MIC2587-1YM TR Micrel Inc, MIC2587-1YM TR Datasheet - Page 12

• Manufacturer Part Number: MIC2587-1YM TR
• Description: IC CTRLR HOT SWAP POS HV 8-SOIC
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2587-1YM TR

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 10 V ~ 80 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MIC2587-1YMTR; MIC2587-1YMTR

Applications Information
External ON/OFF Control
The MIC2587/MIC2587R have an ON pin input that is used
to enable the controller to commence a start-up sequence
upon card insertion or to disable controller operation upon
card removal. In addition, the ON pin can be used to reset
the MIC2587/MIC2587R’s internal electronic circuit breaker
in the event of a load current fault. To reset the electronic
circuit breaker, the ON pin is toggled LOW then HIGH. The
ON pin is internally connected to an analog comparator
with 80mV of hysteresis. When the ON pin voltage falls
below its internal V
immediately pulled low. The GATE pin will be held low until
the ON pin voltage is above its internal V
external circuit's ON threshold voltage level is programmed
using a resistor divider (R1 & R2) as shown in the "Typical
Application” circuit. The equations to set the trip points are
shown below. For the following example, the external
circuit's ON threshold is set to V
commonly used in +48V Central Office power distribution
applications.
Given V
suggested value for R2 is that which will provide
approximately 100µA of current through the voltage divider
chain at V
point:
The closest standard 1% value for R2 is 13kΩ. Now,
solving for R1 yields:
The closest standard 1% value for R1 is 357kΩ.
Using standard 1% resistor values, the external circuit's
nominal ON and OFF thresholds are:
In solving for V
Output Voltage Power-is-Good Detection
The MIC2587/MIC2587R includes an analog comparator
used to monitor the output voltage of the controller through
an external resistor divider as shown in the “Typical
Application” circuit. The FB input pin is connected to the
non-inverting input and is compared against an internal
reference voltage. The analog comparator exhibits a
hysteresis of 80mV.
Setting the “Power-is-Good” threshold for the circuit follows
Micrel
October 2004
R1= R2 ×
V
V
V
R2 =
ONH(EX)
ON(EX)
OFF(EX)
ONH
V
100
CC
ONH(TYP)
= +36V
= V
= +34V
⎡
⎢
⎢
⎣
and R2, a value for R1 can be determined. A
⎛
⎜ ⎜
⎝
= V
µ
V
V
ONH
A
OFF(EX)
ONH(TYP)
ONH(EX)
ONH
=
×
1.313V
100
⎛
⎜
⎝
. This yields the following as a starting
R1+ R2
, replace V
⎞
⎟ ⎟ − 1
⎠
R2
ONL
µ
A
⎤
⎥
⎥
⎦
= 13kΩ ×
= 13.13kΩ
⎞
⎟
⎠
threshold, the GATE pin is
ONH
⎡
⎢
⎣
ONH(EX)
⎛
⎜
⎝
with V
1.313V
37V
ONH
ONL
= +37V, a value
⎞
⎟ − 1
⎠
threshold. The
in Equation 8.
⎤
⎥ = 353.3 kΩ
⎦
(8)
12
a similar approach as setting the circuit’s ON/OFF input
voltage. The equations to set the trip points are shown
below. For the following +48V telecom application, power-
is-good output signal PWRGD (or /PWRGD) is to be de-
asserted when the output supply voltage is lower than
+48V-10% (+43.2V).
Given V
suggested value for R6 is that which will provide
approximately 100µA of current through the voltage divider
chain at V
equation as a starting point:
The closest standard 1% value for R6 is 12.4kΩ. Now,
solving for R5 yields:
The closest standard 1% value for R5 is 422kΩ.
Using standard 1% resistor values, the external circuit's
nominal “power-is-good” and “power-is-not-good” output
voltages are:
In solving for V
Equation 9.
Sense Resistor Selection
The sense resistor is nominally valued at:
where V
threshold voltage (47mV) and I
inrush load current level to trip the internal circuit breaker.
To accommodate worse-case tolerances in the sense
resistor (for a ±1% initial tolerance, allow ±3% tolerance for
variations over time and temperature) and circuit breaker
threshold voltages, a slightly more detailed calculation
must be used to determine the minimum and maximum hot
swap load currents.
As the MIC2587/MIC2587R's minimum current limit
threshold voltage is 39mV, the minimum hot swap load
current is determined where the sense resistor is 3% high:
Keep in mind that the minimum hot swap load current
should be greater than the application circuit's upper
steady-state load current boundary. Once the lower value
of R
R5 = R6 ×
V
V
OUT(GOOD)
OUT(NOT GOOD)
R6 =
R
I
SENSE
V
HOT_SWAP(MIN)
OUT(NOT GOOD)
SENSE(NOM)
FBL
TRIP(TYP)
V
⎡
⎢
⎢
⎣
100
has been calculated, it is good practice to check
⎛
⎜ ⎜
⎝
FBL(TYP)
OUT(NOT GOOD)
V
and R6, a value for R5 can be determined. A
OUT(NOT GOOD)
= +46V
µ
V
A
FBL(TYP)
=
= +43.2V
=
I
is the typical (or nominal) circuit breaker
= V
=
HOT_SWAP(NOM)
(
OUT(GOOD)
1.03 × R
1.233V
V
100
FBL
TRIP(TYP)
µ
×
A
⎞
⎟ ⎟ − 1
⎠
39mV
⎛
⎜
⎝
= V
R5 + R6
SENSE(NOM)
= 12.33 kΩ
, substitute V
⎤
⎥
⎥
⎦
R6
= 12.4kΩ ×
FBL
HOT_SWAP(NOM)
. This yields the following
⎞
⎟
⎠
)
=
MIC2587/MIC2587R
R
⎡
⎢
⎣
⎛
⎜
⎝
SENSE(NOM)
1.233V
37.9mV
43.2V
FBH
[phone]
M9999-102204
is the nominal
⎞
⎟ − 1
⎠
for V
(10)
⎤
⎥ = 422 kΩ
⎦
(9)
FBL
in