application
INFO
UCC1809-1/-2
UCC2809-1/-2
UCC3809-1/-2
available
Economy Primary Side Controller
FEATURES
DESCRIPTION
• User Programmable Soft Start With
Active Low Shutdown
The UCC3809 family of BCDMOS economy low power integrated circuits
contains all the control and drive circuitry required for off-line and isolated
DC-to-DC fixed frequency current mode switching power supplies with
minimal external parts count. Internally implemented circuits include
undervoltage lockout featuring startup current less than 100µA, a user ac-
cessible voltage reference, logic to ensure latched operation, a PWM com-
parator, and a totem pole output stage to sink or source peak current. The
output stage, suitable for driving N-Channel MOSFETs, is low in the off
state.
• User Programmable Maximum Duty
Cycle
• Accessible 5V Reference
• Undervoltage Lockout
• Operation to 1MHz
• 0.4A Source/0.8A Sink FET Driver
• Low 100µA Startup Current
Oscillator frequency and maximum duty cycle are programmed with two
resistors and a capacitor. The UCC3809 family also features full cycle soft
start.
The family has UVLO thresholds and hysteresis levels for off-line and
DC-to-DC systems as shown in the table to the left.
PART
TURN ON
TURN OFF
The UCC3809 and the UCC2809 are offered in the 8 pin SOIC (D), PDIP
(N), TSSOP (PW), and MSOP (P) packages. The small TSSOP and
MSOP packages make the device ideal for applications where board
space and height are at a premium.
NUMBER THRESHOLD THRESHOLD
UCCX809-1
UCCX809-2
10V
15V
8V
8V
TYPICAL APPLICATION DIAGRAM
R
START
V
IN
FB
1
1V
–
+
1V
REF
NOISE
FILTER
+5V
+
–
5V
REF
8
FEEDBACK
C
6µA
SS
REF
2
–
+
V
SLOPE
COMP
OUT
CURRENT
SENSE
0.5V
VDD
C
SS
7
–
+
15/8V
10/8V
DISABLE
UVLO
17.5V
C
VDD
RT1
RT2
PWM
LATCH
3
4
OUT
GND
R
Q
S
CLK
OSC
6
5
–
+
V
REF
C
T
UDG-99036
SLUS166B - NOVEMBER 1999 - REVISED NOVEMBER 2004