MICREL MIC2085-JBQS

MIC2085/2086
Micrel
MIC2085/MIC2086
Single Channel Hot Swap Controllers
General Description
Features
The MIC2085 and MIC2086 are single channel positive
voltage hot swap controllers designed to allow the safe
insertion of boards into live system backplanes. The MIC2085
and MIC2086 are available in 16-pin and 20-pin QSOP
packages, respectively. Using a few external components
and by controlling the gate drive of an external N-Channel
MOSFET device, the MIC2085/86 provide inrush current
limiting and output voltage slew rate control in harsh, critical
power supply environments. Additionally, a circuit breaker
function will latch the output MOSFET off if the current limit
threshold is exceeded for a programmed period of time. The
devices’ array of features provide a simplified yet robust
solution for many network applications in meeting the power
supply regulation requirements and affords protection of
critical downstream devices and components.
All support documentation can be found on Micrel’s web
site at www.micrel.com.
• MIC2085: Pin for pin functional equivalent to the
LTC1642
• 2.3V to 16.5V supply voltage operation
• Surge voltage protection to 33V
• Operating temperature range –40°C to 85°C
• Active current regulation limits inrush current
independent of load capacitance
• Programmable inrush current limiting
• Analog foldback current limiting
• Electronic circuit breaker
• Dual-level overcurrent fault sensing
• Fast response to short circuit conditions (< 1µs)
• Programmable output undervoltage detection
• Undervoltage lockout protection
• Power-on reset (MIC2085/86) and
power-good (MIC2086) status outputs
• /FAULT status output
• Driver for SCR crowbar on overvoltage
Applications
•
•
•
•
•
•
RAID systems
Cellular base stations
LAN servers
WAN servers
InfiniBand™ Systems
Industrial high side switching
Typical Application
Backplane PCB Edge
Connector Connector
VIN
12V
Q1
Si7884DP
(PowerPAKTM SO-8)
RSENSE
0.007Ω
2% 2
Long
Pin
1
3
R1
3.3Ω
CLOAD
220µF
C1
1µF
*R6
10Ω
Short
Pin
16
VCC
R5
47kΩ
6
/FAULT
R3
Medium 1.82kΩ
1%
(or Short)
Pin
R4
10kΩ
1%
GATE
COMP+
11
COMPOUT
ON
12
13
/POR
OV
10
Output Signal
(Power Good)
REF
CRWBR
GND
Power-On Reset
Output
7
1
R8
16.2kΩ
1%
Q2
2N4401
C7
0.033µF
CFILTER
8
PWRGD
LOGIC
CONTROLLER
5
COMP—
C4
0.1µF
R11
47kΩ
C2
0.022µF
FB
3
C3
0.1µF
R10
47kΩ
/FAULT
CPOR
GND
VLOGIC
14
MIC2085
9
R7
127kΩ
1%
15
SENSE
R2
100kΩ
1%
4
VOUT
12V@5A
4
/RESET
Q3
TCR22-4
2
C5
8200pF
C6
0.01µF
**R9
180Ω
Long
Pin
Overvoltage (Input) = 13.3V
Undervoltage Lockout = 10.8V
Undervoltage (Output) &
Power-Good (Output) = 11.4V
POR/START-UP DELAY = 60ms
Circuit-Breaker Response Time = 500µs
*R6 is an optional component used for noise filtering
**R9 needed when using a sensitive gate SCR
InfiniBand is a trademark of InfiniBand Trade Association
PowerPAK is a trademark of Vishay Intertechnology Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
January 2004
1
M0235-121903
MIC2085/2086
Micrel
Ordering Information
Part Number
Fast Circuit Breaker Threshold
Discharge Output
Package
MIC2085-xBQS
x = J, 95mV
x = K, 150mV*
x = L, 200mV*
x = M, Off
NA
16-pin QSOP
MIC2086-xBQS
x = J, 95mV
x = K, 150mV*
x = L, 200mV*
x = M, Off
Yes
20-pin QSOP
*Contact factory for availability.
Pin Configuration
CRWBR 1
16 VCC
CFILTER 2
12 COMP–
/FAULT 6
11 COMP+
FB 7
PWRGD 6
10 COMPOUT
GND 8
19 VCC
/POR 5
13 REF
/POR 5
CFILTER 2
ON 4
14 GATE
ON 4
20 VCC
CPOR 3
15 SENSE
CPOR 3
CRWBR 1
9 OV
MIC2085
16-Pin QSOP (QS)
18 SENSE
17 GATE
16 REF
15 DIS
/FAULT 7
14 COMP–
FB 8
13 COMP+
GND 9
12 COMPOUT
GND 10
11 OV
MIC2086
20-Pin QSOP (QS)
Pin Description
Pin Number
MIC2086
Pin Number
MIC2085
Pin Name
1
1
CRWBR
Overvoltage Timer and Crowbar Circuit Trigger: A capacitor connected to
this pin sets the timer duration for which an overvoltage condition will trigger
an external crowbar circuit. This timer begins when the OV input rises above
its threshold as an internal 45µA current source charges the capacitor. Once
the voltage reaches 470mV, the current increases to 1.5mA.
2
2
CFILTER
Current Limit Response Timer: A capacitor connected to this pin defines the
period of time (tOCSLOW) in which an overcurrent event must last to signal a
fault condition and trip the circuit breaker. If no capacitor is connected, then
tOCSLOW defaults to 5µs.
3
3
CPOR
Power-On Reset Timer: A capacitor connected between this pin and ground
sets the start-up delay (tSTART) and the power-on reset interval (tPOR). When
VCC rises above the UVLO threshold, the capacitor connected to CPOR
begins to charge. When the voltage at CPOR crosses 1.24V, the start-up
threshold (VSTART), a start cycle is initiated if ON is asserted while capacitor
CPOR is immediately discharged to ground. When the voltage at FB rises
above VFB, capacitor CPOR begins to charge again. When the voltage at
CPOR rises above the power-on reset delay threshold (VTH), the timer
resets by pulling CPOR to ground, and /POR is deasserted.
If CPOR = 0, then tSTART defaults to 20µs.
M0235-121903
Pin Function
2
January 2004
MIC2085/2086
Micrel
Pin Description (Cont.)
Pin Number
MIC2086
Pin Number
MIC2085
Pin Name
4
4
ON
ON Input: Active high. The ON pin, an input to a Schmitt-triggered comparator used to enable/disable the controller, is compared to a VTH reference
with 100mV of hysteresis. Once a logic high is applied to the ON pin
(VON > 1.24V), a start-up sequence is initiated as the GATE pin starts
ramping up towards its final operating voltage. When the ON pin receives a
low logic signal (VON < 1.14V), the GATE pin is grounded and /FAULT is
high if VCC is above the UVLO threshold. ON must be low for at least 20µs
in order to initiate a start-up sequence. Additionally, toggling the ON pin
LOW to HIGH resets the circuit breaker.
5
5
/POR
Power-On Reset Output: Open drain N-Channel device, active low. This pin
remains asserted during start-up until a time period tPOR after the FB pin
voltage rises above the power-good threshold (VFB). The timing capacitor
CPOR determines tPOR. When an output undervoltage condition is detected
at the FB pin, /POR is asserted for a minimum of one timing cycle, tPOR. The
/POR pin has a weak pull-up to VCC.
6
N/A
PWRGD
Power-Good Output: Open drain N-Channel device, active high. When the
voltage at the FB pin is lower than 1.24V, the PWRGD output is held low.
When the voltage at the FB pin is higher than 1.24V, then PWRGD is
asserted. A pull-up resistor connected to this pin and to VCC will pull the
output up to VCC. The PWRGD pin has a weak pull-up to VCC.
7
6
/FAULT
Circuit Breaker Fault Status Output: Open drain N-Channel device, active
low. The /FAULT pin is asserted when the circuit breaker trips due to an
overcurrent condition. Also, this pin indicates undervoltage lockout and
overvoltage fault conditions. The /FAULT pin has a weak pull-up to VCC.
8
7
FB
9,10
8
GND
11
9
OV
12
10
COMPOUT
13
11
COMP+
Comparator’s Non-Inverting Input.
14
12
COMP-
Comparator’s Inverting Input.
15
NA
DIS
Discharge Output: When the MIC2086 is turned off, a 550Ω internal resistor
at this output allows the discharging of any load capacitance to ground.
16
13
REF
Reference Output: 1.24V nominal. Tie a 0.1µF capacitor to ground to ensure
stability.
17
14
GATE
January 2004
Pin Function
Power-Good Threshold Input: This input is internally compared to a 1.24V
reference with 3mV of hysteresis. An external resistive divider may be used
to set the voltage at this pin. If this input momentarily goes below 1.24V,
then /POR is activated for one timing cycle, tPOR, indicating an output
undervoltage condition. The /POR signal de-asserts one timing cycle after
the FB pin exceeds the power-good threshold by 3mV. A 5µs filter on this pin
prevents glitches from inadvertently activating this signal.
