LTC4261IUFD#PBF [Linear]
LTC4261 - Negative Voltage Hot Swap Controllers with ADC and I<sup>2</sup>C Monitoring; Package: QFN; Pins: 24; Temperature Range: -40°C to 85°C;型号: | LTC4261IUFD#PBF |
厂家: | Linear |
描述: | LTC4261 - Negative Voltage Hot Swap Controllers with ADC and I<sup>2</sup>C Monitoring; Package: QFN; Pins: 24; Temperature Range: -40°C to 85°C 监控 控制器 |
文件: | 总32页 (文件大小:362K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC4261/LTC4261-2
Negative Voltage
Hot Swap Controllers with
2
ADC and I C Monitoring
FEATURES
DESCRIPTION
Allows Safe Insertion into Live –48V Backplanes
The LTC®4261/LTC4261-2 negative voltage Hot SwapTM
controllersallowaboardtobesafelyinsertedandremoved
■
■
10-Bit ADC Monitors Current and Voltages
2
■
I C/SMBus Interface or Single-Wire Broadcast Mode from a live backplane. Using an external N-channel pass
■
■
Floating Topology Allows Very High Voltage
Operation
Independently Adjustable Inrush and Overcurrent
Limits
Controlled Soft-Start Inrush
transistor, the board supply voltage can be ramped at an
adjustable rate. The devices feature independently adjust-
able inrush current and overcurrent limits to minimize
stresses on the pass transistor during start-up, input
step and output short conditions. The LTC4261 defaults
to latch-off while the LTC4261-2 defaults to auto-retry on
overcurrent faults.
An I2C interface and onboard 10-bit ADC allow monitoring
of board current, voltage and fault status. A single-wire
broadcast mode is available to simplify the interface by
eliminating two optoisolators.
■
■
■
■
■
■
■
Adjustable UV/OV Thresholds and Hysteresis
Sequenced Power Good Outputs with Delays
Adjustable Power Good Input Timeout
Programmable Latchoff or Auto-Retry After Faults
Alerts Host After Faults
Available in 28-Lead Narrow SSOP and 24-Lead
(4mm × 5mm) QFN Packages
The controllers have additional features to interrupt the
host when a fault has occurred, notify when output power
is good, detect insertion of a board and turn off the pass
transistor if an external supply monitor fails to indicate
power good within a timeout period.
APPLICATIONS
■
AdvancedTCA Systems
■
Telecom Infrastructure
■
–48V Distributed Power Systems
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation. Patents pending.
All other trademarks are the property of their respective owners.
■
Power Monitors
TYPICAL APPLICATION
2
–48V/200W Hot Swap Controller with I C and ADC
–48V RTN
Start-Up Behavior
453k
1%
4× 1k IN SERIES
1/4W EACH
–48V INPUT
50V/DIV
V
IN
UV = 38.5V
UVL
UVH
ADIN2
OV
PGI
ALERT
SDAO
SDAI
SCL
ADIN
PGIO
PG
UV RELEASE
AT 43V
16.9k
1%
V
OV = 72.3V
OV RELEASE
AT 71V
OUT
+
LTC4261CGN
+
330µF
100V
50V/DIV
V
IN
INTV
ON
CC
LOAD
ON
SENSE
0.5A/DIV
SS
TMR EN V
SENSE GATE DRAIN RAMP
EE
11.8k
1%
–
V
IN
1M
1k
PG
50V/DIV
47nF
10Ω
1µF
220nF
0.1µF 47nF
42612 TA01b
10nF
100V
5%
10ms/DIV
0.008Ω
1%
V
OUT
–48V INPUT
42612 TA01
Q1
IRF1310NS
42612fb
1
LTC4261/LTC4261-2
(Notes 1, 2)
ABSOLUTE MAXIMUM RATINGS
V (Note 3) ......................................... –0.3V to 10.65V
Operating Temperature Range
IN
Drain (Note 4).......................................... –0.3V to 3.5V
PGI, ON, ALERT, SDAO, SDAI, SCL, ADIN, ADIN2,
OV, SENSE, ADR1, ADR0, FLTIN, TMR,
LTC4261C ................................................ 0°C to 70°C
LTC4261I ............................................. –40°C to 85°C
Storage Temperature Range
SS, RAMP Voltages....................–0.3V to INTV + 0.3V
SSOP ................................................. –65°C to 150°C
QFN.................................................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec)
CC
UVL, UVH, EN ............................................ –0.3V to 10V
GATE Voltage .................................. –0.3V to V + 0.3V
IN
PG, PGIO Voltages .................................... –0.3V to 80V
SSOP Only........................................................ 300°C
Supply Voltage (INTV ).......................... –0.3V to 5.5V
CC
PACKAGE/ORDER INFORMATION
TOP VIEW
1
2
PGIO
PG
28
27
26
25
24
23
22
21
20
19
18
17
16
15
PGI
ON
TOP VIEW
3
EN
ALERT
SDAO
SDAI
SCL
24 23 22 21 20
4
ADR1
ADR0
ADIN
FLTIN
SDAO
SDAI
SCL
1
2
3
4
5
6
7
19
18
17
16
15
14
13
EN
5
ADR1
ADR0
ADIN
6
7
INTV
CC
INTV
25
CC
8
V
UVL
V
IN
UVL
UVH
ADIN2
OV
IN
UVH
OV
TMR
SS
9
TMR
SS
10
11
12
13
14
8
9
10 11 12
RAMP
NC
NC
DRAIN
GATE
V
EE
UFD PACKAGE
24-LEAD (4mm × 5mm) PLASTIC QFN
= 125°C, θ = 45°C/W
SENSE
T
JMAX
JA
GN PACKAGE
28-LEAD PLASTIC SSOP
= 125°C, θ = 85°C/W
EXPOSED PAD (PIN 25) PCB V ELECTRICAL CONNECTION OPTIONAL
EE
T
JMAX
JA
ORDER PART NUMBER
ORDER PART NUMBER
UFD PART MARKING*
LTC4261CGN
LTC4261IGN
LTC4261CGN-2
LTC4261IGN-2
LTC4261CUFD
LTC4261IUFD
LTC4261CUFD-2
LTC4261IUFD-2
4261
4261
42612
42612
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
*The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges.
42612fb
2
LTC4261/LTC4261-2
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at I = 5mA, T = 25°C. (Note 2)
IN
A
SYMBOL
General
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
●
●
●
●
●
●
V
Shunt Regulator Voltage at V
I
I
= 5mA
10.65
11.2
370
2
11.8
600
5
V
mV
mA
V
Z
IN
IN
ΔV
Shunt Regulator Load Regulation
= 5mA to 25mA
Z
IN
I
V
V
V
Supply Current
V
V
= V – 0.3V
IN
IN
IN
IN
IN
IN
Z
V
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Rising
8.5
0.3
9
9.5
1
IN(UVLO)
ΔV
0.7
5
V
IN(UVLO)
INTV
Internal Regulator Voltage
I
= 1mA to 20mA, I = 25mA
4.75
5.25
V
CC
LOAD
IN
Gate Drive
●
●
●
●
●
●
●
V
GATE Pin Output High Voltage
GATE Pin Pull-Up Current
GATE Turn-Off Current
V
V
V
= 10.65V
10
–7.5
60
10.25
–11.5
110
110
0.5
10.5
–15.5
140
140
1.5
V
µA
mA
mA
µs
GATEH
IN
I
I
= 4V
GATE(UP)
GATE(OFF)
GATE
= 300mV, V
= 4V
SENSE
GATE
Gate Off, V
= 4V
60
GATE
t
t
SENSE High to Current Limit
Propagation Delay
V
SENSE
V
SENSE
= 100mV, C
= 300mV, C
= 1pF
= 1pF
PHL(SENSE)
PHL(GATE)
GATE
GATE
0.2
0.5
µs
GATE Off Propagation Delay
Input High (OV, EN, PGI), Input Low (ON, UVL),
0.2
0.5
µs
C
V
V
= 1pF
GATE
●
●
●
●
●
t
I
Circuit Breaker Gate Off Delay
RAMP Pin Current
< 2V, C
= 1pF
440
–18
2.43
–7
530
–20
2.56
–10
12
620
–22
2.69
–13
20
µs
µA
V
PHLCB
GATE
GATE
= 2.56V
RAMP
SS
V
SS
SS Pin Clamp Voltage
SS Pin Pull-Up Current
SS Pin Pull-Down Current
I
I
V
V
= 0V
µA
mA
SS(UP)
SS(DN)
SS
= 2.56V
6
SS
Input Pins
●
●
V
UVH Threshold Voltage
UVL Threshold Voltage
V
V
Rising
Falling
LTC4261C
LTC4261I
2.534
2.522
2.56
2.56
2.586
2.598
V
V
UVH(TH)
UVH
●
●
V
LTC4261C
LTC4261I
2.263
2.254
2.291
2.291
2.319
2.328
UVL(TH)
UVL
●
ΔV
Built-In UV Hysteresis
UVH and UVL Tied Together
256
269
15
282
mV
mV
V
UV(HYST)
δV
UVH, UVL Minimum Hysteresis
UVL Reset Threshold Voltage
UVL Reset Hysteresis
UV
●
V
V Falling
UVL
1.12
1.21
60
1.30
UVLR(TH)
ΔV
mV
V
UVLR(HYST)
●
●
V
OV Pin Threshold Voltage
V
OV
Rising
LTC4261C
LTC4261I
1.744
1.735
1.770
1.770
1.796
1.805
OV(TH)
●
●
●
ΔV
ΔV
OV Pin Hysteresis
18
45
37.5
50
62
55
2
mV
mV
V
OV(HYST)
SENSE
Current Limit Sense Voltage Threshold
ON, EN, PGI, FLTIN Threshold Voltage
ON, EN, PGI, FLTIN Hysteresis
PGIO Pin Input Threshold Voltage
PGIO Pin Input Hysteresis
V
– V
SENSE EE
V
ON, EN, PGI, FLTIN Falling or Rising
0.8
1.4
170
1.25
100
0
INPUT(TH)
ΔV
mV
V
INPUT(HYST)
●
●
V
V
PGIO
Rising
1.10
1.40
2
PGIO(TH)
ΔV
mV
µA
PGIO(HYST)
I
ON, EN, UVH, UVL, OV, SENSE, PGI,
FLTIN Input Current
ON, EN, UVH, UVL, OV, SENSE, PGI, FLTIN = 3V
INPUT
42612fb
3
LTC4261/LTC4261-2
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at I = 5mA, T = 25°C. (Note 2)
IN
A
SYMBOL
Timer
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
●
●
●
V
V
TMR Pin High Threshold
TMR Pin Low Threshold
TMR Pin Pull-Up Current
V
V
Rising
Falling
2.43
40
2.56
75
2.69
110
–13
V
mV
µA
TMR(H)
TMR(L)
TMR
TMR
I
Turn-On and Auto-Retry (Except OC) Delays,
= 0.2V
–7
–10
TMR(UP)
V
TMR
●
●
●
Power Good, PGI Check and OC Auto-Retry
Delays, V = 0.2V
–3.5
6
–5
12
5
–6.5
20
7
µA
mA
µA
TMR
I
TMR Pin Pull-Down Current
Delays Except PGI Check or OC Auto-Retry,
= 2.56V
TMR(DN)
V
TMR
PGI Check and OC Auto-Retry Delays,
= 2.56V
3
V
TRM
Output Pins
●
●
V
PG, PGIO Pins Output Low
I
, I = 3mA
PG PGIO
0.8
0.15
1.6
0.4
V
V
PWRGD
I
, I
= 500µA
PG PGIO
●
I
PG, PGIO Pins Leakage Current
PG, PGIO = 80V
0
10
µA
PWRGD
ADC
●
●
●
●
●
●
●
●
●
●
●
●
Resolution (No Missing Codes)
Integral Nonlinearity
(Note 5)
10
Bits
LSB
LSB
LSB
LSB
mV
V
INL
SENSE
0.5
2.5
1.25
1.75
1.25
65.2
2.606
1.8
ADIN2/OV, ADIN
SENSE
0.25
V
Offset Error
OS
ADIN2/OV, ADIN
SENSE
Full-Scale Voltage
Total Unadjused Error
62.8
64
ADIN2/OV, ADIN
SENSE
2.514
2.560
%
ADIN2/OV, ADIN
1.6
%
Conversion Rate
5.5
2
7.3
10
0
9
Hz
R
ADIN
ADIN, ADIN2 Pins Input Resistance
ADIN, ADIN2 Pins Input Current
ADIN, ADIN2 = 1.28V
ADIN, ADIN2 = 2.56V
MΩ
µA
I
2
ADIN
2
I C Interface
●
V
ADR0, ADR1 Input High Threshold
INTV
INTV
INTV
CC
– 0.3
V
ADR(H)
CC
CC
– 0.8
– 0.5
●
●
●
●
●
●
●
●
V
ADR0, ADR1 Input Low Threshold
ADR0, ADR1 Input Current
0.3
0.5
0.8
V
µA
µA
V
ADR(L)
I
ADR0, ADR1 = 0V, 5V
80
ADR(IN)
ADR0, ADR1 = 0.8V, (INTV – 0.8V)
10
CC
V
ALERT Pin Output Low Voltage
SDAO Pin Output Low Voltage
SDAO, ALERT Input Current
SDAI, SCL Input Threshold
SDAI, SCL Input Current
I
I
= 4mA
= 4mA
0.2
0.2
0
0.4
0.4
5
ALERT(OL)
ALERT
SDAO
V
V
SDAO(OL)
I
SDAO, ALERT = 5V
µA
V
SDAO,ALERT(IN)
V
1.6
1.8
0
2
SDAI,SCL(TH)
SDAI,SCL(IN)
I
SDAI, SCL = 5V
2
µA
42612fb
4
LTC4261/LTC4261-2
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at I = 5mA, T = 25°C. (Note 2)
IN
A
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
2
I C Interface Timing (Note 5)
f
t
t
t
Maximum SCL Clock Frequency
Minimum SCL Low Period
Minimum SCL High Period
400
kHz
µs
SCL(MAX)
LOW
0.65
50
1.3
600
1.3
ns
HIGH
Minimum Bus Free Time Between
Stop/Start Condition
0.12
µs
BUF(MIN)
t
t
Minimum Hold Time After (Repeated)
Start Condition
140
30
600
600
ns
ns
HD,STA(MIN)
Minimum Repeated Start Condition
Set-Up Time
SU,STA(MIN)
t
t
t
t
t
Minimum Stop Condition Set-Up Time
Minimum Data Hold Time Input
Minimum Data Hold Time Output
Minimum Data Set-Up Time Input
30
–100
600
30
600
0
ns
ns
ns
ns
ns
SU,STO(MIN)
HD,DATI(MIN)
HD,DATO(MIN)
SU,DAT(MIN)
SP(MAX)
300
900
100
250
Maximum Suppressed Spike Pulse
Width
50
25
110
t
Stuck-Bus Reset Time
SCL or SDAI Held Low
SDAI Tied to SDAO
66
5
ms
pF
RST
C
SCL,SDA Input Capacitance
10
X
The pin can be safely tied to higher voltages through a resistor that limits
the current below 50mA.
