SUMMIT SMH4811AS

SUMMIT
SMH4811A
MICROELECTRONICS, Inc.
Preliminary
Distributed Power Hot-Swap Controller
FEATURES
DESCRIPTION
l Supply Range ±20VDC to >±500VDC
l Versatile Card Insertion Detection Supports:
w Multi-length Pin Systems
w Card Injector Switch Sensing
w Programmable Debounce Periods
l Control Powering-on of DC/DC Converters
l Highly Programmable Host Voltage Monitoring
w Programmable Under- and Over-voltage
Detection
w Programmable UV Filter
l Programmable Power Good Delay for enabling
the DC/DC Converter
The SMH4811A is designed to control hot swapping of
plug-in cards operating from a single supply ranging from
20V to 500V. It provides under-voltage and over-voltage
monitoring of the host power supply, drives an external
power MOSFET switch that connects the supply to the
load, and also protects against over-current conditions
that might disrupt the host supply. When the input and
output voltages to its controls are within specification, it
provides a Power Good logic output that may be used to
turn loads on (e.g., an isolated-output DC-DC converter,
or drive a LED status light). Additional features of the
SMH4811A include: temperature sense or master enable
input, 2.5V and 5V reference outputs for expanding monitor functions, two Pin-Detect enable inputs for fault protection, and duty-cycle over-current protection.
l Programmable Circuit Breaker Function
w Programmable Over-Current Filter
w Programmable Quick-Trip™ Circuit Breaker
Values
l 2.5V and 5.0V reference outputs
w Easy Expansion of External Monitor
Functions
SIMPLIFIED APPLICATION DRAWING
0V
Disable/Enable
VDD
Pin Detect
ENPG
PD1#
FAULT#
UV
SMH4811A
PG#
DC/DC
OV
Pin Detect
PD2#
VSS
CBSENSE VGATE 2.5VREF 5.0VREF
–48V
2044 SAD 5.1
©SUMMIT MICROELECTRONICS, Inc., 2000 • 300 Orchard City Dr., Suite 131 • Campbell, CA 95008 • Phone 408-378-6461 • FAX 408-378-6586 • www.summitmicro.com
Characteristics subject to change without notice
2044 6.1 2/8/01
1
SMH4811A
Preliminary
PIN CONFIGURATION
16-Pin SOIC
RECOMMENDED OPERATING CONDITIONS
Temperature
DRAIN SENSE
VGATE
EN/TS
PD1#
PD2#
FAULT#
CBSENSE
VSS
–40°C to 85°C.
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VDD
PG#
ENPG
NC
2.5VREF
5VREF
OV
UV
2044 PCon 5.0
FUNCTIONAL BLOCK DIAGRAM
ENPG
14
12VREF
VDD 16
12 2.5VREF
+
DRAIN
1
SENSE
–
11 5.0VREF
50kΩ
200kΩ
50kΩ
PROGRAMMABLE
DELAY
+
EN/TS 3
–
PD1# 4
PD2# 5
15 PG#
+
UV 9
–
FILTER
+
–
OV 10
50kΩ
5V
12V
VGATE
SENSE
2.5V
VSS 8
2 VGATE
PROGRAMMABLE
DELAY
+
–
50mV
+
CBSENSE 7
Programmable
Quick Response
Ref. Voltage
6 FAULT#
DUTY
CYCLE
TIMER
–
2044 BD 5.2
2
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
PIN DESCRIPTIONS
DRAIN SENSE (1)
The DRAIN SENSE input monitors the voltage at the drain
of the external power MOSFET switch with respect to VSS.
An internal 10µA source pulls the DRAIN SENSE signal
towards the 5V reference level. DRAIN SENSE must be
held below 2.5V to enable the PG outputs.
VGATE (2)
The VGATE output activates an external power MOSFET
switch. This signal supplies a constant current output
(100µA typical), which allows easy adjustment of the
MOSFET turn on slew rate.
OV (10)
The OV pin is used as an over-voltage supply monitor,
typically in conjunction with an external resistor ladder.
VGATE will be disabled if OV is greater than 2.5V. A filter
delay is available on the OV input.
