UC1846/7
UC2846/7
UC3846/7
Current Mode PWM Controller
FEATURES
•
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Automatic Feed Forward Compensation
DESCRIPTION
The UC1846/7 family of control ICs provides all of the necessary
features to implement fixed frequency, current mode control
Programmable Pulse-by-Pulse Current
schemes while maintaining a minimum external parts count. The su-
Limiting
perior performance of this technique can be measured in improved
Automatic Symmetry Correction in Push-pull line regulation, enhanced load response characteristics, and a sim-
Configuration
pler, easier-to-design control loop. Topological advantages include
inherent pulse-by-pulse current limiting capability, automatic sym-
Enhanced Load Response Characteristics
metry correction for push-pull converters, and the ability to parallel
Parallel Operation Capability for Modular
“power modules" while maintaining equal current sharing.
Power Systems
Protection circuitry includes built-in under-voltage lockout and pro-
Differential Current Sense Amplifier with
grammable current limit in addition to soft start capability. A shut-
Wide Common Mode Range
down function is also available which can initiate either a complete
shutdown with automatic restart or latch the supply off.
Double Pulse Suppression
500mA (Peak) Totem-pole Outputs
±1%
Bandgap Reference
Under-voltage Lockout
Soft Start Capability
Shutdown Terminal
500kHZ Operation
Other features include fully latched operation, double pulse sup-
pression, deadline adjust capability, and a
±1%
trimmed bandgap
reference.
The UC1846 features low outputs in the OFF state, while the
UC1847 features high outputs in the OFF state.
BLOCK DIAGRAM
1/97
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (Pin 15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +40V
Collector Supply Voltage (Pin 13). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +40V
Output Current, Source or Sink (Pins 11, 14). . . . . . . . . . . . . . . . . . . . . . . . 500mA
Analog Inputs (Pins 3, 4, 5, 6, 16) . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +V
IN
Reference Output Current (Pin 2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -30mA
Sync Output Current (Pin 10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -5mA
Error Amplifier Output Current (Pin 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -5mA
Soft Start Sink Current (Pin 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA
Oscillator Charging Current (Pin 9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mA
Power Dissipation at T
A
=25°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000mW
Power Dissipation at T
C
=25°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000mW
Storage Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C
Lead Temperature (soldering, 10 seconds. . . . . . . . . . . . . . . . . . . . . . . . . +300°C
Note 1. All voltages are with respect to Ground, Pin 13. Currents are positive into,
negative out of the speficied terminal. Consult Packaging Section of Databook for
thermal limitations and considerations of packages. Pin numbers refer to DIL and
SOIC packages only.
UC1846/7
UC2846/7
UC3846/7
CONNECTION DIAGRAMS
DIL-16, SOIC-16
(TOP VIEW)
J or N Package, DW Package
PLCC-20, LCC-20
(TOP VIEW)
Q, L Packages
PACKAGE PIN FUNCTION
FUNCTION
PIN
1
N/C
2
C/L SS
3
V
REF
4
C/S-
5
C/S+
6
N/C
7
E/A+
8
E/A-
9
Comp
10
C
T
11
N/C
12
R
T
13
Sync
14
A Out
15
Gnd
16
N/C
17
V
C
18
B Out
19
V
IN
20
Shutdown
ELECTRICAL CHARACTERISTICS
(Unless otherwise stated, these specifications apply for T
A
=-55°C to +125°C for
UC1846/UC1847
PARAMETER
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
T
J
=25°C, I
O
=1mA
V
IN
=8V to 40V
I
L
=1mA to 10mA
Over Operating Range, (Note 2)
Line, Load, and Temperature (Note 2)
10Hz≤ f
≤10kHz,
T
J
=25°C (Note 2)
T
J
=125°C, 1000 Hrs. (Note 2)
-10
5.00
100
5
-45
-10
5.05
5.10
5
3
0.4
5.20
4.95
100
5
-45
5.15
20
15
5.00
5.10
5
3
0.4
5.25
5.20
20
15
TEST CONDITIONS
UC2846/UC2847
MIN.