Note 4: An internal clamp limits the DRAIN pin to a minimum of 3.5V.
Driving this pin to voltages beyond the clamp may damage the part. The
pin can be safely tied to higher voltages through a resistor that limits the
current below 2mA.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into pins are positive, all voltages are referenced to
device GND (V ) unless otherwise specified.
EE
Note 5: Guaranteed by design and not subject to test.
Note 3: An internal shunt regulator limits the V pin to a minimum of
IN
10.65V. Driving this pin to voltages beyond 10.65V may damage the part.
42612fb
5
LTC4261/LTC4261-2
I
IN
= 5mA, T = 25°C, unless otherwise noted
TYPICAL PERFORMANCE CHARACTERISTICS
A
Shunt Regulator Voltage
vs Input Current
Shunt Regulator Voltage
vs Temperature
INTV vs Load Current
CC
30
25
11.35
11.30
11.25
11.20
5.06
I
= 25mA
I
= 5mA
IN
IN
5.04
5.02
5.00
4.98
4.96
20
15
10
5
11.15
11.10
0
10.8
11
11.2
11.4
11.6
11.8
–50
0
25
50
75
100
–25
5
10
15
0
20
SHUNT REGULATOR VOLTAGE AT V (V)
TEMPERATURE (°C)
IN
LOAD CURRENT (mA)
42612 G01
42612 G02
42612 G03
GATE Output High Voltage
vs Temperature
GATE Pull-Up Current
vs GATE Voltage
GATE Turn-Off Current
vs GATE Voltage
–12
–10
–8
–6
–4
–2
0
10.5
10.4
10.3
10.2
10.1
10.0
150
125
V
= 300mV
SENSE
V
= 10.65V
IN
100
75
50
25
0
0
2
4
6
8
10
–50
0
25
50
75
100
0
4
6
8
10
12
–25
2
V
(V)
TEMPERATURE (°C)
GATE VOLTAGE (V)
GS
42612 G06
42612 G04
42612 G05
UVH Threshold vs Temperature
UVL Threshold vs Temperature
RAMP Pin Current vs Temperature
–22.0
–21.5
–21.0
–20.5
–20.0
–19.5
–19.0
2.575
2.570
2.565
2.560
2.555
2.550
2.545
2.305
2.300
2.295
2.290
2.285
2.280
2.275
–50
0
25
50
75
100
–25
–50
0
25
50
75
100
–50
0
25
50
75
100
–25
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
42612 G07
42612 G08
42612 G09
42612fb
6
LTC4261/LTC4261-2
I
= 5mA, T = 25°C, unless otherwise noted
TYPICAL PERFORMANCE CHARACTERISTICS
IN
A
Current Limit Voltage
vs Temperature
52.0
OV Hysteresis vs Temperature
OV Threshold vs Temperature
1.785
1.780
1.775
1.770
1.765
1.760
1.755
50
45
40
35
51.5
51.0
50.5
50.0
49.5
49.0
30
25
–50
0
25
50
75
100
–25
–50
0
25
50
75
100
–50
0
25
50
75
100
–25
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
42612 G08
42612 G08
42612 G11
Current Limit Propagation Delay
PG, PGIO Output Low
vs Load Current
ADC Total Unadjusted Error
vs Code (ADIN Pin)
(t
) vs V
PHL(SENSE)
SENSE
6
5
1000
1.0
0.5
C
= 1pF
GATE
T
= 85°C
A
4
3
T
= 25°C
A
0
2
1
0
–0.5
–1.0
T
= –40°C
A
100
0
2
4
6
8
10
0
100
200
V
300
400
500
512
768
0
1024
256
LOAD CURRENT (mA)
(mV)
CODE
SENSE
42612 G14
42612 G13
42612 G15
ADC Full-Scale Error vs
Temperature (ADIN Pin)
ADC INL vs Code (ADIN Pin)
ADC DNL vs Code (ADIN Pin)
3
2
1.0
0.5
1.0
0.5
1
0
0
0
–1
–2
–3
–0.5
–1.0
–0.5
–1.0
–50
0
25
50
75
100
–25
512
768
0
1024
256
512
768
0
1024
256
TEMPERATURE (°C)
CODE
CODE
42612 G16
42612 G17
42612 G18
42612fb
7
LTC4261/LTC4261-2
(SSOP/QFN)
PIN FUNCTIONS
ADIN (Pin 23/Pin 16): ADC Input. A voltage between 0V
thresholds, UV and OV conditions are satisified and an
adjustable timer delay expires. During turn-off, short-
and 2.56V applied to this pin is measured by the on-chip
ADC. Tie to V if unused.
circuit or undervoltage lockout (V or INTV ), a 110mA
EE
IN CC
pull-down current between GATE and V is activated.
EE
ADIN2 (Pin 10/NA): Second ADC Input. Not available on
QFN package.
INTV (Pin 7/Pin 4): Low Voltage (5V) Supply Output.
CC
This is the output of the internal linear regulator with an
internal UVLO threshold of 4.25V. This voltage powers up
the data converter and logic control circuitry. Bypass this
ADR0, ADR1 (Pins 24, 25/Pins 17, 18): Serial Bus Ad-
dress Inputs. Tying these pins to V , OPEN or INTV
EE
CC
configures one of nine possible addresses. See Table 1
in Applications Information.
pin with a 0.1µF capacitor to V .
EE
ON (Pin 2/Pin 23): On Control Input. A rising edge turns
on the external N-channel FET while a falling edge turns it
off. This pin is also used to configure the state of the FET
ON register bit D3 in the CONTROL register (and hence
the external FET) at power-up. For example if the ON pin
is tied high, then the register bit D3 goes high one timer
cycle after power-up. Likewise, if the ON pin is tied low,
then the device remains off after power-up until the reg-
ALERT (Pin 3/Pin 24): Fault Alert Output. Open-drain
logic output that pulls to V when a fault occurs to alert
EE
the host controller. A fault alert is enabled by the ALERT
register. See Applications Information. Connect to V if
EE
unused.
DRAIN (Pin 16/Pin 11): Drain Sense Input. Connect an
external1Mresistorbetweenthispinandthedrainterminal
2
(V ) of the N-channel FET. When the DRAIN pin volt-
ister bit D3 is set high using the I C bus. A high-to-low
OUT
age is less than 1.77V and the GATE pin voltage is above
transition on this pin clears faults.
V – 1.2V the power good outputs are asserted after a
Z
OV (Pin 11/Pin 7): Overvoltage Detection Input. Connect
delay. The voltage at this pin is internally clamped to 4V.
this pin to an external resistive divider from V . If the
EE
EN(Pin26/Pin19):DeviceEnableInput.Pulllowtoenable
the N-channel FET to turn-on after a start-up debounce
delay set by the TMR pin. When this pin is pulled high, the
FET is off. Transitions on this pin will be recorded in the
FAULTregister. Ahigh-to-lowtransitionactivatesthelogic
to read the state of the ON pin and clear faults. Requires
external pull-up. Debouncing with an external capacitor
is recommended when used to monitor board present.
voltage at the pin rises above 1.77V, the N-channel FET is
turned off. The overvoltage condition does not affect the
status of the power good outputs. On the QFN package,
this pin is also measured by the on-chip ADC. Connect
to V if unused.
EE
PG (Pin 27/Pin 20): Power Good Status Output. This
open-drain pin pulls low and stays latched a timer delay
after the FET is on (when GATE reaches V – 1.2V and
Z
Connect to V if unused.
EE
DRAIN is within 1.77V of V ). The power good output is
EE
Exposed Pad (Pin 25, QFN Only): Exposed Pad may be
reset in all GATE pull-down events except an overvoltage
left open or connected to device ground (V ).
fault. Connect to V if unused.
EE
EE
FLTIN (Pin 22/NA): General Purpose Fault Input. If this
pin pulls low, the FAULT register bit B7 is latched to “1.”
This pin is used to sense an external fault condition and
its status does not affect the FET control functions of the
LTC4261. Not available on the QFN package. Connect to
PGI (Pin 1/Pin 22): Power Good Input. This pin along
with the PGI check timer serves as a watchdog to monitor
the power-up of the DC/DC converter. The PGI pin must
be low before the PGI check timer expires, otherwise the
GATE pin pulls down and stays latched and a power bad
fault is logged into the FAULT register. The PGI timer is
started after the second power good is latched and its
delay is equal to four times the start-up debounce delay.
INTV if unused.