5.0VREF & 2.5VREF (11 & 12)
These are precision 5V and 2.5V output reference voltages that may be use to expand the logic input functions
on the SMH4803A. The reference outputs are with respect to VSS.
ENPG (14)
EN/TS (3)
The Enable/Temperature Sense input is the master enable input. If EN/TS is less than 2.5V, VGATE will be
disabled. This pin has an internal 200kΩ pull-up to 5V.
This is an active high input that controls the PG# output.
When ENPG is pulled low the PG# output is immediately
placed in a high impedance state. This pin has an internal
50kΩ pull-up to 5V.
PD1# and PD2# (4 & 5)
These are logic level active low inputs that can optionally
be employed to enable VGATE and the PG outputs when
they are at VSS. These pins each have an internal 50kΩ
pull-up to 5V.
PG# (15)
The PG# pin is an open-drain, active-low output with no
internal pull-up resistor. It can be used to switch a load or
enable a DC/DC converter. PG# is enabled immediately
after VGATE reaches VDD – VGT and the DRAIN SENSE
voltage is less than 2.5V. Voltage on these pins cannot
exceed 12V, as referenced to VSS.
FAULT# (6)
This is an open-drain, active-low output that indicates the
fault status of the device.
CBSENSE (7)
The circuit breaker sense input is used to detect overcurrent conditions across an external, low value sense
resistor (RS) tied in series with the Power MOSFET. A
voltage drop of greater than 50mV across the resistor for
longer than tCBD will trip the circuit breaker. A programmable Quick-Trip™ sense point is also available.
VDD (16)
VDD is the positive supply connection. An internal shunt
regulator limits the voltage on this pin to approximately
12V with respect to VSS. A resistor must be placed in
series with the VDD pin to limit the regulator current (RD in
the application illustrations).
VSS (8)
VSS is connected to the negative side of the supply.
UV (9)
The UV pin is used as an under-voltage supply monitor,
typically in conjunction with an external resistor ladder.
VGATE will be disabled if UV is less than 2.5V. Programmable internal hysteresis is available on the UV input,
adjustable in increments of 62.5mV. Also available is a
filter delay on the UV input.
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
3
SMH4811A
Preliminary
ABSOLUTE MAXIMUM RATINGS*
Temperature Under Bias ...................... –55°C to 125°C
Storage Temperature ........................... –65°C to 150°C
Lead Solder Temperature (10 secs) ................... 300 °C
Terminal Voltage with Respect to VSS:
VDD ................................. –0.5V to VDD
OV, UV, DRAIN SENSE,
CBSENSE ........... –0.5V to VDD+0.5V
PD1#, PD2#, ENPG, EN/TS ......... 10V
FAULT#, PG# ........ –0.5V to VDD+0.5V
VGATE ................................ VDD+0.5V
*COMMENT
Stresses listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions
outside those listed in the operational sections of this specification is not
implied. Exposure to any absolute maximum rating for extended
periods may affect device performance and reliability.
AC OPERATING CHARACTERISTICS
Symbol
tCBD
tPGD
Description
Min.
50mV Circuit Breaker Delay (filter)
Programmable Power Good Delay
Typ.
Max.
