Moteur de recherche de fiches techniques de composants électroniques
  French  ▼
ALLDATASHEET.FR

X  

UC284XBD Fiches technique(PDF) 7 Page - Motorola, Inc

No de pièce UC284XBD
Description  HIGH PERFORMANCE CURRENT MODE CONTROLLERS
Download  16 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Fabricant  MOTOROLA [Motorola, Inc]
Site Internet  http://www.freescale.com
Logo MOTOROLA - Motorola, Inc

UC284XBD Fiches technique(HTML) 7 Page - Motorola, Inc

Back Button UC284XBD Datasheet HTML 3Page - Motorola, Inc UC284XBD Datasheet HTML 4Page - Motorola, Inc UC284XBD Datasheet HTML 5Page - Motorola, Inc UC284XBD Datasheet HTML 6Page - Motorola, Inc UC284XBD Datasheet HTML 7Page - Motorola, Inc UC284XBD Datasheet HTML 8Page - Motorola, Inc UC284XBD Datasheet HTML 9Page - Motorola, Inc UC284XBD Datasheet HTML 10Page - Motorola, Inc UC284XBD Datasheet HTML 11Page - Motorola, Inc Next Button
Zoom Inzoom in Zoom Outzoom out
 7 / 16 page
background image
UC3844B, 45B UC2844B, 45B
7
MOTOROLA ANALOG IC DEVICE DATA
OPERATING DESCRIPTION
The UC3844B, UC3845B series are high performance,
fixed frequency, current mode controllers. They are
specifically designed for Off–Line and dc–to–dc converter
applications offering the designer a cost–effective solution
with minimal external components. A representative block
diagram is shown in Figure 15.
Oscillator
The oscillator frequency is programmed by the values
selected for the timing components RT and CT. Capacitor CT
is charged from the 5.0 V reference through resistor RT to
approximately 2.8 V and discharged to 1.2 V by an internal
current sink. During the discharge of CT, the oscillator
generates an internal blanking pulse that holds the center
input of the NOR gate high. This causes the Output to be in a
low state, thus producing a controlled amount of output
deadtime. An internal flip–flop has been incorporated in the
UCX844/5B which blanks the output off every other clock
cycle by holding one of the inputs of the NOR gate high. This
in combination with the CT discharge period yields output
deadtimes programmable from 50% to 70%. Figure 1 shows
RT versus Oscillator Frequency and Figure 2, Output
Deadtime versus Frequency, both for given values of CT.
Note that many values of RT and CT will give the same
oscillator frequency but only one combination will yield a
specific output deadtime at a given frequency. The oscillator
thresholds are temperature compensated to within
±6% at 50
kHz. Also, because of industry trends moving the UC384X
into higher and higher frequency applications, the UC384XB
is guaranteed to within
±10% at 250 kHz.
In many noise–sensitive applications it may be desirable
to frequency–lock the converter to an external system clock.
This can be accomplished by applying a clock signal to the
circuit shown in Figure 17. For reliable locking, the
free–running oscillator frequency should be set about 10%
less than the clock frequency. A method for multi–unit
synchronization is shown in Figure 18. By tailoring the clock
waveform, accurate Output duty cycle clamping can be
achieved to realize output deadtimes of greater than 70%.
Error Amplifier
A fully compensated Error Amplifier with access to the
inverting input and output is provided. It features a typical dc
voltage gain of 90 dB, and a unity gain bandwidth of 1.0 MHz
with 57 degrees of phase margin (Figure 5). The
non–inverting input is internally biased at 2.5 V and is not
pinned out. The converter output voltage is typically divided
down and monitored by the inverting input. The maximum
input bias current is –2.0
µA which can cause an output
voltage error that is equal to the product of the input bias
current and the equivalent input divider source resistance.
The Error Amp Output (Pin 1) is provided for external loop
compensation (Figure 28). The output voltage is offset by two
diode drops (
≈1.4 V) and divided by three before it connects
to the inverting input of the Current Sense Comparator. This
guarantees that no drive pulses appear at the Output (Pin 6)
when Pin 1 is at its lowest state (VOL). This occurs when the
power supply is operating and the load is removed, or at the
beginning of a soft–start interval (Figures 20, 21). The Error
Amp minimum feedback resistance is limited by the
amplifier’s source current (0.5 mA) and the required output
voltage (VOH) to reach the comparator’s 1.0 V clamp level:
Rf(min) ≈
3.0 (1.0 V) + 1.4 V
0.5 mA
= 8800
Current Sense Comparator and PWM Latch
The UC3844B, UC3845B operate as a current mode
controller, whereby output switch conduction is initiated by
the oscillator and terminated when the peak inductor current
reaches the threshold level established by the Error Amplifier
Output/Compensation (Pin 1). Thus the error signal controls
the peak inductor current on a cycle–by–cycle basis. The
Current Sense Comparator PWM Latch configuration used
ensures that only a single pulse appears at the Output during
any given oscillator cycle. The inductor current is converted
to a voltage by inserting the ground–referenced sense
resistor RS in series with the source of output switch Q1. This
voltage is monitored by the Current Sense Input (Pin 3) and
compared to a level derived from the Error Amp Output. The
peak inductor current under normal operating conditions is
controlled by the voltage at Pin 1 where:
Ipk =
V(Pin 1) – 1.4 V
3 RS
Abnormal operating conditions occur when the power
supply output is overloaded or if output voltage sensing is
lost. Under these conditions, the Current Sense Comparator
threshold will be internally clamped to 1.0 V. Therefore the
maximum peak switch current is:
Ipk(max) =
1.0 V
RS
When designing a high power switching regulator it
becomes desirable to reduce the internal clamp voltage in
order to keep the power dissipation of RS to a reasonable
level. A simple method to adjust this voltage is shown in
Figure 19. The two external diodes are used to compensate
the internal diodes, yielding a constant clamp voltage over
temperature. Erratic operation due to noise pickup can result
if there is an excessive reduction of the Ipk(max) clamp
voltage.
A narrow spike on the leading edge of the current
waveform can usually be observed and may cause the power
supply to exhibit an instability when the output is lightly
loaded. This spike is due to the power transformer
interwinding capacitance and output rectifier recovery time.
The addition of an RC filter on the Current Sense Input with a
time constant that approximates the spike duration will
usually eliminate the instability (refer to Figure 23).


