Document Outline
- Application Notes
- Design Notes
1/97
Automatic Feed Forward Compensation
Programmable Pulse-by-Pulse Current
Limiting
Automatic Symmetry Correction in Push-pull
Configuration
Enhanced Load Response Characteristics
Parallel Operation Capability for Modular
Power Systems
Differential Current Sense Amplifier with
Wide Common Mode Range
Double Pulse Suppression
500mA (Peak) Totem-pole Outputs
1% Bandgap Reference
Under-voltage Lockout
Soft Start Capability
Shutdown Terminal
500kHZ Operation
Current Mode PWM Controller
The UC1846/7 family of control ICs provides all of the necessary
features to implement fixed frequency, current mode control
schemes while maintaining a minimum external parts count. The su-
perior performance of this technique can be measured in improved
line regulation, enhanced load response characteristics, and a sim-
pler, easier-to-design control loop. Topological advantages include
inherent pulse-by-pulse current limiting capability, automatic sym-
metry correction for push-pull converters, and the ability to parallel
"power modules" while maintaining equal current sharing.
Protection circuitry includes built-in under-voltage lockout and pro-
grammable current limit in addition to soft start capability. A shut-
down function is also available which can initiate either a complete
shutdown with automatic restart or latch the supply off.
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.
UC1846/7
UC2846/7
UC3846/7
BLOCK DIAGRAM
FEATURES
DESCRIPTION
UC1846/7
UC2846/7
UC3846/7
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C
1
C/L SS
2
V
REF
3
C/S-
4
C/S+
5
N/C
6
E/A+
7
E/A-
8
Comp
9
C
T
10
N/C
11
R
T
12
Sync
13
A Out
14
Gnd
15
N/C
16
V
C
17
B Out
18
V
IN
19
Shutdown
20
DIL-16, SOIC-16
(TOP VIEW)
J or N Package, DW Package
CONNECTION DIAGRAMS
ELECTRICAL CHARACTERISTICS
(Unless otherwise stated, these specifications apply for T
A
=-55C to +125C for
UC1846/7; -40C to +85C for the UC2846/7; and 0C to +70C for the UC3846/7;
V
IN
=15V, R
T
=10k, C
T
=4.7nF, T
A
=T
J
.)
UC1846/UC1847
UC3846/UC3847
PARAMETER
TEST CONDITIONS
UC2846/UC2847
MIN.
TYP.
MAX.
MIN.
TYP.
MAX. UNITS
Reference Section
Output Voltage
T
J
=25C, I
O
=1mA
5.05
5.10
5.15 5.00
5.10
5.20
V
Line Regulation
V
IN
=8V to 40V
5
20
5
20
mV
Load Regulation
I
L
=1mA to 10mA
3
15
3
15
mV
Temperature Stability
Over Operating Range, (Note 2)
0.4
0.4
mV/C
Total Output Variation
Line, Load, and Temperature (Note 2)
5.00
5.20
4.95
5.25
V
Output Noise Voltage
10Hz
f
10kHz, T
J
=25C (Note 2)
100
100
V
Long Term Stability
T
J
=125C, 1000 Hrs. (Note 2)
5
5
mV
Short Circuit Output Current V
REF
=0V
-10
-45
-10
-45 mA
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
=25C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000mW
Power Dissipation at T
C
=25C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000mW
Storage Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65C to +150C
Lead Temperature (soldering, 10 seconds. . . . . . . . . . . . . . . . . . . . . . . . . +300C
ABSOLUTE MAXIMUM RATINGS (Note 1)
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.
PLCC-20, LCC-20
(TOP VIEW)
Q, L Packages
2
UC1846/UC1847
UC3846/UC3847
PARAMETER
TEST CONDITIONS
UC2846/UC2847
MIN.
TYP.
MAX.
MIN.
TYP.
MAX. UNITS
Oscillator Section
Initial Accuracy
T
J
=25C
39
43
47
39
43
47
kHz
Voltage Stability
V
IN
=8V to 40V
-1
2
-1
2
%
Temperature Stability
Over Operating Range (Note 2)
-1
-1
%
Sync Output High Level
3.9
4.35
3.9
4.35
V
Sync Output Low Level
2.3
2.5
2.3
2.5
V
Sync Input High Level
Pin 8=0V
3.9
3.9
V
Sync Input Low Level
Pin 8=0V
2.5
2.5
V
Sync Input Current
Sync Voltage=3.9V, Pin 8=0V
1.3
1.5
1.3
1.5
mA
Error Amp Section
Input Offset Voltage
0.5
5
0.5
10
mV
Input Bias Current
-0.6
-1
-0.6
-2
A
Input Offset Current
40
250
40
250
nA
Common Mode Range
V
IN
=8V to 40V
0
V
IN
-2V
0
V
IN
-2V
V
Open Loop Voltage Gain
V
O
=1.2 to 3V, V
CM
=2V 80
105
80
105
dB
Unity Gain Bandwidth
T
J
=25C (Note 2)
0.7
1.0
0.7
1.0
MHz
CMRR
V
CM
=0V to 38V, V
IN
=40V
75
100
75
100
dB
PSRR
V