Units
400
µs
150
µs
50 *
µs
5
µs
50
µs
250
µs
500
µs
1.5
ms
5*
ms
20
ms
80
ms
160
ms
tFSTSHTDN
Fast Shut Down delay from fault to VGATE off
200
ns
tCYC
Circuit breaker cycle mode time
2.5 *
s
Off *
—
5
ms
80
ms
160
ms
0.5
ms
5
ms
80 *
ms
160
ms
tPUVF
tPDD
Programmable Under-Voltage filter
Programmable Pin Detect Delay
2044 Prog Table
Note: * Indicates default value
4
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
DC OPERATING CHARACTERISTICS
(Over Recommended Operating Conditions; Voltages are relative to VSS)
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Units
VDD
Supply voltage
IDD = 3mA
11
12
13
V
5.0VREF
5V reference output
IDD = 3mA
4.75
5.00
5.25
V
ILOAD5
5V reference output current
IDD = 3mA
–1
1
mA
2.5VREF
2.5V reference output
ILOAD2.5
IDD = 3mA (1)
2.475
2.500
2.525
V
IDD = 3mA
2.425
2.500
2.575
V
2.5V reference output current
IDD = 3mA
–0.2
1
mA
IDD
Power supply current
Output enabled
2
10
mA
VUV
Under-Voltage threshold
VUVHYST
Under-Voltage hysteresis
VOV
Over-Voltage threshold
VOVHYST
Over-Voltage hysteresis
VVGATE
VGATE output voltage
IVGATE
VGATE current output
VSENSE
DRAIN SENSE threshold
ISENSE
DRAIN SENSE current output
VCB
Circuit breaker threshold
VQCB
IDD = 3mA (1)
2.475
2.500
2.525
V
IDD = 3mA
2.425
2.500
2.575
V
IDD = 3mA
10
mV
IDD = 3mA (1)
2.475
2.500
2.525
V
IDD = 3mA
2.425
2.500
2.575
V
IDD = 3mA
10
mV
VDD
100
V
µA
IDD = 3mA (1)
2.475
2.500
2.525
V
IDD = 3mA
2.425
2.500
2.575
V
VSENSE = VSS (1)
9
10
11
µA
IDD = 3mA
40
50
60
mV
Programmable Quick Trip circuit
breaker threshold
200
mV
100
mV
60
mV
Off
—
IDD = 3mA (1)
2.475
2.500
2.525
V
IDD = 3mA
2.425
2.500
2.575
V
VENTS
EN/TS threshold
VENTSHYST
EN/TS hysteresis
VIH
Input high voltage: ENPG
2
5.0VREF
V
VIL
Input low voltage: ENPG
–0.1
0.8
V
VOL
VGT
IDD = 3mA
10
mV
Output low voltage: FAULT#
IOL = 2mA
0
0.4
V
Output low voltage: PG#
ISINK = 2mA
0
0.4
V
Gate threshold
0.7
1.8
3.0
V
2044 Elect Table
Note: (1) TA = 25ºC.
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
5
SMH4811A
Preliminary
FUNCTIONAL DESCRIPTION
GENERAL OPERATION
The SMH4811A is an integrated power controller for hot
swappable add-in cards. The device operates from a wide
supply range and generates the signals necessary to drive
an isolated output DC/DC converter. As a typical add-in
board is inserted into the powered backplane physical
connections must first be made with the chassis to discharge any electrostatic voltage potentials. The board
then contacts the long pins on the backplane that provide
power and ground. As soon as power is applied the device
starts up, but does not immediately apply power to the
output load. Under-voltage and over-voltage circuits
inside the controller check to see that the input voltage is
within a user-specified range, and pin detection signals
determine whether the card is seated properly.
These requirements must be met for a Pin Detect Delay
period of tPDD, after which time the hot-swap controller
enables VGATE to turn on the external power MOSFET
switch. The VGATE output is current limited to IVGATE,
allowing the slew rate to be easily modified using external
passive components. During the controlled turn-on period
the VDS of the MOSFET is monitored by the DRAIN
SENSE input. When the drain sense drops below 2.5V,
and VGATE gets above VDD – VGT, the power good output
can turn on the DC/DC controller. A Power Good Enable
input may be used to activate or deactivate an output load.
Steady state operation is maintained as long as all conditions are normal. Any of the following events may cause
the device to disable the DC/DC controller by shutting
down the power MOSFET: an under-voltage or overvoltage condition on the host power supply; an overcurrent event detected on the CBSENSE input; a failure of
the power MOSFET sensed via the DRAIN SENSE pin;
the pin detect signals becoming invalid; or the master
enable (EN/TS) falling below 2.5V. The SMH4811A may
be configured so that after any of these events occur the
VGATE output shuts off and either latches into an off state
or recycles power after a cooling down period, tCYC.
System Enables
There are several enabling inputs, which allow a host
system to control the SMH4811A. The Pin Detect pins
(PD1# & PD2#) are two active low enables that are
generally used to indicate that the add-in circuit card is
properly seated. This is typically done by clamping the
inputs to VSS through the implementation of an injector
switch, or alternatively through the use of a staggered pins
at the card-cage interface. Two shorter pins arrayed at
opposite ends of the connector force the card to be fully
seated (not canted) before both pin detects are enabled.
