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PDF AP3844 Data sheet ( Hoja de datos )
| Número de pieza | AP3844 | |
| Descripción | (AP3842 - AP3845) High Performance Current Mode PWM Controller | |
| Fabricantes | Anachip | |
| Logotipo |  |
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High Performance Current Mode PWM Controller
AP3842/3/4/5
Features
• Optimized for Off-Line and DC to DC Converters
• Low Start-Up Current (≦0.5mA)
• Automatic Feed Forward Compensation
• Pulse-by-Pulse Current Limiting
• Enhanced Load Response Characteristics
• Under-Voltage Lockout (UVLO) with Hysteresis
• Double Pulse Suppression
• High Current Totem Pole Output
• Internally Trimmed Bandgap Reference
• Current Mode Operation to 500KHZ
• Low Ro Error Amplifier
Pin Connections
PDIP-8L, SOP-8L
Top View
COMP. 1
VFB 2
ISENSE 3
RT/CT 4
8 VREF
7 VI
6 OUTPUT
5 GROUND
General Description
The AP3842/3/4/5 family of control ICs provides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with a minimal external parts count. Internally
implemented circuits include under voltage lockout
featuring start-up current less than 0.5 mA, a
precision reference trimmed for accuracy at the
error amp input, logic to insure latched operation, a
PWM comparator which also provides current limit
control, and a totem pole output stage designed to
source or sink high peak current. The output stage,
suitable for driving N-Channel MOSFETs, is low in
the off-state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges. The AP3842 and AP3844 have
UVLO thresholds of 16V(on) and 10V(off), ideally
suited for off-line applications. The corresponding
thresholds for the AP3843 and AP3845 are 8.5V
and 7.6V. The AP3842 and AP3843 can operate to
duty cycles approaching 100%. A range of the zero
to < 50% is obtained by the AP3844 and AP3845
by the addition of an internal toggle flip flop which
blanks the output off every other clock cycle.
Ordering Information
AP 384X X X X
Part No.
2:3842
3:3843
4:3844
5:3845
Package
Lead Free
Packing
S8:SOP-8L Blank : Normal
Blank: Tube
N8:PDIP-8L L : Lead Free Package A : Taping
This datasheet contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of
this product. No rights under any patent accompany the sale of the product.
Rev.1.0 Oct.11, 2004
1/8
DataSheet4 U .com
1 page  
www.DataSheet4U.com
High Performance Current Mode PWM Controller
AP3842/3/4/5
Peak current(is) is determined by the formula
IS max ≈
1.0V
RS
A small RC filter may be required to suppress switch transients.
Figure 4.
VREF 8
RT/CT 4
GROUND 5
RT
CT
Figure 5 : Open Loop Test Circuit.
4.7K 2N2222
ERROR AMP.
ADJUST
100K
1K
4.7K
ISENSE
ADJUST
5K
for RT > 5KΩ
f= 1.72
RTCT
RT
1 COMP.
VREF 8
2 VFB
Vi 7
AP3842
3 ISENSE
OUTPUT 6
4 RT/CT
5
GROUND
VREF
A Vi
0.1
uF
0.1 TW
uF 1K
OUTPUT
GROUND
CT
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and
bypass apacitors should be connected close to pin 5 in a single point ground. The transistor and 5 KΩ
potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3.
Figure 6 : Shutdown Techniques.
1K
B VREF
330K
SHUTDOWN
500K
3 ISENSE
TO CURRENT
SENSE RESISTOR
SHUTDOWN
1 COMP
Anachip Corp.
www.anachip.com.tw
DataSheet4 U .com
Rev.1.0 Oct.11, 2004
5/8
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet AP3844.PDF ] | |
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