Ground Connection: Tie to analog ground.
OV Input: When the voltage on OV exceeds its trip threshold, the GATE pin
is pulled low and the CRWBR timer starts. If OV remains above its threshold
long enough for CRWBR to reach its trip threshold, the circuit breaker is
tripped. Otherwise, the GATE pin begins to ramp up one POR timing cycle
after OV drops below its trip threshold.
Uncommitted Comparator’s Open Drain Output.
Gate Drive Output: Connects to the gate of an external N-Channel
MOSFET. An internal clamp ensures that no more than 13V is applied
between the GATE pin and the source of the external MOSFET. The GATE
pin is immediately brought low when either the circuit breaker trips or an
undervoltage lockout condition occurs.
3
M0235-121903
MIC2085/2086
Micrel
Pin Description (Cont.)
Pin Number
MIC2086
Pin Number
MIC2085
Pin Name
18
15
SENSE
Pin Function
Circuit Breaker Sense Input: A resistor between this pin and VCC sets the
current limit threshold. Whenever the voltage across the sense resistor
exceeds the slow trip current limit threshold (VTRIPSLOW), the GATE voltage
is adjusted to ensure a constant load current. If VTRIPSLOW (48mV) is
exceeded for longer than time period tOCSLOW, then the circuit breaker is
tripped and the GATE pin is immediately pulled low. If the voltage across the
sense resistor exceeds the fast trip circuit breaker threshold, VTRIPFAST, at
any point due to fast, high amplitude power supply faults, then the GATE pin
is immediately brought low without delay. To disable the circuit breaker, the
SENSE and VCC pins can be tied together.
The default VTRIPFAST for either device is 95mV. Other fast trip thresholds
are available: 150mV, 200mV, or OFF(VTRIPFAST disabled). Please contact
factory for availability of other options.
19,20
M0235-121903
16
VCC
Positive Supply Input: 2.3V to 16.5V. The GATE pin is held low by an
internal undervoltage lockout circuit until VCC exceeds a threshold of 2.18V.
If VCC exceeds 16.5V, an internal shunt regulator protects the chip from
VCC and SENSE pin voltages up to 33V.
4
January 2004
MIC2085/2086
Micrel
Absolute Maximum Ratings(1)
Operating Ratings(2)
(All voltages are referred to GND)
Supply Voltage (VCC) ..................................... –0.3V to 33V
SENSE Pin .......................................... –0.3V to VCC + 0.3V
GATE Pin ....................................................... –0.3V to 22V
ON, DIS, /POR, PWRGD, /FAULT,
COMP+, COMP–, COMPOUT ....................... –0.3V to 20V
CRWBR, FB, OV, REF ..................................... –0.3V to 6V
Maximum Currents
Digital Output Pins ..................................................... 10mA
(/POR, /FAULT, PWRGD, COMPOUT)
DIS Pin ....................................................................... 30mA
ESD Rating:
Human Body Model ................................................... 2kV
Machine Model ........................................................ 200V
Supply Voltage (VCC) .................................... 2.3V to 16.5V
Operating Temperature Range .................. –40°C to +85°C
Junction Temperature (TJ) ........................................ 125°C
Package Thermal Resistance Rθ(J-A)
16-pin QSOP ..................................................... 112°C/W
20-pin QSOP ....................................................... 91°C/W
Electrical Characteristics(3)
VCC = 5.0V, TA = 25°C unless otherwise noted. Bold indicates specifications over the full operating temperature range of –40°C to +85°C.
Symbol
Parameter
Condition
Min
VCC
Supply Voltage
ICC
Supply Current
VUV
Undervoltage Lockout Threshold
VUVHYST
UV Lockout Hysteresis
VFB
FB (Power-Good) Threshold Voltage FB rising
VFBHYST
FB Hysteresis
VOV
OV Pin Threshold Voltage
OV pin rising
∆VOV
OV Pin Threshold Voltage
Line Regulation
2.3V < VCC < 16.5V
VOVHYST
OV Pin Hysteresis
IOV
OV Pin Current
VTH
POR Delay and Overcurrent (CFILTER) VCPOR, VCFILTER rising
Timer Threshold
1.19
ICPOR
Power-On Reset Timer Current
Timer on
Timer off
ITIMER
Current Limit /Overcurrent
Timer Current (CFILTER)
VCR
Typ
Max
Units
16.5
V
1.6
2.5
mA
2.18
2.0
2.28
2.10
V
V
2.3
VCC rising
VCC falling
2.05
1.85
180
1.19
1.24
mV
1.29
3
1.19
V
mV
1.24
1.29
mV
5
15
mV
3
mV
0.2
µA
1.24
1.29
V
–2.5
–2.0
5
–1.5
µA
mA
Timer on
Timer off
–30
–20
2.5
–15
µA
mA
CRWBR Pin Threshold Voltage
2.3V < VCC < 16.5V
445
470
495
mV
∆VCR
CRWBR Pin Threshold Voltage
Line Regulation
2.3V < VCC < 16.5V
4
15
mV
ICR
CRWBR Pin Current
CRWBR On, VCRWBR = 0V
CRWBR On, VCRWBR = 2.1V
CRWBR Off, VCRWBR = 1.5V
–60
–45
–1.5
3.3
–30
–1.0
µA
mA
mA
VTRIP
Circuit Breaker Trip Voltage
VTRIP = VCC –VSENSE
VTRIPSLOW
40
48
55
mV
(Current Limit Threshold)
2.3V ≤ VCC ≤ 16.5V
VTRIPFAST
80
95
150
200
110
mV
mV
mV
External Gate Drive
VGATE – VCC
VCC < 3V
4
8
9
V
5V < VCC < 9V
9V < VCC < 15.0V
11
12
13
V
4.5
21–VCC
13
V
VGS
January 2004
5
x=J
x=K
x=L
M0235-121903
MIC2085/2086
Micrel
Electrical Characteristics (Cont.)
Symbol
Parameter
Condition
Min
Typ
Max
Units
IGATE
GATE Pin Pull-up Current
Start cycle, VGATE = 0V
VCC =16.5V
VCC = 2.3V
–22
–20
–16
–14
–8
–8
µA
µA
/FAULT = 0, VGATE>1V
VCC = 16.5V
VCC = 2.3V
25
12
50
20
1.19
1.09
1.24
1.14
IGATEOFF
GATE Pin Sink Current
VON
ON Pin Threshold Voltage
VONHYST
ON Pin Hysteresis
ION
ON Pin Input Current
VON = VCC
VSTART
Undervoltage Start-up
Timer Threshold
VCPOR rising
VOL
/FAULT, /POR, PWRGD Output
Voltage
IOUT = 1.6mA
(PWRGD for MIC2086 only)
IPULLUP
Output Signal Pull-up Current
/FAULT, /POR, PWRGD, COMPOUT
/FAULT, /POR, PWRGD = GND
(PWRGD for MIC2086 only)
VREF
Reference Output Voltage
ILOAD = 0mA; CREF = 0.1µF
∆VLNR
Reference Line Regulation
2.3V < VCC < 16.5V
∆VLDR
Reference Load Regulation
IRSC
ON rising
ON falling
mA
mA
1.29
1.19
100
1.19
1.24
mV
0.5
µA
1.29
V
0.4
V
µA
–20
1.21
V
V
1.24
1.27
V
5
10
mV
IOUT = 1mA
2.5
7.5
mV
Reference Short-Circuit Current
VREF= 0V
3.5
VCOS
Comparator Offset Voltage
VCM = VREF
VCHYST
Comparator Hysteresis
VCM = VREF
RDIS
Discharge Pin Resistance
ON pin toggles from HI to LOW
100
550
1000
Ω
Min
Typ
Max
Units
–5
mA
5
3
mV
mV
AC Electrical Characteristics(4)
Symbol
Parameter
Condition
tOCFAST
Fast Overcurrent Sense to GATE
Low Trip Time
VCC = 5V
VCC –VSENSE = 100mV
CGATE = 10nF, See Figure 1
1
µs
tOCSLOW
Slow Overcurrent Sense to Gate
Low Trip Time
VCC = 5V
VCC –VSENSE = 50mV
CFILTER = 0, See Figure 1
5
µs
tONDLY
ON Delay Filter
20
µs
tFBDLY
FB Delay Filter
20
µs
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Specification for packaged product only.