Care must be taken not to exceed the maximum voltage
rating of these pins during the insertion process. Refer to
details in the Applications Section for proper circuit implementation.
The EN/TS input provides an active high comparator input
that may be used as a master enable or temperature
sense input. These inputs must be held low for a period of
tPDD before a power-up sequence may be initiated.
Under-/Over-Voltage Sensing
The Under-Voltage (UV) and Over-Voltage (OV) inputs
provide a set of comparators that act in conjunction with an
external resistive divider ladder to sense when the host
supply voltage exceeds the user defined limits. If the input
to the UV pin rises above 2.5V, or the input to the OV pin
falls below 2.5V for a period of tPDD, the power-up sequence may be initiated. The tPDD filter helps prevent
spurious start-up sequences while the card is being inserted. If UV falls below 2.5V or OV rises above 2.5V, the
PG and VGATE outputs will be shut down immediately.
2.5V
Powering VDD
The SMH4811A contains a shunt regulator on the VDD pin
that prevents the voltage from exceeding 12V. It is
necessary to use a dropper resistor (RD) between the host
power supply and the VDD pin in order to limit current into
the device and prevent possible damage. The dropper
resistor allows the device to operate across a wide range
of system supply voltages, and also helps protect the
device against common-mode power surges. Refer to the
Applications Section for help on calculating the RD resistance value.
OV / UV
tUOFLTR
FAULT#
2044 Fig01 5.0
Figure 1. Under-/Over-Voltage Filter Timing
6
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
Under-/Over-Voltage Filtering
The SMH4811A may also be configured so that an out of
tolerance condition on UV/OV will not shut off the output
immediately. Instead, a filter delay may be inserted so that
only sustained under-voltage or over-voltage conditions
will shut off the output. When the UV/OV filter option is
enabled an out of tolerance condition on UV or OV for
longer than the filter delay time, tUOFLTR, activates the
FAULT# output, and the VGATE and PG outputs will be
latched in the off state. To initiate another power-up
sequence the FAULT# output must first be reset. Refer to
the appropriate section on resetting the FAULT# output.
The Under-/Over-Voltage Filtering feature is disabled in
the default configuration of the device.
VDD
Under-Voltage Hysteresis
The Under-Voltage comparator input may be configured
with a programmable level of hysteresis. The compare
level may be set in steps (up to 15) of 62.5mV below 2.5V.
The default under-voltage hysteresis level is set to
62.5mV.
Soft Start Slew Rate Control
Once all of the preconditions for powering up the DC/DC
controller have been met, the SMH4811A provides a
means to soft start the external power FET. It is important
to limit in-rush current to prevent damage to the add-in
card or disruptions to the host power supply. For example,
11 ≤ VDD ≤ 13
<tPUVF
UV
2.5VREF
OV
PD1# +
PD2#
tPDD
VDD – VGT
VDD
VGATE
2.5VREF
5V
DRAIN
SENSE
50mVREF
CBSENSE
<tCBD
PG#
ENPG
2044 Fig02 5.0
Figure 2. Complete Power On Timing Sequence
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
7
SMH4811A
Preliminary
charging the filter capacitance (normally required at the
input of the DC/DC controller) too quickly may generate
very high current. The VGATE output of the SMH4811A
is current limited to IVGATE, allowing the slew rate to be
easily modified using external passive components. The
slew rate may be found by dividing IVGATE by the gate-todrain capacitance placed on the external FET. A complete
design example is given in the Applications Section.
Load Control — Sequencing the Secondary Supplies
Once power has been ramped to the DC/DC controllers,
two conditions must be met before the PG# output can be
enabled: the Drain Sense voltage must be below 2.5V,
and the VGATE voltage must be greater than VDD –VGT.
