MIC2341R-2YTQ Micrel Inc, MIC2341R-2YTQ Datasheet - Page 19

• Manufacturer Part Number: MIC2341R-2YTQ
• Description: Dual -Slot PCI Express Hot-Plug Controller
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2341R-2YTQ

• Applications: General Purpose, PCI Express
• Internal Switch(s): No
• Current Limit: Adjustable
• Voltage - Supply: 3.3V, 12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 48-TQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-2987

For the same p-channel power MOSFET in the previous
example, if C
100µF, the 12VOUT[A/B] inrush current charging this
load capacitance is:
Calculating the 12VOUT[A/B] voltage rate-of-change for
a given capacitive load can be determined by the
following expression:
and, using the same quantities in the current example, is
given by:
To determine (to first-order) the time point at which the
12VOUT[A/B] voltage crosses its corresponding output
“Power Good” threshold, the following equation can be
used:
To determine 3VGATE[A/B] pin voltage slew rates,
inrush currents, 3VOUT[A/B] output voltage slew rates,
and time to assert its corresponding internal “Power
Good”
3VOUT[A/B], simple computations can be made using
the same equations by substituting I
I
channel power MOSFET) for C
C
and V
For example, if a Si4420BDY n-channel power MOSFET
is used with the MIC2341 to control inrush currents at
3VOUT[A/B], its C
3V. The 3VGATE[A/B] pin voltage rate of change is
given by:
Assuming a 300-µF capacitive load, the 3VOUT[A/B]
inrush current charging this load capacitance is given by:
The 3VOUT[A/B] output voltage slew rate is given by:
and the time to assert the internal 3VOUT[A/B] “Power
Good” flag is given by:
I
=
GATE(12VSINK)
INRUSH(12V
Micrel, Inc.
October 2007
t
LOAD(12VOUT[A/B])
I
PWRGD(12VO
GATE(12VSN
UVTH(3V)
dV
I
INRUSH(3VO
flag
OUT[A/B])
I
3VGATE[A/B
INRUSH(12V
K)
, C
UT[A/B])
dt
dV
for V
×
dV
ISSN
C
into
ISSP
12VOUT[A/B
12VOUT[A/B
, I
dV
LOAD(12VOU
=
UVTH(12V)
3VOUT[A/B]
dt
=
]
dt
ISSN
dV
INRUSH(3VOUT[A/B])
OUT[A/B])
(the input gate capacitance of an N-
=
UT[A/B])
(
dt
C
= 1700pF and C
V
12VGATE[A/
I
capacitive
GATE(3VCHA
ISSP
UVTH(12V)
is approximately 4100pF at V
dV
dt
]
]
C
=
T[A/B])
12VOUT[A/B
.
=
=
ISSN
=
I
=
INRUSH(12V
C
25µA
100
1.47
300
dt
1.82
25 µ 5
LOAD(12VOU
B]
+
RGE)
×
V
µ
µ
A
×
A
HYSPG
C
F
F
ISSP
×
1700pF
loads
LOAD(12VOU
]
100µF
≈
=
4100pF
=
300 µ 0
for I
6.1
OUT[A/B])
14.7
4100pF
, C
25µ5
)
T[A/B])
ms
=
V
GATE(3VCHARGE)
LOAD(12VOUT[A/B])
LOAD(3VOUT[A/B])
=
14.7
INRUSH(12VOUT[A/B])
ms
10.53V
V
=
connected
1.47A
T[A/B])
=
1.82
ms
6.1
V
ms
A
V
≈
0.72ms
DS
for
for
to
=
=
,
19
Mode 2: Charging 12VOUT and 3VOUT Capacitive
Loads in Current Limit
In x4 and x8 PCI Express applications, capacitive loads
at 12VOUT[A/B] and 3VOUT[A/B] can be as large as
1000µF. As a result, the inrush load charging currents at
start-up can be large enough to cause a voltage drop
across the external sense resistor larger than 50mV. In
these
12VGATE[A/B] and 3VGATE[A/B] modulate the drive to
the gates of their corresponding power MOSFETs to
regulate the load current to:
In the typical application circuit, the external sense
resistor
12VSENSE[A/B] pins was selected to be 20mΩ. The
regulated current charging the load capacitance at
12VOUT[A/B] is given by:
Once current-regulation control is activated, the circuit
breaker’s t
external power MOSFET against potentially excessive
power dissipation. For additional information on this
timer and the MIC2341’s circuit breaker operation,
please consult the section labeled “Circuit Breaker
Function.” The output voltage rate of change at
12VOUT[A/B] during current limit charging into a 1000µF
capacitive load is given by:
In this fashion, the inrush current is controlled and the
load capacitance is charged up slowly during the start-up
cycle. The gate drive circuits will maintain control of the
inrush current until the 12VOUT[A/B] or 3VOUT[A/B]
voltages have reached their corresponding “Power
Good”
respectively)
approaches its nominal steady-state level, the voltage
across the external sense resistor drops below the circuit
breaker’s V
internal “Power-is-Good” flag is asserted. For the
12VOUT[A/B] example, its internal “Power-is-Good” flag
is asserted at:
Calculating the current limit for charging the 3VOUT[A/B]
load capacitance, the output voltage slew rate at
3VOUT[A/B], and when the internal 3VOUT[A/B] “Power
I
LIMIT(12VO
t
t
PWRGD(12VO
PWRGD(3VOU
I
dV
LIMIT(12VO
12VOUT[A/B
applications,
UT[A/B])
thresholds
dt
connected
FLT
THLIMIT
UT[A/B])
T[A/B])
UT[A/B])
at
timer is also activated to protect the
=
]
50
20
=
=
=
C
which
I
m
threshold, and the corresponding
(
mV
LIMIT(12VO
LOAD(12VOU
(
V
V
=
UVTH(3V)
Ω
UVTH(12V)
R
(V
dV
12VSENSE[A
=
dV
internal
UVTH(12V)[A/B]
V
between
2.5
3VOUT[A/B]
12VOUT[A/B
THLIMIT
UT[A/B])
dt
time
dt
A
+
T[A/B])
+
V
V
HYSPG
HYSPG
/B]
]
=
the
servo
=
1000
)
R
2.5
12VIN[A/B]
)
=
12VSENSE[A
MIC2341/2341R
=
or
M9999-102507-A
6.1
2.77V
A
µ
inrush
10.53V
50
2.5
[phone]
F
ms
mV
=
V
ms
circuits
V
V
2.5
UVTH(3V)[A/B]
≈
≈
0.45
/B]
ms
V
4.2
current
ms
ms
and
at
,