TYP.
MAX.
UC1846/7; -40°C to +85°C for the UC2846/7; and 0°C to +70°C for the UC3846/7;
V
IN
=15V, R
T
=10k, C
T
=4.7nF, T
A
=T
J
.)
UC3846/UC3847
MIN.
TYP.
MAX. UNITS
V
mV
mV
mV/°C
V
µV
mV
mA
Short Circuit Output Current V
REF
=0V
2
UC1846/7
UC2846/7
UC3846/7
(Unless otherwise stated, these specifications apply for T
A
=-55°C to +125°C for UC1846/7; -40°C
ELECTRICAL
CHARACTERISTICS (cont.)
to +85°C for the UC2846/7; and 0°C to +70°C for the UC3846/7; V
IN
=15V, R
T
=10k, C
T
=4.7nF,
T
A
=T
J
.)
UC1846/UC1847
PARAMETER
Oscillator Section
Initial Accuracy
Voltage Stability
Temperature Stability
Sync Output High Level
Sync Output Low Level
Sync Input High Level
Sync Input Low Level
Sync Input Current
Error Amp Section
Input Offset Voltage
Input Bias Current
Input Offset Current
Common Mode Range
Open Loop Voltage Gain
Unity Gain Bandwidth
CMRR
PSRR
Output Sink Current
Output Source Current
High Level Output Voltage
Low Level Output Voltage
Current Sense Amplifier Section
Amplifier Gain
Maximum Differential Input
Signal (V
PIN 4
-V
PIN 3
)
Input Offset Voltage
CMRR
PSRR
Input Bias Current
Input Offset Current
Input Common Mode Range
Delay to Outputs
Current Limit Adjust Section
Current Limit Offset
Input Bias Current
Shutdown Terminal Section
Threshold Voltage
Input Voltage Range
Minimum Latching Current
(I
PIN 1
)
(Note 6)
3.0
1.5
3.0
1.5
mA
250
0
350
400
V
IN
250
0
350
400
V
IN
mV
V
V
PIN 3
=0V, V
PIN 4
=0V, Pin 7 Open
(Note 3)
V
PIN 5
=V
REF
, V
PIN 6
=0V
0.45
0.5
-10
0.55
-30
0.45
0.5
-10
0.55
-30
V
µA
T
J
=25°C, (Note 2)
V
PIN 3
=0V, Pin 1 Open (Notes 3 & 4)
Pin 1 Open (Note 3)
R
L
(Pin 7)=15kW
V
PIN 1
=0.5V, Pin 7 Open (Note 3)
V
CM
=1V to 12V
V
IN
=8V to 40V
V
PIN 1
=0.5V, Pin 7 Open (Note 3)
V
PIN 1
=0.5V, Pin 7 Open (Note 3)
0
200
60
60
1.1
1.2
5
83
84
-2.5
0.08
-10
1
V
IN
-3
500
0
200
25
60
60
1.1
1.2
5
83
84
-2.5
0.08
-10
1
V
IN
-3
500
25
V
mV
dB
dB
µA
µA
V
ns
2.5
2.75
3.0
2.5
2.75
3.0
V
V
IN
=8V to 40V
∆V
O
=1.2 to 3V, V
CM
=2V
T
J
=25°C (Note 2)
V
CM
=0V to 38V, V
IN
=40V
V
IN
=8V to 40V
V
ID
=-15mV to -5V, V
PIN 7
=1.2V
V
ID
=15mV to 5V, V
PIN 7
=2.5V
R
L
=(Pin 7) 15kΩ
0
80
0.7
75
80
2
-0.4
4.3
105
1.0
100
105
6
-0.5
4.6
0.7
1
0.5
-0.6
40
5
-1
250
V
IN
-2V
0
80
0.7
75
80
2
-0.4
4.3
105
1.0
100
105
6
-0.5
4.6
0.7
1
0.5
-0.6
40
10
-2
250
V
IN
-2V
mV
µA
nA
V
dB
MHz
dB
dB
mA
mA
V
V
Pin 8=0V
Pin 8=0V
Sync Voltage=3.9V, Pin 8=0V
1.3
3.9
2.5
1.5
1.3
T
J
=25°C
V
IN
=8V to 40V
Over Operating Range (Note 2)
3.9
39
43
-1
-1
4.35
2.3
2.5
3.9
2.5
1.5
3.9
47
2
39
43
-1
-1
4.35
2.3
2.5
47
2
kHz
%
%
V
V
V
V
mA
TEST CONDITIONS
UC2846/UC2847
MIN.
