UC3844/3845
HIGH PERFORMANCE
CURRENT MODE PWM
CONTROLLERS
DESCRIPTION
The HG
UC3844/3845
are high performance fixed frequency
current mode controllers that specifically designed for Off-Line and
DC to DC converter applications with minimal external parts count.
The differences between
UC3844
and
UC3845
are the maximum
duty cycle ranges and under-voltage lockout thresholds. The
UC3844
ideally suited to off-line applications with UVLO thresholds
of 16V
(ON)
and 10V
(OFF)
, and
UC3845
has UVLO thresholds of
8.5V
(ON)
and 7.6V
(OFF)
for lower voltage applications.
FEATURES
* Operation output switching frequency up to 500 kHz
* Output deadtime adjustable from 50% to 70%
* Automatic feed forward compensation
* Latching PWM for cycle-by-cycle current limiting
* High current totem pole output
* Internally trimmed reference with under voltage lockout
* UVLO with hysteresis
* Low startup and operating current
PIN CONFIGURATION
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2016 APR
UC3844/3845
PIN DESCRIPTION
PIN NO
1
2
3
4
5
6
7
8
PIN NAME
FUNCTION
Compensation Error amplifier output, this pin is made available for loop compensation.
Voltage Feedback, the inverting input of the Error Amplifier. It is normally connected to the
V
FB
switching power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM uses this
I
SENSE
information to terminate the output switch conduction.
The Oscillator frequency and maximum output duty cycle are programmed by connecting
R
T
/C
T
resistor R
T
to Vref and capacitor C
T
to ground. Operation to 1 MHz is possible.
GND
Power ground.
This output directly drives the gate of a power MOSFET. Peak currents up to 1A are
Output
sourced and sunk by this pin. The output switches at one-half the oscillator frequency.
V
CC
Positive supply.
V
REF
Reference output, provides charging current for capacitor C
T
though resistor R
T
.
BLOCK DIAGRAM
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2016 APR
UC3844/3845
ABSOLUTE MAXIMUM RATINGS
(Ta=25°C)
RATINGS
UNIT
30
mA
1.0
A
5.0
μJ
-0.3 ~ +5.5
V
10
mA
SOP-8
862
mW
Power Dissipation
P
D
DIP-8
1250
mW
Junction Temperature
T
J
+150
°C
Operation Temperature Range
T
OPR
0 ~ 70
°C
Storage Temperature Range
T
STG
-65 ~ +150
°C
Note:1.Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
2.Maxmum package power dissipation limits must be observed.
PARAMETER
Total Power Supply and Zener Current
Output Current, Source or Sink (Note 2)
Output Energy (Capacitive Load per cycle)
Current Sense and Voltage feedback Inputs
Error Amp Output Sink Current
SYMBOL
(I
CC
+Iz)
I
OUT
W
V
IN
I
SINK
THERMAL DATA
PARAMETER
Thermal Resistance(Junction-to-Air)
SOP-8
DIP-8
SYMBOL
θ
JA
RATINGS
145
100
UNIT
°C/W
°C/W
ELECTRICAL CHARACTERISTICS
(Ta=25°C, V
CC
=15V, R
T
=10k, C
T
=3.3nF, 0°C
≤
T
A
≤
70°C, unless otherwise specified)
PARAMETER
REFERENCE SECTION
Reference Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Output Variation over Line,
Load, Temperature
Output Noise Voltage
Long Term Stability
Output Short Circuit Current
OSCILLATOR SECTION
Oscillator Voltage Swing
Discharge Current
Frequency
Frequency Change with Voltage
Frequency Change with Temperature
ERROR AMPLIFIER SECTION
Voltage Feedback Input
High
Output Voltage Swing
Low
Sink
Output Current
Source
Input Bias Current
Open Loop Voltage Gain
Power Supply Rejection Ratio
Unity Gain Bandwidth
SYMBOL
V
REF
△V
OUT
△V
OUT
t
S
V
REF
eN
S
I
SC
V
OSC
I
DSG
f
OSC
Δf
OSC
/ΔV
Δf
OSC
/ΔT
V
FB
V
OH
V
OL
I
SINK
I
SOURCE
I
I(BIAS)
G
VO
PSRR
GB
W
f=10Hz ~ kHz, T
J
=25°C
T
A
=125°C for 1000 Hours
-30
4.82
50
5
-85
1.6
10.8
52
0.2
5.0
2.42
5.0
2.0
-0.5
65
60
0.7
2.50
6.2
0.8
12
-1.0
-0.1
90
70
1.0
TEST CONDITIONS
I
OUT
=1.0mA,T
J
=25 C
V
CC
=12V ~ 25V
I
OUT
=1.0mA ~ 20mA
MIN
4.9
TYP
5.0
2.0
3.0
0.2
MAX
5.1
20
25
5.18
UNIT
V
mV
mV
mV/°C
V
μV
mV
mA
V
mA
57
60
1.0
kHz
%
%
V
V
mA
-2.0
μA
dB
dB
MHz
-180
V
OSC
=2.0V, T
J
=25°C
T
J
=25°C,
0°C
≤
T
A
≤
70°C
V
CC
=12V ~ 25V
0°C
≤
T
A
≤
70°C
V
OUT
=2.5V
R
L
=15k to ground, V
FB
=2.3V
R
L
=15k to V
REF
, V
FB
=2.7V
V
OUT
=1.1V, V
FB
=2.7V
V
OUT
=5.0V, V
FB
=2.3V
V
FB
=2.7V
V
OUT
=2.0V ~ 4.0V
V
CC
=12V ~ 25V
T
J
=25°C
47
46
2.58
1.1
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2016 APR
UC3844/3845
ELECTRICAL CHARACTERISTICS(Cont.)
