application
INFO
available
UCC1809-1/-2
UCC2809-1/-2
UCC3809-1/-2
Economy Primary Side Controller
FEATURES
•
User Programmable Soft Start With
Active Low Shutdown
•
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
DESCRIPTION
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.
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
NUMBER THRESHOLD THRESHOLD
UCCX809-1
10V
8V
UCCX809-2
15V
8V
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.
TYPICAL APPLICATION DIAGRAM
R
START
V
IN
FB
1V
1
1V
NOISE
FILTER
FEEDBACK
REF
+5V
SS
5V
REF
8
C
REF
V
OUT
6µA
2
CURRENT
SENSE
SLOPE
COMP
0.5V
C
SS
DISABLE
UVLO
VDD
7
15/8V
10/8V
17.5V
C
VDD
RT1
3
OSC
4
C
T
PWM
LATCH
CLK
R
Q
S
6
OUT
RT2
GND
5
V
REF
UDG-99036
SLUS166A - NOVEMBER 1999
ETC [ ETC ]