4. Specification for packaged product only.
M0235-121903
6
January 2004
MIC2085/2086
Micrel
Timing Diagrams
VTRIPFAST
48mV
(VCC Ð VSENSE)
0
tOCFAST
tOCSLOW
1V
VGATE
1V
0
1.24V
CFILTER
0
Figure 1. Current Limit Response
1.24V
FB
tPOR
0
1.24V
CPOR
0
/POR
0
Figure 2. Power-On Reset Response
tONDLY
Arm Fast Comparator
Arm Slow Comparator
1.24V
ON
0
tSTART
tPOR
1.24V
CPOR
0
GATE
0
1.24V
FB
0
/POR
0
Current Limit Threshold (mV)
Figure 3. Power-On Start-Up Delay Timing
50
20
0
200
600
400
800
1000
FB Voltage (mV)
Figure 4. Foldback Current Limit Response
January 2004
7
M0235-121903
MIC2085/2086
Micrel
Typical Characteristics
2.6
3.5
2.4
VCC = 16.5V
2.5
VCC = 5V
2.0
1.5
1.0
VCC = 2.3V
0.5
1.4
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Overcurrent Timer Current
vs. Temperature
Overcurrent Timer (Off) Current
vs. Temperature
VCC = 16.5V
18
VCC = 2.3V
VCC = 5V
14
5
30
4
25
VCC = 16.5V
3
2
VCC = 2.3V
1
VCC = 5V
VCC = 2.3V
VCC = 5V
Gate Pull-Up Current
vs. Temperature
20
VCC = 16.5V
15
10
VCC = 2.3V
VCC = 5V
5
10
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Gate Pull-Up Current
vs. VCC
External Gate Drive
vs. Temperature
External Gate Drive
vs. VCC
25
16
VCC = 5V
14
20
12
10
10
VCC = 16.5V
VGS (V)
VGS (V)
15
8
6
4
5
VCC = 2.3V
2
0
2
4
6
8
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
10 12 14 16 18
VCC
(V)
Gate Sink Current
vs. Temperature
100
40
30
VCC = 5V
VCC = 2.3V
8
10 12 14 16 18
1.25
1.24
VCC = 16.5V
400
12VCC
VTH (mV)
50
IGATEOFF (mA)
VCC = 16.5V
6
POR Delay/Overcurrent
Timer Threshold
vs. Temperature
80
60
4
VCC (V)
500
70
22
20
18
16
14
12
10
8
6
4
2
0
2
Gate Sink Current
vs. Gate Voltage
600
90
IGATEOFF (mA)
5
4
1
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
IGATE (µA)
22
ITIMER (mA)
26
VCC = 16.5V
7
6
3
2
1.6
30
ITIMER (µA)
VCC = 2.3V
0.0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
34
IGATE ( A)
9
8
2.0
1.8
10
VCC = 16.5V
VCC = 5V
2.2
Power-On Reset Timer (Off) Current
vs. Temperature
ICPOR (mA)
3.0
ICPOR (µA)
SUPPLY CURRENT (mA)
Power-On Reset Timer Current
vs. Temperature
Supply Current
vs. Temperature
4.0
300
200
5VCC
100
1.23
VCC = 2.3V
1.22
VCC = 5V
1.21
20
10
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
M0235-121903
0
0
2
4
6
8
VGATE (V)
8
10
12
14
1.20
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
January 2004
MIC2085/2086
Micrel
Typical Characteristics
Current Limit Threshold
(Slow Trip)
vs. Temperature
55
115
53
VCC = 2.3V
100
95
90 V = 5V
CC
85
49
VCC = 5V
VCC = 16.5V
2.4
2.3
UVLO+
2.2
2.1
2.0
1.9
UVLO–
1.8
45
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
1.7
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
ON Pin Threshold (Rising)
vs. Temperature
ON Pin Threshold (Falling)
vs. Temperature
ON Pin Input Current
vs. Temperature
VCC = 2.3V
1.20
1.30
VCC = 16.5V
1.25
1.20
VCC = 5V
VCC = 2.3V
1.15
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Comparator Offset Voltage
vs. Temperature
0.5
1.10
VCC = 16.5V VCC = 5V
1.05
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
OVERVOLTAGE PIN THRESHOLD (V)
FB (Power-Good) Threshold
vs. Temperature
1.15
ON PIN INPUT CURRENT (nA)
VCC = 5V
VCC = 2.3V
40
1.20
25
20
VCC = 16.5V
15
10
VCC = 2.3V
VCC = 5V
5
26
VCC = 16.5V
VCC = 2.3V
30
Output Signal Pull-Up Current
vs. Temperature
Overvoltage Pin Threshold
vs. Temperature
1.30
1.25
35
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
22
IPULLUP (µA)
1.25
1.20
1.15
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
18
VCC = 16.5V
VCC = 5V
VCC = 2.3V
14
1.15
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
10
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Discharge Pin Resistance
vs. Temperature
1000
900
0.4
0.3
800
VCC = 5V
0.2
VCC = 16.5V
0.1
VCC = 2.3V
0.0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
January 2004
RDIS (Ω)
FB THRESHOLD (V)
VCC = 2.3V
47
VCC = 16.5V
VCC = 16.5V
COMPARATOR OFFSET VOLTAGE (V)
51
UVLO Threshold
vs. Temperature
80
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
1.30
ON THRESHOLD (V)
VTRIPSLOW (mV)
105
ON THRESHOLD (V)
VTRIPFAST (mV)
110
2.5
UVLO THRESHOLD (V)
120
Current Limit Threshold
(Fast Trip)
vs. Temperature
700
2.3V
5V
600
500
16.5V
400
300
200
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
9
M0235-121903
MIC2085/2086
Micrel
Test Circuit
V
12VIN
3
C1
0.47mF
VCC
4
MIC2086
GATE
17
FB
8
/POR
5
CLOAD
Downstream
Signal
DIS
GND CFILTER
9,10
2
C4
0.047mF
R6
4.4kW
R7
1.5kW
C5
0.033mF
10
RLOAD
C2
0.022mF
SW2
DIS
M0235-121903
R4
97.6kW
1%
R5
12.4kW
1%
15
CPOR
3
C3
0.047mF
Not all pins shown for clarity.
VOUT
R1
10W
18
SENSE
ON
R3
20kW
1%
IOUT
4
19,20
R2
154kW
1%
SW1
ON/OFF
Q1
Si7892DP
(PowerPAKTM SO-8)
RSENSE
0.01W
1 5% 2
IIN
Q2
ZTX788A
Q3
TCR22-4
R8
330W
January 2004
MIC2085/2086
Micrel
Functional Characteristics
12V Turn On Response
CPOR
1V/div
VCC
CPOR ON
1V/div 1V/div 5V/div
ON
1V/div
12V Hot Insert Response
VOUT
5V/div
TIME (20ms/div.)
Inrush Current Response
Power-Good Response
PG
FB
10V/div 1V/div
VIN = 12V
RLOAD = 3.4Ω
CLOAD = 5700µF
IIN
1A/div
TIME (10ms/div.)
Turn Off — Normal Discharge
Turn Off — Crowbar Discharge
ON
IIN = IOUT GATE
2A/div 20V/div 1V/div
TIME (10ms/div.)
VIN = 12V
RDIS(External) = 0
RLOAD = 4.8Ω
CLOAD = 1000µF
SW2 = HIGH
VIN = 12V
RLOAD = 4.8Ω
CLOAD = 1000µF
SW2 = LOW
VOUT
5V/div
ON
IIN = IOUT GATE
20V/div 1V/div
2A/div
VOUT
5V/div
VIN = 12V
RLOAD = 4.8Ω
CLOAD = 1000µF
VOUT
5V/div
VOUT /FAULT VCC
10V/div 10V/div 5V/div
ON
1V/div
TIME (20ms/div.)
TIME (2.5ms/div.)
January 2004
VIN = 12V
RLOAD = 4.8Ω
CLOAD = 1000µF
/POR
10V/div
IIN =IOUT
1A/div
VIN = 12V
RLOAD = 4.8Ω
CLOAD = 1000µF
TIME (2.5ms/div.)
11
M0235-121903
MIC2085/2086
Micrel
Functional Characteristics (continued)
VIN = 12V
RLOAD = 0
CLOAD = 1000µF
VOUT
5V/div
/FAULT
10V/div
CFILTER ON
1V/div 1V/div
Turn On Into Short Circuit
TIME (10ms/div.)
M0235-121903
12
January 2004
MIC2085/2086
Micrel
Functional Block Diagram
MIC2086
SENSE
VCC
Charge
Pump
18 (15)
19,20 (16)
48mV
95mV
+
Ð
REG2
+
Ð
550W
GND
FB
1.24V
15
VCC1
20mA
2 (2)
Circuit Breaker Response
or
UVLO
UVLO
2.2V
+
Ð
20mA
20mA
Logic
20mA
VCC1
1.24V
+
Ð
Glitch
Filter
VCC1
1.5mA
4 (4)
/POR
6
1 (1)
2.5mA
ON
5 (5)
PWRGD*
45mA
VCC1
3 (3)
/FAULT
VCC1
8 (7)
DIS*
7 (6)
VCC1
9,10 (8)
CPOR
REF
COMPOUT
COMP+
COMPÐ
13 (11)
14 (12)
VCC1
CFILTER
16 (13)
12 (10)
+
Ð
VCC1
REG1
GATE
21V
1.24V
13V
17 (14)
1.24V
+
Ð
1.24V
+
Ð
+
Ð
CRWBR
0.45V
Glitch
Filter
Glitch
Filter
+
Ð
11 (9)
1.24V
OV
*DIS and PWRGD are not available on MIC2085.
