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PDF SG3844D Data sheet ( Hoja de datos )
| Número de pieza | SG3844D | |
| Descripción | CURRENT MODE PWM CONTROLLER | |
| Fabricantes | Microsemi Corporation | |
| Logotipo |  |
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THE IN F I N I T E P O W E R OF IN N O VAT I O N
L I N D O C # : 1844
SG1844/SG1845 Series
CURRENT MODE PWM CONTROLLER
PRODUCTION DATA SHEET
DESCRIPTION
The SG1844/45 family of control ICs
provides all the necessary features to
implement off-line fixed frequency,
current-mode switching power supplies
with a minimum number of external
components. Current-mode architecture
demonstrates improved line regulation,
improved load regulation, pulse-by-
pulse current limiting and inherent
protection of the power supply output
switch.
The bandgap reference is trimmed to
±1% over temperature. Oscillator
discharge current is trimmed to less than
±10%. The SG1844/45 has under-
voltage lockout, current-limiting circuitry
and start-up current of less than 1mA.
The totem-pole output is optimized to
drive the gate of a power MOSFET. The
output is low in the off state to provide
direct interface to an N-channel device.
Both operate up to a maximum duty
cycle range of zero to <50% due to an
internal toggle flip-flop which blanks the
output off every other clock cycle.
The SG1844/45 is specified for
operation over the full military ambient
temperature range of -55°C to 125°C.
The SG2844/45 is specified for the
industrial range of -25°C to 85°C, and
the SG3844/45 is designed for the
commercial range of 0°C to 70°C.
PRODUCT HIGHLIGHT
TYPICAL APPLICATION OF SG3844 IN A FLYBACK CONVERTER
AC
INPUT
RST
IST
VCC
SG3844
KEY FEATURES
s OPTIMIZED FOR OFF-LINE CONTROL
s LOW START-UP CURRENT (<1mA)
s AUTOMATIC FEED FORWARD
COMPENSATION
s TRIMMED OSCILLATOR DISCHARGE
CURRENT
s PULSE-BY-PULSE CURRENT LIMITING
s ENHANCED LOAD RESPONSE
CHARACTERISTICS
s UNDER-VOLTAGE LOCKOUT WITH 6V
HYSTERESIS (SG1844 only)
s DOUBLE PULSE SUPPRESSION
s HIGH-CURRENT TOTEM-POLE OUTPUT
s INTERNALLY TRIMMED BANDGAP
REFERENCE
s 500kHz OPERATION
s UNDERVOLTAGE LOCKOUT
SG1844 - 16 volts
SG1845 - 8.4 volts
s LOW SHOOT-THROUGH CURRENT <75mA
OVER TEMPERATURE
HIGH RELIABILITY FEATURES
s AVAILABLE TO MIL-STD-883B
s LINFINITY LEVEL "S" PROCESSING AVAILABLE
TA (°C)
M
Plastic DIP
8-pin
0 to 70
SG3844M
SG3845M
-25 to 85
SG2844M
SG2845M
-55 to 125
—
—
MIL-STD/883
—
—
DESC
—
PACKAGE ORDER INFORMATION
N
Plastic DIP
14-pin
DM
Plastic
8-pin
SOIC
D
Plastic SOIC
14-pin
Y
Ceramic DIP
8-pin
J
Ceramic DIP
14-pin
F
Cer. Flatpack
10-pin
L
Ceramic LCC
20-pin
SG3844N
SG3844DM
SG3844D
SG3844Y
SG3844J
—
—
SG3845N
SG3845DM
SG3845D
SG3845Y
SG3845J
—
—
SG2844N
SG2844DM
SG2844D
SG2844Y
SG2844J
—
—
SG2845N
SG2845DM
SG2845D
SG2845Y
SG2845J
—
—
——
—
SG1844Y
SG1844J
— SG1844L
——
—
SG1845Y
SG1845J
— SG1845L
——
— SG1844Y/883B SG1844J/883B
— SG1844L/883B
——
— SG1845Y/883B SG1845J/883B
— SG1845L/883B
——
— SG1844Y/DESC SG1844J/DESC SG1844F/DESC SG1844L/DESC
— — SG1845Y/DESC SG1845J/DESC SG1845F/DESC SG1845L/DESC
Note: All surface-mount packages are available in Tape & Reel.
Copyright © 2000
Rev. 1.4 4/00
FOR FURTHER INFORMATION CALL (714) 898-8121
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841
1
1 page  
PRODUCT DATABOOK 1996/1997
SG1844/SG1845 Series
CURRENT-MODE PWM CONTROLLER
PRODUCTION DATA SHEET
VCC*
GROUND**
34V
16V (1844)
8.4 (1845)
2.5V
BLOCK DIAGRAM
UVLO
6V (1844)
0.8V (1845)
S/R
5V
REF
INTERNAL
BIAS
RT/CT
VFB
COMP
CURRENT SENSE
OSCILLATOR
ERROR AMP
VREF
GOOD LOGIC
T
2R S
R 1V
R PWM
LATCH
CURRENT SENSE
COMPARATOR
*-
V and V are internally connected for 8-pin packages.
CC C
** - POWER GROUND and GROUND are internally connected for 8-pin packages.
VREF
5.0V
50mA
VC*
OUTPUT
POWER GROUND**
Copyright © 2000
Rev. 1.4 4/00
5
5 Page 
PRODUCT DATABOOK 1996/1997
SG1844/SG1845 Series
CURRENT-MODE PWM CONTROLLER
PRODUCTION DATA SHEET
TYPICAL APPLICATION CIRCUITS
Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package.
VCC
VIN
VCC VIN
7 (12)
7 (12)
7 (11)
Q1
6 (10)
SG1844/45
5 (8)
R
3 (5)
C
RS
IPK
IPK(MAX)
=
1.0V
RS
SG1844/45
7 (11)
6 (10)
R1
Q1
5 (8)
3 (5)
RS
FIGURE 14. — CURRENT SENSE SPIKE SUPPRESSION
The RC low-pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
IB
VC +
» R2
VC1
» R1||R2 _
VC
SG1844/45
7 (11)
R2
6 (10)
VC1
C1
R1
5 (8)
3 (5)
VIN
Q1
RS
FIGURE 16. — BIPOLAR TRANSISTOR DRIVE
The 1844/45 output stage can provide negative base current to
remove base charge of power transistor (Q1) for faster turn off. This
is accomplished by adding a capacitor (C1) in parallel with a resistor
(R1). The resistor (R1) is to limit the base current during turn on.
FIGURE 15. — MOSFET PARASITIC OSCILLATIONS
A resistor (R1) in series with the MOSFET gate reduce overshoot and
ringing caused by the MOSFET input capacitance and any inductance
in series with the gate drive. (Note: It is very important to have a
low inductance ground path to insure correct operation of the I.C.
This can be done by making the ground paths as short and as wide
as possible.)
VCC
7 (12)
Isolation
Boundary
7 (11)
6 (10)
SG1844/45
5 (8)
3 (5)
R
C
RS
VIN
Q1
VGS Waveforms
+
0_
50% DC
+
0_
NS NP 25% DC
V (PIN 1) - 1.4
IPK =
3RS
NP
NS
FIGURE 17. — ISOLATED MOSFET DRIVE
Current transformers can be used where isolation is required
between PWM and Primary ground. A drive transformer is then
necessary to interface the PWM output with the MOSFET.
Copyright © 2000
Rev. 1.4 4/00
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet SG3844D.PDF ] | |
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