application
INFO
available
UC1848
UC2848
UC3848
Average Current Mode PWM Controller
FEATURES
BLOCK DIAGRAM
• Practical Primary Side Control of
Isolated Power Supplies with DC
Control of Secondary Side Current
• Accurate Programmable Maximum
Duty Cycle Clamp
• Maximum Volt-Second Product Clamp
to Prevent Core Saturation
• Practical Operation Up to 1MHz
• High Current (2A Pk) Totem Pole
Output Driver
• Wide Bandwidth (8MHz) Current Error
Amplifier
• Under Voltage Lockout Monitors VCC,
VIN and VREF
• Output Active Low During UVLO
• Low Startup Current (500µA)
• Precision 5V Reference (1%)
UDG-93003-1
DESCRIPTION
The UC3848 family of PWM control ICs makes primary
side average current mode control practical for isolated
switching converters. Average current mode control insures that both cycle by cycle peak switch current and
maximum average inductor current are well defined and
will not run away in a short circuit situation. The UC3848
can be used to control a wide variety of converter topologies.
In addition to the basic functions required for pulse width
modulation, the UC3848 implements a patented technique of sensing secondary current in an isolated buck
derived converter from the primary side. A current waveform synthesizer monitors switch current and simulates
the inductor current down slope so that the complete current waveform can be constructed on the primary side
without actual secondary side measurement. This information on the primary side allows for full DC control of
output current.
The UC3848 circuitry includes a precision reference, a
wide bandwidth error amplifier for average current control, an oscillator to generate the system clock, latching
PWM comparator and logic circuits, and a high current
SLUS225A - April 1996 - REVISED MARCH 2004
output driver. The current error amplifier easily interfaces
with an optoisolator from a secondary side voltage sensing circuit.
A full featured undervoltage lockout (UVLO) circuit is contained in the UC3848. UVLO monitors the supply voltage
to the controller (VCC), the reference voltage (VREF),
and the input line voltage (VIN). All three must be good
before soft start commences. If either VCC or VIN is low,
the supply current required by the chip is only 500µA and
the output is actively held low.
Two on board protection features set controlled limits to
prevent transformer core saturation. Input voltage is monitored and pulse width is constrained to limit the maximum volt-second product applied to the transformer. A
unique patented technique limits maximum duty cycle
within 3% of a user programmed value.
These two features allow for more optimal use of transformers and switches, resulting in reduced system size
and cost.
Patents embodied in the UC3848 belong to Lambda
Electronics Incorporated and are licensed for use in applications employing these devices.
UC1848
UC2848
UC3848
ABSOLUTE MAXIMUM RATINGS
Analog Output Currents, Source or Sink (Pins 5 & 10) . . . 5mA
Power Dissipation at TA = 60°C . . . . . . . . . . . . . . . . . . . . . . 1W
Storage Temperature Range . . . . . . . . . . . . . . . −65°C to +150°C
Lead Temperature (Soldering 10 seconds) . . . . . . . . . . +300°C
Supply Voltage (Pin 15). . . . . . . . . . . . . . . . . . . . . . . . . . . . 22V
Output Current, Source or Sink (Pin 14)
DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A
Pulse (0.5 s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2A
Power Ground to Ground (Pin 1 to Pin 13) . . . . . . . . . . . ± 0.2V
Analog Input Voltages
(Pins 3, 4, 7, 8, 12, 16) . . . . . . . . . . . . . . . . . . . . . –0.3 to 7V
Analog Input Currents, Source or Sink
(Pins 3, 4, 7, 8, 11, 12, 16) . . . . . . . . . . . . . . . . . . . . . . 1mA
CONNECTION DIAGRAMS
PLCC-20 & LCC-20
(Top View)
Q & L Packages
DIL-16, SOIC-16 (Top View)
J, N, or DW Packages
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C
1
GND
2
VREF
3
NI
4
INV
5
N/C
6
CAO
7
CT
8
VS
9
DMAX
10
N/C
11
CDC
12
CI
13
IOFF
14
ION
15
N/C
16
PGND
17
OUT
18
VCC
19
UV
20
THERMAL RATINGS TABLE
Package
DIL-16J
DIL-16N
SOIC-16DW
PLCC-20
LCC-20
QJA
80-120
90(1)
50-100(1)
43-75(1)
70-80
QJC
28(2)
45
27
34
20(2)(3)
Q
Q
Q
2
UC1848
UC2848
UC3848
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, all specifications are over the junction temperature range
of −55°C to +125°C for the UC1848, −40°C to +85°C for the UC2848, and 0°C to +70°C for the UC3848. Test conditions are: VCC
= 12V, CT = 400pF, CI = 100pF, IOFF = 100µA, CDC = 100nF, Cvs = 100pF, and Ivs = 400µA, TA = TJ.