CC
GATE (Pin 15/Pin 10): N-Channel FET Gate Drive Output.
This pin is pulled up by an internal current source I
GATE
Connect to V if unused.
EE
(11.5µA when the SS pin reaches its clamping voltage).
GATE stays low until V and INTV cross the UVLO
IN
CC
42612fb
8
LTC4261/LTC4261-2
(SSOP/QFN)
PIN FUNCTIONS
PGIO(Pin28/Pin21):GeneralPurposeInput/Output.Open-
drain logic output and logic input. Defaults to pull low a
timer delay after the PG pin goes low to indicate a second
power good output. Configure according to Table 6.
SS(Pin19/Pin13):Soft-StartInput.Connectacapacitorto
this pin to control the rate of rise of inrush current (dI/dt)
during start-up. An internal 10µA current source charging
the external soft-start capacitor (C ) creates a voltage
SS
ramp. This voltage is converted to a current to charge the
GATE pin up and to ramp the output voltage down. The
RAMP (Pin 18/Pin 12): Inrush Current Ramp Control
Pin. The inrush current is set by placing a capacitor (C )
R
SS pin is internally clamped to 2.56V limiting I
to
GATE(UP)
between the RAMP pin and the drain terminal of the FET.
11.5µA and I
to 20µA. If the SS capacitor is absent,
RAMP
At start-up, the GATE pin is pulled up by I
until the
GATE(UP)
the SS pin ramps from 0V to 2.56V in 220µs.
pass transistor begins to turn on. A current, I
, then
RAMP
flows through C to ramp down the output voltage V
.
TMR(Pin20/Pin14):DelayTimerInput.Connectacapaci-
R
OUT
The value of I
is controlled by the SS pin voltage.
tor (C
) to this pin to create timing delays at start-up,
RAMP
TMR
When the SS pin reaches its clamp voltage (2.56V), I
= 20µA. The ramp rate of V
set the inrush current: I
whenpowergoodoutputspulldown,duringPGIcheckand
when auto-retrying after faults (except overvoltage fault).
Internal pull-up currents of 10µA and 5µA and pull-down
currents of 5µA and 12mA configure the delay periods as
RAMP
and the load capacitor C
= (C /C ) • I
OUT
L
.
INRUSH
L
R
RAMP
SCL (Pin 6/Pin 3): Serial Bus Clock Input. Data at the
SDAI pin is shifted in and data at the SDAO pin is shifted
out on rising edges of SCL. This is a high impedance pin
that is generally connected to the output of the incoming
optoisolatordrivenbytheSCLportofthemastercontroller.
An external pull-up resistor or current source is required.
multiples of a nominal delay of 256ms • C /µF. Delays
TMR
forstart-upandauto-retryfollowingundervoltageorpower
bad fault are the same as the nominal delay. Delays for
sequenced power good outputs are twice of the nominal
delay. Delays for PGI check and auto-retry following over-
current fault are four times the nominal delay.
Pull up to INTV if unused.
CC
UVH (Pin 9/Pin 6): Undervoltage High Level Input. Con-
SDAI (Pin 5/Pin 2): Serial Bus Data Input. This is a high
impedance input pin used for shifting in command or
data bits. An external pull-up resistor or current source is
required.Normallyconnectedtotheoutputoftheincoming
optoisolator that is driven by the SDA port of the master
nect this pin to an external resistive divider from V . If
EE
the voltage at the UVH pin rises above 2.56V the pass
transistor is allowed to turn on. A small capacitor at this
pinpreventstransientsandswitchingnoisefromaffecting
the UVH threshold. Connect to INTV if unused.
CC
controller. Pull up to INTV if unused.
CC
UVL (Pin 8/Pin 5): Undervoltage Low Level Input. Con-
SDAO (Pin 4/Pin 1): Serial Bus Data Output. Open-drain
output used for sending data back to the master controller
or acknowledging a write operation. An external pull-up
resistororcurrentsourceisrequired. Normallyconnected
to the input of the outgoing optoisolator that outputs to
the SDA port of the master controller. In the single-wire
broadcast mode, the SDAO pin sends out selected data
that is encoded with an internal clock.
nect this pin to an external resistive divider from V . If
EE
the voltage at the UVL pin drops below 2.291V, the pass
transistor is turned off and the power good outputs go
high impedance. Pulling this pin below 1.21V resets faults
and allows the pass transistor to turn back on. Connect
to INTV if unused.
CC
V
(Pin 13/Pin 8): Negative Supply Voltage Input and
EE
Device Ground. Connect this pin to the negative side of
SENSE (Pin 14/Pin 9): Current Limit Sense Input. Load
the power supply.
current through the external sense resistor (R ) is moni-
S
tored and controlled by an active current limit amplifier to
V (Pin 21/Pin 15): Positive Supply Input. Connect this
IN
50mV/R . Once V
reaches 50mV, a circuit breaker
pin to the positive supply through a dropping resistor. An
S
SENSE
timerstartsandturnsoffthepasstransistorafter530µs.In
internal shunt regulator clamps V at 11.2V. An internal
IN
the event of a catastrophic short circuit, if V crosses
undervoltage lockout (UVLO) circuit holds the GATE low
SENSE
150mV, a fast response comparator immediately pulls the
until V is above 9V. Bypass this pin with a 1µF capaci-
IN
GATE pin down to turn off the N-channel FET.
tor to V .
EE
42612fb
9
LTC4261/LTC4261-2
BLOCK DIAGRAM
V
IN
INTV
CC
V
IN
11.2V
UVLO:
= 9V
V
–
CC
V
IN
+
GATE
INTV = 4.25V
CC
20µA
V
5V
EE
SSA
RAMP
SENSE
+
–
10µA
50nA
3pF
V
EE
–
+
ACL
50mV
+
V
EE
–
V
EE
+
–
2.56V
SS
V
EE
40×
V
SENSE
SSC
PG
UVL
UVH
OV
UVL
UVH
+
–
2.291V
2.56V
V
EE
PGIO
+
–
V
OV
EE
FLTIN
PGI
+
–
LOGIC
1.77V
EN
5µA
5µA
ON
–
+
DRAIN
DC
TMR
TMR
+
–
1.77V
4V
2.56V
–
+
GC
V
EE
V
Z
– 1.2V
12mA
5µA
GATE
2
ADR0
ADR1
SCL
8
I C DEVICE ADDRESS
SINGLE-WIRE ENABLE
= 2.56V
A0
•
•
DECODER
MUX
SDAI
A7
A8
SDAO
2
I C
INTERFACE
V
REF
ADIN
10
10
ALERT
ADIN2/OV
10-BIT ADC
REGISTER
V
SENSE
V
EE
42612 BD
42612fb
10
LTC4261/LTC4261-2
OPERATION
The LTC4261/LTC4261-2 are designed to turn a board’s
supply voltage on and off in a controlled manner, allow-
ing the board to be safely inserted or removed from a
live –48V backplane. The devices also feature an onboard
10-bit ADC and I2C interface that allows monitoring board
current, voltages and faults. The main functional circuits
of the LTC4261/LTC4261-2 are illustrated in the Block
Diagram.
The DRAIN and the GATE voltages are monitored to de-
termine if power is available for the load. Two power good
signals are sequenced on the PG pin (first power good
signal)andthePGIOpin(secondpowergoodsignal),each
with a debounce delay that is twice the start-up delay. The
PGIO pin can also be used as a general purpose input or
output. The PGI pin serves as a watchdog to monitor the
output of the DC/DC module. If the module output fails to
come up, the LTC4261/LTC4261-2 shut down.
In normal operation after a start-up debounce delay, the
GATE pin turns on the external N-channel FET passing
power to the load. The GATE pin is powered by a shunt
regulated 11.2V supply on the VIN pin that is derived
from –48V RTN through a dropping resistor. The turn-on
sequence starts by pulling the SS pin up. The voltage at
the SS pin is converted to a current, IGATE(UP), pulling the
GATE up. When the pass FET starts to turn on and charge
the load capacitor, the inrush current flowing through the
FET is a function of the capacitor at RAMP (CR), the load
capacitor (CL) and the ramp current (IRAMP) that flows
from the RAMP pin to CR:
TheTMRpingeneratesdelaysforinitialstart-up,auto-retry
following a fault, power good outputs and PGI check.
The logic circuits a re powered by an internally generated
5V supply (available on the INTVCC pin). Prior to turning
on the pass FET, both VIN and INTVCC voltages must ex-
ceed their undervoltage lockout thresholds. In addition,
the control inputs UVH, UVL, OV, EN, ON and PGI are
monitored by comparators. The FET is held off until all
start-up conditions are met.
A10-bitanalog-to-digitalconverter(ADC)isincludedinthe
LTC4261/LTC4261-2. The ADC measures SENSE resistor
voltageaswellasvoltageattheADIN2/OV(SSOP/QFN)and
ADIN pins. The results are stored in on-board registers.
CL
CR
IINRUSH = IRAMP •
An I2C interface is provided to read the ADC data registers.
It also allows the host to poll the device and determine if a
faulthasoccurred.IftheALERTlineisusedasaninterrupt,
the host can respond to a fault in real time. The SDA line
is divided into SDAI (input) and SDAO (output) to facili-
tate opto coupling with the system host. Two three-state
pins, ADR0 and ADR1, are used to decode eight device
addresses. The interface can also be configured through
the ADR0 and ADR1 pins for a single-wire broadcast
mode, sending ADC data and faults status through the
SDAO pin to the host without clocking the SCL line. This
single-wire, one-way communication simplifies system
design by eliminating two optocouplers on SCL and SDAI
that are required by an I2C interface.
IRAMP and IGATE(UP) are approximately proportional to the
SSpinvoltageandarelimitedto20µAand11.5µA,respec-
tively when SS reaches its clamping voltage (2.56V).
TheACLamplifierisusedforovercurrentandshort-circuit
protection.ItmonitorstheloadcurrentthroughtheSENSE
pin voltage and a sense resistor RS. In an overcurrent con-
dition, the ACL amplifier limits the current to 50mV/RS by
pulling down GATE in an active servo loop. After a 530µs
timeout, the ACL amplifier turns off the pass FET. In the
event of a catastrophic short circuit, when VSENSE crosses
150mV, a fast response comparator pulls the GATE pin
down with a 110mA current.
42612fb
11
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
The LTC4261/LTC4261-2 are ideally suited for –48V
distributed power systems and AdvancedTCA systems.
A basic 200W application circuit using the LTC4261 is
shown in Figure 1. A more complete application circuit
with AdvancedTCA connections is shown in Figure 2.