Pin numbers for MIC2085 are in parenthesis ( ) where applicable.
MIC2086 Block Diagram
January 2004
13
M0235-121903
MIC2085/2086
Micrel
where VTRIPSLOW is the current limit slow trip threshold found
in the electrical table and RSENSE is the selected value that
will set the desired current limit. There are two basic start-up
modes for the MIC2085/86: 1)Start-up dominated by load
capacitance and 2)start-up dominated by total gate capacitance. The magnitude of the inrush current delivered to the
load will determine the dominant mode. If the inrush current
is greater than the programmed current limit (ILIM), then load
capacitance is dominant. Otherwise, gate capacitance is
dominant. The expected inrush current may be calculated
using the following equation:
Functional Description
Hot Swap Insertion
When circuit boards are inserted into live system backplanes
and supply voltages, high inrush currents can result due to
the charging of bulk capacitance that resides across the
supply pins of the circuit board. This inrush current, although
transient in nature, may be high enough to cause permanent
damage to on-board components or may cause the system’s
supply voltages to go out of regulation during the transient
period which may result in system failures. The MIC2085/86
acts as a controller for external N-Channel MOSFET devices
in which the gate drive is controlled to provide inrush current
limiting and output voltage slew rate control during hot plug
insertions.
Power Supply
VCC is the supply input to the MIC2085/86 controller with a
voltage range of 2.3V to 16.5V. The VCC input can withstand
transient spikes up to 33V. In order to help suppress transients and ensure stability of the supply voltage, a capacitor
of 1.0µF to 10µF from VCC to ground is recommended.
Alternatively, a low pass filter, shown in the typical application
circuit, can be used to eliminate high frequency oscillations as
well as help suppress transient spikes.
Start-Up Cycle
When the voltage on the ON pin rises above its threshold of
1.24V, the MIC2085/86 first checks that its supply (VCC) is
above the UVLO threshold. If so, the device is enabled and
an internal 2µA current source begins charging capacitor
CPOR to 1.24V to initiate a start-up sequence (i.e., start-up
delay times out). Once the start-up delay (tSTART) elapses,
CPOR is pulled immediately to ground and a 15µA current
source begins charging the GATE output to drive the external
MOSFET that switches VIN to VOUT. The programmed startup delay is calculated using the following equation:
t START = CPOR ×
VTH
≅ 0.62 × CPOR (µF)
ICPOR
INRUSH ≅ IGATE ×
M0235-121903
VTRIPSLOW
48mV
=
RSENSE
RSENSE
CGATE
≅ 15µA ×
CLOAD
CGATE
(3)
where IGATE is the GATE pin pull-up current, CLOAD is the
load capacitance, and CGATE is the total GATE capacitance
(CISS of the external MOSFET and any external capacitor
connected from the MIC2085/86 GATE pin to ground).
Load Capacitance Dominated Start-Up
In this case, the load capacitance, CLOAD, is large enough to
cause the inrush current to exceed the programmed current
limit but is less than the fast-trip threshold (or the fast-trip
threshold is disabled, ‘M’ option). During start-up under this
condition, the load current is regulated at the programmed
current limit value (ILIM) and held constant until the output
voltage rises to its final value. The output slew rate and
equivalent GATE voltage slew rate is computed by the
following equation:
Output Voltage Slew Rate, dVOUT /dt =
ILIM
CLOAD
(4)
where ILIM is the programmed current limit value. Consequently, the value of CFILTER must be selected to ensure that
the overcurrent response time, tOCSLOW, exceeds the time
needed for the output to reach its final value. For example,
given a MOSFET with an input capacitance CISS = CGATE =
4700pF, CLOAD is 2200µF, and ILIMIT is set to 6A with a 12V
input, then the load capacitance dominates as determined by
the calculated INRUSH > ILIM. Therefore, the output voltage
slew rate determined from Equation 4 is:
(1)
where VTH, the POR delay threshold, is 1.24V, and ICPOR,
the POR timer current, is 2µA. As the GATE voltage continues ramping toward its final value (VCC + VGS) at a defined
slew rate (See “Load Capacitance”/“Gate Capacitance Dominated Start-Up” sections), a second CPOR timing cycle
begins if: 1)/FAULT is high and 2)CFILTER is low (i.e., not
an overvoltage, undervoltage lockout, or overcurrent state).
This second timing cycle, tPOR, starts when the voltage at the
FB pin exceeds its threshold (VFB) indicating that the output
voltage is valid. The time period tPOR is equivalent to tSTART
and sets the interval for the /POR to go Low-to-High after
“power is good” (See Figure 2 of “Timing Diagrams”). Active
current regulation is employed to limit the inrush current
transient response during start-up by regulating the load
current at the programmed current limit value (See “Current
Limiting and Dual-Level Circuit Breaker” section). The following equation is used to determine the nominal current
limit value:
ILIM =
CLOAD
Output Voltage Slew Rate, dVOUT /dt =
6A
V
= 2.73
2200µF
ms
and the resulting tOCSLOW needed to achieve a 12V output is
approximately 4.5ms. (See “Power-On Reset, Start-Up, and
Overcurrent Timer Delays” section to calculate tOCSLOW.)
GATE Capacitance Dominated Start-Up
In this case, the value of the load capacitance relative to the
GATE capacitance is small enough such that the load current
during start-up never exceeds the current limit threshold as
determined by Equation 3. The minimum value of CGATE that
will ensure that the current limit is never exceeded is given by
the equation below:
I
CGATE (min) = GATE × CLOAD
ILIM
(5)
(2)
14
January 2004
MIC2085/2086
Micrel
where CGATE is the summation of the MOSFET input
capacitance (CISS) and the value of the external capacitor
connected to the GATE pin of the MOSFET. Once CGATE is
determined, use the following equation to determine
the output slew rate for gate capacitance dominated start-up.
dVOUT /dt (output) =
IGATE
CGATE
Output Undervoltage Detection
The MIC2085/86 employ output undervoltage detection by
monitoring the output voltage through a resistive divider
connected at the FB pin. During turn on, while the voltage at
the FB pin is below the threshold (VFB), the /POR pin is
asserted low. Once the FB pin voltage crosses VFB, a 2µA
current source charges capacitor CPOR. Once the CPOR pin
voltage reaches 1.24V, the time period tPOR elapses as the
CPOR pin is pulled to ground and the /POR pin goes HIGH.
If the voltage at FB drops below VFB for more than 10µs, the
/POR pin resets for at least one timing cycle defined by tPOR
(see Applications Information for an example).
Input Overvoltage Protection
The MIC2085/86 monitors and detects overvoltage conditions in the event of excessive supply transients at the input.
Whenever the overvoltage threshold (VOV) is exceeded at
the OV pin, the GATE is pulled low and the output is shut off.
The GATE will begin ramping one POR timing cycle after the
OV pin voltage drops below its threshold. An external CRWBR
circuit, as shown in the typical application diagram, provides
a time period that an overvoltage condition must exceed in
order to trip the circuit breaker. When the OV pin exceeds the
overvoltage threshold (VOV), the CRWBR timer begins charging the CRWBR capacitor initially with a 45µA current source.
Once the voltage at CRWBR exceeds its threshold (VCR) of
0.47V, the CRWBR current immediately increases to 1.5mA
and the circuit breaker is tripped, necessitating a device reset
by toggling the ON pin LOW to HIGH.
Power-On Reset, Start-Up, and Overcurrent Timer
Delays
The Power-On Reset delay, tPOR, is the time period for the
/POR pin to go HIGH once the voltage at the FB pin exceeds
the power-good threshold (VTH). A capacitor connected to
CPOR sets the interval, tPOR, and tPOR is equivalent to the
start-up delay, tSTART (see Equation 1).
A capacitor connected to CFILTER is used to set the timer
which activates the circuit breaker during overcurrent conditions. When the voltage across the sense resistor exceeds
the slow trip current limit threshold of 48mV, the overcurrent
timer begins to charge for a period, tOCSLOW, determined by
CFILTER. If no capacitor is used at CFILTER, then tOCSLOW
defaults to 5µs. If tOCSLOW elapses, then the circuit breaker
is activated and the GATE output is immediately pulled to
ground. The following equation is used to determine the
overcurrent timer period, tOCSLOW.
(6)
Table 1 depicts the output slew rate for various values of CGATE.
IGATE = 15µA
CGATE
dVOUT/dt
0.001µF
15V/ms
0.01µF
1.5V/ms
0.1µF
0.150V/ms
1µF
0.015V/ms
Table 1. Output Slew Rate Selection for GATE
Capacitance Dominated Start-Up
Current Limiting and Dual-Level Circuit Breaker
Many applications will require that the inrush and steady state
supply current be limited at a specific value in order to protect
critical components within the system. Connecting a sense
resistor between the VCC and SENSE pins sets the nominal
current limit value of the MIC2085/86 and the current limit is
calculated using Equation 2. However, the MIC2085/86 exhibits foldback current limit response. The foldback feature
allows the nominal current limit threshold to vary from 24mV
up to 48mV as the FB pin voltage increases or decreases.