The Drain Sense input helps ensure that the power MOSFET is not absorbing too much steady state power from
operating at a high VDS. This sensor remains active at all
times (except during the current regulation period). The
VGATE sensor makes sure that the power MOSFET is
operating well into its saturation region before allowing the
load to be switched on. Once VGATE reaches VDD –VGT
this sensor is latched.
Once the external MOSFET is properly switched on the
PG# output may be enabled (if ENPG is high). The PG#
output has a 12V withstand capability, so high voltages
must not be connected to this pin. A bipolar transistor or
opto-isolator can be used to boost the withstand voltage to
that of the host supply.
Circuit Breaker Operation
The SMH4811A provides a number of circuit breaker
functions to protect against over current conditions. A
sustained over-current event could damage the host supply and/or the load circuitry. The board’s load current
passes through a series resistor (RS) connected between
the MOSFET source (which is tied to CBSENSE) and VSS.
The breaker trips whenever the voltage drop across RS is
greater than 50mV for more than tCBD (a factory programmable filter delay ranging from 10µs to 500µs).
Current Regulation
The current regulation mode is an optional feature that
provides a means to regulate current through the MOSFET for a programmable period of time. If enabled the
device will start the internal timer when the voltage at
CBSENSE exceeds 50mV. Also, it attempts to limit the
voltage at CBSENSE to 60mV by regulating the VGATE
output. The circuit breaker will trip if the over-current
condition remains after the time-out. However, if CBSENSE drops below 50mV before the timer ends, the
timer is reset and VGATE resumes normal operation. If
the Quick-Trip level is exceeded then the device will
bypass the current regulation timer and shut down immediately. The Current Regulation feature is disabled in the
default configuration.
Non-Volatile Fault Latch
The SMH4811A also provides an optional nonvolatile fault
latch (NVFL) circuit breaker feature. The nonvolatile fault
latch essentially provides a programmable fuse on the
circuit breaker. When enabled the nonvolatile fault latch
will be set whenever the circuit breaker trips. Once set, it
cannot be reset by cycling power.
NOTE: THE
DEVICE REMAINS PERMANENTLY DISABLED
UNTIL IT IS REPROGRAMMED AT THE FACTORY.
As long as the NVFL is set the FAULT# output will be
driven active. The Non-Volatile Fault Latch feature is
disabled in the default configuration.
Resetting FAULT#
When the circuit breaker trips the VGATE output is turned
off and FAULT# is driven low. In the default condition the
breaker resets automatically after a time of tCYC. In the
latched condition cycling power to the board or toggling the
EN/TS input will also reset the circuit breaker. If the over
current condition still exists after the MOSFET switches
back on, the circuit breaker will re-trip.
Quick-TripTM Circuit Breaker
Additionally, the SMH4811A provides a Quick-Trip feature
that will cause the circuit breaker to trip immediately if the
voltage drop across RS exceeds VQCB. The Quick-Trip
level may be factory set to 60mV, 100mV (default),
200mV, or the feature may be disabled.
8
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
PROGRAMMABLE FEATURES
<TCBD
VQCB
50mV
CBSENSE
TFSTSHTDN
VGATE
2044 Fig03 5.0
Figure 3. Circuit Breaker Timing — Quick Trip
The SMH4811A has programmable time and voltage
functions that can be fine-tuned for a wide variety of
applications. Because of this a manufacturer can use a
common part type across a wide range of boards that are
used on a common host but have different electrical loads,
power-on timing requirements, host voltage monitoring
needs, etc. This ability shifts the focus of design away
from designing a new power interface for each board to
concentrating on the value added back-end logic. Because the programming is done at final test all combinations (all 128 possibilities) are readily available as off the
shelf stock items.
Also see the AC Operating Characteristics Table.
Pin Detect
The Pin Detect function can be enabled or disabled.
Circuit Breaker Delay
The circuit breaker delay defines the period of time the
voltage drop across RS is greater than 50mV but less than
VQCB before the VGATE output will be shut down. This is
effectively a filter to prevent spurious shutdowns of
VGATE.
13
VDD (V)
12
Temp, ºC
–40
0
25
85
125
11
10
9
0
2
4
6
IDD (mA)
8
Power Good Delay
The PG delay timer that controls the delay to PG# being
asserted.