Input Power Supply
Power for the LTC4261/LTC4261-2 is derived from the
–48V RTN through an external current limiting resistor
(R ) to the V pin. An internal shunt regulator clamps
IN
IN
–48V RTN
R
IN
R3
453k
1%
4× 1k IN SERIES
1/4W EACH
7
21
8
9
22
1
6
5
4
INTV
V
IN
CC
UVL
UVH
ADIN2
OV
SS
TMR
EN
FLTIN
PGI
SCL
SDAI
SDAO
ALERT
UV = 38.5V
R2
16.9k
1%
UV RELEASE
AT 43V
10
11
19
20
26
2
+
C
L
OV = 72.3V
+
330µF
V
IN
OV RELEASE
AT 71V
100V
3
LTC4261CGN
MODULE2
+
ON
–
V
IN
PGIO 28 PWRGD2
V
IN
MODULE1
ON
ADR1
ADRO
25
24
27 PWRGD1
PG
23
ON
–
V
IN
ADIN
V
SENSE GATE DRAIN RAMP
EE
13
14
15
16
18
C
C
C
UV
100nF
IN
SS
220nF
1µF
R
10Ω
R
1M
R
1k
C
G
47nF
G
D
F
R1
11.8k
1%
C
C
VCC
0.1µF
TMR
47nF
C
R
10nF
100V
5%
C
F
R
S
33nF 0.008Ω
V
OUT
1%
–48V INPUT
R10
10k 1%
R11
402k 1%
Q1
IRF1310NS
V
EE
42612 F01
Figure 1. –48V/200W Hot Swap Controller Using LTC4261 with Current,
Input Voltage and V Monitoring (5.6A Current Limit, 0.66A Inrush)
DS
MBRM5100
10A
RTN A
A
MBRM5100
10A
R3
412k
1%
RTN B
UV TURN OFF = 34.2V
UV RELEASE = 37.5V
OV TURN OFF = 74.8V
OV RELEASE = 73.2V
R12
10k
Q9
2N5401
ENABLE A
ENABLE B
R13
10k
R
H
604Ω
Q10
2N5401
1%
8
9
UVL
UVH
ADIN2
OV
SS
TMR
EN
R2
19.1k
1%
R10
R11
R14
R15
100k
10
11
19
20
26
2
100k 100k
100k
1N4148
×2
C
UV
100nF
LTC4261CGN
ON
ADR1
ADR0
25
24
V
SENSE GATE DRAIN RAMP
EE
13
14
15
16
18
C
SS
330nF
R
10Ω
R
1M
R
1k
C
G
47nF
G
D
F
R1
10.5k
1%
C
R16
100k
TMR
330nF
LTC4354
C
R
7A
7A
10nF
100V
5%
C
EN
1µF
C
R
S
F
–48V A
–48V B
HZS5C1
33nF 0.008Ω
5%
B
42612 F02a
Q1
IRF1310NS
V
EE
BACKPLANE
PLUG-IN
CARD
Figure 2a. 200W AdvancedTCA Hot Swap Controller with Input/Output Monitoring
2
and Power Good Watchdog Using LTC4261 in I C Mode (Part One)
42612fb
12
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Initial Start-Up and Inrush Control
the voltage at V to 11.2V (V ) and provides power to the
IN
Z
GATE driver. The data converter and logic control circuits
are powered by an internal linear regulator that derives
5V from the 11.2V supply. The 5V output is available at
SeveralconditionsmustbesatisfiedbeforetheFETturn-on
sequence is started. First the voltage at V must exceed
IN
its 9V undervoltage lockout level. Next the internal supply
the INTV pin for driving external circuits (up to 20mA
CC
INTV must cross its 4.25V undervoltage lockout level.
CC
load current).
This generates a 100µs to 160µs power-on-reset pulse
during which the FAULT register bits are cleared and the
CONTROL register bits are set or cleared as described in
the register section. After the power-on-reset pulse, the
voltages at the UVH, UVL and OV pins must satisfy UVH
> 2.56V, UVL > 2.291V and OV < 1.77V to indicate that
the input power is within the acceptable range and the EN
pin must be pulled low. All the above conditions must be
satisfiedthroughoutthedurationofthestart-updebounce
Bypass capacitors of 1µF and 0.1µF are recommended
at V and INTV , respectively. R should be chosen
IN
CC
IN
to accommodate the maximum supply current require-
ment of the LTC4261/LTC4261-2 (5mA) plus the supply
current required by any external devices driven by the
V and INTV pins at the minimum intended operation
IN
CC
voltage.
V48V(MIN) – VZ(MAX)
delaythatissetbyanexternalcapacitor(C
)connected
TMR
RIN ≤
to the TMR pin. C
is charged with a pull-up current of
IIN(MAX) +IEXTERNAL
TMR
10µA until the voltage at TMR reaches 2.56V. C
is then
TMR
The maximum power dissipation in the resistor is:
quickly discharged with a 12mA current. The initial delay
expires when TMR is brought below 75mV. The duration
of the start-up delay is given by:
2
)
V
48V(MAX) – VZ(MIN)
(
PMAX
=
RIN
CTMR
tD = 256ms •
1µF
If the power dissipation is too high for a single resistor,
use multiple low power resistors in series.
–48V RTN OUTPUT
A
R17
R18
100k
1%
R4
20k
OUTPUT
100k
SENSE
R
1%
SUPPLY
IN
8 × 240Ω IN SERIES
MONITOR
+
Q11
2N5401
Q12
2N5401
V
IN
1/4W EACH
5V
+
+
+
V
OUT
V
V
IN
V
DD
OUT
R21
1k
LUCENT
LTC2900
RST
LUCENT
FLTR100V10
MOC207
Q8
JW050A1-E
ON/OFF
R19
2.49k
1%
R20
2.49k
1%
C
C
IN
1µF
VCC
0.1µF
R6
R7A
10k
R7B
10k
R7
–
–
–
GND
100k
100k
V
V
V
OUT
CASE
IN
OUT
CASE
V
EE
V
V
V
OUT
–
EE
R8
7.5k
R9
5.1k
EE
V
V
7
21
23
ADIN
IN
22
1
6
INTV
V
IN
CC
FLTIN
PGI
SCL
V
EE
OUT
5V
5
C
L
SDAI
R22
1k
R23
1k
R24
5.1k
4000µF
+
100V
Q5
28
27
Q6
Q7
LTC4261CGN
PGIO
PG
0V TRANSIENT
RESEVOIR
CAPACITOR
V
V
CC
ANODE
CC
ANODE
CATHODE
V
O
V
O
V
DD
SCL
SDA
4
3
CATHODE
GND
MOC207
SDAO
ALERT
GND
Q3
Q4
MICRO-
CONTROLLER
PS9113
PS9113
V
V
CC
ANODE
CC
ANODE
V
EE
R
V
O
ALERT RST
GND
L
CATHODE V
GND
CATHODE
GND
OUT
R
L
HCPL-0300
6N139
343Ω
V
OUT
MBRM5100
7 × 2.4k, 0805
EACH 28.7W
42612 F02b
B
Figure 2b. 200W AdvancedTCA Hot Swap Controller with Input/Output Monitoring
2
and Power Good Watchdog Using LTC4261 in I C Mode (Part Two)
42612fb
13
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Ifanyoftheaboveconditionsisviolatedbeforethestart-up
Power Good Monitors
delay expires, C
is quickly discharged and the turn-on
TMR
When V of the pass transistor falls below 1.77V and
DS
sequenceisrestarted. Afteralltheconditionsarevalidated
throughout the start-up delay, the ON pin is then checked.
If it is high, the FET will be turned on. Otherwise, the FET
will be turned on when the ON pin is raised high or the FET
ON bit D3 in the CONTROL register is set to “1” through
GATE pulls above V – 1.2V, an internal power good
Z
signal is latched and a series of three delay cycles are
started as shown in Figure 3. When the first delay cycle
with a duration of 2t expires, the PG pin pulls low as a
D
power good signal to turn on the first module. When the
2
the I C interface.
second delay cycle (2t ) expires, the PGIO pin pulls low
D
The FET turn-on sequence follows by charging an external
as a power good signal to turn on the second module. The
capacitor at the SS pin (C ) with a 10µA pull-up current
third delay cycle with a duration of 4t is for PGI check.
SS
D
and the voltage at SS (V ) is converted to a current
Before the third delay cycle expires, the PGI pin must be
pulled low by an external supply monitor (such as the
LTC2900 in Figure 2) to keep the FET on. Otherwise, the
FET is turned off and the power bad fault (PBAD) is logged
SS
(I
) of 11.5µA· V /2.56V for GATE pull-up. When
GATE(UP)
SS
the GATE reaches the FET threshold voltage, the inrush
current starts to flow through the FET and a current
(I
RAMP
) of 20µA· V /2.56V flows out of the RAMP pin
in the FAULT register. The 2t timer delay is obtained by
SS
D
andthroughanexternalcapacitor(C )connectedbetween
charging C with a 5µA current and discharging C
TMR TMR
R
RAMPandV .TheSSvoltageisclampedto2.56V,which
with a 12mA current when TMR reaches 2.56V. For the
4t timer delay, the charging and discharging currents of
OUT
corresponds to I
= 11.5µA and I
= 20µA. The
GATE(UP)
RAMP
D
TMR
RAMP pin voltage is regulated at 1.1V and the ramp rate
C
are both 5µA. The power good signals at PG and
of V
determines the inrush current:
PGIO are reset in all FET turn-off conditions except the
overvoltage fault.
OUT
CL
CR
IINRUSH = 20µA •
Turn-Off Sequence and Auto-Retry
The ramp rate of V determines dI/dt of the inrush
In any of the following conditions, the FET is turned off
by pulling down GATE with a 110mA current, and CSS
and CTMR are discharged with 12mA currents.
SS
current:
dIINRUSH
dt
CL
1µF
= 20µA •
•
1. The ON pin is low or the ON bit in the CONTROL reg-
ister is set to 0.
CR 256ms •CSS
If C is absent, an internal circuit pulls the SS pin from
SS
2. The EN pin is high.
0V to 2.56V in about 220µs.
3. The voltage at UVL is lower than 2.291V and the volt-
age at UVH is lower than 2.56V (undervoltage fault).
When V
is ramped down to V , I
returns to
GATEH
OUT
EE GATE
the GATE pin and pulls the GATE up to V
. Figure 3
illustrates the start-up sequence of the LTC4261/
LTC4261-2.
4. The voltage at OV is higher than 1.77V (overvoltage
fault).
During board insertion and input power step, an internal
5. The voltage at V is lower than 9V (V undervoltage
IN
IN
clamp turns on to hold the RAMP pin low. Capacitor C
F
lockout).
and resistor R suppress the noise at the RAMP pin. For
F
proper operation, R • C should not exceed 50µs. The
F
R
recommended value of C is 3 • C .
F
R
42612fb
14
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
RTN_V
EE
UVH
PWRGD1
DELAY
PWRGD2
DELAY
PGI CHECK
DELAY
START-UP DELAY
TMR
SS
1x
2x
2x
4x
V
– 1.2V
Z
GATE
V
OUT
1.77V
50mV
LOAD 1 + LOAD 2
LOAD 1
SENSE
INRUSH
LATCHED
INTERNAL
PWRGD
PWRGD1
READY
PG
PWRGD2
READY
PGIO
PGI
POWER BAD
NORMAL PGI
42612 F03
Figure 3. LTC4261 Turn-On Sequence
to 0, the FET is latched off upon the fault condition. If
the auto-retry bit is set to 1, after the fault condition is
cleared, a delay timer is started. After the timer expires,
the FET enters the auto-retry mode and GATE is pulled
up. The auto-retry delay following the undervoltage fault
6. The voltage at INTV is lower than 4.25V (INTV
CC
CC
undervoltage lockout).
7. V
> 50mV and the condition lasts longer than
SENSE
530µs (overcurrent fault).
or the power bad fault has a duration of t . The auto-
8. The PGI pin is high when the PGI check timer expires
(power bad fault).
D
retry delay following the overcurrent fault has a duration
of 4t for extra cooling time. The auto-retry following the
D
For conditions 1, 2, 5, 6, after the condition is cleared,
the LTC4261/LTC4261-2 will automatically enter the FET
turn-on sequence as previously described.
overvoltage fault does not have a delay. The auto-retry
control bits and their defaults at power up are listed in
Table 6. Note that the LTC4261 defaults to latch-off while
the LTC4261-2 defaults to auto-retry following the over-
current fault.
For any of the fault conditions 3, 4, 7, 8, the FET off
mode is programmable by the corresponding auto-retry
bit in the CONTROL register. If the auto-retry bit is set
42612fb
15
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
EN and ON
and starting a 530µs circuit breaker timer and 150mV for
a fast GATE pull-down to limit peak current in the event
of a catastrophic short circuit or an input step.
Figure 4 shows a logic diagram for EN and ON as they
relate to GATE, ALERT and internal registers A4, A7, B4,
C4 and D3. Also affecting GATE is the status of UV, OV
and several other fault conditions. The EN and ON pins
have 0.8V to 2V logic thresholds relative to V with a
maximum input leakage current of 2µA.