PARAMETER
CURRENT SENSE SECTION
Current Sense Input Voltage Gain
(Note 2 & 3)
Maximum Current Sense Input
Threshold (Note 2)
Input Bias Current
Power Supply Rejection Ratio
Propagation Delay
OUTPUT SECTION
Low
Output Voltage
High
V
OH
SYMBOL
G
V
V
I(THR)
I
I(BIAS)
PSRR
t
PLH(IN/OUT)
V
OL
I
SINK
=20mA
I
SINK
=200mA
I
SINK
=20mA
I
SINK
=200mA
V
CC
=6.0V, I
SINK
=1.0mA
C
L
=1.0nF,T
J
=25°C
C
L
=1.0nF,T
J
=25°C
V
CC
=12V ~ 25V (Note4)
TEST CONDITIONS
MIN
2.85
0.9
TYP
3.0
1.0
-2.0
70
150
0.1
1.6
13.5
13.4
0.1
50
50
MAX
3.15
1.1
-10
300
0.4
2.2
UNIT
V/V
V
μA
dB
ns
V
V
13
12
Output Voltage with U
VLO
Activated
V
OL
(U
VLO
)
1.1
V
Output Voltage Rise Time
t
R
150
ns
Output Voltage Fall Time
t
F
150
ns
UNDERVOLTAGE LOCKOUT SECTION
UC3844
14.5
16.0
17.5
Startup Threshold
V
THR
V
UC3845
7.8
8.4
9.0
Minimum Operating
UC3844
8.5
10.0
11.5
V
V
CC(MIN)
Voltage After Turn-On
7.0
7.6
8.2
UC3845
PWM SECTION
Max
DC
MAX
47
48
50
%
Duty Cycle
Min
DC
MIN
0
%
TOTAL DEVICE
Power Supply Zener Voltage
V
Z
I
CC
=25mA
30
36
-
V
UC3845
V
CC
=6.5V
0.5
1.0
Power Supply Current
I
CC
mA
(Note 4)
V
CC
=14V
12
17
UC3844
Note: 1. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient
as possible.
2. This parameter is measured at the latch trip point with V
FB
=0V.
3. Comparator gain is defined as:
ΔV
Output Compensation
A
V
=
ΔV
Current Sense Input
4. Adjust V
CC
above the startup threshold before setting to 15V.
TYPICAL CHARACTERISTICS
Timing Resistor vs. Oscillator Frequency
100
50
Timing Resistor, R
T
(kΩ)
20
1.0
2.0 nF
nF
Output Deadtime vs. Oscillator Frequency
75
50
20
0p
F
0p
F
Percent Output Deadtime, DT (%)
10
0p
F
V
CC
= 15V
T
A
= 25℃
1.0nF
70
5.0nF
65
C
T
= 10nF
2.0nF
10
5.0
5.0
nF
C
T
=
10
nF
60
2.0
Note: Output Switches At
One-Half The Oscillator
Frequency
55
500pF
20k
50k
100k
200k
Oscillator Frequency, I
OSC
(Hz)
100pF
200pF
1.0M
1.0
10k
20k
50k
100k
200k
500k 1.0M
50
10k
500k
Oscillator Frequency, I
OSC
(Hz)
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2016 APR
UC3844/3845
Current Sense Input Threshold vs. Error Amp
Output Voltage
Current Sense Input Threshold, V
IN(THR)
(V)
0
V
CC
= 15V
V
OUT
= 2.0V ~ 4.0V
R
L
= 100k
T
A
= 25℃
Error Amp Open Loop Gain Phase vs. Frequency
100
Open Loop Voltage Gain, G
V
(dB)
80
Gain
60
40
Phase
20
0
-20
120
150
180
10M
1.2
1.0
30
Excess Phase Degrees,
φ
60
90
T
A
= 125℃
0.8
T
A
= 25℃
0.6
0.4
T
A
= -55℃
0.2
0
V
CC
= 15V
10
100
1.0k
10k
100k
1.0M
0
2.0
4.0
6.0
8.0
Frequency, f (Hz)
Error Amp Output Voltage, V
OUT
(V)
TYPICAL CHARACTERISTICS(Cont.)
Output Saturation Voltage, V
O(SAT)
(V)
Supply Current, I
CC
(mA)
UCX845
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UCX844
2016 APR
微控制器 MCU
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