Numéro de pièce similaire - UC284XBD

FabricantNo de pièceFiches techniqueDescription
logo
ON Semiconductor
UC284XBD ONSEMI-UC284XBD Datasheet
295Kb / 20P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
July, 2011 ??Rev. 15
UC284XBD ONSEMI-UC284XBD Datasheet
433Kb / 20P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
September, 2004 ??Rev. 3
UC284XBD1 ONSEMI-UC284XBD1 Datasheet
295Kb / 20P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
July, 2011 ??Rev. 15
UC284XBD1 ONSEMI-UC284XBD1 Datasheet
433Kb / 20P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
September, 2004 ??Rev. 3
UC284XBD1G ONSEMI-UC284XBD1G Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
More results

Description similaire - UC284XBD

FabricantNo de pièceFiches techniqueDescription
logo
Motorola, Inc
UC3842B MOTOROLA-UC3842B Datasheet
401Kb / 16P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
logo
Freescale Semiconductor...
MC34129EF FREESCALE-MC34129EF Datasheet
444Kb / 16P
   high performance current mode controllers
logo
ON Semiconductor
UC3844BNG ONSEMI-UC3844BNG Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
UC3845BDR2G ONSEMI-UC3845BDR2G Datasheet
387Kb / 19P
   High Performance Current Mode Controllers
December, 2012 ??Rev. 11
UC3845BVDG ONSEMI-UC3845BVDG Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
UC3845BVDR2G ONSEMI-UC3845BVDR2G Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
UC3844BVDG ONSEMI-UC3844BVDG Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
logo
Unisonic Technologies
UC3842B UTC-UC3842B_08 Datasheet
518Kb / 11P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
logo
Motorola, Inc
UC3844 MOTOROLA-UC3844 Datasheet
376Kb / 14P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
logo
ON Semiconductor
UC3842A ONSEMI-UC3842A Datasheet
399Kb / 14P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
1996 REV 1
UC3844 ONSEMI-UC3844 Datasheet
376Kb / 14P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
1996 REV 1
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16


Fiches technique Télécharger

Go To PDF Page


Lien URL




Politique de confidentialité
ALLDATASHEET.FR
ALLDATASHEET vous a-t-il été utile ?  [ DONATE ] 

À propos de Alldatasheet   |   Publicité   |   Contactez-nous   |   Politique de confidentialité   |   Echange de liens   |   Fabricants
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com