IR2157_07 IRF [International Rectifier], IR2157_07 Datasheet - Page 16

• Manufacturer Part Number: IR2157_07
• Description: FULLY INTEGRATED BALLAST CONTROL IC
• Manufacturer: IRF [International Rectifier]

IR2157
Figure 18: Auto restart for lamp replacement
Figure 17: Operation below resonance
ADVANCED INFORMATION
16
Recovery from such a fault condition is accomplished
by cycling either SD pin or the VCC pin. When a
lamp is removed, the SD pin goes high, the fault
latch is reset, and the chip is held off in an unlatched
state. Lamp replacement causes the SD pin to go
low again, reinitiating the startup sequence. The
fault latch can also be reset by the undervoltage
lockout signal, if VCC falls below the lower
undervoltage threshold.
Bootstrap Supply Considerations
Power is normally supplied to the high-side circuitry
by means of a simple charge pump from VCC, as
shown in Figure 19 below.
A high voltage, fast recovery diode DBOOT (the so-
called bootstrap diode) is connected between VCC
(anode) and VB (cathode), and a capacitor CBOOT
(the so-called bootstrap capacitor) is connected
between the VB and VS pins. During half-bridge
switching, when MOSFET Q2 is on and Q1 is off, the
bootstrap capacitor CBOOT is charged from the VCC
decoupling capacitor, through the bootstrap diode
DBOOT, and through Q2. Alternately, when Q2 is off
and Q1 is on, the bootstrap diode is reverse-biased,
V D C
C P H
R P H
R U N
RT
C T
D T
S D
1
2
3
4
5
6
7
8
with VCC charge pump from half-bridge output
Figure 19: Typical bootstrap supply connection
1 6
1 5
1 4
1 3
1 2
1 1
1 0
9
C O M
N/C
V C C
H O
V S
V B
L O
C S
(shaded area)
C
R
D
B O O T
G H S
B O O T
rectified
AC line
R
G L S
R
C
S U P P L Y
R 3
V C C
D 1
V
B U S
+V
B U S
return
Q 1
Q 2
R
C S
R
C
D 2
S N U B B E R
S N U B B E R
1
/
2
Bridge output