Data Sheet No. PD94173 revD
IRU3037/IRU3037A & (PbF)
8-PIN SYNCHRONOUS PWM CONTROLLER
DESCRIPTION
The IRU3037 controller IC is designed to provide a low
cost synchronous Buck regulator for on-board DC to DC
converter applications. With the migration of today’s ASIC
products requiring low supply voltages such as 1.8V and
lower, together with currents in excess of 3A, traditional
linear regulators are simply too lossy to be used when
input supply is 5V or even in some cases with 3.3V
input supply. The IRU3037 together with dual N-channel
MOSFETs such as IRF7313, provide a low cost solution
for such applications. This device features an internal
200KHz oscillator (400KHz for "A" version), under-volt-
age lockout for both Vcc and Vc supplies, an external
programmable soft-start function as well as output un-
der-voltage detection that latches off the device when an
output short is detected.
FEATURES
Synchronous Controller in 8-Pin Package
Operating with single 5V or 12V supply voltage
Internal 200KHz Oscillator
(400KHz for IRU3037A)
Soft-Start Function
Fixed Frequency Voltage Mode
500mA Peak Output Drive Capability
Protects the output when control FET is shorted
SOIC 8-Lead also available LEAD-FREE
APPLICATIONS
DDR memory source sink Vtt application
Low cost on-board DC to DC such as 5V to 3.3V,
2.5V or 1.8V
Graphic Card
Hard Disk Drive
TYPICAL APPLICATION
5V
12V
C3
1uF
C4
1uF
C2
10TPB100M,
100uF, 55m
Ω
L1
1uH
C1
47uF
Vcc
Vc
HDrv
Q1
1/2 of IRF7313
L2
1.5V/5A
C7
2x 6TPC150M,
150uF, 40m
Ω
SS/SD
C8
0.1uF
U1
IRU3037
D05022P-562, 5.6uH, 5.3A
LDrv
Q2
1/2 of IRF7313
R3
Fb
249, 1%
R5
1.24K, 1%
C9
2200pF
R4
24k
Comp
Gnd
Figure 1 - Typical application of IRU3037 or IRU3037A.
PACKAGE ORDER INFORMATION
T
A
(°C)
0 To 70
0 To 70
0 To 70
0 To 70
DEVICE
IRU3037CF
IRU3037CS
IRU3037ACF
IRU3037ACS
LEADFREE DEVICE PACKAGE
IRU3037CFPbF
8-Pin Plastic TSSOP (F)
IRU3037CSPbF
8-Pin Plastic SOIC NB (S)
IRU3037ACFPbF
8-Pin Plastic TSSOP (F)
IRU3037ACSPbF
8-Pin Plastic SOIC NB (S)
FREQUENCY
200KHz
200KHz
400KHz
400KHz
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1
IRU3037/IRU3037A & (PbF)
ABSOLUTE MAXIMUM RATINGS
Vcc Supply Voltage .................................................. 25V
Vc Supply Voltage ...................................................... 30V (not rated for inductive load)
Storage Temperature Range ...................................... -65°C To 150°C
Operating Junction Temperature Range ..................... 0°C To 125°C
CAUTION:
Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device.
PACKAGE INFORMATION
8-PIN PLASTIC TSSOP (F)
8-PIN PLASTIC SOIC (S)
Fb
1
Vcc
2
LDrv
3
Gnd
4
8
SS/SD
7
Comp
6
Vc
5
HDrv
Fb
1
Vcc
2
LDrv
3
Gnd
4
8
SS/SD
7
Comp
6
Vc
5
HDrv
θ
JA
=124°C/W
θ
JA
=160°C/W
(Also available LEAD-FREE)
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vcc=5V, Vc=12V and T
A
=0 to 70°C. Typical values refer
to T
A
=25°C. Low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient
temperature.