In an overcurrent condition, when the voltage drop across
R exceeds 50mV, the current limit loop is engaged and
S
an internal 530µs circuit breaker timer is started. The
EE
current limit loop servos the GATE to maintain a constant
output current of 50mV/R . When the circuit breaker
S
Register bit A4 indicates the present state of EN, and B4
is set high whenever EN changes state. Rising and falling
edges at the ON pin set and clear FET-on control bit, D3.
Another path allows a falling edge at EN to latch a high
state at the ON pin (such as when ON is permanently
pulled high) into D3 after a time delay. Both B4 and D3
can be set or cleared directly by I C, and both are cleared
low whenever INTV drops below its UVLO threshold.
The condition of the GATE pin output is controlled by
register bit A7, which is the AND of A4, D3 and the ab-
sence of UV, OV and other faults.
timer expires, the FET is turned off by pulling GATE down
with a 110mA current, the capacitors at SS and TMR are
discharged and the power good signals are reset. At this
time, the overcurrent present bit A2 and the overcurrent
fault bit B2 are set, and the circuit breaker timer is reset.
2
After the FET is turned off, the overcurrent present bit
A2 is cleared. If the overcurrent auto-retry bit D2 has
been set, the FET will turn on again automatically after
CC
a cooling time of 4t . Otherwise, the FET will remain off
D
until the overcurrent fault bit B2 is reset. When the over-
current fault bit is reset (see Resetting Faults), the FET
Overcurrent Protection and Overcurrent Fault
is allowed to turn on again after a delay of 4t . The 4t
D
D
cooling time associated with the overcurrent fault will not
be interrupted by any other fault condition. See Figure 5
for operation of LTC4261/LTC4261-2 under overcurrent
condition followed by auto-retry.
The LTC4261/LTC4261-2 feature two levels of protec-
tion from short-circuit and overcurrent conditions. Load
current is monitored by the SENSE pin and resistor
R . There are two distinct thresholds for the voltage at
S
SENSE: 50mV for engaging the active current limit loop
ABSENCE OF UV/OV AND OTHER FAULTS
GATE ON
ALERT
A4
A7
INTV UVLO
CC
CLR
STATE-CHANGE
DETECTOR
ALERT*
S
Q
B4
C4
S
Q
EN
ON
R/W
CLR
1 t
D
TIMER
DELAY
2
I C ALERT RESPONSE
READ ANY REGISTER
2
I C
*B4 • C4 IS ONE OF SEVEN CONDITIONS
THAT CAN GENERATE AN ALERT OUTPUT.
SEE TABLE 5
R/W
CLR
S
R
EDGE
DETECTOR
42612 F04
D3
Q
INTV UVLO
CC
Figure 4. Logic Block Diagram of EN and ON Pins
42612fb
16
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
PWRGD1
DELAY
PWRGD2
DELAY
OC COOLING DELAY
TMR
2x
2x
4x
SS
V
Z
– 1.2V
GATE
V
OUT
1.77V
50mV
SENSE
530µs
INRUSH
PG
PGIO
42612 F05
Figure 5. Overcurrent Fault and Auto-Retry
In the case of a low impedance short circuit on the load
side or an input step during battery replacement, cur-
rent overshoot is inevitable. A fast SENSE comparator
with a threshold of 150mV detects the overshoot and
immediately pulls GATE low with a 110mA current. Once
the SENSE voltage drops to 50mV, the current limit loop
takes over and servos the current as previously de-
scribed. If the short-circuit condition lasts longer than
530µs, the FET is shut down and the overcurrent fault is
registered.
current and the inrush current to avoid engagement of
the current limit loop in the event of an input step. The
maximum value of the inrush current is given by:
45mV
RS
IINRUSH ≤ 0.8 •
–ILOAD
where the 0.8 factor is used as a worst case margin com-
bined with the minumum threshold (45mV).
The active current limit circuit is compensated using the
capacitor C with a series resistor R (10Ω) connected
G
G
Inthecaseofaninputstep,afteraninternalclamppullsthe
RAMP pin down to 1.1V, the inrush control circuit takes
over and the current limit loop is disengaged before the
circuitbreakertimerexpires.Fromthispointon,thedevice
between GATE and V , as shown in Figure 1. The sug-
EE
gested value for C is 50nF. This value should work for
G
most pass transistors (Q1).
works as in the initial start-up: V
is ramped down at the
Overvoltage Fault
OUT
rate set by I
and C followed by GATE pull-up. The
RAMP
R
An overvoltage fault occurs when the OV pin rises above
its 1.77V threshold. This shuts off the pass transistor
immediately, sets the overvoltage present bit A0 and
the overvoltage fault bit B0, and pulls the SS pin down.
Note that the power good signals are not affected by the
overvoltage fault. If the OV pin subsequently falls back
power good signals on the PG and PGIO pins, the TMR
pin, and the SS pin are not interrupted through the input
step sequence. The waveform in Figure 6 shows how the
LTC4261/LTC4261-2respondstoaninputstep.
Note that the current limit threshold should be set
sufficiently high to accommodate the sum of the load
below the threshold, the pass transistor will be allowed
42612fb
17
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
72V
RTN – V
EE
36V
0V
TMR
SS
2.56V
V
GATEH
GATE
FET V
TH
V
OUT
50mV
LOAD + INRUSH
SENSE
LOAD
0V
LOAD
PG
0V
PGIO
42612 F06
Figure 6. –36V to –72V Step Response
to turn on again immediately (without delay) unless the
overvoltage auto-retry has been disabled by clearing reg-
ister bit D0.
an undervoltage shutdown threshold of 38.5V and an
overvoltage shutdown threshold of 72.3V.
The UV hysteresis can be adjusted by separating the
UVH and the UVL pins with a resistor R (Figure 7). To
H
Undervoltage Comparator and Undervoltage Fault
increase the UV hysteresis, the UVL tap should be placed
above the UVH tap as in Figure 7a. To reduce the UV hys-
teresis, place the UVL tap under the UVH tap as in Figure
7b. UV hysteresis referred to the UVL pin is given by:
The LTC4261/LTC4261-2 provide two undervoltage pins,
UVH and UVL, for adjustable UV threshold and hyster-
esis. The UVH and UVL pins have the following accurate
thresholds:
for VUVL ≥ VUVH
,
For UVH rising, V
For UVL falling, V
= 2.56V, turn on
= 2.291V, turn off
UVH(TH)
UVL(TH)
RH
R1+R2
∆VUVL(HYST) = ∆VUV(HYST) + 2.56V •
or for VUVL < VUVH
,
Both UVH and UVL pins have a minimum hysteresis of
δV (15mV typical). In either a rising or a falling input
RH
UV
∆VUVL(HYST) = ∆VUV(HYST) – 2.56V •
supply, the undervoltage comparator works in such a way
that both the UVH and the UVL pins have to cross their
thresholds for the comparator output to change state.
R1+R2+RH
For V
< V , the minimum UV hysteresis allowed is
UVH
UVL
the minimum hysteresis at UVH and UVL: δV = 15mV
UV
The UVH, UVL, and OV threshold ratio is designed to
match the standard telecom operating range of 43V to
71V and UV hysteresis of 4.5V when UVH and UVL are
tied together as in Figure 1, where the built-in UV hyster-
esis referred to the UVL pin is:
when R
= 0.11 • (R1 + R2)
H(MAX)
The design of the LTC4261/LTC4261-2 protects the UV
comparator from chattering even when R is larger than
H
R
.
H(MAX)
An undervoltage fault occurs when the UVL pin falls be-
ΔV
= V
– V
= 0.269V
UV(HYST)
UVH(TH)
UVL(TH)
low 2.291V and the UVH pin falls below 2.56V – δV .
UV
Using R1 = 11.8k, R2 = 16.9k and R3 = 453k as in Figure 1
gives a typical operating range of 43.0V to 70.7V, with
This activates the FET turn-off and sets the undervoltage
42612fb
18
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
–48V RTN
–48V RTN
Power Bad Fault
R3
R3
After the FET is turned on and the power good outputs
453k
453k
1%
1%
pull PG and PGIO low, a delay timer with duration of 4t is
D
UVL
UVH
0V
UVH
UVL
0V
R
H
1.91k
1%
R
H
1.91k
1%
started and the level of the PGI pin is checked (Figure 3).
If the PGI pin is pulled below its 1.4V threshold before
the PGI check timer expires, the FET will remain on.
Otherwise, the FET is immediately turned off, the power
good signals are reset and the power bad present bit A3
and the power bad fault bit B3 are set. After the FET is
turned off, the power bad present bit A3 will be cleared.
If the PGI pin is subsequently pulled low, the FET will
remain off unless the power bad auto-retry has been en-
abled by setting bit D4 or the power bad fault bit B3 is
cleared. In either of those two conditions, the FET will
TURN-ON = 46V
TURN-OFF = 38.5V
HYSTERESIS = 7.5V
TURN-ON = 43V
TURN-OFF = 41.2V
HYSTERESIS = 1.8V
R2
15k
1%
R2
15k
1%
R1
11.8k
1%
R1
11.8k
1%
42612 F07
–48V INPUT
–48V INPUT
(7a)
(7b)
Figure 7. Adjustment of Undervoltage Thresholds
for Larger (7a) or Smaller (7b) Hysteresis
turn on again following a delay of t and the PGI pin is
D
present bit A1 and the undervoltage fault bit B1. The
power good signals at PG and PGIO are also reset.
checked again as described above.
External Fault Monitors
The undervoltage present bit A1 is cleared when the
UVH pin rises above 2.56V and the UVL pin rises above
The FLTIN pin (SSOP only) and the PGIO pin, when con-
figured as general purpose input, allow monitoring of ex-
ternal fault conditions such as broken fuses. If FLTIN is
pulled below its 1.4V threshold, bit B7 in the FAULT reg-
ister is set. An associated alert bit, C7, is also available
in the ALERT register. When the PGIO pin is configured
as general purpose input, if the voltage at PGIO is above
1.25V, both bit A6 in the STATUS register and bit B6 in
the FAULT register are set, though there is no alert bit as-
sociated with this fault. The external fault conditions do
not directly affect the GATE control functions.
2.291V + δV . After a delay of t , the FET will turn on
UV
D
again unless the undervoltage auto-retry has been dis-
abled by clearing bit D1.
When power is applied to the device, if UVL is below
the 2.291V threshold and UVH is below 2.56V – δV
UV
after INTV crosses its undervoltage lock out threshold
CC
(4.25V), an undervoltage fault will be logged in the fault
register.
Because of the compromises of selecting from a table of
discrete resistor values (1% resistors in 2% increments,
0.1% resistors in 1% increments), best possible OV and
UV accuracy is achieved using separate dividers for each
pin. This increases the total number of resistors from
three or four to as many as six, but maximizes accuracy,
greatly simplifies calculations and facilitates running
changes to accommodate multiple standards or custom-
ization without any board changes.
Fault Alerts
When any of the fault bits in FAULT register B is set, an
optionalbusalertcanbegeneratedbysettingtheappropri-
ate bit in the ALERT register C. This allows only selected
faultstogeneratealerts.Atpower-upthedefaultstateisnot
to alert on faults. If an alert is enabled, the corresponding
fault will cause the ALERT pin to pull low. After the bus
master controller broadcasts the alert response address,
the LTC4261/LTC4261-2 will respond with its address on
the SDA line and release ALERT as shown in Figure 14.
If there is a collision between two LTC4261’s responding
with their addresses simultaneously, then the device with
FET Short Fault
AFETshortfaultwillbereportedifthedataconvertermea-
sures a current sense voltage greater than or equal to 2mV
while the FET is turned off. This condition sets the FET
short present bit A5 and the FET short fault bit B5.