When FB is at 0V, the current limit threshold is 24mV and for
FB ≥ 0.6V, the current limit threshold is the nominal 48mV.
(See Figure 4 for Foldback Current Limit Response characteristic).
The MIC2085/86 also features a dual-level circuit breaker
triggered via 48mV and 95mV current limit thresholds sensed
across the VCC and SENSE pins. The first level of the circuit
breaker functions as follows. Once the voltage sensed across
these two pins exceeds 48mV, the overcurrent timer, its
duration set by capacitor CFILTER, starts to ramp the voltage
at CFILTER using a 2µA constant current source. If the
voltage at CFILTER reaches the overcurrent timer threshold
(VTH) of 1.24V, then CFILTER immediately returns to ground
as the circuit breaker trips and the GATE output is immediately shut down. For the second level, if the voltage sensed
across VCC and SENSE exceeds 95mV at any time, the
circuit breaker trips and the GATE shuts down immediately,
bypassing the overcurrent timer period. To disable current
limit and circuit breaker operation, tie the SENSE and VCC
pins together and the CFILTER pin to ground.
January 2004
V
t OCSLOW = CFILTER × TH ≅ 0.062 × CFILTER (µF) (7)
I
TIMER
where VTH, the CFILTER timer threshold, is 1.24V and
ITIMER, the overcurrent timer current, is 20µA. Tables 2 and
3 provide a quick reference for several timer calculations
using select standard value capacitors.
15
M0235-121903
MIC2085/2086
Micrel
CPOR
Using some basic algebra and simplifying Equation 8 to
isolate R5, yields:
tPOR = tSTART
0.01µF
6ms
0.02µF
12ms
0.033µF
18.5ms
0.05µF
30ms
0.1µF
60ms
0.33µF
200ms
Table 2. Selected Power-On Reset and
Start-Up Delays
CFILTER
tOCSLOW
1800pF
4700pF
8200pF
0.010µF
0.020µF
100µs
290µs
500µs
620µs
1.2ms
 V
 
OUT(Good)
R5 = R6 
 – 1
 VFB(MAX)  


where VFB(MAX) = 1.29V, VOUT(Good) = 11V, and R6 is
13.3kΩ. Substituting these values into Equation 8.1 now
yields R5 = 100.11kΩ. A standard 100kΩ ± 1% is selected.
Now, consider the 11.4V minimum output voltage, the lower
tolerance for R6 and higher tolerance for R5, 13.17kΩ and
101kΩ, respectively. With only 11.4V available, the voltage
sensed at the FB pin exceeds VFB(MAX), thus the /POR and
PWRGD (MIC2086) signals will transition from LOW to
HIGH, indicating “power is good” given the worse case
tolerances of this example.
Input Overvoltage Protection
The external CRWBR circuit shown in Figure 5 consists of
capacitor C4, resistor R7, NPN transistor Q2, and SCR Q3.
The capacitor establishes a time duration for an overvoltage
condition to last before the circuit breaker trips. The CRWBR
timer duration is approximated by the following equation:
0.033µF
2.0ms
0.050µF
3.0ms
0.1µF
6.2ms
0.33µF
20.75ms
Table 3. Selected Overcurrent Timer Delays
t OVCR ≅
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 (VFB). For this example,
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 Figure 5, use the following iterative design procedure.
1) Choose R6 so as to limit the current through the
divider to approximately 100µA or less.
VFB(MAX)
1.29V
≥ 12.9kΩ .
100µA
100µA
R6 is chosen as 13.3kΩ ± 1%.
2) Next, determine R5 using the output “good”
voltage of 11V and the following equation:
M0235-121903
ICR
(9)
VOV(MIN)
1.19V
≥ 11.9kΩ .
100µA
100µA
R3 is chosen as 13.7kΩ ±1%.
2) Thus, following the previous example and
substituting R2 and R3 for R5 and R6, respectively, and 13.2V overvoltage for 11V output
“good”, the same formula yields R2 of 138.3kΩ.
The next highest standard 1% value is 140kΩ.
Now, consider the 12.6V maximum input voltage (VCC +5%),
the higher tolerance for R3 and lower tolerance for R2, 13.84k
and 138.60kΩ, respectively. With a 12.6V input, the voltage
sensed at the OV pin is below VOV(MIN), and the MIC2085/86
will not indicate an overvoltage condition until VCC exceeds
at least 13.2V.
R3 ≥
≥
 (R5 + R6) 
VOUT(Good) = VFB 

 R6

(C4 × VCR ) ≅ 0.01× C4(µF)
where VCR, the CRWBR pin threshold, is 0.47V and ICR, the
CRWBR pin current, is 45µA during the timer period (see the
CRWBR timer pin description for further description). A
similar design approach as the previous undervoltage detection example is recommended for the overvoltage protection
circuitry, resistors R2 and R3 in Figure 5. For input overvoltage protection, the first consideration is to establish the input
voltage level that indicates an overvoltage triggering a system (output voltage) shut down. For this example, the input
value for which a 12V supply will signal an “output shut down”
is 13.2V (+10%). Similarly, from the previous example:
1) Choose R3 to satisfy 100µA condition.
Applications Information
R6 ≥
(8.1)
(8)
16
≥
January 2004
MIC2085/2086
Micrel
Q1
IRF7822
(SO-8)
RSENSE
0.012Ω
1 2% 2
VIN
12V
3
R2
140kΩ
1%
R1
100kΩ
VOUT
12V@3A
4
CLOAD
220µF
C1
1µF
16
VCC
R4
10Ω
15
SENSE
14
GATE
4
C2
0.022µF
ON
FB
7
MIC2085
9
R6
13.3kΩ
1%
/POR
OV
/FAULT
R3
13.7kΩ
1%
R5
100kΩ
1%
CPOR
GND
3
CRWBR
5
6
Downstream
Signals
Q2
2N4401
1
C4
0.01µF
8
C3
0.05µF
C5
0.033µF
Q3
TCR22-4
*R7
180Ω
Overvoltage (Input) = 13.3V
Undervoltage (Output) = 11.0V
POR/START-UP Delay = 30ms
*R7 needed when using a sensitive gate SCR.
Additional pins omitted for clarity.
Figure 5. Undervoltage/Overvoltage Circuit
January 2004
17
M0235-121903
MIC2085/2086
Micrel
PCB Connection Sense
There are several configuration options for the MIC2085/86’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 MIC2085/86 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 (VON)
Backplane PCB Edge
Connector Connector
VIN
12V
of 1.24V and the MIC2085/86 initiates a start-up cycle. In
Figure 6, the connection sense consisting of a logic-level
discrete MOSFET and a few resistors allows for interrupt
control from the processor or other signal controller to shut off
the output of the MIC2085/86. R4 keeps the GATE of Q2 at
VIN until the connectors are fully mated. A logic LOW at the
/ON_OFF signal turns Q2 off and allows the ON pin to pull up
above its threshold and initiate a start-up cycle. Applying a
logic HIGH at the /ON_OFF signal will turn Q2 on and short
the ON pin of the MIC2085/86 to ground which turns off the
GATE output charge pump.
RSENSE
0.008Ω
1 2% 2
Long
Pin
3
C1
1µF
Q1
Si7860DP
(PowerPAKTM SO-8)
CLOAD
220µF
R5
10Ω
Short
Pin
16
R4
10kΩ
4
SENSE
GATE
14
ON
C2
0.01µF
R1
20kΩ
/ON_OFF
R6
127kΩ
1%
15
VCC
R2
20kΩ
R3
100Ω
VOUT
12V@5A
4
FB
7
R7
16.2kΩ
1%
MIC2085
*Q2
/POR
/FAULT
PCB Connection Sense
CPOR
3
5
1
Downstream
Signals
GND
8
C2
0.05µF
GND
Long
Pin
Undervoltage (Output) = 11.4V
POR/START-UP DELAY = 30ms
*Q2 is TN0201T (SOT-23)
Additional pins omitted for clarity.
Figure 6. PCB Connection Sense with ON/OFF Control
M0235-121903
18
January 2004
MIC2085/2086
Micrel
Higher UVLO Setting
Once a PCB is inserted into a backplane (power supply), the
internal UVLO circuit of the MIC2085/86 holds the GATE
output charge pump off until VCC exceeds 2.18V. If VCC falls
below 2V, the UVLO circuit pulls the GATE output to ground
and clears the overvoltage and/or current limit faults. For a
higher UVLO threshold, the circuit in Figure 7 can be used to
delay the output MOSFET from switching on until the desired
input voltage is achieved. The circuit allows the charge pump
 R1
 × 1.24V . The GATE
to remain off until VIN exceeds 1 +
R2 
drive output will be shut down when VIN falls below
 R1
 × 1.14V . In the example circuit (Figure 7), the rising
1+
 R2 
UVLO threshold is set at approximately 11V and the falling
UVLO threshold is established as 10.1V. The circuit consists
of an external resistor divider at the ON pin that keeps the
GATE output charge pump off until the voltage at the ON pin
exceeds its threshold (VON) and after the start-up timer
elapses.
