UCC28220, UCC28221

SLUS544A − SEPTEMBER 2003 − REVISED AUGUST 2004

7

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Terminal Functions

TERMINAL

PIN NUMBER

FUNCTION

UCC28220D

UCC28220PW

UCC28221D

UCC28221PW

NAME

I/O

FUNCTION

1

1

2

LINEOV

I

Input for line over voltage comparator

2

2

3

LINEHYS

I

Sets line comparator hysteresis

3

3

4

VDD

I

Device supply input

4

4

5

CS1

I

Channel 1 current sense input

5

5

6

SLOPE

I

Sets slope compensation

6

6

7

CS2

I

Channel 2 current sense input

7

7

8

SS

I

Soft-start input

8

8

9

CTRL

I

Feedback control input

9

9

12

DISCHG

I

Sets oscillator discharge current

10

10

13

CHG

I

Sets oscillator charge current

11

11

14

GND

−

Device ground

12

12

15

OUT2

O

PWM output from channel 2

13

13

16

OUT1

O

PWM output from channel 1

14

14

17

REF

O

Reference voltage output

15

15

18

LINEUV

I

Input for line under voltage comparator

−

16

20

VIN

I

High voltage start-up input

16

−

1, 10, 11, 19

N/C

−

No connection

PIN DESCRIPTIONS

VDD: This is used to supply power to the device, monitoring this pin is a the UVLO circuit. This is used to insure

glitch-free startup operation. Until VDD reaches its UVLO threshold, it remains in a low power mode, drawing

approximately 150

µA of current and forcing pins, SS, CS1, CS2, OUT1, and OUT2 to logic 0 states. If the VDD

falls below 8 V after reaching turn-on, it will go back into this low power state. In the case of the UCC28221, the

UVLO threshold is 13 V. It is 10 V for the UCC28220. Both versions have a turn-off threshold of 8 V.

VIN (UCC28221 only): This pin has an internal high voltage JFET used for startup. The drain is connected to

VIN, while its’ source is connected to VDD. During startup, this JFET delivers 12 mA typically with a minimum

of 4 mA to VDD, which in turn, charges up the VDD bypass capacitor. When VDD gets to 13 V, the JFET is turned

off.

CS1 and CS2: These 2 pins are the current sense inputs to the device. The signals are internally level shifted

by 0.5 V before the signal gets to the PWM comparator. Internally the slope compensation ramp is added to this

signal. The linear operating range on this input is 0 to 1.5 V. Also, this pin gets pulled to ground each time its

respective output goes low. (ie: OUT1 and OUT2).

SLOPE: This pin sets up a current used for the slope compensation ramp. A resistor to ground sets up a current,

which is internally divided by 25 and then applied to an internal 10-pF capacitor. Under normal operation th dc

voltage on this pin is 2.5 V..

SS: A capacitor to ground sets up the soft-start time for the open loop soft-start function. The source and sink

current from this pin is equal to 3/7th of the oscillator charge current set by the resistor on the CHG pin. The

soft start capacitor is held low during UVLO and during a Line OV or UV condition. Once an OV or UV fault

occurs, the soft-start capacitor is discharged by a current equal to its charging current. The capacitor does NOT

quickly discharge during faults. In this way, the controller has the ability to recover quickly from very short line

transients. This pin can also be used as an Enable/Disable function.