TYP.
MAX.
UC3846/UC3847
MIN.
TYP.
MAX. UNITS
3
UC1846/7
UC2846/7
UC3846/7
(Unless otherwise stated, these specifications apply for T
A
=-55°C to +125°C for UC1846/7; -40°C
ELECTRICAL
CHARACTERISTICS (cont.)
to +85°C for the UC2846/7; and 0°C to +70°C for the UC3846/7; V
IN
=15V, R
T
=10k, C
T
=4.7nF,
T
A
=T
J
.)
UC1846/UC1847
PARAMETER
Shutdown Terminal Section (cont.)
Maximum Non-Latching
Current (I
PIN 1
)
Delay to Outputs
Output Section
Collector-Emitter Voltage
Collector Leakage Current
Output Low Level
Output High Level
Rise Time
Fall Time
Start-Up Threshold
Threshold Hysteresis
Total Standby Current
Supply Current
17
21
17
21
mA
V
C
=40V (Note 5)
I
SINK
=20mA
I
SINK
=100mA
I
SOURCE
=20mA
I
SOURCE
=100mA
C
L
=1nF, T
J
=25°C (Note 2)
C
L
=1nF, T
J
=25°C (Note 2)
13
12
0.1
0.4
13.5
13.5
50
50
7.7
0.75
300
300
8.0
40
200
0.4
2.1
13
12
0.1
0.4
13.5
13.5
50
50
7.7
0.75
300
300
8.0
40
200
0.4
2.1
V
µA
V
V
V
V
ns
ns
V
V
T
J
=25°C (Note 2)
(Note 7)
1.5
300
0.8
600
1.5
300
0.8
600
mA
ns
TEST CONDITIONS
UC2846/UC2847
MIN.
TYP.
MAX.
UC3846/UC3847
MIN.
TYP.
MAX. UNITS
Under-Voltage Lockout Section
Note 2. These parameters, although guaranteed over the recommended operating conditions, are not 100% tested in production.
Note 3. Parameter measured at trip point of latch with V
PIN 5
= V
REF
, V
PIN 6
= 0V.
∆
V
PIN
7
;
∆
V
PIN
4
=
0 to 1.0V.
Note 4. Amplifier gain defined as:
G
=
∆
V
PIN
4
Note 5. Applies to UC1846/UC2846/UC3846 only due to polarity of outputs.
Note 6. Current into Pin 1 guaranteed to latch circuit in shutdown state.
Note 7. Current into Pin 1 guaranteed not to latch circuit in shutdown state.
APPLICATIONS DATA
Oscillator Circuit
I
D
Output deadtime is determined by the external capacitor, C
T
, according to the formula:
τ
d
(µs) =
145C
T
(µf )
.
I
D
−
3.6
I
D
= Oscillator discharge current at 25°C is typically 7.5.
R
T
(
kΩ
)
For large values of R
T
:
τ
d
(µs) ≈
145C
T
(µf )
.
2.2
Oscillator frequency is approximated by the formula:
f
T
(
kHz
) ≈
.
R
T
(
kΩ
)•
C
T
(µf )
4
APPLICATIONS DATA (cont.)
Error Amp Output Configuration
UC1846/7
UC2846/7
UC3846/7
Error Amp Gain and Phase vs Frequency
Error Amp Open-Logic D.C. Gain vs Load Resistance
Parallel Operation
5
