UC3845BVDG Datasheet, PDF (1/19 Pages) ON Semiconductor – High Performance Current Mode Controllers

UC3844B, UC3845B,
UC2844B, UC2845B
High Performance
Current Mode Controllers
The UC3844B, UC3845B series are high performance fixed frequency
current mode controllers. They are specifically designed for Off−Line
and dc−dc converter applications offering the designer a cost−effective
solution with minimal external components. These integrated circuits
feature an oscillator, a temperature compensated reference, high gain
error amplifier, current sensing comparator, and a high current totem pole
output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle−by−cycle
current limiting, a latch for single pulse metering, and a flip−flop
which blanks the output off every other oscillator cycle, allowing
output deadtimes to be programmed from 50% to 70%.
These devices are available in an 8−pin dual−in−line and surface
mount (SOIC−8) plastic package as well as the 14−pin plastic surface
mount (SOIC−14). The SOIC−14 package has separate power and
ground pins for the totem pole output stage.
The UCX844B has UVLO thresholds of 16V (on) and 10V (off), ideally
suited for off−line converters. The UCX845B is tailored for lower voltage
applications having UVLO thresholds of 8.5V (on) and 7.6V (off).
Features
• Trimmed Oscillator for Precise Frequency Control
• Oscillator Frequency Guaranteed at 250 kHz
• Current Mode Operation to 500 kHz Output Switching Frequency
• Output Deadtime Adjustable from 50% to 70%
• Automatic Feed Forward Compensation
• Latching PWM for Cycle−By−Cycle Current Limiting
• Internally Trimmed Reference with Undervoltage Lockout
• High Current Totem Pole Output
• Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
• These Devices are Pb−Free and are RoHS Compliant
• NCV Prefix for Automotive and Other Applications Requiring
Unique Site and Control Change Requirements; AEC−Q100
Qualified and PPAP Capable
V_CC 7(12)
V_ref
8(14)
R_T/C_T
4(7)
Voltage
Feedback
Input
2(3)
Output/
Compensation
1(1)
5.0V
Reference
R
V_ref
R
Undervoltage
Lockout
Oscillator
Latching
PWM
Error
Amplifier
V_CC
Undervoltage
Lockout
GND 5(9)
Pin numbers in parenthesis are for the D suffix SOIC-14 package.
Figure 1. Simplified Block Diagram
V_C
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense Input
3(5)
© Semiconductor Components Industries, LLC, 2013
1
August, 2013 − Rev. 11
http://onsemi.com
8
1
14
1
8
1
PDIP−8
N SUFFIX
CASE 626
SOIC−14
D SUFFIX
CASE 751A
SOIC−8
D1 SUFFIX
CASE 751
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
8 V_ref
7 V_CC
Current Sense ³
6 _Output
R_T/C_T 4
5 GN
D
(Top View)
Compensation 1
NC 2
Voltage Feedback 3
NC ⁴
Current Sense ⁵
NC 6
R_T/C_T 7
14 V_ref
13 NC
12 V_CC
11 _VC
10 _Output
9 GND
8 Power Ground
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 15 of this data sheet.
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 16 of this data sheet.
Publication Order Number:
UC3844B/D