@vic
AV3842A / 3843A
LINEAR INTEGRATED CIRCUIT
QW-R103-002,B
CURRENT MODE PWM CONTROL
CIRCUITS
DESCRIPTION
The
@vic AV3842A/3843A provide the necessary functions
to implement off-line or DC to DC fixed frequency current
mode , controlled switching circuits with a minimal external
part count
FEATURES
*Low external part count.
*Low start up current ( Typical 0.12mA )
*Automatic feed forward compensation
*Pulse-by-Pulse current limiting
*Under-voltage lockout with hysteresis
*Double pulse Suppression
*High current totem pole output to drive MOSFET directly
*Internally trimmed band gap reference
*500kHz operation
DIP-8
SOP-8
BLOCK DIAGRAM
7
5
7
6
5
4
3
1
2
8
Internal
Bias
5V REF
S/R
U.V.L.O
R
S
PWM
LATCH
Vref
Good
Logic
ERROR
AMPLIFIER
1/2Vref
1/3Vref
1V
OSCILLATOR
Vref
VFB
COMP
CURRENT SENSE
RT/CT
Vcc
GND
OUTPUT
Vcc
GND
CURRENT
SENSE
COMPARATOR
ABSOLUTE MAXIMUM RATINGS
(Ta=25
C)
PARAMETER SYMBOL
VALUE
UNIT
Supply Voltage(Low Impedance Source)
V
CC
30
V
Supply Voltage(Icc<30mA)
Vcc
Self Limiting
V
Output Current ( Peak )
Io
+-1
A
Output Energy(capacity Load)
5
J
Analog Inputs(pin 2,3)
V
I(ANA)
-0.3 ~ +6.3
V
Error Amplifier Output Sink Current
I
SINK(EA)
10 mA
Power Dissipation
PD DIP-8
at T
amb
<=25
C 1.0
W
SOP-8
at T
amb
<=25
C 0.5
W
Lead Temperature( Soldering 10 Sec )
Tlead
300
C
QW-R103-002,B
(continued)
PARAMETER SYMBOL
VALUE
UNIT
Storage Temperature
Tstg
-65 ~ +150
C
Operating junction temperature
Tj
+150
C
Note 1: Ta>25
C, P
D
derated with 8mW/
C.
ELECTRICAL CHARACTERISTICS
(0
C <=Ta<=70
C,V
CC
=15V,R
T
=10k
,C
T
=3.3nF,unless otherwise
specified)
PARAMETER SYMBOL
TEST
CONDITIONS MIN
TYP
MAX
UNIT
Reference Section
Output Voltage
V
REF
Tj=25
C,Io=1mA
4.9
5 5.1 V
Line Regulation
V
REF
12<=V
IN
<=25V
6
20
mV
Load Regulation
V
REF
1<=Io=20mA
6
25
mV
Temperature Stability
(Note 2)
0.2
0.4
mV/
C
Total Output Variation
Line, Load, Temp(note 2)
4.82
5.18
V
Output Noise Voltage
Vosc
10Hz<=f<=10kHz,Tj=25
C (note 2)
50 uV
Long Term Stability
Ta=25
C,1000Hrs(note 2)
5
25
mV
Output Short Circuit
I
SC
-30
-100
-180
mA
Oscillator Section
Initial Accuracy
f
Tj=25
C
47 52 57 kHz
Voltage Stability
f/
Vcc
12<=Vcc<=25V
0.2
1
%
Temperature Stability
Tmin<=T
A
<=Tmax(note 2)
5
%
Amplitude
Vosc
Vpin 4 peak to peak
1.7
V
Error Amplifier Section
Input Voltage
V
I(EA)
Vpin
1=2.5V 2.42
2.50
2.58
V
Input Bias Current
I
BIAS
-0.3
-2
A
A
VOL
2
<=Vo<=4V
60
90
dB
Unity Gain Bandwidth
Tj=25
C (note 2)
0.7
1
MHz
PSRR
I2<=Vcc<=25V
60
70
dB
Output Sink Current
Isink
Vpin 2=2.7V,Vpin 1=1.1V
2
6
mA
Output Source Current
Isource
Vpin 2=2.3V,Vpin 1=5V
-0.5
-0.8
mA
Vout High
V
OH
Vpin 2=2.3V, RL=15k
to GND
5 6 V
Vout Low
V
OL
Vpin 2=2.7V,Vpin 1=1.1V
0.7
1.1
V
Current Sense section
Gain G
V
(note
3,4)
2.85
3