42612fb
19
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
the lower address wins arbitration and responds first. The
ALERT line will also be released if the device is addressed
by the bus master.
Turning the LTC4261/LTC4261-2 On and Off
Many methods of on/off control are possible using the
2
ON, EN, UV/OV, FLTIN or PGIO pins along with the I C
port. The EN pin works well with logic inputs or float-
Once the ALERT signal has been released for one fault,
it will not be pulled low again until the FAULT register
indicates a different fault has occurred, or the original
fault is cleared and it occurs again. Note that this means
repeated or continuing faults will not generate alerts until
the associated FAULT register bit has been cleared.
2
ing switch contacts; I C control is intended for systems
where the board operates only under command of a
central control processor and the ON pin is useful with
signals referenced to RTN, as are the UV (UVH, UVL) and
OV pins. PGIO and FLTIN control nothing directly, but are
2
useful for I C monitoring of connection sense or other
Resetting Faults
important signals.
2
Faults are reset with any of the following conditions.
First, writing zeros to the FAULT register B will clear the
associated fault bits. Second, the entire FAULT register is
cleared when either the ON pin or bit D3 goes from high
On/off control is possible with or without I C interven-
tion. Further, the LTC4261/LTC4261-2 may reside on
either the removable board or on the backplane. Even
when operating autonomously, the I C port can still ex-
2
to low, or if INTV falls below its 4.25V undervoltage
ercise control over the GATE output, although depending
on how they are connected, EN and ON could subse-
CC
lockout. Pulling the UVL pin below its 1.21V reset thresh-
old also clears the entire FAULT register. When the UVL
pin is brought back above 1.21V but below 2.291V, the
undervoltage fault bit B1 is set if the UVH pin is below
2.56V. This can be avoided by holding the UVH pin above
2.56V while toggling the UVL pin to reset faults. Finally,
when EN is brought from high to low, all fault bits except
bit B4 are cleared. The bit B4 that indicates an EN change
of state will be set.
2
quently override conditions set by I C. UV, OV and other
fault conditions seize control as needed to turn off the
2
GATE output, regardless of the state of EN, ON or the I C
port. Figure 8 shows five configurations of on/off control
of the LTC4261/LTC4261-2.
Determining factors in selecting a pin configuration for
autonomous operation are the polarity and voltage of the
controlling signal.
Fault bits with associated conditions that are still pres-
ent (as indicated in the STATUS Register A) cannot be
cleared. The FAULT register will not be cleared when
auto-retrying. When auto-retry is disabled, the existence
of B0 (overvoltage), B1 (undervoltage), B2 (overcurrent)
or B3 (power bad) fault keeps the FET off. After the fault
Optical Isolation. Figure 8a shows an optoisolator driv-
ing the ON pin. Rising and falling edges at the ON pin
turn the GATE output on and off. If ON is already high
when power is applied, GATE is delayed one t period.
D
The status of ON can be examined or overridden through
2
the I C port at register bit D3. This circuit works in both
bit is cleared and a delay of t (for B0, B1 and B3) or 4t
D
D
backplane and board resident applications.
(for B4) expires, the FET will turn on again. Note that if
Logic Control. Figure 8b shows an application using log-
ic signal control. Again, the ON pin is used as an input;
all remarks made concerning optoisolator control apply
here as well.
the overvoltage fault bit B0 is cleared by writing a zero
2
through I C, the FET is allowed to turn on without a de-
lay. If auto-retry is enabled, then a high value in A0, A1,
A2 or A3 will hold the FET off and the FAULT register is
ignored. Subsequently, when the A0, A1, A2 and A3 bits
are cleared, the FET is allowed to turn on again.
42612fb
20
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Ejector Switch or Loop-Through Connection Sense.
Floating switch contacts or a connection sense loop also
work well with the ON pin, replacing the phototransistor
in Figure 8a. If an insertion debounce delay is desired,
use the EN pin as shown in Figure 8c. Like Figures 8a
and 8b, this circuit works on either side of the backplane
connector.
Data Converter
The LTC4261/LTC4261-2 incorporates a 10-bit analog-
to-digital converter (ADC) that continuously monitors
three different voltages at (in the sequence of) SENSE,
ADIN2/OV (SSOP/QFN) and ADIN. The voltage between
the SENSE pin and V is monitored with a 64mV full
EE
scale and 62.5µV resolution, and the data is stored in
registers E and F. The ADIN and the ADIN2/OV pins are
monitored with a 2.56V full scale and 2.5mV resolution.
The data for the ADIN2/OV pin is stored in registers G
and H. The data for the ADIN pin is stored in registers I
and J.
Short Pin to RTN. Figure 8d uses the UV divider string to
detect board insertion. This method works equally well in
both backplane and board resident applications.
AdvancedTCA Style Control. Figure 2 shows an ATCA
application using EN as the interface to the LTC4261.
2
Register bit A4 allows the I C port to monitor the status
The results in registers E, F, G, H, I and J are updated at
a frequency of 7.3Hz. Setting CONTROL register bit D5
invokes a test mode that halts updating of these registers
so that they can be written to and read from for software
testing. By invoking the test mode right before reading
the ADC data registers, the 10-bit data separated in two
registers are synchronized.
of EN and by setting C4 high, bit B4 can generate an alert
to instantly report any changes in the state of EN.
2
I C Only Control. To lock out EN and ON, use the con-
figuration shown in Figure 8e and control the GATE pin
with register bit D3. The circuit defaults off at power up.
To default on, connect the ON pin to INTV . Either FLTIN
CC
or PGIO can be used as an input to monitor a connection
sense or other control signal. PGIO is configured as an
input by setting register bits D6 and D7 high; its input
state is stored at location B6. FLTIN is always an input
whose state is available from register bit B7. FLTIN gen-
erates an alert if C7 is set high.
The ADIN and ADIN2 pins can be used to monitor input
and output voltages of the Hot Swap controller as shown
in Figures 1 and 2.
LOOP OR
SWITCH
5V
1k
1M
INTV
INTV
INTV
CC
CC
CC
100k
LTC4261
LTC4261
LTC4261
ON
EN
ON
EN
EN
ON
V
V
EE
V
EE
EE
10nF
47k
–48V
–48V
–48V
(8a) Optoisolator Control
(8b) Logic Control
(8c) Contact Debounce Delay Upon
Insertion for Use with an Ejector
Switch or Loop-Through Style
Connection Sense
–48V
RTN
453k
INTV
INTV
ON
CC
ON
EN
CC
DEFAULT
ON
SDAO
SDAI
SCL
LTC4261
2
UVL
UVH
I C
LTC4261
DEFAULT
OFF
28.7k
V
V
EE
EE
EN
–48V
INPUT
–48V
42612 F08
2
(8d) Short Pin Connection Sense to RTN
(8e) I C-Only Control
Figure 8. On/Off Control of the LTC4261
42612fb
21
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Configuring the PGIO Pin
The FET is selected to handle the maximum power dissi-
pation during start-up or an input step. The latter usually
results in a larger power due to summation of the inrush
Table 6 describes the possible states of the PGIO pin us-
ing the CONTROL register bits D6 and D7. At power-up
the default state is for the PGIO pin to pull low when
the second power good signal is ready. Other uses for
the PGIO pin are to go high impedence when the sec-
ond power good is ready, a general purpose output and a
general purpose input. When the PGIO pin is configured
as a general purpose output, the status of bit C6 is sent
out to the pin. When it is configured as a general pur-
pose input, if the input voltage at PGIO is higher than
1.25V, both bit A6 in the STATUS register and bit B6 in
the FAULT register are set. If the input voltage at PGIO
subsequently drops below 1.25V, bit A6 is cleared. Bit
B6 can be cleared by resetting the FAULT register as de-
scribed previously.
current charging C and the load current. For a 36V input
L
2
step, the total P t in the FET is approximated by:
t
3
2
P2t = 36V •I
•
(
)
MAX
where t is the time it takes to charge up C :
L
CL • 36V 330µF • 36V
t =
=
= 18ms
IINRUSH
0.66A
2
2
which gives a P t value of 244W s.
2
Now the P t given by the SOA (safe operating area)
2
curves of candidate FETs must be lower than 244W s.
The SOA curves of the IRF1310NS provide for 5A at 50V
2
2
(250W) for 10ms, which gives a P t value of 625W s and
satisfies the requirement.
Design Example
As a design example, consider the 200W application with
Sizing R1, R2 and R3 for the required UV and OV thresh-
old voltages:
C = 330µF as shown in Figure 1. The operating voltage
L
range is from 43V to 71V with a UV turn-off threshold of
V
V
= 43V, V
= 38.5V, (using
38.5V.
UV(RISING)
UV(FALLING)
= 2.56V and V
= 2.291V)
UVH(TH)
UVH(TH)
The design flow starts with calculating the maximum in-
put current:
V
V
= 72.3V, V
OV(FALLING)
= 70.7V (using
OV(RISING)
= 1.77V rising and 1.7325V falling)
OV(TH)
200W
36V
IMAX
=
= 5.6A
Layout Considerations
where 36V is the minimum input voltage.
To achieve accurate current sensing, a Kelvin connection
is recommended. The minimum trace width for 1oz cop-
per foil is 0.02" per amp to make sure the trace stays at a
reasonable temperature. Using 0.03" per amp or wider is
recommended. Note that 1oz copper exhibits a sheet re-
sistance of about 530µΩ/square. Small resistances add
up quickly in high current applications. To improve noise
immunity, put the resistive divider to the UV and OV pins
The selection of the sense resistor, R , is determined by
S
the minimum current limit threshold and maximum input
current:
∆VSENSE(MIN)
45mV
5.6A
RS =
=
= 8mΩ
IMAX
The inrush current is set to 0.66A using C :
R
close to the chip and keep traces to V and V short.
IN
EE
A 0.1µF capacitor from the UVH or UVL pin (and OV pin
IRAMP
IINRUSH
20µA
0.66A
CR = CL •
= 330µF •
= 10nF
through resistor R2) to V helps reject supply noise.
EE
The value of R and C are chosen to 1k and 33nF as
F
F
discussed previously.
42612fb
22
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
2
I C Interface
line is used as an interrupt for the host to respond to a
fault in real time, connect the ALERT to an optoisolator in
a way similar to that for the SDAO as shown in Figure 2.
2
The LTC4261/LTC4261-2 feature an I C interface to pro-
vide access to the ADC data registers and four other reg-
isters for monitoring and control of the pass FET. Figure 9
START and STOP Conditions
2
shows a general data transfer format using the I C. The
When the bus is idle, both SCL and SDA must be high. A
bus master signals the beginning of a transmission with
a START condition by transiting SDA from high to low
while SCL is high. When the master has finished com-
municating with the slave, it issues a STOP condition by
transiting SDA from low to high while SCL is high. The
bus is then free for another transmission.
LTC4261/LTC4261-2 are read-write slave devices and
supportSMBusbusReadByte,WriteByte,ReadWordand
Write Word commands. The second word in a Read Word
command will be identical to the first word. The second
word in a Write Word command is ignored. The data for-
matsforthesecommandsareshowninFigures10to13.
