IRS2500SPBF International Rectifier, IRS2500SPBF Datasheet - Page 13

• Manufacturer Part Number: IRS2500SPBF
• Description: PFC SMPS control IC designed to drive Boost or Flyback switching regulators providing high power factor
• Manufacturer: International Rectifier

Specifications of IRS2500SPBF

• Channels: 2
• Topology: PFC IC
• Application: SMPS/Lighting
• Io+ (ma): 500
• Io- (ma): 500
• Over Current Protection: Yes
• Vbsuv+ / Vccuv+ Min (v): 11.5
• Vbsuv+ / Vccuv+ Typ (v): 12.5
• Vbsuv+ / Vccuv+ Max (v): 13.5
• Vbsuv- / Vccuv- Min (v): 9.5
• Vbsuv- / Vccuv- Typ (v): 10.5
• Vbsuv- / Vccuv- Max (v): 11.5
• T On Typ (ns): 60
• T On Max (ns): 110
• T Off Typ (ns): 30
• T Off Max (ns): 70
• Package: 8-Lead SOIC
• Part Status: Active & Preferred

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level and the discharge time will be longer giving a
lower switching frequency.
10) includes six control pins: VBUS, COMP, ZX,
OUT, VDC and OC. The VBUS pin measures the
DC bus voltage through an external resistor voltage
divider. The COMP pin voltage determines the on-
time of MPFC and sets the feedback loop response
speed with an external RC integrator. The ZX pin
detects when the inductor current discharges to
zero each switching cycle using a secondary
winding from the PFC inductor. The OUT pin is the
low-side gate driver output for the external
MOSFET, MPFC. The VDC pin senses the line
input cycle providing phase information to control
the on time modulation described in the next
section. The OC pin senses the current flowing
through MPFC and performs cycle-by-cycle over-
current protection.
2.5V reference voltage for regulating the DC output
voltage (Figure 11).
amplifier increases or decreases the COMP pin
voltage. The resulting voltage on the COMP pin
sets the threshold for the charging of the internal
timing capacitor (C1, Figure 11) and therefore
determines the on-time of MPFC.
The error amplifier operates at a slow loop speed
preventing rapid changes in PWM duty cycle during
a single input line cycle. This prevents distortion
achieving high power factor and low THD.
The PFC control circuit of the IRS2500 (Figure
The VBUS pin is compared with a fixed internal
Figure 10:
(+)
(-)
RVBUS1
RVBUS2
RVBUS
RDC
RIN
CCOMP
IRS2500 simplified PFC control
COMP
VBUS
VDC
circuit.
Control
The feedback loop error
PFC
LPFC
COM
OUT
ZX
OC
RZX
RPFC
MPFC
ROC
DFPC
CBUS
13
takes the LPFC current to discharge to zero. The
zero current level is detected by a secondary
winding on LPFC that is connected to the ZX pin
through an external current limiting resistor RZX. A
positive-going
threshold VZX+ signals the beginning of the off-
time. A negative-going edge on the ZX pin falling
below VZX- will occur when the LPFC current
discharges to zero, which signals the end of the off-
time and MPFC is turned on again (Figure 12). The
ZX pin is internally biased to ensure that the voltage
detected from the inductor drops fully to zero before
triggering the next PWM cycle. A wide hysteresis
prevents false triggering by ringing oscillations.
The cycle repeats itself indefinitely until the
IRS2500 is disabled through an over-voltage
condition on the DC bus or if the negative transition
of ZX pin voltage does not occur. Should the
negative edge on the ZX pin not occur, MPFC will
remain off until the watch-dog timer forces a turn-on
of MPFC for an on-time duration programmed by
the voltage on the COMP pin. The watch-dog
pulses occur every 300-400us (tWD) indefinitely
until a correct positive and negative-going signal is
detected at the ZX pin and normal operation is
resumed. Should the OC pin voltage exceed the
VOCTH over-current threshold during the on-time
the gate drive output will turn off. The circuit will
then wait for a negative-going transition on the ZX
pin or a forced turn-on from the watch-dog timer to
turn the output on again.
Figure 11: IRS2500 detailed PFC control circuit.
The off-time of MPFC is determined by the time it
COMP
VBUS
VDC
ZX
1
2
3
5
5.1V
Modulator
On Time
2.5V
2.0V
edge
COMP3
M1
C1
2.75
M2
COMP5
COMP4
exceeding
R1
© 2012 International Rectifier
S
R2 Q
Q
S
R Q
RS3
RS4
Q
IRS2500S
WATCH
TIMER
DOG
the
VCC
internal
1.2V
7
4
OUT
OC