IN
=8V to 40V
80
105
80
105
dB
Output Sink Current
V
ID
=-15mV to -5V, V
PIN 7
=1.2V 2
6
2
6
mA
Output Source Current
V
ID
=15mV to 5V, V
PIN 7
=2.5V -0.4
-0.5
-0.4
-0.5
mA
High Level Output Voltage
R
L
=(Pin 7) 15k
4.3
4.6
4.3
4.6
V
Low Level Output Voltage
0.7
1
0.7
1
V
Current Sense Amplifier Section
Amplifier Gain
V
PIN 3
=0V, Pin 1 Open (Notes 3 & 4)
2.5
2.75
3.0
2.5
2.75
3.0
V
Maximum Differential Input
Pin 1 Open (Note 3)
Signal (V
PIN 4
-V
PIN 3
)
R
L
(Pin 7)=15kW
1.1
1.2
1.1
1.2
V
Input Offset Voltage
V
PIN 1
=0.5V, Pin 7 Open (Note 3)
5
25
5
25
mV
CMRR
V
CM
=1V to 12V
60
83
60
83
dB
PSRR
V
IN
=8V to 40V
60
84
60
84
dB
Input Bias Current
V
PIN 1
=0.5V, Pin 7 Open (Note 3)
-2.5
-10
-2.5
-10
A
Input Offset Current
V
PIN 1
=0.5V, Pin 7 Open (Note 3)
0.08
1
0.08
1
A
Input Common Mode Range
0
V
IN
-3
0
V
IN
-3 V
Delay to Outputs
T
J
=25C, (Note 2)
200
500
200
500
ns
Current Limit Adjust Section
Current Limit Offset
V
PIN 3
=0V, V
PIN 4
=0V, Pin 7 Open
(Note 3)
0.45
0.5
0.55
0.45
0.5
0.55
V
Input Bias Current
V
PIN 5
=V
REF
, V
PIN 6
=0V
-10
-30
-10
-30
A
Shutdown Terminal Section
Threshold Voltage
250
350
400
250
350
400
mV
Input Voltage Range
0
V
IN
0
V
IN
V
Minimum Latching Current
(Note 6)
(I
PIN 1
)
3.0
1.5
3.0
1.5
mA
ELECTRICAL
CHARACTERISTICS (cont.)
(Unless otherwise stated, these specifications apply for T
A
=-55C to +125C for UC1846/7; -40C
to +85C for the UC2846/7; and 0C to +70C for the UC3846/7; V
IN
=15V, R
T
=10k, C
T
=4.7nF,
T
A
=T
J
.)
UC1846/7
UC2846/7
UC3846/7
3
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.
Note 4. Amplifier gain defined as: G
=
V
PIN 7
V
PIN 4
;
V
PIN 4
=
0 to 1.0V.
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.
UC1846/7
UC2846/7
UC3846/7
UC1846/UC1847
UC3846/UC3847
PARAMETER
TEST CONDITIONS
UC2846/UC2847
MIN.
TYP.
MAX.
MIN.
TYP.
MAX. UNITS
Shutdown Terminal Section (cont.)
Maximum Non-Latching
(Note 7)
Current (I
PIN 1
)
1.5
0.8 1.5
0.8
mA
Delay to Outputs
T
J
=25C (Note 2)
300
600
300
600
ns
Output Section
Collector-Emitter Voltage
40
40
V
Collector Leakage Current
V
C
=40V (Note 5)
200
200
A
Output Low Level
I
SINK
=20mA
0.1
0.4
0.1
0.4
V
I
SINK
=100mA
0.4
2.1
0.4
2.1
V
Output High Level
I
SOURCE
=20mA
13
13.5
13
13.5
V
I
SOURCE
=100mA
12
13.5
12
13.5
V
Rise Time
C
L
=1nF, T
J
=25C (Note 2)
50
300
50
300
ns
Fall Time
C
L
=1nF, T
J
=25C (Note 2)
50
300
50
300
ns
Under-Voltage Lockout Section
Start-Up Threshold
7.7
8.0
7.7
8.0
V
Threshold Hysteresis
0.75
0.75
V
Total Standby Current
Supply Current
17
21
17
21
mA
Oscillator Circuit
Output deadtime is determined by the external capacitor, C
T
, according to the formula:
d
(
s
)
=
145C
T
(
f
)
I
D
I
D
-
3.6
R
T
(
k
)
.
For large values of R
T
:
d
(
s
)
145C
T
(
f
)
.
Oscillator frequency is approximated by the formula:
f
T
(
kHz
)
2.2
R
T
(
k
)
C
T
(
f
)
.
ELECTRICAL
CHARACTERISTICS (cont.)
(Unless otherwise stated, these specifications apply for T
A
=-55C to +125C for UC1846/7; -40C
to +85C for the UC2846/7; and 0C to +70C for the UC3846/7; V
IN
=15V, R
T
=10k, C
T
=4.7nF,
T
A
=T
J
.)
APPLICATIONS DATA
I
D
= Oscillator discharge current at 25C is typically 7.5.
4
Error Amp Output Configuration
Error Amp Open-Logic D.C. Gain vs Load Resistance
Error Amp Gain and Phase vs Frequency
UC1846/7
UC2846/7
UC3846/7
APPLICATIONS DATA (cont.)
Parallel Operation
5
Pulse by Pulse Current Limiting
Soft Start and Shutdown /Restart Functions
UC1846/7
UC2846/7
UC3846/7
Peak Current (I
S
) is determined by the formula: I
S
=
R
2
V
REF
R
1
+
R
2
-
0.5
3R
S
APPLICATIONS DATA (cont.)
6
Current Sense Amp Connection
UC1846 Open Loop Test Circuit
UC1846/7
UC2846/7
UC3846/7
UNITRODE CORPORATION
7 CONTINENTAL BLVD.
MERRIMACK, NH 03054
TEL. (603) 424-2410
FAX (603)424-3460
APPLICATIONS DATA (cont.)
A small RC filter may be required in some applications to reduce switch transients.
Differential input allows remote, noise free sensing.
7
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1999, Texas Instruments Incorporated
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