PARAMETER
Reference Voltage
Fb Voltage
Fb Voltage Line Regulation
UVLO
UVLO Threshold - Vcc
UVLO Hysteresis - Vcc
UVLO Threshold - Vc
UVLO Hysteresis - Vc
UVLO Threshold - Fb
UVLO Hysteresis - Fb
Supply Current
Vcc Dynamic Supply Current
Vc Dynamic Supply Current
Vcc Static Supply Current
Vc Static Supply Current
Soft-Start Section
Charge Current
SYM
V
FB
L
REG
UVLO Vcc
UVLO Vc
UVLO Fb
TEST CONDITION
IRU3037
IRU3037A
5<Vcc<12
Supply Ramping Up
Supply Ramping Up
Fb Ramping Down (IRU3037)
(IRU3037A)
MIN
1.225
0.784
TYP
1.250
0.800
0.2
4.2
0.25
3.3
0.2
0.6
0.4
0.1
5
7
3.3
1
-20
MAX
1.275
0.816
0.35
4.4
3.5
0.8
0.5
UNITS
V
%
V
V
V
V
V
V
4.0
3.1
0.4
0.3
Dyn Icc
Dyn Ic
I
CCQ
I
CQ
SS
IB
Freq=200KHz, C
L
=1500pF
Freq=200KHz, C
L
=1500pF
SS=0V
SS=0V
SS=0V
2
2
1
0.5
-10
8
10
6
4.5
-30
mA
mA
mA
mA
µA
2
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IRU3037/IRU3037A & (PbF)
PARAMETER
Error Amp
Fb Voltage Input Bias Current
Fb Voltage Input Bias Current
Transconductance
Oscillator
Frequency
Ramp-Amplitude Voltage
Output Drivers
Rise Time
Fall Time
Dead Band Time
Max Duty Cycle
Min Duty Cycle
SYM
I
FB1
I
FB2
TEST CONDITION
SS=3V, Fb=1V
SS=0V, Fb=1V
MIN
TYP
-0.1
-64
600
200
400
1.25
50
50
150
90
0
MAX
UNITS
µA
µA
µmho
KHz
V
ns
ns
ns
%
%
g
m
Freq
V
RAMP
T
r
T
f
T
DB
T
ON
T
OFF
410
IRU3037
IRU3037A
180
345
1.225
830
220
440
1.275
100
100
250
95
C
L
=1500pF
C
L
=1500pF
Fb=1V, Freq=200KHz
Fb=1.5V
50
85
0
PIN DESCRIPTIONS
PIN#
1
PIN SYMBOL
PIN DESCRIPTION
Fb
This pin is connected directly to the output of the switching regulator via resistor divider to
provide feedback to the Error amplifier.
Vcc
This pin provides biasing for the internal blocks of the IC as well as power for the low side
driver. A minimum of 1µF, high frequency capacitor must be connected from this pin to
ground to provide peak drive current capability.
Output driver for the synchronous power MOSFET.
This pin serves as the ground pin and must be connected directly to the ground plane. A
high frequency capacitor (0.1 to 1µF) must be connected from V5 and V12 pins to this pin
for noise free operation.
Output driver for the high side power MOSFET. Connect a diode, such as BAT54 or 1N4148,
from this pin to ground for the application when the inductor current goes negative (Source/
Sink), soft-start at no load and for the fast load transient from full load to no load.
This pin is connected to a voltage that must be at least 4V higher than the bus voltage of
the switcher (assuming 5V threshold MOSFET) and powers the high side output driver. A
minimum of 1µF, high frequency capacitor must be connected from this pin to ground to
provide peak drive current capability.
Compensation pin of the error amplifier. An external resistor and capacitor network is
typically connected from this pin to ground to provide loop compensation.
This pin provides soft-start for the switching regulator. An internal current source charges
an external capacitor that is connected from this pin to ground which ramps up the output
of the switching regulator, preventing it from overshooting as well as limiting the input
current. The converter can be shutdown by pulling this pin below 0.5V.
2
3
4
LDrv
Gnd
5
HDrv
6
Vc
7
Comp
8
SS / SD
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IRU3037/IRU3037A & (PbF)
BLOCK DIAGRAM
Vcc
0.2V
Bias
Generator
3V
1.25V
POR
0.2V
4.0V
3V
Vc
20uA
3.5V
SS/SD 8
POR
1.25V
Error Comp
25K
25K
0.5V
Comp 7
POR
FbLo Comp
Error Amp
R
Reset Dom
Q
64uA Max
Ct
Oscillator
S
6 Vc
5 HDrv
2 Vcc
3 LDrv
Fb 1
4 Gnd
Figure 2 - Simplified block diagram of the IRU3037.
THEORY OF OPERATION
Introduction
The IRU3037 is a fixed frequency, voltage mode syn-
chronous controller and consists of a precision refer-
ence voltage, an error amplifier, an internal oscillator, a
PWM comparator, 0.5A peak gate driver, soft-start and
shutdown circuits (see Block Diagram).
The output voltage of the synchronous converter is set
and controlled by the output of the error amplifier; this is
the amplified error signal from the sensed output voltage
and the reference voltage.