10
Quick-Trip Circuit Breaker Threshold
This is the threshold voltage drop across RS that is placed
between VSS and CBSENSE.
12
2044 Fig04
Figure 4. Effect of Temperature on Current Consumption Over Voltage Range
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
9
SMH4811A
Preliminary
APPLICATIONS
Operating at High Voltages
The breakdown voltage of the external active and passive
components limits the maximum operating voltage of the
SMH4811A hot-swap controller. Components that must
be able to withstand the full supply voltage are: the input
and output decoupling capacitors, the protection diode in
series with the DRAIN SENSE pin, the power MOSFET
switch and the capacitor connected between its drain and
gate, the high-voltage transistors connected to the power
good output, and the dropper resistor connected to the
controller’s VDD pin.
IDMIN =
Substituting:
IDMIN =
Telecom Design Example
A hot-swap telecom application may use a 48V power
supply with a –25% to +50% tolerance (i.e., the 48V supply
can vary from 36V to 72V). The formulae for calculating
R1, R2, and R3 follow.
First a peak current, IDMAX, must be specified for the
resistive network. The value of the current is arbitrary, but
it can't be too high (self-heating in R3 will become a
problem), or too low (the value of R3 becomes very large,
and leakage currents can reduce the accuracy of the OV
and UV trip points). The value of IDMAX should be ≥200µA
for the best accuracy at the OV and UV trip points. A value
of 250µA for IDMAX will be used to illustrate the following
calculations.
With VOV (2.5V) being the over-voltage trip point, R1 is
calculated by the formula:
R1 =
VOV
IDMAX .
Substituting:
R1 =
R3 =
VSMIN − VUV
.
IDMIN
VUV is the under-voltage trip point, also 2.5V. Substituting:
R3 =
36V − 2.5V
= 268kΩ .
125µ A
The closest standard 1% resistor value is 267kΩ
Then R2 is calculated:
(R1+ R2) =
VUV
IDMIN ,
or
R2 =
VUV
− R1.
IDMIN
Substituting:
R2 =
2.5V
− 10kΩ = 20kΩ − 10kΩ = 10kΩ .
125µ A
An Excel spread sheet is available on Summit's website
(www.summitmicro.com) to simplify the resistor value
calculations and tolerance analysis for R1, R2, and R3.
Dropper Resistor Selection
The SMH4811A is powered from the high-voltage supply
via a dropper resistor, RD. The dropper resistor must
provide the SMH4811A (and its loads) with sufficient
operating current under minimum supply voltage conditions, but must not allow the maximum supply current to be
exceeded under maximum supply voltage conditions.
The dropper resistor value is calculated from:
2.5V
= 10kΩ .
250µ A
Next the minimum current that flows through the resistive
divider, IDMIN, is calculated from the ratio of minimum and
maximum supply voltage levels:
10
250µ A × 36V
= 125µ A .
72V
Now the value of R3 is calculated from IDMIN:
Over-Voltage and Under-Voltage Resistors
In the following examples the three resistors, R1, R2, and
R3, connected to the OV and UV inputs must be capable
of withstanding the maximum supply voltage of several
hundred volts. The trip voltage of the UV and OV inputs is
2.5V relative to VSS. As the input impedance of UV and OV
is very high, large value resistors can be used in the
resistive divider. The divider resistors should be high
stability, 1% metal-film resistors to keep the under-voltage
and over-voltage trip points accurate.
IDMAX × VSMIN
.
VSMAX
2044 6.1 2/8/01
RD =
VSMIN − VDDMAX
IDD + ILOAD
,
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
where VSMIN is the lowest operating supply voltage,
VDDMAX is the upper limit of the SMH4811A supply voltage,
IDD is minimum current required for the SMH4811A to
operate, and ILOAD is any additional load current from the
2.5V and 5V outputs and between VDD and VSS.
The min/max current limits are easily met using the dropper resistor, except in circumstances where the input
voltage may swing over a very wide range (e.g., input
varies between 20V and 100V). In these circumstances it
may be necessary to add an 11V zener diode between
VDD and VSS to handle the wide current range. The zener
voltage should be below the nominal regulation voltage of
the SMH4811A so that it becomes the primary regulator.
