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PDF IRU3038 Data sheet ( Hoja de datos )
| Número de pieza | IRU3038 | |
| Descripción | SYNCHRONOUS PWM CONTROLLER FOR TERMINATION POWER SUPPLY APPLICATIONS | |
| Fabricantes | International Rectifier | |
| Logotipo |  |
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Data Sheet No. PD94250
IRU3038
SYNCHRONOUS PWM CONTROLLER
FOR TERMINATION POWER SUPPLY APPLICATIONS
PRELIMINARY DATA SHEET
FEATURES
DESCRIPTION
Synchronous Controller in 14-Pin Package
Operating with single 5V or 12V supply voltage
200KHz to 400KHz operation set by an external
resistor
Soft-Start Function
Fixed Frequency Voltage Mode
500mA Peak Output Drive Capability
Uncommitted Error Amplifier available for DDR
voltage tracking application
1.25V Reference Voltage
Protects the output when control FET is shorted
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
The IRU3038 controller IC is designed to provide a low
cost synchronous Buck regulator for voltage tracking
applications such DDR memory and general purpose
on-board DC to DC converter. Modern micro processors
combined with DDR memory, need high-speed bandwidth
data bus which requires a particular bus termination volt-
age. This voltage will be tightly regulated to track the
half of chipset voltage for best performance. The IRU3038
together with dual N-channel MOSFETs such as IRF7313,
provide a low cost solution for such applications. This
device features a programmable frequency set from
200KHz to 400KHz, under-voltage lockout for both Vcc
and Vc supplies, an external programmable soft-start
function as well as output under-voltage detection that
latches off the device when an output short is detected.
TYPICAL APPLICATION
VDDQ
(2.5V)
DDR
Memory
C1
0.1uF
R1
1K
R2
1K C5
0.1uF
C7
2200pF
R3
33K
Vcc
VREF
Vc
HDrv
VP
SS U1
IRU3038
LDrv
Rt
Comp
PGnd
Fb
Gnd
12V
C2
1uF
C3
10TPB100M,
100uF, 55mV
L1
1uH
D1
BAT54
or 1N4148
Q1
1/2 of IRF7313
L2
D03316P-103, 10uH, 3.9A
Q2
1/2 of IRF7313
5V
C4
47uF
Vtt
1.25V @ 3A
C6
2x 6TPB150M,
150uF, 55mV
Figure 1 - Typical application of IRU3038 when Vtt tracks the VDDQ.
PACKAGE ORDER INFORMATION
TA (°C)
0 To 70
0 To 70
DEVICE
IRU3038CF
IRU3038CS
PACKAGE
14-Pin Plastic TSSOP (F)
14-Pin Plastic SOIC NB (S)
Rev. 2.0
09/12/02
www.irf.com
www.DataSheet4U.com
1
1 page  
IRU3038
APPLICATION INFORMATION
Design Example:
The following example is a typical application for IRU3038,
the schematic is Figure 11 on page 12.
VIN = 5V
VOUT = 2.5V
IOUT = 8A
DVOUT = 100mV
fS = 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 referenced to the voltage
on non-inverting pin of error amplifier. For this applica-
tion, this pin (VP) is connected to reference voltage (VREF).
The output voltage is defined by using the following equa-
tion:
( )VOUT = VP 3
1+
R6
R5
---(1)
VP = VREF = 1.25V
When an external resistor divider is connected to the
output as shown in Figure 3.
IRU3038
VREF
VP
Fb
VOUT
R6
R5
Figure 3 - Typical application of the IRU3038 for
programming the output voltage.
Equation (1) can be rewritten as:
( )R6 = R5 3 VOUT - 1
VP
Choose R5 = 1KV
This will result to R6 = 1KV
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.
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:
tSTART = 753Css (ms)
---(2)
Where CSS is the soft-start capacitor (mF)
For a start-up time of 7.5ms, the soft-start capacitor will
be 0.1mF. Choose a ceramic capacitor at 0.1mF.
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 11. The capacitor is charged up to
approximately twice the bus voltage. A capacitor in the
range of 0.1mF to 1mF 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
ripple current generated during the on time of control
MOSFET should be provided by input capacitor. The RMS
value of this ripple is expressed by:
IRMS = IOUT D3(1-D)
---(3)
Where:
D is the Duty Cycle, D=VOUT/VIN.
IRMS is the RMS value of the input capacitor current.
IOUT is the output current for each channel.
For VIN=5V, IOUT=8A and D=0.5, the IRMS=4A
For higher efficiency, a low ESR capacitor is recom-
mended. Choose two Poscap from Sanyo 10TPB100ML
(10V, 100mF, 55mV) with a maximum allowable ripple
current of 1.9A.
Rev. 2.0
09/12/02
www.irf.com
5
5 Page 
IRU3038
TYPICAL PERFORMANCE CHARACTERISTICS
IRU3038
Output Voltage
1.3
IRU3038
Transconductance (GM)
900
1.28
1.26
Max
800
700
600
500
1.24
1.22
Min
400
300
200
1.2
-40°C -25°C
0°C +25°C +50°C +75°C +100°C +125°C +150°C
Output Voltage Spec Max. Spec Min.
Figure 8 - Output voltage of IRU3038.
100
0
-40°C
-25°C
0°C
+25°C +50°C
+75°C
Transconductance (GM)
+100°C
Figure 9 - Transconductance of IRU3038.
IRU3038
Rise Time / Fall Time
CL = 1500pF
50
45
40
35
30
25
20
15
10
5
0
-40°C
-25°C
0°C
+25°C
+50°C
+75°C
Rise Time Fall time
+100°C
Figure 10 - Rise and fall time of IRU3038.
Rev. 2.0
09/12/02
www.irf.com
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet IRU3038.PDF ] | |
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