This voltage is compared to a fixed frequency linear
sawtooth ramp and generates fixed frequency pulses of
variable duty-cycle, which drives the two N-channel ex-
ternal MOSFETs.The timing of the IC is provided through
an internal oscillator circuit which uses on-chip capaci-
tor to set the oscillation frequency to 200 KHz (400 KHz
for “A” version).
Soft-Start
The IRU3037 has a programmable soft-start to control
the output voltage rise and limit the current surge at the
start-up. To ensure correct start-up, the soft-start se-
quence initiates when the Vc and Vcc rise above their
threshold (3.3V and 4.2V respectively) and generates
the Power On Reset (POR) signal. Soft-start function
operates by sourcing an internal current to charge an
external capacitor to about 3V. Initially, the soft-start func-
tion clamps the E/A’s output of the PWM converter. As
the charging voltage of the external capacitor ramps up,
the PWM signals increase from zero to the point the
feedback loop takes control.
Short-Circuit Protection
The outputs are protected against the short-circuit. The
IRU3037 protects the circuit for shorted output by sens-
ing the output voltage (through the external resistor di-
vider). The IRU3037 shuts down the PWM signals, when
the output voltage drops below 0.6V (0.4V for IRU3037A).
The IRU3037 also protects the output from over-voltaging
when the control FET is shorted. This is done by turning
on the sync FET with the maximum duty cycle.
Under-Voltage Lockout
The under-voltage lockout circuit assures that the
MOSFET driver outputs remain in the off state whenever
the supply voltage drops below set parameters. Lockout
occurs if Vc or Vcc fall below 3.3V and 4.2V respec-
tively. Normal operation resumes once Vc and Vcc rise
above the set values.
4
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IRU3037/IRU3037A & (PbF)
APPLICATION INFORMATION
Design Example:
The following example is a typical application for IRU3037,
the schematic is Figure 18 on page 14.
V
IN
= 5V
V
OUT
= 3.3V
I
OUT
= 4A
∆V
OUT
= 100mV
f
S
= 200KHz
Output Voltage Programming
Output voltage is programmed by reference voltage and
external voltage divider. The Fb pin is the inverting input
of the error amplifier, which is internally referenced to
1.25V (0.8V for IRU3037A). The divider is ratioed to pro-
vide 1.25V at the Fb pin when the output is at its desired
value. The output voltage is defined by using the follow-
ing equation:
V
OUT
= V
REF
×
Soft-Start Programming
The soft-start timing can be programmed by selecting
the soft start capacitance value. The start up time of the
converter can be calculated by using:
t
START
= 75×Css (ms)
---(2)
Where:
C
SS
is the soft-start capacitor (µF)
For a start-up time of 7.5ms, the soft-start capacitor will
be 0.1µF. Choose a ceramic capacitor at 0.1µF.
Shutdown
The converter can be shutdown by pulling the soft-start
pin below 0.5V. The control MOSFET turns off and the
synchronous MOSFET turns on during shutdown.
Boost Supply Vc
To drive the high-side switch it is necessary to supply a
gate voltage at least 4V greater than the bus voltage.
This is achieved by using a charge pump configuration
as shown in Figure 18. The capacitor is charged up to
approximately twice the bus voltage. A capacitor in the
range of 0.1µF to 1µF is generally adequate for most
applications. In application, when a separate voltage
source is available the boost circuit can be avoided as
shown in Figure 1.
Input Capacitor Selection
The input filter capacitor should be based on how much
ripple the supply can tolerate on the DC input line. The
larger capacitor, the less ripple expected but consider
should be taken for the higher surge current during the
power-up. The IRU3037 provides the soft-start function
which controls and limits the current surge. The value of
the input capacitor can be calculated by the following
formula:
C
IN
=
I
IN
× ∆t
∆V
---(3)
(
R
6
1+
R
5
)
---(1)
When an external resistor divider is connected to the
output as shown in Figure 3.
V
OUT
IRU3037
Fb
R
5
R
6
Figure 3 - Typical application of the IRU3037 for
programming the output voltage.
Equation (1) can be rewritten as:
R
6
= R
5
×
(
V
V
OUT
REF
-1
)
Choose R
5
= 1KΩ
This will result to R
6
= 1.65KΩ
If the high value feedback resistors are used, the input
bias current of the Fb pin could cause a slight increase
in output voltage. The output voltage set point can be
more accurate by using precision resistor.
Where:
C
IN
is the input capacitance (µF)
I
IN
is the input current (A)
∆t
is the turn on time of the high-side switch (µs)
∆V
is the allowable peak to peak voltage ripple (V)
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