MOSFET VDS(ON) Threshold
The drain sense input on the SMH4811A monitors the
voltage at the drain of the external power MOSFET switch
with respect to VSS. When the MOSFET’s VDS is below the
user-defined threshold the MOSFET switch is considered
to be ON. The VDS(ON)THRESHOLD is adjusted using the
resistor, RT, in series with the drain sense protection
diode. This protection, or blocking, diode prevents high
voltage breakdown of the drain sense input when the
MOSFET switch is OFF. A low leakage MMBD1401 diode
offers protection up to 100V. For high voltage applications
(up to 500V) the Central Semiconductor CMR1F-10M
diode should be used. The VDS(ON)THRESHOLD is calculated from:
VDS (ON)THRESHOLD = VSENSE − (ISENSE × RT ) − VDIODE ,
where VDIODE is the forward voltage drop of the protection
diode. The VDS(ON)THRESHOLD varies over temperature
due to the temperature dependence of VDIODE and ISENSE.
The calculation below gives the VDS(ON)THRESHOLD under
the worst case condition of 85°C ambient. Using a 68kΩ
resistor for RT gives:
VDS (ON)THRESHOLD = 2.5V − (15µ A × 68kΩ ) − 0.5V = 1V .
The voltage drop across the MOSFET switch and sense
resistor, VDSS, is calculated from:
VDSS = ID (RS + RON ) ,
where ID is the MOSFET drain current, RS is the circuit
breaker sense resistor, and RON is the MOSFET on
resistance.
Note: Figures 5 through 8 — the *10Ω resistor must be located as close as possible to the MOSFET
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
11
SMH4811A
Preliminary
APPLICATIONS CIRCUITS
0V
0V
10nF
100V
UV
EN/TS
2.5VREF
VDD
R3
ENPG
RD
6.8kΩ
MMBTA06LT1
R2
PG#
OV
1N4148
SMH4811A
10kΩ
PD1#
DRAIN SENSE
10kΩ
VSS
FAULT#
R1
100nF
50V
VGATE
CBSENSE
PD2#
47kΩ
5VREF
100nF
*10Ω
RS
20mΩ
100nF
50V
RT
68kΩ
1kΩ
10nF
100V
100µF
100V
MMBD1401
–48V
–48V
2044 Fig05
Figure 5. Changing Polarity of Power Good Output
0V
0V
NTC
50kΩ
@TMAX
10nF
100V
RD
6.8kΩ
R3
1kΩ
UV
LMV331
ENPG
2.5VREF
EN/TS
–
VDD
1MΩ
+
MMBTA06LT1
PG#
R2
100kΩ
OV
SMH4811A
10kΩ
PD1#
10kΩ
100nF
50V
DRAIN SENSE
R1
VGATE
50kΩ
VSS
FAULT#
CBSENSE
PD2#
5VREF
100nF
1kΩ
*10Ω
RS
20mΩ
10nF
100V
RT
68kΩ
100µF
100V
100nF
50V
100nF
50V
MMBD1401
–48V
–48V
2044 Fig06
Figure 6. Overtemperature Shutdown
12
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
0V
0V
10kΩ
10nF
100V
RD
6.8kΩ
R3
1kΩ
UV
ENPG
EN/TS
–
2.5VREF
+
EN1
VDD
1MΩ
MMBTA06LT1
PG#
R2
+
–
OV
LMV
339
5VREF
PD1#
+
PD2#
R1
–
100nF
50V
VGATE
VSS
FAULT#
+
EN4
DRAIN SENSE
10kΩ
–
EN3
100kΩ
SMH4811A
10kΩ
CBSENSE
EN2
100nF
1kΩ
*10Ω
10nF
100V
RS
20mΩ
RT
68kΩ
100nF
50V
100µF
100V
100nF
50V
MMBD1401
–48V
–48V
2044 Fig07
Figure 7. Expanding Input Monitoring Capability
0V
DC / DC
Converters
ENPG
EN/TS
VDD
RD
6.8kΩ
R3
UV
PG#
R2
OV
+VIN
+VOUT
–VIN
–VOUT
ON/OFF
V
0V
100kΩ
SMH4811A
10kΩ
MMBTA06LT1
DRAIN SENSE
PD1#
10kΩ
100nF
50V
VGATE
VSS
R1
CBSENSE
PD2#
5VREF
100nF
1kΩ
10nF
100V
*10Ω
10nF
100V
68kΩ
100nF
50V
100µF
100V
MMBD1401
RS
2044 Fig08
–48V
Figure 8. Typical Application with DC/DC Converter
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
13
SMH4811A
Preliminary
PACKAGES
SSOP PACKAGE
D
JEDEC
MO-137
H
1
S
E
A
hx45
C
0 to 8
typ
L
A2
e
B
A1
2044 SSOP
Dimension
Inches
Min.