3.15
V/V
Maximum Input signal
V
I(MAX)
Vpin 1=5V( note 3)
0.9
1
1.1
V
PSRR
12<=Vcc<=25V
70 dB
Input Bias Current
I
BIAS
-2
-10
A
Delay to Output
Vpin 3=0 to 2V
150
300
ns
Output Section
Output Low Level
V
OL
Isink=20mA
0.1
0.4
V
Isink=200mA
1.5
2.2
V
Output High Level
V
OH
Isource=20mA 13
13.5
V
Isource=200mA
12
13.5
V
Rise Time
t
R
Tj=25
C,C
L
=1nF(note 2)
50
150
ns
Fall Time
t
F
Tj=25
C,C
L
=1nF(note 2)
50
150
ns
Under-Voltage Lockout Output Section
Start Threshold
V
TH(ST)
UTC3842A 14.5
16
17.5
V
UTC3843A
7.8
8.4
9
V
Min. Operating Voltage
V
OPR(min)
After Turn On
UTC3842A
8.5
10 11.5
UTC3843A
7
7.6
8.2
V
PWM Section
@vic
AV3842A / 3843A
LINEAR INTEGRATED CIRCUIT
QW-R103-002,B
PARAMETER SYMBOL
TEST
CONDITIONS MIN
TYP
MAX
UNIT
Maximum Duty Cycle
D
(MAX)
95
97
100
%
Minimum Duty Cycle
D
(MIN)
0
%
Total Standby Current
Start-up Current
I
ST
0.12 0.3 mA
Operating Supply Current
I
CC(opr)
Vpin 2=Vpin 3=0V
11
17
mA
Vcc Zener Voltage
Vz
Icc=25mA
34
V
note 2:These parameters, although guaranteed ,are not 100% tested in production.
note 3:Parameters measured at trip point of latch with Vpin 2=0.
note 4:Gain defined as:
Vpin 1
Vpin 3
A=
; 0<=Vpin3<=0.8V
note 5:Adjust Vcc above the start threshold before setting at 15V.
OPEN-LOOP LABORATORY TEST FIXTURE
1
2
8
7
3
6
4
5
A
Vref
Vcc
1k
/ 1W
0.
1
F
CT
RT
100k
5k
4.
7k
4.
7k
0.
1
F
Error Amp
Adjust
I
s
ens
e
Adj
us
t
OUTPUT
High peak current associated with capacity loads necessitate careful grounding techniques. Timing and bypass
capacitors should be connected close to pin 5 in single point GND. The transistor and 5k
potentio-meter are used
to sample the oscillator waveform and apply an adjustable Ramp to Pin 3.
UNDER-VOLTAGE LOCKOUT
7
Vcc
Von=16V
Voff=10V
ON/OFF Command
to rest of IC
Von
Voff
<1mA
<15mA
Icc
Vcc
During Under-Voltage Lockout, the output driver is biased to a high impedance state. Pin 6 should be shunt to
GND with a bleeder resistor to prevent activating the power switch with output leakage currents.
@vic
AV3842A / 3843A
LINEAR INTEGRATED CIRCUIT
QW-R103-002,B
ERROR AMPLIFIER CONFIGURATION
2
1
0.5mA
2.5V
Zf
Zi
Error amplifier can source or sink up to 0.5mA
CURRENT SENSE CIRCUIT
5
3
1
2R
R
1V
C
Rs
R
Is
Error
Amplifier
Current Sense
Comparator
Peak current (Is) determined by the formula:
Ismax=10V/Rs.
A small RC filter be required to suppress switch transients.
SLOPE COMPENSATION
8
4
3
Isense
R1
R2
Rsense
C
RT
CT
0.1
F
A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope
compensation for converts requiring duty cycles over 50%.Note that capacitor C, forms a filter with R2 to suppress
the leading edge switch spikes.
@vic
AV3842A / 3843A
LINEAR INTEGRATED CIRCUIT
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