RSENSE
0.010Ω
1 2% 2
VIN
12V
3
Q1
IRF7822
(SO-8)
VOUT
12V@4A
4
CLOAD
220µF
C1
1µF
R1
392kΩ
1%
16
VCC
R3
10Ω
15
SENSE
GATE
4
R4
127kΩ
1%
14
C2
0.01µF
ON
FB
MIC2085
R5
16.2kΩ
1%
R2
49.9kΩ
1%
/POR
CPOR
3
7
GND
5
Downstream
Signal
8
C3
0.1µF
Undervoltage Lockout (Rising) = 11.0V
Undervoltage Lockout (Falling) = 10.1V
Undervoltage (Output) = 11.4V
POR/START-UP Delay = 60ms
Additional pins omitted for clarity.
Figure 7. Higher UVLO Setting
January 2004
19
M0235-121903
MIC2085/2086
Micrel
Fast Output Discharge for Capacitive Loads
In many applications where a switch controller is turned off by
either removing the PCB from the backplane or the ON pin is
reset, capacitive loading will cause the output to retain
voltage unless a ‘bleed’ (low impedance) path is in place in
order to discharge the capacitance. The MIC2086 is equipped
with an internal MOSFET that allows the discharging of any
load capacitance to ground through a 550Ω path. The discharge feature is configured by wiring the DIS pin to the
output (source) of the external MOSFET and becomes active
Q1
Si7892DP
(PowerPAKTM SO-8)
RSENSE
0.007
1 5% 2
V
12VIN
W
3
C1
1F
(DIS pin output is low) once the ON pin is deasserted. Figure
8(a) illustrates the use of the discharge feature with an
optional resistor (R5) that can be used to provide added
resistance in the output discharge path. For an even faster
discharge response of capacitive loads, the configuration of
Figure 8(b) can be utilized to apply a crowbar to ground
through an external SCR (Q3) that is triggered when the DIS
pin goes low which turns on the PNP transistor (Q2). See the
different “Functional Characteristic” curves for a comparison
of the discharge response configurations.
R2
10
m
R1
47k
19,20
VCC
W
ON Signal
4
CLOAD
1500 F
4
W
18
SENSE
ON
R3
110k
1%
GATE
17
VOUT
12V@5A
m
W
C2
0.022 F
m
FB
8
R4
14.7k
1%
MIC2086
DIS
*R5
15
/POR 5
PWRGD 6
GND CFILTER
9,10
2
C4
0.01 F
CPOR
3
C3
0.01 F
m
W
Downstream
Signals
m
(a)
Q1
Si7892DP
(PowerPAKTM SO-8)
RSENSE
0.007
1 5% 2
V
12VIN
W
3
C1
1F
R1
47k
ON Signal
19,20
VCC
W
4
R2
10
R3
110k
1%
W
18
SENSE
ON
GATE
17
C2
0.022 F
FB
/POR
8
5
R4
14.7k
1%
Downstream
Signal R6
4.4k
m
Undervoltage (Output) = 11V
POR/START-UP Delay = 6ms
Circuit Breaker Response Time = 620 s
*R5 of Figure 8(a) is optional to combine in series
with internal 550
Additional pins omitted for clarity.
m
m
W
m
MIC2086
CPOR
3
C3
0.01 F
CLOAD
1500 F
4
m
VOUT
12V@5A
DIS 15
GND CFILTER
9,10
2
C4
0.01 F
m
W
R5
1.5k
C5
0.022 F
m
W
Q2
ZTX788A
W
R7
220
Q3
TCR22-4
W
(b)
W.
Figure 8. MIC2086 Fast Discharge of Capacitive Load
M0235-121903
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MIC2085/2086
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Auto-Retry Upon Overcurrent Faults
The MIC2085/86 can be configured for automatic restart after
a fault condition. Placing a diode between the ON and
/FAULT pins, as shown in Figure 9, will enable the autorestart capability of the controller. When an application is
configured for auto-retry, the overcurrent timer should be set
to minimize the duty cycle of the overcurrent response to
prevent thermal runaway of the power MOSFET. See
“MOSFET Transient Thermal Issues” section for further
detail. A limited duty cycle is achieved when the overcurrent
timer duration (tOCSLOW) is much less than the start-up delay
timer duration (tSTART) and is calculated using the following
equation:
Auto − Retry Duty Cycle =
t OCSLOW
t START
× 100%
The circuit in Figure 10 distributes 12V from the backplane to
the MIC2182 DC/DC converter that steps down +12V to
+3.3V for local bias. The pass transistor, Q1, isolates the
MIC2182’s input capacitance during module plug-in and
allows the backplane to accommodate additional plug-in
modules without affecting the other modules on the backplane.
The two control input signals are VBxEn_L (active LOW) and
a Local Power Enable (active HIGH). The MIC2085 in the
circuit of Figure 10 performs a number of functions. The gate
output of Q1 is enabled by the two bit input signal VBxEn_L,
Local Power Enable = [0,1]. Also, the MIC2085 limits the drain
current of Q1 to 7A, monitors VB_In for an overvoltage
condition greater than 16V, and enables the MIC2182 DC/DC
converter downstream to supply a local voltage rail. The
uncommitted comparator is used to monitor VB_In for an
undervoltage condition of less than 10V, indicated by a logic
LOW at the comparator output (COMPOUT). COMPOUT
may be used to control a downstream device such as another
DC/DC converter. Additionally, the MIC2085 is configured for
auto-retry upon an overcurrent fault condition by placing a
diode (D1) between the /FAULT and ON pins of the controller.
(10)
An InfiniBand™ Application Circuit
The circuit in Figure 10 depicts a single 50W InfiniBand™
module using the MIC2085 controller. An InfiniBand™
backplane distributes bulk power to multiple plug-in modules
that employ DC/DC converters for local supply requirements.
Q1
IRF7822
(SO-8)
RSENSE
0.012Ω
1 5% 2
VIN
5V
3
VOUT
[email protected]
4
CLOAD
220µF
C1
1µF
R1
47kΩ
16
VCC
R3
10Ω
15
SENSE
GATE
R2
33kΩ
ON SIGNAL
4
ON
FB
MIC2085
6
14
C2
0.022µF
D1
1N914
/FAULT
OUTPUT
R4
34kΩ
1%
7
R5
14.7kΩ
1%
/FAULT
/POR
CPOR
3
GND
5
CFILTER
Downstream
Signal
2
8
C3
0.02µF
C4
4700pF
Undervoltage (Output) = 4.27V
POR/START-UP Delay = 12ms
Circuit Breaker Response Time = 290µs
Auto-Retry Duty Cycle = 2.5%
Additional pins omitted for clarity.
Figure 9. Auto-Retry Configuration
January 2004
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InfiniBand™ Application
InfiniBandª
Backplane
InfiniBandª
MODULE
RSENSE
0.007
W
5% 2
Long
VB_In
(12V)
Q1
IRF7822
(SO-8)
1
3
Short
VBxEn_L
R3W
13.3k1%
R5W
11k1%
Long
VB_Ret
0.033C5
mF
0.01C1
mF
LocalEnable
Power
VIN
4
R2W
165k1%
16
R4W
78.7k1%
MIC2182
DC/DC
Converter
VCC
9
OV
11
COMP+
3
CPOR
12
COMPÐ
R6
10W
15
SENSE
GATE
14
COMPOUT 10
/POR 5
MIC2085
13
REF
CFILTER GND
C3
0.1mF
2
8
0.022C4
mF
R1
10kW
FB
/FAULT
7
6
ON
CRWBR
4
R7
174k
1% W
C2
0.022mF
/UV
Power-On Reset RUN/SS
Output
R8
25.5kW
D1
1N914 1%
3.3V @ 4A
1
GND
Overvoltage (Input) = 16.0V
Undervoltage (Input) = 10.0V
Undervoltage (Output) &
Power-Good (Output) = 10.0V
Circuit Breaker Response Time = 1.2ms
POR/START-UP Delay = 18.5ms
Auto-Retry Duty Cycle = 6.5%
Figure 10. A 50W InfiniBand™ Application
Sense Resistor Selection
The next lowest standard value is 6.0mW. At the other set
The MIC2085 and MIC2086 use a low-value sense resistor to
of tolerance extremes for the output in question:
measure the current flowing through the MOSFET switch
(and therefore the load). This sense resistor is nominally
56.7mV
ILOAD(CONT,MAX) =
= 9.45A ,
valued at 48mV/ILOAD(CONT). To accommodate worst-case
6.0mΩ
tolerances for both the sense resistor (allow ±3% over time
almost 10A. Knowing this final datum, we can determine
and temperature for a resistor with ±1% initial tolerance) and
the necessary wattage of the sense resistor, using P = I2R,
still supply the maximum required steady-state load current,
where I will be ILOAD(CONT, MAX), and R will be
a slightly more detailed calculation must be used.
