low ESR, ESL and small size.
To meet the transient response requirements, the output capacitors should also meet the following criterion.
Final Datasheet
>
� × ∆�
ax
× ∆� × �
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Design example
Where ∆VOL is the allowable Vo deviation during the load transient. ∆Io(max) is the maximum step load current.
Please note that the impact of ESL, ESR, control loop response, transient load slew rate, and PWM latency is not
considered in the calculation shown above. Extra capacitance is usually needed to meet the transient
requirements. As a rule of thumb, we can triple the Co that is calculated above as a starting point, and then
optimize the design based on the bench measurement. In this case, to meet the transient load requirement (i.e.
∆VOL= 30 mV, ∆Io(max) = 9 A), select Co = ~600 µF. For more accurate estimation of Co, simulation tool should be
used to aid the design.
13.6
Output Voltage Programming
Output voltage can be programmed with an external voltage divider. The FB voltage is compared to an internal
reference voltage of 0.8 V. The divider ratio is set to provide 0.8 V at the FB pin when the output is at its desired
value. The calculation of the feedback resistor divider is shown below.
� =�
×
+
Where RFB1 and RFB2 are the top and bottom feedback resistors. Select RFB1 =
Vo = 1 V.
13.7
. kΩ and RFB2 =
. kΩ, to achieve
Feedforward Capacitor
A small MLCC capacitor, Cff, can be placed in parallel with the top feedback resistor, RFB1, to improve the transient
response. Based on Section 12.14, Cff can be selected using the following formula.
=
√�
. × .8
With Lo = 150 nH, Co = 600 µF and RFB1 = . kΩ, Cff = ~125 pF. Cff can be further optimized on the bench test based
on bode plot measurement and transient load response.
13.8
Bootstrap Capacitor
For most applications, a 0.1 µF ceramic capacitor is recommended for bootstrap capacitor placed between
PHASE and BOOT Pin. For applications requiring PVin equal to or above 14 V, a small resistor of ~ Ω should be
used in series with the BOOT pin to ensure the maximum SW node spike voltage does not exceed 20 V.
13.9
Vin, VCC/LDO and VDRV bypass Capacitor
Please see the recommendation in Section 12.7. A 10 µF MLCC is selected for VCC/LDO and VDRV bypass
capacitor and a 4.7 µF MLCC is selected for Vin bypass capacitor.
Final Datasheet
35 of 50
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Application Information
Application Information
14
Application Diagram
14.1
Cin
CinHF
4.7uF 10 x 22uF
REN2
7.5k
REN1
49.9k
+
Cvin
4.7uF
EN
RBoot
0
Vin PVin
VCC/LDO
Boot
Phase
VDRV
RPG
49.9k
SW
PGood
PGood
NC
IR3889
Co1
1x470uF
+
Co2
9x47uF
CoHF
0.1uF
Cff
220pF
Fb
Ton/Mode
VSENM
ILIM
AGnd
L
150nH
GATEL
SS/Latch
RTon
1.5k
CBoot
0.1uF
Vo=1V
Cvcc
10uF
RSS
1.5k
Vin = 12V ±10%
Optional
PGnd
NC
NC
NC
RLIM
24.9k
RFB2
64.9k
RFB1
16.2k
Figure 15 Application diagram of IR3889. PVin = 12 V, Vo = 1V, Io = 30 A, fsw = 800 kHz.
14.2
Typical Operating Waveforms
PVin = Vin = 12.0 V, Vo = 1 V, Io = 0 – 30 A, fsw = 800 kHz, Room Temperature, no airflow
Figure 16
Final Datasheet
Start up at 30 A Load, (Ch1: PVin, Ch2: Vo, Ch3:PGood ,Ch4:En)
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Application Information
Figure 17
Pre-bias Start up at 0 A Load, (Ch1: PVin, Ch2: Vo, Ch3: PGood, Ch4: En)
Figure 18
Vo ripple at 30 A Load, fsw = 800 kHz, (Ch1: Vo)
Figure 19
SW node, 30 A load, fsw = 800 kHz
Final Datasheet
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Application Information
Figure 20
SW node (in DEM), 3.5 A load
Figure 21
Short circuit and UVP (Hiccup), (Ch2: Vo, Ch3:PGood)
Figure 22
Final Datasheet
Transient response at 9 A step load current @ 30 A/µs slew rate: Io= 16 A – 25 A, (Ch1: Vo,
Ch4: Io), pk-pk: 60.8 mV, fsw = 800 kHz
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OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Layout Recommendations
15
Layout Recommendations
PCB layout is very important when designing high frequency switching converters. Layout will affect noise pickup
and can cause a good design to perform with less than expected results. Following design guidelines are
recommended to achieve the best performance.
Bypass capacitors, including input/output capacitors, Vin, VCC and VDRV bypass capacitors, should be placed
near the corresponding pins as close as possible.
Place bypass capacitors from IR3889 power input (Drain of Control MOSFET) to PGND (Source of Synchronous
MOSFET) to reduce noise and ringing in the system. The output capacitors should be terminated to a ground
plane that is away from the input PGND to mitigate the switching spikes on the Vo. The bypass capacitor shared
by VCC and VDRV should be terminated to PGND.
Place a boot strap capacitor near the IR3889 BOOT and PHASE pin as close as possible to minimize the loop
inductance.
SW node copper should only be routed on the top layer to minimize the impact of switching noises
Connect AGND pin to the PGND pad through a single point connection. On the IR3889 demo board, AGND pin
is connected to the exposed PGND pad with a copper trace.
Via holes can be placed on PVin and PGND pads to aid thermal dissipation.
Wide copper polygons are desired for PVin and PGND connections in favor of power losses reduction and
thermal dissipation. Sufficient via holes should be used to connect power traces between different layers.
Single-ended Vo sensing is often used for local sensing. To implement this configuration, following design
guidelines should be followed, as illustrated in Figure 23.
o The output voltage can be sensed from a high-frequency bypass capacitor of 0.1 µF or higher,
through a 15 mil PCB trace.
o Keep the Vo sense line away from any noise sources and shield the sense line with ground planes.
o The sense trace is connected to a feedback resistor divider with the lower resistor terminated at
VSENM pin.
o Short VSENM pin and AGND pin with a short trace.
If it is required to sense the output voltage at a remote location, pseudo remoting sensing can be implemented
as follows. The configuration is also shown in Figure 24.
o A pair of PCB traces with at least 15 mil trace width, running close to each other and away from
any noise sources such as inductor and SW nodes, should be used to implement Kelvin sensing of
the voltage across a high bypass capacitor of 0.1 µF or higher.
o The ground connection of the remote sensing signal must be terminated at VSENM pin.
o The Vo connection of the remote sensing signal must be connected to the feedback resistor divider
with the lower feedback resistor terminated at VSENM pin.
o Shield the pair of remote sensing lines with ground planes above and below.
o Do NOT connect VSENM pin and AGND pin in this configuration
The En pin and configuration pins including SS/LATCH, TON/MODE, and ILIM should be terminated to a quiet
ground. On the IR3889 standard demo board, they are terminated to the PGND copper plane away from the
power current flow. Alternatively, they can be terminated to a dedicated AGND PCB trace.
Final Datasheet
39 of 50
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IR
OptiMOS™ IPOL
30 A single-voltage synchronous Buck regulator
Layout Recommendations
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