DN-27
Design Note
UC1842/UC1842A FAMILY
SUMMARY OF FUNCTIONAL DIFFERENCES
The industry standard series of UC1842/43/44/45 de-
vices has been improved for higher frequency, off-line
power supplies. This new "A" series of controllers,
UC1842A/43A/44A/45A, feature three major advantages
over their predecessors as shown in the summary be-
low.
Start Up Current
UC1842/45
Typical (T
J
= 25°C)
Maximum (T
J
= 25°C)
0.5ma
1.0ma
UC1842A/45A
0.3ma
0.5ma
Oscillator Discharge Current
At T
J
= 25°C (mA)
Overtemp. Range
UC1842/45
MIN
TYP MAX
7
10
13
6
—
14
UC1842A/45A
MIN
TYP MAX
7.8
8.3
8.8
7.5
—
8.8
Output Saturation
During UVLO
UC1842/45
1V @ 0.2ma
UC1842/45A
1V @ 10ma
The reduced start-up current is of particular concern in
offline supplies where the IC is "powered-up" from the
high voltage DC rail, then bootstrapped to an auxiliary
winding on the main transformer. Power is then dissi-
pated in the start-up resistor which is sized by the IC’s
start-up current. Lowering this by 50% in the "A" version
family will reduce the resistors power loss by the same
percentage.
Precision operation at high frequencies with an accurate
maximum duty cycle can now be obtained with the "A"
family of devices due to its trimmed oscillator discharge
current. This nullifies the effects of production variations
in the initial discharge current or deadtime.
Another significant improvement has been made in the
output section, specifically to the lower totem-pole tran-
sistor’s operation during undervoltage lockout. The "A"
series of devices prevent the power MOSFETs from
parasitically turning-on at powerup due to the "Miller" ef-
fect. This new technique allows the IC to sink higher cur-
rents at lower saturation voltages than it’s predecessors.
UNITRODE CORPORATION
7 CONTINENTAL BLVD.
•
MERRIMACK, NH 03054
TEL. (603) 424-2410
•
FAX (603) 424-3460
IMPORTANT NOTICE
Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
to verify, before placing orders, that information being relied on is current and complete. All products are sold
subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those
pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent
TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily
performed, except those mandated by government requirements.
CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF
DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL
APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR
WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER
CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO
BE FULLY AT THE CUSTOMER’S RISK.
In order to minimize risks associated with the customer’s applications, adequate design and operating
safeguards must be provided by the customer to minimize inherent or procedural hazards.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
semiconductor products or services might be or are used. TI’s publication of information regarding any third
party’s products or services does not constitute TI’s approval, warranty or endorsement thereof.
Copyright
©
1999, Texas Instruments Incorporated
stm32/stm8
京公网安备 11010802033920号
EEWORLD
