IRS2153DS International Rectifier, IRS2153DS Datasheet - Page 9

• Manufacturer Part Number: IRS2153DS
• Description: SELF-OSCILLATING HALF-BRIDEGE DRIVER IC
• Manufacturer: International Rectifier

Functional Description
Under-voltage Lock-Out Mode (UVLO)
The under-voltage lockout mode (UVLO) is defined as the state
the IC is in when VCC is below the turn-on threshold of the IC.
The IRS2153D under voltage lock-out is designed to maintain an
ultra low supply current of less than 155uA, and to guarantee the
IC is fully functional before the high and low side output drivers
are activated. During under voltage lock-out mode, the high and
low-side driver outputs HO and LO are both low.
Supply voltage
Fig. 1 shows an example of supply voltage. The start-up
capacitor (C
(R
chosen to provide sufficient current to supply the IRS2153D from
the DC bus. C
Vcc above the UVLO threshold for one half cycle of the line
voltage as it will only be charged at the peak, typically 0.1uF. It
will be necessary for RVCC to dissipate around 1W.
The use of a two diode charge pump made of DC1, DC2 and
CVS (Fig. 2) from the half bridge (VS) is also possible however
the above approach is simplest and the dissipation in R
not be unacceptably high.
The supply resistor (R
supply current is available over all operating conditions.
Once the capacitor voltage on VCC reaches the start-up
threshold VCCUV+, the IC turns on and HO and LO begin to
oscillate.
+ AC Rectified Line
- AC Rectified Line
+ AC Rectified Line
- AC Rectified Line
VCC
CVCC
CVCC
RVCC
RVCC
) minus the start-up current drawn by the IC. This resistor is
VCC
CT
RT
COM
VCC
CT
RT
COM
VCC
VCC
RT
CT
Fig. 1 Typical Connection Diagram
) is charged by current through supply resistor
RT
CT
1
2
3
4
should be large enough to hold the voltage at
1
2
3
4
Fig. 2 Charge pump circuit
VCC
) must be selected such that enough
8
7
6
5
8
7
6
5
VB
HO
VS
LO
VB
HO
VS
LO
CBOOT
CBOOT
MHS
MLS
DC2
MLS
MHS
DC1
CVS
L
VCC
L
should
RL
RL
Bootstrap MOSFET
The internal bootstrap FET and supply capacitor (C
comprise the supply voltage for the high side driver circuitry. The
internal boostrap FET only turns on when LO is high. To
guarantee that the high-side supply is charged up before the first
pulse on pin HO, the first pulse from the output drivers comes
from the LO pin.
Normal operating mode
Once the VCCUV+ threshold is passed, the MOSFET M1 opens,
RT increases to approximately VCC (VCC-VRT+) and the
external CT capacitor starts charging. Once the CT voltage
reaches VCT- (about 1/3 of VCC), established by an internal
resistor ladder, LO turns on with a delay equivalent to the
deadtime td. Once the CT voltage reaches VCT+ (approximately
2/3 of VCC), LO goes low, RT goes down to approximately
ground (VRT-), the CT capacitor discharges and the deadtime
circuit is activated. At the end of the deadtime, HO goes high.
Once the CT voltage reaches VCT-, HO goes low, RT goes high
again, the deadtime is activated. At the end of the deadtime, LO
goes high and the cycle starts over again.
The following equation provides the oscillator frequency:
Shut-down
If CT is pulled down below V CTSD (approximately 1/6 of VCC) by
an external circuit, CT doesn’t charge up and oscillation stops.
LO is held low and the bootstrap FET is off. Oscillation will
resume once CT is able to charge up again to VCT-.
f
=
2
×
ln(
) 2
×
1
RT
×
CT
=
. 1
3863
IRS2153D
×
1
RT
×
CT
BOOT
)
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