www.vishay.com
6
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.
THE PRODUCT DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
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
COMP at a low voltage (V
COMP
0 V) until V
CC
and V
REF
are
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 V
CC
CS OUT
RC GND
SOIC-8
6
7
8
2
3
4
1
To p V i e w
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
V
CC
Positive supply voltage for the IC
8 REF IC Reference Voltage
