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PDF IR3638SPBF Data sheet ( Hoja de datos )
| Número de pieza | IR3638SPBF | |
| Descripción | HIGH FREQUENCY SYNCHRONOUS PWM BUCK CONTROLLER | |
| Fabricantes | International Rectifier | |
| Logotipo |  |
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Data Sheet No.PD94724
IR3638SPbF
www.DataSheet4U.com
HIGH FREQUENCY SYNCHRONOUS PWM BUCK CONTROLLER
FOR TRACKING APPLIACTIONS
Features
• Power up Sequencing / Tracking
• Enable Input
• Internal 400kHz Oscillator
• Programmable Soft-Start
• Fixed Frequency Voltage Mode
• Output Voltage as low as 0.6V
Applications
• Tracking Applications
• Game Consoles
• Computing Peripheral Voltage Regulators
• Graphics Cards
• General DC/DC Converters
Description
The IR3638 controller IC is designed to provide a
simple synchronous Buck regulator for on-board
DC to DC applications in a 14-pin SOIC. The
IR3638 is designed specifically for tracking
applications by providing the track input.
The IR3638 operates at a fixed internal 400kHz
switching frequency allowing the use of small
external components.
The device features a programmable soft start set
by an external capacitor, under-voltage lockout
and output under-voltage detection that latches
off the device when an output short is detected.
12V 5V
C1 C2 C3
V_CPUCore
C6
C5
Vcc Vc
HDrv
Vp / Enable
LDrv
SS
PGnd
Comp
C4 Gnd
Fb
R3
D1
Q1
L1
Q2
R1
R2
Vout
C7
3/19/07
Fig. 1: Typical Application Circuit
ORDERING INFORMATION
PKG PACKAGE
DESIG DESCRIPTION
S IR3638STRPbF
PIN PARTS
COUNT PER TUBE
14 ----
PARTS
PER REEL
2500
T&R
ORIANTAION
Figure A
1 page  
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Recommended Operating Conditions
IR3638SPbF
Symbol
Vcc
Vc
Tj
Definition
Supply Voltage
Supply Voltage
Junction Temperature
Min
5
Converter Voltage + 5V
0
Max
13.2
20
125
Units
V
V
oC
Electrical Specifications
Unless otherwise specified, these specification apply over Vcc=Vc=12V, 0oC<Tj< 125oC
Parameter
SYM
Test Condition
Min TYP
Supply Current
VCC Supply Current
(Static)
VCC Supply Current
(Dynamic)
VC Supply Current (Static)
ICC(Static)
ICC(Dynamic)
IC(Static)
Enable=0V, No Switching
Fs=400kHz, CLOAD=1.5nF
Enable=0V, No Switching
6.5
15
3.3
MAX
10
25
10
Units
mA
mA
mA
VC Supply Current
(Dynamic)
IC(Dynamic)
Fs=400kHz, CLOAD=1.5nF
Under Voltage Lockout
Vcc-Start-Threshold
Vcc-Stop-Threshold
Vcc-Hysteresis
Enable-Start-Threshold
Enable-Stop-Threshold
Enable-Hysteresis
Fb_UVLO
Vcc UVLO(R)
Vcc UVLO(F)
Vcc(Hyst)
En UVLO (R)
En UVLO (F)
En(Hyst)
Fb_UVLO
Supply ramping up
Supply ramping down
Supply ramping up and down
Supply ramping up
Supply ramping down
Supply ramping up and down
Fb ramping down
Oscillator
Frequency
Ramp Amplitude
FS
Vramp
Note1
Min Duty Cycle
Max Duty Cycle
Dmin
Dmax
Fb=1V, Vp=0.8V
Fs=400kHz, Fb=0.6V,
Vp=0.8V
Error Amplifier
Fb Input Bias Current
Fb Input Bias current
Vp Input Bias Current
Transconductance
IFB1 SS=3V
IFB2 SS=0V
Ivp SS=3V
gm
Input Offset Voltage
Vos Vp=0.8V
Vp Common Mode Range
Vcomn
4.0
3.8
0.2
0.6
0.56
25
0.3
360
81
440
-6
0.6
13
4.25
4.0
0.25
0.65
0.6
42.5
0.4
400
1.25
85
-0.1
64
-0.1
0
20
4.5
4.2
0.35
0.7
0.66
60
0.5
440
0
95
-0.5
-0.5
1300
+6
1.5
mA
V
V
V
mV
V
kHz
V
%
%
μA
uA
uA
μmho
mV
V
Note1: Guaranteed by Design but not tested in production.
3/19/07
5
5 Page 
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Power MOSFET Selection (Cont..)
The IRF8910 has the following data:
Vds = 20V, Id =10A
Rds(on) =13.4mΩ @Vgs =10V
The conduction losses will be: Pcon=0.724W
The switching loss is more difficult to calculate,
even though the switching transition is well
understood. The reason is the effect of the
parasitic components and switching times during
the switching procedures such as turn-on / turn-
off delays and rise and fall times. The control
MOSFET contributes to the majority of the
switching losses in synchronous Buck converter.
The synchronous MOSFET turns on under zero
voltage conditions, therefore, the turn on losses
for synchronous MOSFET can be neglected.
With a linear approximation, the total switching
loss can be expressed as:
Psw
= V 2ds(off )
*
tr
+
T
tf
* Iload
- - - (7)
Where:
V ds(off) = Drain to source voltage at the off time
tr = Rise time
tf = Fall time
T = Switching period
Iload = Load current
The switching time waveforms is shown in
figure9.
VDS
90%
10%
VGS
td(ON)
tr td(OFF)
tf
Fig. 9: switching time waveforms
From IRF8910 data sheet:
tr = 10ns, tf = 4.1ns
These values are taken under a certain condition
test. For more details please refer to the IRF8910
data sheet.
By using equation (7), we can calculate the
switching losses. Psw=0.37W
3/19/07
IR3638SPbF
Feedback Compensation
The IR3638 is a voltage mode controller; the
control loop is a single voltage feedback path
including error amplifier and error comparator. To
achieve fast transient response and accurate
output regulation, a compensation circuit is
necessary. The goal of the compensation
network is to provide a closed loop transfer
function with the highest 0dB crossing frequency
and adequate phase margin (greater than 45o).
The output LC filter introduces a double pole, –
40dB/decade gain slope above its corner
resonant frequency, and a total phase lag of 180o
(see figure 10). The resonant frequency of the LC
filter expressed as follows:
FLC
= 2∗π
1
Lo ∗Co
- - - (8)
Figure 10 shows gain and phase of the LC filter.
Since we already have 180o phase shift just from
the output filter, the system risks being unstable.
Gain
0dB
Phase
0
-40dB/decade
-180
FLC Frequency
FLC Frequency
Fig. 10: Gain and Phase of LC filter
The IR3638’s error amplifier is a differential-input
transconductance amplifier. The output is
available for DC gain control and AC phase
compensation.
The error amplifier can be compensated either in
type II or typeIII compensation. When it is used in
typeII compensation the transconductance
properties of the error amplifier become evident
and can be used to cancel one of the output filter
poles. This will be accomplished with a series RC
circuit from Comp pin to ground as shown in
figure 11.
This method requires that the output capacitor
should have enough ESR to satisfy stability
requirements. In general the output capacitor’s
ESR generates a zero typically at 5kHz to 50kHz
which is essential for an acceptable phase
margin.
11
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| PDF Descargar | [ Datasheet IR3638SPBF.PDF ] | |
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