IR2166
I. Ballast Section
VC1
Functional Description
CVCC
DISCHARGE
INTERNAL VCC
ZENER CLAMP VOLTAGE
Under-voltage Lock-Out Mode (UVLO)
VUVLO+
VHYST
The under-voltage lock-out mode (UVLO) is
defined as the state the IC is in when VCC is
below the turn-on threshold of the IC. To identify
the different modes of the IC, refer to the State
Diagram shown on page 7 of this document. The
IR2166 undervoltage lock-out is designed to
maintain an ultra low supply current of less than
400uA, and to guarantee the IC is fully functional
before the high and low side output drivers are
activated. Figure 1 shows an efficient supply
voltage using the start-up current of the IR2166
together with a charge pump from the ballast
output stage (RSUPPLY, CVCC, DCP1 and DCP2).
VUVLO-
DISCHARGE
TIME
CHARGE PUMP
OUTPUT
RSUPPLY & CVCC
TIME
CONSTANT
t
Figure 2, Supply capacitor (C
) voltage.
VCC
During the discharge cycle, the rectified current
from the charge pump charges the capacitor above
the IC turnoff threshold. The charge pump and
the internal 15.6V zener clamp of the IC take over
as the supply voltage. The start-up capacitor and
snubber capacitor must be selected such that
enough supply current is available over all ballast
operating conditions. A bootstrap diode (DBOOT)
and supply capacitor (CBOOT) comprise the
supply voltage for the high side driver circuitry.
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.
During under-voltage lockout mode, the high-
and low-side driver outputs HO and LO are both
low, pin CT is connected internally to COM to
disable the oscillator, and pin CPH is connected
internally to COM for resetting the preheat time.
VBUS(+)
R SUPPLY
D BOOT
HO
M1
16
Half-Bridge
Output
VS
15
14
13
12
VB
C BOOT
CVCC
VCC
CSNUB
IR2166
COM
LO
11
M2
D CP1
RCS
D CP2
VBUS(-)
Figure 1, Start-up and supply circuitry.
The start-up capacitor (CVCC) is charged by
current through supply resistor (RSUPPLY)
minus the start-up current drawn by the IC. This
resistor is chosen to set the line input voltage
turn-on threshold for the ballast . Once the
capacitor voltage on VCC reaches the start-up
threshold, and the SD pin is below 5.0 volts, the
IC turns on and HO and LO begin to oscillate.
The capacitor begins to discharge due to the
increase in IC operating current (Figure 2).
Preheat Mode (PH)
The preheat mode is defined as the state the IC
is in when the lamp filaments are being heated to
their correct emission temperature. This is
necessary for maximizing lamp life and reducing
the required ignition voltage. The IR2166 enters
preheat mode when VCC exceeds the UVLO
positive-going threshold. HO and LO begin to
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