Using Optoisolators with SDA
Stuck-Bus Reset
The LTC4261/LTC4261-2 split the SDA line into SDAI (in-
put) and SDAO (output) for convenience of opto-coupling
with the host. If optoisolators are not used then tie SDAI
and SDAO together to form a normal SDA line. When us-
ing optoisolators, connect the SDAI to the output of the
incoming optoisolator and connect the SDAO to the input
of the outgoing optoisolator (see Figure 2). If the ALERT
2
The LTC4261/LTC4261-2 I C interface features a stuck-
bus reset timer. The low conditions of the SCL and the
SDAI pins are ORed to start the timer. The timer is reset
when both SCL and SDAI are pulled high. If the SCL pin
or the SDAI pin is held low for over 66ms, the stuck-bus
2
timer will expire and the internal I C state machine will be
SDA
SCL
a6 - a0
1 - 7
b7 - b0
b7 - b0
8
9
1 - 7
8
9
1 - 7
8
9
S
P
START
CONDITION
ADDRESS
R/W
ACK
DATA
ACK
DATA
ACK
STOP
CONDITION
42612 F09
2
Figure 9. Data Transfer over I C or SMBus
S
ADDRESS W A
0 0 1 a3:a0
COMMAND
A
DATA
A
P
S
ADDRESS W A
0 0 1 a3:a0
COMMAND
A
DATA
b7:b0
A
DATA
A
P
0
0
X X X X b3:b0
0
b7:b0
0
0
0
X X X X b3:b0
0
0
X X X X X X X X
0
42612 F11
FROM MASTER TO SLAVE
FROM SLAVE TO MASTER
A: ACKNOWLEDGE (LOW)
A: NOT ACKNOWLEDGE (HIGH)
R: READ BIT (HIGH)
Figure 11. LTC4261 Serial Bus SDA Write Word Protocol
W: WRITE BIT (LOW)
S: START CONDITION
S
ADDRESS W A
0 0 1 a3:a0
COMMAND
A
S
ADDRESS
R
A
DATA
A
P
P: STOP CONDITION
0
0
X X X X b3:b0
0
0 0 1 a3:a0
1
0
b7:b0
1
42612 F10
42612 F12
Figure 10. LTC4261 Serial Bus SDA Write Byte Protocol
Figure 12. LTC4261 Serial Bus SDA Read Byte Protocol
S
ADDRESS W A
0 0 1 a3:a0
COMMAND
A
S
ADDRESS
R
A
DATA
A
DATA
A
P
0
0
X X X X b3:b0
0
0 0 1 a3:a0
1
0
b7:b0
0
b7:b0
1
42612 F13
Figure 13. LTC4261 Serial Bus SDA Read Word Protocol
42612fb
23
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
reset to allow normal communication after the stuck-low
condition is cleared. When the SCL pin and the SDAI pin
are held low alternatively, if the ORed low period of SCL
and SDAI exceeds 66ms before the timer reset condi-
tion (both SCL and SDAI are high) occurs, the stuck-bus
acknowledge this and then the master sends a command
byte which indicates which internal register the master
wishes to write. The LTC4261/LTC4261-2 acknowledge
this and then latch the lower four bits of the command
byte into its internal Register Address pointer. The master
then delivers the data byte and the LTC4261/LTC4261-2
acknowledge once more and latch the data into its inter-
nal register. The transmission is ended when the master
sends a STOP condition. If the master continues sending
a second data byte, as in a Write Word command, the
second data byte will be acknowledged by the LTC4261/
LTC4261-2 but ignored.
2
timer will expire and the I C state machine is reset.
2
I C Device Addressing
2
Any of eight distinct I C bus addresses are selectable us-
ing the three-state pins ADR0 and ADR1, as shown in
Table 1. Note that the configuration of ADR0 = L and ADR1
= H is used to enable the single-wire broadcasting mode.
2
For the eight I C bus addresses, address bits B6, B5 and
Read Protocol
B4 are configured to (001) and the least significant bit B0
is the R/W bit. In addition, the LTC4261/LTC4261-2 will
respond to two special addresses. Address (0011 111)
is a mass write used to write to all LTC4261/LTC4261-2s,
regardless of their individual address settings. Address
(0001 100) is the SMBus Alert Response Address. If the
LTC4261/LTC4261-2 are pulling low on the ALERT pin,
it will acknowledge this address using the SMBus Alert
Response Protocol.
The master begins a read operation with a START con-
dition followed by the seven bit slave address and the
R/W bit set to zero. The addressed LTC4261/LTC4261-2
acknowledge this and then the master sends a command
byte that indicates which internal register the master
wishes to read. The LTC4261/LTC4261-2 acknowledge
this and then latch the lower four bits of the command
byte into its internal Register Address pointer. The mas-
ter then sends a repeated START condition followed by
the same seven bit address with the R/W bit now set to
one. The LTC4261/LTC4261-2 acknowledge and send the
contents of the requested register. The transmission is
ended when the master sends a STOP condition. If the
master acknowledges the transmitted data byte, as in a
Read Word command, the LTC4261/LTC4261-2 will re-
peat the requested register as the second data byte. Note
that the Register Address pointer is not cleared at the
end of the transaction. Thus the Receive Byte protocol
can be used to repeatedly read a specific register.
Acknowledge
The acknowledge signal is used for handshaking between
the transmitter and the receiver to indicate that the last
byte of data was received. The transmitter always re-
leases the SDA line during the acknowledge clock pulse.
When the slave is the receiver, it must pull down the SDA
line so that it remains LOW during this pulse to acknowl-
edge receipt of the data. If the slave fails to acknowl-
edge by leaving SDA HIGH, then the master can abort
the transmission by generating a STOP condition. When
the master is receiving data from the slave, the master
must pull down the SDA line during the clock pulse to
indicate receipt of the data. After the last byte has been
received the master will leave the SDA line HIGH (not
acknowledge) and issue a STOP condition to terminate
the transmission.
Alert Response Protocol
The LTC4261/LTC4261-2 implement the SMBus Alert
Response Protocol as shown in Figure 14. If enabled
to do so through the ALERT register C, the LTC4261/
LTC4261-2 will respond to faults by pulling the ALERT
pin low. Multiple LTC4261/LTC4261-2s can share a com-
mon ALERT line and the protocol allows a master to de-
termine which LTC4261/LTC4261-2s are pulling the line
low. The master begins by sending a START bit followed
Write Protocol
The master begins communication with a START con-
dition followed by the seven bit slave address and the
R/W bit set to zero. The addressed LTC4261/LTC4261-2
by the special Alert Response Address (0001 100)b with
42612fb
24
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
this means repeated or continuing faults will not gener-
ate alerts until the associated FAULT register bit has been
cleared.
ALERT
RESPONSE
ADDRESS
DEVICE
S
R
P
A
A
ADDRESS
0 0 0 1 1 0 0
1
0
0 0 1 a3:a0 0
1
42612 F14
Figure 14. LTC4261 Serial Bus SDA Alert Response Protocol
Single-Wire Broadcast Mode
TheLTC4261/LTC4261-2providesasingle-wirebroadcast
mode in which selected register data are sent out to the
SDAO pin without clocking the SCL line (Figure 15). The
single-wire broadcast mode is enabled by setting the
the R/W bit set to one. Any LTC4261/LTC4261-2 that is
pulling its ALERT pin low will acknowledge and begin
sending back its individual slave address.
2
An arbitration scheme ensures that the LTC4261/
LTC4261-2 with the lowest address will have priority;
all others will abort their response. The successful re-
sponder will then release its ALERT pin while any others
will continue to hold their ALERT pins low. Polling may
also be used to search for any LTC4261/LTC4261-2 that
have detected faults. Any LTC4261/LTC4261-2 pulling its
ALERT pin low will also release it if it is individually ad-
dressed during a read or write transaction.
ADR1 pin high and the ADR0 pin low (the I C interface is
disabled). At the end of each conversion of the three ADC
channels, a stream of eighteen bits are broadcasted to
SDAO with a serial data rate of 15.3kHz 20% in a format
as illustrated in Figure 16. The data bits are encoded with
an internal clock in a way similar to Manchester encoding
that can be easily decoded by a microcontroller or FPGA.
Each data bit consists of a noninverting phase and an
inverting phase. During the conversion of each ADC chan-
nel, SDAO is idle at high. At the end of the conversion, the
SDAO pulls low. The START bit indicates the beginning of
data broadcasting and is used along with the dummy bit
The ALERT signal will not be pulled low again until the
FAULT register indicates a different fault has occurred or
the original fault is cleared and it occurs again. Note that
–48V RTN
6 × 0.51k IN SERIES
1/4W EACH
5V
7.5k
INTV
V
IN
CC
ADR1
ADR0
SDAI
SCL
V
CC
LTC4261
1µF
V
DD
ANODE
R
D
IN
L
MICRO-
CONTROLLER
0.1µF
CATHODE V
GND
SDAO
V
EE
OUT
–48V INPUT
HCPL-0300
42612 F15
Figure 15. Single-Wire Broadcast Mode
INTERNAL
CLK
.. .. ..
DATA
START DMY
CH1
CH0 ADC9
ADC0
OC
UV
OV
PRTY
SDAO
4261 F16
START
Figure 16. Single-Wire Broadcast Data Format
42612fb
25
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
(DMY) to measure the internal clock cycle (i.e., the serial
datarate).FollowingtheDMYbitaretwochannelcodebits
CH1 and CH0 labeling the ADC channel (see Table 10). Ten
data bits of the ADC channel (ADC9-0) and three FAULT
register bits (B2, B1 and B0) are then sent out. A parity bit
(PRTY) ends each data stream. After that the SDAO line
enters the idle mode with SDAO pulled high.
7. Wait 3/4 of a clock cycle.
8. Sample bit CH0, wait for transistion.
9. Wait 3/4 of a clock cycle.
10. Sample ADC9, wait for transistion.
11. Continue until all bits are read.
The above procedure can be ported to a microcontroller
or used to design a state machine in FPGA. Code should
have timeouts in case an edge is missed. Abort the read
if it takes more than double the typical time (1.2ms) for
all 18 bits to be clocked out.
The following data reception procedure is recommended:
0. Wait for INTV rising edge.
CC
1. Wait for SDAO falling edge.
2. The first falling edge could be a glitch, so check again
after a delay of 10µs. If back to high, wait again. If still
low, it is the START bit.
A typical application circuit with the LTC4261/LTC4261-2
in the broadcast mode is illustrated in Figure 17, where
input voltage, V of the FET and V
are monitored.
DS
SENSE
3. Use the following low-to-high and high-to-low transis-
tions to measure 1/2 of the internal clock cycle.
Register Addresses and Contents
4. Wait for the second low-to-high transistion (middle of
DMY bit).
The register addresses and contents are summerized in
Table 1 and Table 2. The function of each register bit is
detailed in Tables 3 to 9.
5. Wait 3/4 of a clock cycle.
6. Sample bit CH1, wait for transistion.
42612fb
26
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Table 1. LTC4261 Device Addressing
HEX DEVICE
ADDRESS
LTC4261
ADDRESS PINS
DESCRIPTION
BINARY DEVICE ADDRESS
h
6
0
0
0
0
0
0
0
0
0
0
5
0
0
0
0
0
0
0
0
0
0
4
1
0
1
1
1
1
1
1
1
1
3
1
1
0
0
0
0
0
0
0
0
2
1
1
0
0
0
0
1
1
1
1
1
1
0
0
0
1
1
0
0
1
1
0
1
0
0
1
0
1
0
1
0
1
R/W
0
ADR1
X
ADR0
X
Mass Write
3E
19
20
22
24
26
28
2A
2C
2E
Alert Response
1
X
X
0
1
2
3
4
5
6
7
8
X
L
L
X
L
NC
NC
H
X
H
X
L
X
NC
NC
H
L
X
NC
H
X
X
NC
H
H
Single-Wire Broadcast Mode
L
H = Tie to INV ; L = Tie to V ; NC = No connect, open; X = Don’t care
CC
EE
Table 2. LTC4261 Register Address and Contents
REGISTER
ADDRESS*
REGISTER
NAME
READ/WRITE
DESCRIPTION
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
STATUS (A)
FAULT (B)
R
System Status Information
Fault Log and PGIO Input
R/W
ALERT (C)
CONTROL (D)
SENSE (E)
SENSE (F)
ADIN2/OV (G)
ADIN2/OV (H)
ADIN (I)
R/W
Controls Whether the ALERT Pin is Pulled Low After a Fault is Logged in the Fault Register
Controls Whether the Part Retries After Faults, Set the On/Off Switch State
ADC Current Sense Voltage Data (8 MSBs)
R/W
R/W**
R/W**
R/W**
R/W**
R/W**
R/W**
ADC Current Sense Voltage Data (2 LSBs)
ADC ADIN2/OV (SSOP/QFN) Voltage Data (8 MSBs)
ADC ADIN2/OV (SSOP/QFN) Voltage Data (2 LSBs)
ADC ADIN Voltage Data (8 MSBs)
ADIN (J)
ADC ADIN Voltage Data (2 LSBs)
*Register address MSBs b7-b4 are ignored. **Writable if bit D5 set.