Nom.
Millimeters
Max.
Min.
Nom.
Max.
A
0.061
0.064
0.068
1.55
1.63
1.73
A1
0.004
0.006
0.0098
0.12
0.15
0.25
A2
0.055
0.058
0.061
1.4
1.47
1.55
B
0.008
0.010
0.012
0.20
0.25
0.31
C
0.0075
0.008
0.0098
0.19
0.20
0.25
D
0.337
0.342
0.344
8.56
8.69
8.74
E
0.150
0.155
0.157
3.81
3.94
3.99
e
0.025BSC
0.635BSC
H
0.230
0.236
0.244
5.84
5.99
6.20
h
0.010
0.013
0.016
0.25
0.33
0.41
L
0.016
0.025
0.035
0.41
0.64
0.89
S
0.0500
0.0525
0.0550
1.27
1.33
1.40
2044 SSOP DIM Table
14
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.
SMH4811A
Preliminary
16 PIN SOIC PACKAGE
.0085 ± .0010
(After Plating)
0.390 ± 0.005
9
0.155±0.005
0.236 ± 0.008
16
6
1
OIC
0.151 ± 0.005
155 ± 0.005
S
Pin 1 Index
1
8
0.05 BSC
0 ±8
0.016 ± 0.003
DETAIL A
.016 ±.002
7 ±1
7 ±1
0.024 ± 0.002
45 ± 1
0.054 ± 0.005
0.069 MAX
.004
.007 ± .003
0.007 ± 0.003
7 ±1
0.390 ± 0.005
0.023 ± 0.005
0.041
Note:
DETAIL A
1. Reference: JEDEC publication MS-012 PTX 360-120
2. Unit: Inches
3. Mold flash, protrusion & gate burr shall not exceed 0.006 inch per side.
2044 SOIC 1.0
ORDERING INFORMATION
SMH4811A
G
Package
G = SSOP
S = SOIC
Base Part Number
2044 Tree 5.0
SUMMIT MICROELECTRONICS, Inc.
2044 6.1 2/8/01
15
SMH4811A
Preliminary
NOTICE
SUMMIT Microelectronics, Inc. reserves the right to make changes to the products contained in this publication in order
to improve design, performance or reliability. SUMMIT Microelectronics, Inc. assumes no responsibility for the use of
any circuits described herein, conveys no license under any patent or other right, and makes no representation that
the circuits are free of patent infringement. Charts and schedules contained herein reflect representative operating
parameters, and may vary depending upon a user’s specific application. While the information in this publication has
been carefully checked, SUMMIT Microelectronics, Inc. shall not be liable for any damages arising as a result of any
error or omission.
SUMMIT Microelectronics, Inc. does not recommend the use of any of its products in life support or aviation applications
where the failure or malfunction of the product can reasonably be expected to cause any failure of either system or to
significantly affect their safety or effectiveness. Products are not authorized for use in such applications unless
SUMMIT Microelectronics, Inc. receives written assurances, to its satisfaction, that: (a) the risk of injury or damage has
been minimized; (b) the user assumes all such risks; and (c) potential liability of SUMMIT Microelectronics, Inc. is
adequately protected under the circumstances.
© Copyright 2000 SUMMIT Microelectronics, Inc.
16
2044 6.1 2/8/01
SUMMIT MICROELECTRONICS, Inc.