(0.97)(RSENSE(NOM)). These numbers yield the following:
The current limit threshold voltage (the “trip point”) for the
PMAX = (10A)2 (5.82mΩ) = 0.582W.
MIC2085/86 may be as low as 40mV, which would equate to
In this example, a 1W sense resistor is sufficient.
a sense resistor value of 40mV/ILOAD(CONT). Carrying the
MOSFET
Selection
numbers through for the case where the value of the sense
resistor is 3% high yields:
Selecting the proper external MOSFET for use with the
MIC2085/86 involves three straightforward tasks:
40mV
38.8mV
RSENSE(MAX) =
=
• Choice of a MOSFET which meets minimum
(1.03) ILOAD(CONT) ILOAD(CONT) (11)
voltage requirements.
Once the value of RSENSE has been chosen in this manner,
• Selection of a device to handle the maximum
it is good practice to check the maximum ILOAD(CONT) which
continuous current (steady-state thermal
the circuit may let through in the case of tolerance build-up in
issues).
the opposite direction. Here, the worst-case maximum cur• Verify the selected part’s ability to withstand any
rent is found using a 55mV trip voltage and a sense resistor
peak currents (transient thermal issues).
that is 3% low in value. The resulting equation is:
MOSFET Voltage Requirements
55mV
56.7mV
The first voltage requirement for the MOSFET is that the drainILOAD(CONT,MAX) =
=
(0.97) RSENSE(NOM) RSENSE(NOM) (12)
source breakdown voltage of the MOSFET must be greater
than VIN(MAX). For instance, a 16V input may reasonably be
As an example, if an output must carry a continuous 6A
expected to see high-frequency transients as high as 24V.
without nuisance trips occurring, Equation 11 yields:
Therefore, the drain-source breakdown voltage of the MOSFET
38.8mV
must be at least 25V. For ample safety margin and standard
RSENSE(MAX) =
= 6.5mΩ .
6A
availability, the closest minimum value should be 30V.
M0235-121903
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The second breakdown voltage criterion that must be met is
a bit subtler than simple drain-source breakdown voltage. In
MIC2085/86 applications, the gate of the external MOSFET
is driven up to a maximum of 21V by the internal output
MOSFET. At the same time, if the output of the external
MOSFET (its source) is suddenly subjected to a short, the
gate-source voltage will go to (21V – 0V) = 21V. Since most
power MOSFETs generally have a maximum gate-source
breakdown of 20V or less, the use of a Zener clamp is
recommended in applications with VCC ≥ 8V. A Zener diode
with 10V to 12V rating is recommended as shown in Figure
11. At the present time, most power MOSFETs with a 20V
gate-source voltage rating have a 30V drain-source breakdown rating or higher. As a general tip, choose surface-mount
devices with a drain-source rating of 30V or more as a starting
point.
Finally, the external gate drive of the MIC2085/86 requires a
low-voltage logic level MOSFET when operating at voltages
lower than 3V. There are 2.5V logic level MOSFETs available. Please see Table 4, “MOSFET and Sense Resistor
Vendors” for suggested manufacturers.
MOSFET Steady-State Thermal Issues
The selection of a MOSFET to meet the maximum continuous
current is a fairly straightforward exercise. First, arm yourself
with the following data:
• The value of ILOAD(CONT, MAX.) for the output in
question (see “Sense Resistor Selection” ).
• The manufacturer’s data sheet for the candidate
MOSFET.
• The maximum ambient temperature in which the
device will be required to operate.
• Any knowledge you can get about the heat
sinking available to the device (e.g., can heat be
dissipated into the ground plane or power plane,
if using a surface-mount part? Is any airflow
available?).
The data sheet will almost always give a value of on resistance given for the MOSFET at a gate-source voltage of 4.5V,
and another value at a gate-source voltage of 10V. As a first
approximation, add the two values together and divide by two
to get the on-resistance of the part with 8V of enhancement.
Call this value RON. Since a heavily enhanced MOSFET acts
as an ohmic (resistive) device, almost all that’s required to
determine steady-state power dissipation is to calculate I2R.
The one addendum to this is that MOSFETs have a slight
increase in RON with increasing die temperature. A good
approximation for this value is 0.5% increase in RON per °C
rise in junction temperature above the point at which RON was
initially specified by the manufacturer. For instance, if the
selected MOSFET has a calculated RON of 10mΩ at a
TJ = 25°C, and the actual junction temperature ends up
at 110°C, a good first cut at the operating value for RON
would be:
RON ≅ 10mΩ[1 + (110 - 25)(0.005)] ≅ 14.3mΩ
The final step is to make sure that the heat sinking available
to the MOSFET is capable of dissipating at least as much
power (rated in °C/W) as that with which the MOSFET’s
performance was specified by the manufacturer. Here are a
few practical tips:
1. The heat from a surface-mount device such as
an SO-8 MOSFET flows almost entirely out of
the drain leads. If the drain leads can be soldered down to one square inch or more, the
copper will act as the heat sink for the part. This
copper must be on the same layer of the board
as the MOSFET drain.
Q1
IRF7822
(SO-8)
RSENSE
0.007Ω
1 2% 2
VIN
12V
3
*D1
1N5240B
10V
4
CLOAD
220µF
C1
1µF
R1
47kΩ
16
VCC
VOUT
12V@5A
R3
10Ω
15
SENSE
GATE
14
R4
100kΩ
1%
C2
0.01µF
4
ON
FB
7
MIC2085
R2
33kΩ
R5
13.3kΩ
1%
/FAULT
/POR
CPOR
3
6
5
Downstream
Signals
GND
8
C3
0.1µF
Undervoltage (Output) = 11.0V
POR/START-UP Delay = 60ms
*Recommended for MOSFETs with gate-source
breakdown of 20V or less (IRF7822 VGS(MAX) = 12V)
for catastrophic output short circuit protection.
Additional pins omitted for clarity.
Figure 11. Zener Clamped MOSFET GATE
January 2004
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M0235-121903
MIC2085/2086
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2. Airflow works. Even a few LFM (linear feet per
minute) of air will cool a MOSFET down substantially. If you can, position the MOSFET(s)
near the inlet of a power supply’s fan, or the
outlet of a processor’s cooling fan.
3. The best test of a surface-mount MOSFET for
an application (assuming the above tips show it
to be a likely fit) is an empirical one. Check the
MOSFET's temperature in the actual layout of
the expected final circuit, at full operating
current. The use of a thermocouple on the drain
leads, or infrared pyrometer on the package, will
then give a reasonable idea of the device’s
junction temperature.
MOSFET Transient Thermal Issues
Having chosen a MOSFET that will withstand the imposed
voltage stresses, and the worse case continuous I2R power
dissipation which it will see, it remains only to verify the
MOSFET’s ability to handle short-term overload power dissipation without overheating. A MOSFET can handle a much
higher pulsed power without damage than its continuous
dissipation ratings would imply. The reason for this is that, like
everything else, thermal devices (silicon die, lead frames,
etc.) have thermal inertia.
In terms related directly to the specification and use of power
MOSFETs, this is known as “transient thermal impedance,”
or Zθ(J-A). Almost all power MOSFET data sheets give a
Transient Thermal Impedance Curve. For example, take the
following case: VIN = 12V, tOCSLOW has been set to 100msec,
ILOAD(CONT. MAX) is 2.5A, the slow-trip threshold is 48mV
nominal, and the fast-trip threshold is 95mV. If the output is
accidentally connected to a 3Ω load, the output current from
the MOSFET will be regulated to 2.5A for 100ms (tOCSLOW)
before the part trips. During that time, the dissipation in the
MOSFET is given by:
P = E x I EMOSFET = [12V-(2.5A)(3Ω)] = 4.5V
PMOSFET = (4.5V x 2.5A) = 11.25W for 100msec.
At first glance, it would appear that a really hefty MOSFET is
required to withstand this sort of fault condition. This is where
the transient thermal impedance curves become very useful.
Figure 12 shows the curve for the Vishay (Siliconix) Si4410DY,
a commonly used SO-8 power MOSFET.
Taking the simplest case first, we’ll assume that once a fault
event such as the one in question occurs, it will be a long time
– 10 minutes or more – before the fault is isolated and the
channel is reset. In such a case, we can approximate this as
a “single pulse” event, that is to say, there’s no significant duty
cycle. Then, reading up from the X-axis at the point where
“Square Wave Pulse Duration” is equal to 0.1sec (=100msec),
we see that the Zθ(J-A) of this MOSFET to a highly infrequent
event of this duration is only 8% of its continuous Rθ(J-A).
This particular part is specified as having an Rθ(J-A) of
50°C/W for intervals of 10 seconds or less. Thus:
Assume TA = 55°C maximum, 1 square inch of copper at the
drain leads, no airflow.
Recalling from our previous approximation hint, the part has
an RON of (0.0335/2) = 17mΩ at 25°C.
Assume it has been carrying just about 2.5A for some time.