PARAMETER
TEST CONDITIONS
MIN
TYP
0.95
1
20
25
MAX UNITS
Real Time Current Waveform Synthesizer
Ion Amplifier
Offset Voltage
Slew Rate (Note 1)
lib
1.05
V
V/µs
-2
-20
µA
IOFF Current Mirror
Input Voltage
0.95
1
1.05
V
Current Gain
0.9
1
1.1
A/A
60
100
10
mV
-3
µA
Current Error Amplifier
AVOL
Vio
12V ≤ VCC
20V, 0V
VCM
5V
lib
-0.5
Voh
IO = −200µA
Vol
IO = 200µA
Source Current
VO = 1V
GBW Product
f = 200kHz
3
Slew Rate (Note 1)
dB
3.3
V
0.3
0.6
V
1.4
1.6
2.0
5
8
MHz
8
10
V/µs
240
250
mA
Oscillator
Frequency
TA = 25°C
235
Ramp Amplitude
260
kHz
265
kHz
1.5
1.65
1.8
V
73.5
76.5
79.5
%
1100
ns
14
V
Duty Cycle Clamp
Max Duty Cycle
V(DMAX) = 0.75 • VREF
Volt Second Clamp
Max On Time
900
VCC Comparator
Turn-on Threshold
13
Turn-off Threshold
Hysteresis
3
9
10
2.5
3
V
3.5
V
UC1848
UC2848
UC3848
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, all specifications are over the junction temperature range
of −55°C to +125°C for the UC1848, −40°C to +85°C for the UC2848, and 0°C to +70°C for the UC3848. Test conditions are: VCC
= 12V, CT = 400pF, CI = 100pF, IOFF = 100µA, CDC = 100nF, Cvs = 100pF, and Ivs = 400µA, TA = TJ.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
UV Comparator
Turn-on Threshold
RHYSTERESIS
4.1
4.35
4.6
V
Vuv = 4.2V
77
90
103
kΩ
TA = 25°C
4.95
5
5.05
V
0 < IO < 10mA, 12 < VCC < 20
4.93
Reference
VREF
Line Regulation
12 < VCC < 20V
Load Regulation
0 < IO < 10mA
Short Circuit Current
VREF = 0V
4
30
5.07
V
15
mV
3
15
mV
50
70
mA
Output Stage
Rise & Fall Time (Note 1)
Cl = 1nF
20
45
ns
Output Low Saturation
IO = 20mA
0.25
0.4
V
IO = 200mA
1.2
2.2
V
Output High Saturation
IO = -200mA
2.0
3.0
V
UVLO Output Low Saturation
IO = 20mA
0.8
1.2
V
ISTART
VCC = 12V
0.2
0.4
mA
ICC (pre-start)
VCC = 15V, V(UV) = 0
0.5
1
mA
22
26
mA
ICC
ICC (run)
APPLICATION INFORMATION
Under Voltage Lockout
When the UV comparator is low, ICC is low (500µA) and
the output is low.
The Under Voltage Lockout block diagram is shown in
Fig 1. The VCC comparator monitors chip supply voltage.
Hysteretic thresholds are set at 13V and 10V to facilitate
off-line applications. If the VCC comparator is low, ICC is
low (T(osc) / 80k, where
T(osc) is the oscillator period. CDC also sets the soft start
time constant, so values of CDC larger than minimum may
be desired. The soft start time constant is approximately:
T(ss) = 20k • CDC.
UDG-93012-1
8
UDG-93013-1
UC1848
UC2848
UC3848
UDG-93014
UDG-93015
9
PACKAGE OPTION ADDENDUM
www.ti.com
10-Jun-2014
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
UC1848J
OBSOLETE
CDIP
J
16
TBD
Call TI
Call TI
-55 to 125
UC2848DW
LIFEBUY
SOIC
DW
16
40
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
UC2848DW
UC2848DWG4
LIFEBUY
SOIC
DW
16
40
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
UC2848DW
UC2848J
OBSOLETE
CDIP
J
16
TBD
Call TI
Call TI
-40 to 85
UC3848DW
LIFEBUY
SOIC
DW
16
40
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
0 to 70
UC3848DW
UC3848DWG4
LIFEBUY
SOIC
DW
16
40
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
0 to 70
UC3848DW
UC3848DWTR
LIFEBUY
SOIC
DW
16
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
0 to 70
UC3848DW
UC3848N
LIFEBUY
PDIP
N
16
25
Green (RoHS
& no Sb/Br)
CU NIPDAU
N / A for Pkg Type
0 to 70
UC3848N
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
10-Jun-2014
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
OTHER QUALIFIED VERSIONS OF UC1848, UC3848 :
• Catalog: UC3848
• Military: UC1848
NOTE: Qualified Version Definitions:
• Catalog - TI's standard catalog product
• Military - QML certified for Military and Defense Applications
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Jul-2012
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
UC3848DWTR
Package Package Pins
Type Drawing
SOIC
DW
16
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
2000
330.0
16.4
Pack Materials-Page 1
10.75
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
10.7
2.7
12.0
16.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Jul-2012
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
UC3848DWTR
SOIC
DW
16
2000
367.0
367.0
38.0
Pack Materials-Page 2
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