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Document Number: 72660

S11-0598-Rev. E, 25-Apr-11

Vishay Siliconix

SiP2800, SiP2801, SiP2802, SiP2803, SiP2804, SiP2805

This datasheet is subject to change without notice.

PIN CONFIGURATION

Additional voltage options are available.

DETAILED PIN DESCRIPTION

COMP

COMP is the output of the Voltage Error Amplifier (VEA). The

VEA is a low output impedance operational amplifier,

providing the input to the PWM cycle-by-cycle current limit

comparator. As the SiP280X series of parts use a true

operational amplifier for the VEA, the COMP terminal can

both source and sink current. To add flexibility to these parts,

the VEA is internally current limited, which allows OUT to be

forced to zero duty cycle by taking the COMP pin to GND.

The voltage on COMP is passed through an internal diode to

develop an offset voltage of approximately 0.6 V, and then

through a resistive divider with a gain of 0.606 V/V, before

being presented to the control input of the cycle-by-cycle

current limit comparator. Clamping the COMP pin to less

than the diode’s forward voltage (i.e., < 0.5 V) will command

the current loop to deliver 0 A, by holding the control input of

the cycle-by-cycle current comparator at 0 V. Similarly, the

current loop will command the maximum inductor current on

each cycle when COMP is at 2.25 V or greater, which drives

the control input of the cycle-by-cycle current comparator to

1 V (since [2.25 V - 0.6 V] x 0.606 V/V = 1 V).

The SiP280X series additionally features a built-in soft-start

function, which functions by clamping the output level of the

VEA to an internally generated voltage. This clamp will hold

at their proper levels. When these levels are appropriate for

circuit operation, the internal voltage will begin rising, at the

rate of 1 V/ms. This rising clamp level allows the voltage on

the COMP pin to rise, which in turn allows the voltage at the

control input of the cycle-by-cycle current comparator to

increase. The maximum soft-start interval occurs under

conditions requiring full duty cycle (50 % or 100 %,

depending upon the part type), and is given by the time

required for the voltage on the cycle-by-cycle current

comparator’s control input to reach 1 V. Since 1 V at the

control input to the comparator requires that the COMP pin

be

at

2.25

V,

the

maximum

soft-start

interval

is

approximately 2.25 ms.

CS

Input to both the cycle-by-cycle and overcurrent fault current

sense

comparators.

The

cycle-by-cycle

current

limit

comparator is the mechanism by which the VEA’s output

voltage commands the level of inductor or transformer

current during a given "on" interval, thereby regulating the

overall circuit’s output.This comparator forms the inner loop

of the two loops used in current-mode regulation.

The overcurrent comparator has a trip threshold that is 50 %

higher than that of the cycle-by-cycle comparator. Under

normal operating conditions, this comparator will not trip: its

purpose is to provide enhanced protection of the power path

components during severe faults (e.g., a short circuit). If the

overcurrent comparator is tripped by a fault condition, it will

command the SiP280X to do a "full-cycle restart". During this

restart, the power supply will be quickly driven to the "off"

state, and will be required to wait for five milliseconds

(typical) before restarting. When the supply does restart, it

will do so using the built-in soft-start function of the SiP280X.

5

COMP

REF

FB

CS

OUT

RC

GND

SOIC-8

6

7

8

2

3

4

1

To p View

ORDERING INFORMATION

SOIC-8

Part Number

Lead (Pb)-free

Part Number

Marking

Temperature

SiP2800DY-T1

SiP2800DY-T1-E3

2800

- 40 °C to 85 °C

SiP2801DY-T1

SiP2801DY-T1-E3

2801

SiP2802DY-T1

SiP2802DY-T1-E3

2802

SiP2803DY-T1

SiP2803DY-T1-E3

2803

SiP2804DY-T1

SiP2804DY-T1-E3

2804

SiP2805DY-T1

SiP2805DY-T1-E3

2805

PIN DESCRIPTION

Pin Number

Name

Function

1

COMP

Output of the Voltage Error Amplifier, and the inverting input to the PWM’s Current Sense Comparator

2

FB

Inverting input of the Voltage Error Amplifier

3CS

Non-inverting input of the PWM Current Sense Comparator, and inverting input of the Overcurrent Fault

Comparator (both comparators are fed from the output of the internal 100 ns Leading Edge Blanking circuit)

4

RC

Connection for the PWM Oscillator’s timing resistor and timing capacitor

5

GND

Ground Pin

6

OUT

PWM Output Signal (capable of driving ± 750 mA into the gate of an external MOSFET power switch)

7

Positive supply voltage for the IC

8

REF

IC Reference Voltage