Rainbow Electronics MAX5929 User Manual
Page 20
MAX5927/MAX5929
With a 22nF gate capacitor, the inrush current, charge,
and discharge times are:
Case B: Fast Turn-On (With Current Limit)
In applications where the board capacitance (C
BOARD
)
is high, the inrush current causes a voltage drop across
R
SENSE
that exceeds the startup fast-comparator
threshold. The fast comparator regulates the voltage
across the sense resistor to V
FC,TH
. This effectively reg-
ulates the inrush current during startup. In this case,
the current charging C
BOARD
can be considered con-
stant and the turn-on time is:
t
C
V
R
V
ON
BOARD
IN
SENSE
FC TH
=
Ч
Ч
,
I
F
pF
nF
A
mA
t
nF
V
nC
A
ms
t
nF
V
nC
mA
ms
t
nF
V
nC
mA
s
INRUSH
CHARGE
DISCHARGE
DISCHARGE STRONG
=
µ
+
Ч
+
=
=
Ч
+
µ
=
=
Ч
+
=
=
Ч
+
=
6
600
22
100
0
26 5
22
10 4
60
100
2 89
22
10 4
60
3
0 096
22
10 4
60
50
5 8
.
.
.
.
.
.
.
(
)
µ
µ
Low-Voltage, Quad, Hot-Swap
Controllers/Power Sequencers
20
______________________________________________________________________________________
INY
GATEY
INZ
GATEZ
Q1
R
SENSEY
SENSEY
R
SENSEZ
SENSEZ
Q2
C
BOARDZ
OUTY
C
BOARDY
OUTZ
V
Y
C
1
R
1
V
EN
V
Z
ON
OFF
GND
MAX5927
MAX5929
ON
GND
V
ONY, TH
V
ONZ, TH
t
DELAY
V
EN
t
1
= -R
1
C
1
ln
( )
V
EN
- V
ONY, TH
V
EN
V
ON
V
Y
V
Z
t
0
t
1
t
2
t
2
= -R
1
C
1
ln
( )
V
EN
- V
ONZ, TH
V
EN
t
DELAY
= -R
1
C
1
ln
( )
V
EN
- V
ONY, TH
V
EN
- V
ONZ, TH
Figure 11. Power Sequencing: Channel Z Turns On t
DELAY
After Channel Y