MIC2583 Micrel Semiconductor, MIC2583 Datasheet - Page 15

• Manufacturer Part Number: MIC2583
• Description: Single Channel Hot Swap Controllers
• Manufacturer: Micrel Semiconductor

Applications Information
Output Undervoltage Detection
For output undervoltage detection, the first consideration is to
establish the output voltage level that indicates “power is
good.” For this example, the output value for which a 12V
supply will signal “good” is 11V. Next, consider the tolerances
of the input supply and FB threshold (V
the 12V supply varies 5%, thus the resulting output voltage
may be as low as 11.4V and as high as 12.6V. Additionally,
the FB threshold has 50mV tolerance and may be as low as
1.19V and as high as 1.29V. Thus, to determine the values of
the resistive divider network (R5 and R6) at the FB pin, shown
in the typical application circuit on page 1, use the following
iterative design procedure.
Using some basic algebra and simplifying Equation 9 to
isolate R5, yields:
April 2003
MIC2582/MIC2583
/ON_OFF
/FAULT
1) Choose R6 so as to limit the current through the
2) Next, determine R5 using the output “good”
GND
R6 is chosen as 12.4k
R6
V
divider to approximately 100 A or less.
voltage of 11V and the following equation:
V
5V
OUT(Good)
IN
V
100 A
Backplane
Connector
FB(MAX)
V
FB
PCB Edge
Connector
100 A
1.29V
R5 R6
Medium or
Short
Short Pin
20k
Long
Pin
Pin
R6
R5
Long
12.9k
Figure 6. PCB Connection Sense with ON/OFF Control
Pin
1%.
33k
100
PCB Connection Sense
20k
R1
R3
FB
R4
.
). For this example,
Undervoltage (Output) = 4.45V
/POR Delay = 25ms
START-UP Delay = 6ms
*Q2 is TN0201T (SOT-23)
**R8 is optional for noise filtering
Additional pins omitted for clarity.
*Q2
33k
R2
C1
1 F
(9)
0.05 F
11
3
C3
ON
/FAULT
CPOR
VCC
3
16
1
4
0.010
15
R
SENSE
5%
where V
12.4k . Substituting these values into Equation 9.1 now
yields R5 = 93.33k . A standard 93.1k
Now, consider the 11.4V minimum output voltage, the lower
tolerance for R6 and higher tolerance for R5, 12.28k
94.03k , respectively. With only 11.4V available, the voltage
sensed at the FB pin exceeds V
PWRGD (MIC2583/83R) signals will transition from LOW to
HIGH, indicating “power is good” given the worse case
tolerances of this example.
PCB Connection Sense
There are several configuration options for the MIC2582/83’s
ON pin to detect if the PCB has been fully seated in the
backplane before initiating a start-up cycle. In the typical
applications circuit, the MIC2582/83 is mounted on the PCB
with a resistive divider network connected to the ON pin. R2
is connected to a short pin on the PCB edge connector. Until
the connectors mate, the ON pin is held low which keeps the
GATE output charge pump off. Once the connectors mate,
the resistor network is pulled up to the input supply, 12V in this
example, and the ON pin voltage exceeds its threshold (V
of 1.24V and the MIC2582/83 initiates a start-up cycle. In
Figure 6, the connection sense consisting of a discrete
logic-level MOSFET and a few resistors allows for interrupt
MIC2583
SENSE
GND
2
4
15
7,8
R5 R6
FB(MAX)
GATE
/POR
DIS
FB
(PowerPAK“ SO-8)
14
13
12
1
Si7860DP
V
V
OUT(Good)
= 1.29V, V
Q1
FB(MAX)
V
IN
**R8
R9
20
10
C2
0.01 F
Downstream
Signal
– 1
OUT(Good)
FB(MAX)
R6
27.4k
1%
R7
10.5k
1%
, thus the /POR and
= 11V, and R6 is
MIC2582/MIC2583
1% is selected.
C
220 F
LOAD
5V@3A
(9.1)
V
Micrel
OUT
and
ON
)