When performing this calculation, be sure to use the highest
anticipated ambient temperature (TA(MAX)) in which the
MOSFET will be operating as the starting temperature, and
find the operating junction temperature increase (∆TJ) from
that point. Then, as shown next, the final junction temperature
is found by adding TA(MAX) and ∆TJ. Since this is not a closedform equation, getting a close approximation may take one or
two iterations, but it’s not a hard calculation to perform, and
tends to converge quickly.
Then the starting (steady-state)TJ is:
TJ ≅ TA(MAX) + ∆TJ
≅ TA(MAX) + [RON + (TA(MAX) – TA)(0.005/°C)(RON)]
x I2 x Rθ(J-A)
TJ ≅ 55°C + [17mΩ + (55°C-25°C)(0.005)(17mΩ)]
x (2.5A)2 x (50°C/W)
TJ ≅ (55°C + (0.122W)(50°C/W)
≅ 61.1°C
Iterate the calculation once to see if this value is within a few
percent of the expected final value. For this iteration we will
start with TJ equal to the already calculated value of 61.1°C:
TJ ≅ TA + [17mΩ + (61.1°C-25°C)(0.005)(17mΩ)]
x (2.5A)2 x (50°C/W)
TJ ≅ ( 55°C + (0.125W)(50°C/W) ≅ 61.27°C
Normalized Thermal Transient Impedance, Junction-to-Ambient
2
1
Normalized Effective Transient
Thermal Impedance
Duty Cycle = 0.5
0.2
Notes:
0.1
PDM
0.1
0.05
t1
t2
t1
1. Duty Cycle, D =
t2
2. Per Unit Base = RthJA = 50° C/W
0.02
3. TJM – TA = PDMZthJA(t)
Single Pulse
4. Surface Mounted
0.01
10–4
10–3
10–2
10–1
1
10
30
Square Wave Pulse Duration (sec)
Figure 12. Transient Thermal Impedance
M0235-121903
24
January 2004
MIC2085/2086
Micrel
So our original approximation of 61.1°C was very close to the
correct value. We will use TJ = 61°C.
Finally, add (11.25W)(50°C/W)(0.08) = 45°C to the steadystate TJ to get TJ(TRANSIENT MAX.) = 106°C. This is an acceptable maximum junction temperature for this part.
PCB Layout Considerations
Because of the low values of the sense resistors used with the
MIC2085/86 controllers, special attention to the layout must
be used in order for the device’s circuit breaker function to
operate properly. Specifically, the use of a 4-wire Kelvin
connection to measure the voltage across RSENSE is highly
recommended. Kelvin sensing is simply a means of making
sure that any voltage drops in the power traces connecting to
the resistors does not get picked up by the traces themselves.
Additionally, these Kelvin connections should be isolated
from all other signal traces to avoid introducing noise onto
these sensitive nodes. Figure 13 illustrates a recommended,
multi-layer layout for the RSENSE, Power MOSFET, timer(s),
overvoltage and feedback network connections. The feedback and overvoltage resistive networks are selected for a
12V application (from Figure 5). Many hot swap applications
will require load currents of several amperes. Therefore, the
power (VCC and Return) trace widths (W) need to be wide
enough to allow the current to flow while the rise in temperature for a given copper plate (e.g., 1 oz. or 2 oz.) is kept to a
maximum of 10°C ~ 25°C. Also, these traces should be as
short as possible in order to minimize the IR drops between
the input and the load. For a starting point, there are many
trace width calculation tools available on the web such as the
following link:
http://www.aracnet.com/cgi-usr/gpatrick/trace.pl
Finally, plated-through vias are utilized to make circuit connections to the power and ground planes. The trace connections with indicated vias should follow the example shown for
the GND pin connection in Figure 13.
Current Flow
Current Flow
to the Load
to the Load
*SENSE RESISTOR
*POWER MOSFET
(2512)
(SO-8)
W
D
G
D
S
D
S
D
S
W
**R4
10
W
Via to GND Plane
**CGATE
R3
13.7k
12
11
10
9
COMP-
COMP+
COMPOUT
OV
/POR
/FAULT
FB
GND
6
7
8
13
REF
5
14
GATE
CPOR
3
Current Flow
ON
15
SENSE
CFILTER
2
**CFILTER
W
4
16
VCC
CRWBR
1
MIC2085
1%
R2
140k
1%
W
Via to POWER (VCC)
Plane
R5
100k
1%
**CPOR
Via to GND Plane
W
R6
13.3k
1%
W
from the Load
W
DRAWING IS NOT TO SCALE
*See Table 4 for part numbers and vendors
**Optional components
Trace width (W) guidelines given in "PCB Layout.
Recommendations" section of the datasheet.
Figure 13. Recommended PCB Layout for Sense Resistor, Power MOSFET,
and Feedback/Overvoltage Network
January 2004
25
M0235-121903
MIC2085/2086
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MOSFET and Sense Resistor Vendors
Device types and manufacturer contact information for power
MOSFETs and sense resistors is provided in Table 4. Some
of the recommended MOSFETs include a metal heat sink on
the bottom side of the package. The recommended trace for
the MOSFET Gate of Figure 13 must be redirected when
using MOSFETs packaged in this style. Contact the device
manufacturer for package information.
MOSFET Vendors
Vishay (Siliconix)
Key MOSFET Type(s)
Si4420DY (SO-8 package)
Si4442DY (SO-8 package)
Si3442DV (SO-8 package)
Si7860DP (PowerPAK™ SO-8)
Si7892DP (PowerPAK™ SO-8)
Si7884DP (PowerPAK™ SO-8)
SUB60N06-18 (TO-263)
SUB70N04-10 (TO-263)
*Applications
IOUT ≤ 10A
IOUT = 10A-15A, VCC ≤ 5V
IOUT ≤ 3A, VCC ≤ 5V
IOUT ≤ 12A
IOUT ≤ 15A
IOUT ≤ 15A
IOUT ≥ 20A, VCC ≥ 5V
IOUT ≥ 20A, VCC ≥ 5V
Contact Information
www.siliconix.com
(203) 452-5664
International Rectifier
IRF7413 (SO-8 package)
IRF7457 (SO-8 package)
IRF7822 (SO-8 package)
IRLBA1304 (Super220™)
IOUT ≤ 10A
IOUT ≤ 10A
IOUT = 10A-15A, VCC ≤ 5V
IOUT ≥ 20A, VCC ≥ 5V
www.irf.com
(310) 322-3331
Fairchild Semiconductor
FDS6680A (SO-8 package)
FDS6690A (SO-8 package)
PH3230 (SOT669-LFPAK)
HAT2099H (LFPAK)
IOUT ≤ 10A
IOUT ≤ 10A, VCC ≤ 5V
IOUT ≥ 20A
IOUT ≥ 20A
www.fairchildsemi.com
(207) 775-8100
www.philips.com
www.halsp.hitachi.com
(408) 433-1990
Philips
Hitachi
* These devices are not limited to these conditions in many cases, but these conditions are provided as a helpful reference for customer applications.
Resistor Vendors
Vishay (Dale)
IRC
M0235-121903
Sense Resistors
“WSL” Series
Contact Information
www.vishay.com/docswsl_30100.pdf
(203) 452-5664
“OARS” Series
www.irctt.com/pdf_files/OARS.pdf
“LR” Series
www.irctt.com/pdf_files/LRC.pdf
(second source to “WSL”)
(828) 264-8861
Table 4. MOSFET and Sense Resistor Vendors
26
January 2004
MIC2085/2086
Micrel
Package Information
PIN 1
DIMENSIONS:
INCHES (MM)
0.157 (3.99)
0.150 (3.81)
0.009 (0.2286)
REF
0.025 (0.635)
BSC
0.0098 (0.249)
0.0040 (0.102)
0.012 (0.30)
0.008 (0.20)
0.196 (4.98)
0.189 (4.80)
SEATING 0.0688 (1.748)
PLANE 0.0532 (1.351)
45¡
0.0098 (0.249)
0.0075 (0.190)
8¡
0¡
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.229 (5.82)
Rev. 04
16-Pin QSOP (QS)
0.344 (8.74)
0.337 (8.56)
0.0575 REF
0.157 (3.99)
0.150 (3.81)
8¡
0¡
0.244 (6.20)
0.229 (5.82)
0.009 (0.229)
0.007 (0.178)
0.012 (0.305)
0.008 (0.203)
0.025 BSC
(0.635)
Rev. 04
0.068 (1.73)
0.053 (1.35)
Note:
1. All Dimensions are in Inches (mm) excluding mold flash.
2. Lead coplanarity should be 0.004" max.
3. Max misalignment between top and bottom.
4. The lead width, B to be determined at 0.0075" from lead tip.
0.010 (0.254)
0.004 (0.102)
7¡ BSC
0.050 (1.27)
0.016 (0.40)
20-Pin QSOP (QS)
January 2004
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MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2003 Micrel, Incorporated.
M0235-121903
28
January 2004