ir3088a International Rectifier Corp., ir3088a Datasheet - Page 14

• Manufacturer Part Number: ir3088a
• Description: Xphase Ic With Fault And Overtemp Detect
• Manufacturer: International Rectifier Corp.

DESIGN PROCEDURES - IR3081A AND IR3088A CHIPSET
IR3081A EXTERNAL COMPONENTS
Oscillator Resistor Rosc
The oscillator of IR3081A generates a triangle waveform to synchronize the phase ICs, and the switching frequency
of the each phase converter equals the oscillator frequency, which is set by the external resistor R
the curve in Figure 13 of IR3081A Data Sheet.
Soft Start Capacitor C
Because the capacitor C
over-current latch delay time, and power good delay time, they should be considered together while choosing
C
The SS/DEL pin voltage controls the slew rate of the converter output voltage, as shown in Figure 10 of IR3081A
data sheet. After the ENABLE pin voltage rises above 0.6V, there is a soft-start delay time
error amplifier output is released to allow the soft start. The soft start time
converter voltage rises from zero to V
Equation (1).
Once C
delay time
and (4) respectively.
VDAC Slew Rate Programming Capacitor C
The slew rate of VDAC down-slope SR
Equation(5), where I
R
SR
of VDAC pin as shown in Figure15 of IR3081A Data Sheet.
SS/DEL
VDAC
UP
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is proportional to that of VDAC down-slope and is given by Equation (7), where I
is used to compensate VDAC circuit and is determined by Equation (6). The slew rate of VDAC up-slope
SS/DEL
.
t
VccPG
is chosen, the soft start delay time
from output voltage (V
C
t
t
t
SINK
C
R
SR
VccPG
SSDEL
OCDEL
VDAC
VDAC
SS
UP
SS/DEL
/
DEL
is the sink current of VDAC pin as shown in Figure 15 of IR3081A Data Sheet. The resistor
SS/DEL
=
=
=
=
=
=
I
C
C
0
C
=
SR
C
SOURCE
SS
5 .
SS
VDAC
I
SS
I
SINK
I
DOWN
CHG
/
+
/
I
/
OCDISCHG
DEL
DEL
programs four different time parameters, i.e. soft start delay time, soft start time,
CHG
DEL
3
V
2 .
C
O
*
*
1 *
VDAC
*
∗
t
3 (
SS
. 0
10
3 .
O.
8 .
115
DOWN
I
−
=
=
2
t
−
O
CHG
15
SS
) in regulation to Power Good are fixed and shown in Equations (2), (3)
70
C
. 0
=
SS
065
70
can be programmed by an external capacitor, which is determined by
*
C
/
VDAC
10
DEL
*
can be programmed by the external capacitor C
SS
V
−
10
40
−
O
/
V
6
DEL
1 *
−
O
*
6
*
t
and Resistor R
−
10
SSDEL,
3 .
t
*
SS
. 1
. 0
−
) 3
6
115
=
the over-current fault latch delay time
C
SS
/
DEL
( *
VDAC
70
. 3
*
735
10
−
−
6
V
t
O
SS
−
. 1
represents the time during which
) 3
SOURCE
t
(1)
(2)
(3)
(4)
(5)
(6)
(7)
SSDEL,
IR3088A
is the source current
VDAC
1/15
OSC
t
OCDEL
after which the
as defined in
/05
according to
, and the