max5051auit Maxim Integrated Products, Inc., max5051auit Datasheet - Page 13

• Manufacturer Part Number: max5051auit
• Description: Max5051 Parallelable, Clamped Two-switch Power-supply Controller Ic
• Manufacturer: Maxim Integrated Products, Inc.

Figure 2. Typical Application Circuit
If the charge stored on the boost capacitor is not ade-
quately replenished then the gate-driver lockout for the
high-side MOSFET is triggered, stopping the high side
from switching. The low side continues switching, even-
tually recharging the capacitor, at which point the high
side starts switching again. To prevent this behavior,
use the boost capacitor’s cycle-by-cycle charging cir-
cuit to prevent unwanted shutdowns of the high side
(Figure 2). Connect the gate of a small high-voltage
FET (with the same voltage rating or higher as the main
FETs) to the DRVB output of the MAX5051. Connect the
drain of this FET to XFRMRH, and connect the source
to the primary ground. DRVB will briefly (300ns) turn
this FET ON every cycle after the main PWM clock ter-
minates. This allows the boost capacitor to be replen-
ished under all conditions, even when switching stops
completely. A suitable FET for this is BSS123 or equiva-
lent (100V, 170mA rated). The boost-capacitor charge
V
V
IN+
IN-
1MΩ
100kΩ
220nF
100pF
390pF
R12
C12
R13
C13
C14
24.9kΩ
1MΩ
R15
R14
______________________________________________________________________________________
0.1µF
FLTINT
GND
RCOSC
STARTUP
RCFF
CON
COMP
C11
39.2kΩ
R11
Parallelable, Clamped Two-Switch
MAX5051
15kΩ
C10
4.7µF
R9
10Ω
R10
C9
1µF
MA111CT
D4
C8
4.7µF
XFRMRH
DRVDD
2.2kΩ
PGND
DRVH
DRVB
DRVL
R8
CS
Power-Supply Controller IC
270nF
360Ω
BSS123
C6
N3
R7
C7
4.7µF
47Ω
10Ω
R6
R5
Figure 3. Boost Capacitor Charging Path During Transformer
Reset
PRECHARGE
CAPACITOR
V
USED FOR
IN
BOOST
BAT46W
D3
SI4486
28mΩ
SI4486
N1
N2
R4
I
BST
REG9
1µF
C5
D1
B2100
D2
BST
I
GD
L
M
P: 14T
: 150µH
S: 4T
T: 6T
T1
T1
I
BST
DRVH
D5
DRVL
220nF
fs = 250kHz
PS2913
C2
U2
475Ω
R3
2µH
L1
3 x 270µF
MAX8515
C4
C1
47nF
XFMRH
C3
150nF
R1
11.5kΩ
R2
2.55kΩ
I
LM
R
LOAD
3.3V
10A
L
13
M