IR21592/IR21593
(
S
)
&
(
PbF
)
www.irf.com 15
-90.0
-85.0
-80.0
-75.0
-70.0
-65.0
-60.0
0 5 10 15 20 25 30
Lamp Power [Watts]
Phase [degrees]
Figure 4, Lamp power vs. phase of output stage.
Under-voltage Lock-Out (UVLO)
The IR21592/IR21593 undervoltage lock-out is
designed to maintain an ultra low quiescent
current of less than 200uA, while guaranteeing
the IC is fully functional before the high and low
side output drivers are activated. Figure 5 shows
an efficient supply voltage using the start-up
current of the IR21592/IR21593 together with a
charge pump from the ballast output stage (R1,
C1, C2, D1 and D2).
16
15
14
13
12
11
LO
COM
VCC
VB
VS
HO
Rectified
AC Line
Half-Bridge
Output
C1
R1
D1
D2
Q2
Q1
RVDC
C2
V
BUS
(+)
D3
C3
RCS
V
BUS
(-)
1
VDC
R3
CVDC
DISCHARGE
TIME
INTERNAL
CLAMP VOLTAGE
VHYST
V
UVLO+
V
UVLO-
CHARGE PUMP
OUTPUT
t
V
C1
R1 & C1 TIME
CONSTANT
C1
DISCHARGE
Figure 6, Start-up capacitor (C1) voltage.
During the discharge cycle, the rectified current
from the charge pump charges the capacitor above
the minimum operating voltage of the device and
the charge pump and 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 worst case IC conditions are
satisfied. A bootstrap diode (D3) and supply
capacitor (C3) 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 UVLO,
the high and low side driver outputs are low, pin
VCO is pulled-up internally to 5V resetting the
starting frequency to the maximum, and pin CPH
is short-circuited internally to COM resetting the
preheat time.
Figure 5, Typical application of start-up circuitry.
The start-up capacitor (C1) is charged by current
through resistor (R1) minus the start-up current
drawn by the IC. This resistor is typically chosen
to provide 2X the maximum start-up current at
low line to guarantee start-up under the worst case
condition. Once the capacitor voltage reaches the
start-up threshold, and, the voltage on pin VDC is
above 5.1V (see Brown-out Protection), 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 6).
