MIC2582/MIC2583
Micrel
Applications Information
Output Undervoltage Detection
VOUT(Good)
R5 = R6
where V
–1
(9.1)
= 11V, and R6 is
OUT(Good)
VFB(MAX)
Foroutputundervoltagedetection,thefirstconsiderationisto
establish the output voltage level that indicates “power is
good.” For this example, the output value for which a 12V
supplywillsignal“good”is11V. Next, considerthetolerances
= 1.29V, V
FB(MAX)
12.4kΩ. Substituting these values into Equation 9.1 now
yields R5 = 93.33kΩ. A standard 93.1kΩ ± 1% is selected.
Now, consider the 11.4V minimum output voltage, the lower
tolerance for R6 and higher tolerance for R5, 12.28kΩ and
94.03kΩ, respectively. With only 11.4V available, the voltage
of the input supply and FB threshold (V ). For this example,
FB
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
theresistivedividernetwork(R5andR6)attheFBpin, shown
in the typical application circuit on page 1, use the following
iterative design procedure.
sensed at the FB pin exceeds V
, thus the /POR and
FB(MAX)
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
1) Choose R6 so as to limit the current through the
ThereareseveralconfigurationoptionsfortheMIC2582/83’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,
theresistornetworkispulleduptotheinputsupply,12Vinthis
divider to approximately 100µA or less.
VFB(MAX)
1.29V
R6
12.9kΩ
.
100µA
100µA
R6 is chosen as 12.4kΩ ± 1%.
2) Next, determine R5 using the output “good”
voltage of 11V and the following equation:
R5 +R6
(
)
example, and the ON pin voltage exceeds its threshold (V
)
ON
VOUT(Good) = VFB
(9)
R6
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
Using some basic algebra and simplifying Equation 9 to
isolate R5, yields:
RSENSE
0.010Ω
Q1
Si7860DP
(PowerPAK“ SO-8)
Backplane PCB Edge
Long
Connector Connector
Pin
5%
VIN
5V
1
2
VOUT
5V@3A
3
4
C1
1 F
CLOAD
220 F
**R8
10Ω
16
15
R5
20kΩ
R4
20kΩ
VCC
SENSE
14
GATE
R6
3
ON
27.4kΩ
1%
R1
R2
33kΩ
C2
0.01 F
33kΩ
*Q2
R3
100Ω
/ON_OFF
13
12
MIC2583
DIS
FB
PCB Connection Sense
VIN
Short
Pin
R7
10.5kΩ
1%
R9
20Ω
11
/FAULT
GND
/FAULT
1
/POR
CPOR
GND
7,8
Downstream
Signal
Medium or
Short Pin
4
C3
0.05 F
Long
Pin
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.
Figure 6. PCB Connection Sense with ON/OFF Control
April 2003
15
MIC2582/MIC2583
MICREL [ MICREL SEMICONDUCTOR ]
