MIC2594-1YM Micrel Inc, MIC2594-1YM Datasheet - Page 11

• Manufacturer Part Number: MIC2594-1YM
• Description: Negative Voltage Hot-Swap Controller -
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2594-1YM

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: -19 V ~ -80 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Family Name: MIC2594
• Package Type: SOIC
• Operating Supply Voltage (min): -19V
• Operating Supply Voltage (max): -80V
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 3.94mm
• Product Height (mm): 1.48mm
• Product Length (mm): 4.93mm
• Mounting: Surface Mount
• Pin Count: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

MIC2588/MIC2594
Functional Description
Hot Swap Insertion
When circuit boards are inserted into systems carrying live
supply voltages (“hot swapped”), high inrush currents often
result due to the charging of bulk capacitance that resides
across the circuit board’s supply pins. These current spikes
can cause the system’s supply voltages to temporarily go
out of regulation, causing data loss or system lock-up. In
more extreme cases, the transients occurring during a hot
swap event may cause permanent damage to connectors or
on-board components.
The MIC2588 and the MIC2594 are designed to address these
issues by limiting the magnitude of the transient or inrush cur-
rent during hot swap events. This is achieved by controlling
the rate at which power is applied to the circuit board (di/dt
and dv/dt management). Additionally, the MIC2588 and the
MIC2594 incorporate input voltage supervisory functions and
current limiting, thereby providing robust protection for both
the system and the circuit board.
Start-Up Cycle
When the input voltage to the controller is between the over-
voltage and undervoltage thresholds (MIC2588) or is greater
than V
to the load. At this time, the GATE pin of the controller ap-
plies a constant charging current (I
external MOSFET (M1). C
out of the MOSFET circuit, which limits the slew-rate of the
voltage at the drain of M1. The drain voltage rate-of-change
(dv/dt) of M1 is:
where I
I
tance values of power MOSFETs; and
Relating the above to the maximum transient (or inrush) current
charging the load capacitance upon hot swap or power-up
involves an extension of the same formula:
The presence of C3 and R
external pass device by limiting the hot swap current
surges induced by AC coupled transients from the drain
to the gate of M1 (i.e., C
value for C3 may be determined using the formula for a
capacitive voltage divider.
M9999-083005
GATE(–)
ON
dv M1
I
I
I
GATE(+)
| I
INRUSH
INRUSH
GATE(–)
≅ –I
(MIC2594), a start cycle is initiated to deliver power

INRUSH
GATE(+)
dt
DRAIN
= Gate Charging Current = I



C
C
C
|

LOAD
, due to the extremely high transconduc-
FDBK
LOAD


C
C



I
LOAD
FDBK
GATE(–)
C
FDBK



FDBK
–
dv M1
FDBK
dv M1
FDBK
dt



I


 I
GATEON
C
+ C
FDBK
GATEON

 

dt
prevent turn-on of the
DRAIN
DRAIN
creates a Miller integrator
GD
GATEON
–
(M1)). An appropriate






I
GATEON


C
FDBK
) to the gate of the
GATEON



(1)
;
11
The maximum voltage on C3 at turn-on must be less than
V
For example, we can determine appropriate capacitor values
given a hot swap controller that is required to maintain the
inrush current into a 220µF load capacitance at 2A maximum
and an input supply voltage as high as V
of the suggested MOSFETs to be used with the MIC2588/
MIC2594 is an SUM110N10-09,a 100V D
has a typical C
Calculating a value for C
Good engineering practice suggests the use of the worst-
case parameter values for I
Characteristics” section:
where the nearest standard 5% value is 6.8nF. Substituting
6.8nF into Equation 2 from above yields:
For C3, the nearest standard 5% value is 0.22µF.
While the value for R
to allow a maximum of a few milliamperes to flow in the
gate-drain circuit of M1 during turn-on. While the final value
for R
R
of V
Resistor R4, in series with the MOSFET's gate, minimizes
the potential for parasitic high frequency oscillations from
occurring in M1. While the exact value of R4 is not critical,
commonly used values for R4 range from 10Ω to 33Ω.
Power-Good (PWRGD or /PWRGD) Output
For the MIC2588-1 and the MIC2594-1, the Power-Good
output signal (PWRGD) will be high impedance when
V
when V
MIC2594-2, /PWRGD will pull down to the potential of the
V
high impedance when V
-1 parts have an active-high PWRGD signal and the -2 parts
have an active-low /PWRGD output. Either PWRGD or
/PWRGD may be used as an enable signal for one or more
where V
THRESHOLD
DRAIN
DRAIN
FDBK
C
V
V
3 
C3 =
1. For a standard 10V enhancement N-Channel
2. Choose 2V as the maximum voltage to avoid turn-
IN
GS
GS
FDBK
(max) = 75V are appropriate.
(M1) × [C3 +
(M1) × C3 =
MOSFET, V
on transients.

C
C

DRAIN
= 15kΩ to 27kΩ for systems with a maximum value
6.8nF 750pF
C
drops below V
pin when V
IN
FDBK
FDBK
FDBK
(max) = V
is determined empirically, initial values between
+ C
of M1.

is above V


GD
GD


V
C
220 F
220 F
(M1)
IN
FDBK
(max) – V
of 750pF.
THRESHOLD
DRAIN

DD
 
 
+ C
FDBK
×

2A
2A
PGTH
GD
V
– V

IN
DRAIN
FBDK
PGTH
(M1)
GS
45 A
60 A

(max) – V
75V – 2V
is not critical, it should be chosen
drops below V
(M1)
EE


GATEON
V
, and will pull down to V

] = V
GS
(min).
2V
. For the MIC2588-2 and the

using Equation 1 yields:
is about 4.25V.
(M1)
is above V


C
IN
FDBK
GS
4.95nF
6.6nF
(max) ×
(M1)

+ C
from the “DC Electrical
GD


IN
C
(M1)
0.275 F
2
FDBK
PGTH
PAK device which
(max) = 75V. One
PGTH
September 2005

+ C

, and will be
. Hence, the
GD
(M1)

Micrel
DRAIN
(2)