42612fb
27
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Table 3. STATUS Register A (00h)—Read Only
BIT
A7
A6
A5
A4
A3
A2
A1
A0
NAME
OPERATION
FET On
Indicates State of FET; 1 = FET On, 0 = FET Off
PGIO Input
FET Short
EN
Indicates State of the PGIO Pin when Configured to General Purpose Input: 1 = PGIO High, 0 = PGIO Low
Indicates Potential FET Short if Current Sense Voltage Exceeds 2mV While FET is Off; 1 = FET is Shorted, 0 = FET is Not Shorted
Indicates State of the EN Pin; 1 = EN Pin High, 0 = EN Pin Low
Power Bad
Overcurrent
Undervoltage
Overvoltage
Indicates Power is Bad when PGI is High at the End of the PGI Check Timer; 1 = PGI High, 0 = PGI Low
Indicates Overcurrent Condition; 1 = Overcurrent, 0 = Not Overcurrent
Indicates Input Undervoltage when Both UVH and UVL are Low; 1 = UVH and UVL Low, 0 = UVH or UVL High
Indicates Input Overvoltage when OV is High; 1 = OV High, 0 = OV Low
Table 4. FAULT Register B (01h)—Read/Write
BIT
NAME
OPERATION
B7
External Fault
Occurred
Latched to 1 if FLTIN Goes Low; 1 = FLTIN Low State Detected, 0 = FLTIN has Not Been Low
B6
B5
B4
B3
B2
B1
B0
PGIO Input
Latched to 1 if the PGIO Pin Goes High when Configured to General Purpose Input; 1 = PGIO High Detected,
0 = PGIO has Been Low
High Occurred
FET Short Fault Indicates Potential FET Short was Detected When Measured Current Sense Voltage Exceeded 2mV While FET was Off;
Occurred
1 = FET Short Fault Occurred, 0 = No FET Short Fault
EN Changed
State
Indicates That a Board was Inserted or Extracted when EN Changed State; 1 = EN Changed State, 0 = EN Unchanged
Power Bad
Fault Occurred 0 = No Power Bad Fault
Indicates Power was Bad when PGI was High at the End of the PGI Check Timer; 1 = Power Bad Fault Occurred,
Overcurrent
Fault Occurred
Indicates Overcurrent Fault Occurred; 1 = Overcurrent Fault Occurred, 0 = No Overcurrent Fault
Indicates Input Undervoltage Fault Occurred when Both UVH and UVL went Low; 1 = Undervoltage Fault Occurred,
Undervoltage
Fault Occurred 0 = No Undervoltage Fault
Overvoltage
Fault Occurred
Indicates Input Overvoltage Fault Occurred when OV was High; 1 = Overvoltage Fault Occurred, 0 = No Overvoltage Fault
Table 5. ALERT Register C (02h)—Read/Write
BIT
NAME
OPERATION
C7
External Fault
Alert
Enables Alert for External Fault When FLTIN was Low; 1 = Enable Alert, 0 = Disable Alert (Default)
C6
C5
C4
PGIO Output
Output Data Bit to PGIO Pin when Configured as Output. Defaults to 0
FET Short Alert Enables Alert for FET Short Fault; 1 = Enable Alert, 0 = Disable Alert (Default)
EN State
Change Alert
Enables Alert when EN Changed State; 1 = Enable Alert, 0 Disable Alert (Default)
Enables Alert for Power Bad Fault; 1 = Enable Alert, 0 Disable Alert (Default)
Enables Alert for Overcurrent Fault; 1 = Enable Alert, 0 Disable Alert (Default)
Enables Alert for Undervoltage Fault; 1 = Enable Alert, 0 Disable Alert (Default)
Enables Alert for Overvoltage Fault; 1 = Enable Alert, 0 Disable Alert (Default)
C3
C2
C1
C0
Power Bad
Alert
Overcurrent
Alert
Undervoltage
Alert
Overvoltage
Alert
42612fb
28
LTC4261/LTC4261-2
APPLICATIONS INFORMATION
Table 6. CONTROL Register D (03h)—Read/Write
BIT
NAME
OPERATION
D7:6 PGIO Configure
Configures Behavior of PGIO Pin
FUNCTION
D6
D7
0
PGIO PIN
Open Drain
Open Drain
PGIO = C6
PGIO = Hi-Z
Power Good (Default)
Power Good
0
0
1
1
1
General Purpose Output
General Purpose Input
0
1
D5
D4
Test Mode Enable Test Mode Halts ADC Operation and Enables Writes to ADC Registers; 1 = Enable Test Mode, 0 = Disable Test Mode (Default)
Power Bad
Auto-Retry
Enables Auto-Retry After a Power Bad Fault; 1 = Retry Enabled, 0 = Retry Disabled (Default)
D3
D2
FET On Control
Turns FET On and Off; 1 = Turn FET On, 0 = Turn FET Off. Defaults to ON Pin State at End of Start-Up Debounce Delay
Overcurrent
Auto-Retry
Enables Auto-Retry After an Overcurrent Fault; 1 = Retry Enabled (Default, LTC4261-2),
0 = Retry Disabled (Default, LTC4261)
D1
D0
Undervoltage
Auto-Retry
Enables Auto-Retry After an Undervoltage Fault; 1 = Retry Enabled (Default), 0 = Retry Disabled
Overvoltage
Auto-Retry
Enables Auto-Retry After an Overvoltage Fault; 1 = Retry Enabled (Default), 0 = Retry Disabled
Table 7. SENSE Registers E (04h) and F (O5h)—Read/Write
BIT
NAME
OPERATION
E7:0, F7:6
F5:0
SENSE Voltage Data
Reserved
10-Bit Data of Current Sense Voltage with 62.5µV LSB and 64mV Full Scale
Always Returns 0, Not Writable
Table 8. ADIN2/OV Registers G (06h) and H (O7h)—Read/Write
BIT
NAME
ADIN2/OV Voltage Data 10-Bit Data of ADIN2/OV (SSOP/QFN) Voltage with 2.5mV LSB and 2.56V Full Scale
Reserved Always Returns 0, Not Writable
OPERATION
G7:0, H7:6
H5:0
Table 9. ADIN Registers I (08h) and J (O9h)—Read/Write
BIT
NAME
OPERATION
I7:0, J7:6
J5:0
ADIN Voltage Data
Reserved
10-Bit Data of ADIN Voltage with 2.5mV LSB and 2.56V Full Scale
Always Returns 0, Not Writable
Table 10. ADC Channel Labeling for Single-Wire Broadcast Mode
CH1
0
CH0
0
ADC CHANNEL
SENSE Voltage
0
1
ADIN2/OV (SSOP/QFN) Voltage
ADIN Voltage
1
0
42612fb
29
LTC4261/LTC4261-2
PACKAGE DESCRIPTION
GN Package
28-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.386 – .393*
(9.804 – 9.982)
.045 .005
.033
(0.838)
REF
28 27 26 25 24 23 22 21 20 19 18 17 1615
.254 MIN
.150 – .165
.229 – .244
.150 – .157**
(5.817 – 6.198)
(3.810 – 3.988)
.0165 .0015
.0250 BSC
1
2
3
4
5
6
7
8
9 10 11 12 13 14
RECOMMENDED SOLDER PAD LAYOUT
.015 .004
(0.38 0.10)
.0532 – .0688
(1.35 – 1.75)
× 45°
.004 – .0098
(0.102 – 0.249)
.0075 – .0098
(0.19 – 0.25)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
.008 – .012
.0250
(0.635)
BSC
GN28 (SSOP) 0204
(0.203 – 0.305)
TYP
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
3. DRAWING NOT TO SCALE
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
42612fb
30
LTC4261/LTC4261-2
PACKAGE DESCRIPTION
UFD Package
24-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1696 Rev A)
0.70 0.05
4.50 0.05
3.10 0.05
2.65 0.05
2.00 REF
3.65 0.05
PACKAGE OUTLINE
0.25 0.05
0.50 BSC
3.00 REF
4.10 0.05
5.50 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.05 TYP
PIN 1 NOTCH
2.00 REF
R = 0.20 OR C = 0.35
R = 0.115
TYP
0.75 0.05
4.00 0.10
(2 SIDES)
23
24
0.40 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 0.10
(2 SIDES)
3.00 REF
3.65 0.10
2.65 0.10
(UFD24) QFN 0506 REV A
0.25 0.05
0.200 REF
0.50 BSC
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
42612fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
31
LTC4261/LTC4261-2
TYPICAL APPLICATIONS
–48V RTN
R
6
IN
0.51k IN SERIES
R3
1/4W EACH
432k
1%
R4
5V
7.5k
INTV
V
IN
CC
UVL
SDAI
SCL
R2
15.8k
1%
UVH
ADIN2
OV
V
CC
V
C
DD
L
ANODE
R
L
D
LTC4261CGN
IN
330 F
100V
MICRO-
CONTROLLER
ADR1
ADR0
SDAO
ADIN
CATHODE V
GND
OUT
R1
11.5k
1%
V
SENSE GATE
EE
C
HCPL-0300
IN
1 F
R
S
C
VCC
0.02
5%
0.1 F
V
OUT
–48V INPUT
Q1
R6
10k 1%
R7
402k 1%
IRF1310NS
V
EE
4261 F17
Figure 17. Application Circuit of the LTC4261 in Single-Wire Broadcast Mode
–48V RTN
6 × 0.51k IN SERIES
1/4W EACH
VISHAY
2381 615 4.104
100k AT 25°C
1%
•
V
IN
30.1k
1%
LTC4261CGN
SDAO
2
ADIN
SDAI
SCL
I C
10k
1µF
1%
V
EE
–48V INPUT
42612 F18
T (°C) = 38.05 × (V
(V) – 0.1458), 20°C < T < 60°C
ADIN
Figure 18. Using the LTC4261 and a Thermistor to Monitor Temperature
RELATED PARTS
PART NUMBER
LT1640AH/LT1640AL
LTC1921
DESCRIPTION
COMMENTS
Negative High Voltage Hot Swap Controllers in SO-8 Negative High Voltage Supplies from –10V to –80V
Dual –48V Supply and Fuse Monitor
–48V Hot Swap Controllers in SO-8
–48V Hot Swap Controllers in SOT-23
–48V Hot Swap Controllers in MS8
UV/OV Monitor, –10V to –80V Operation, MSOP Package
LT4250L/LT4250H
LTC4251/LTC4251-1
Active Current Limiting, Supplies from –20V to –80V
Fast Active Current Limiting, Supplies from –15V
LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
Fast Active Current Limiting, Supplies from –15V,
1% UV/OV (LTC4252A)
LTC4253
–48V Hot Swap Controller with Sequencer
Fast Current Limiting with Three Sequenced Power Good Outputs,
Supplies from –15V
2
LTC4260
LTC4354
Positive High Voltage Hot Swap Controller
With I C and ADC, Supplies from 8.5V to 80V
Negative Voltage Diode-OR Controller and Monitor
Controls Two N-Channel MOSFETs, 1µs Turn-Off, 80V Operation
42612fb
LT 0706 REV B • PRINTED IN USA
32 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
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© LINEAR TECHNOLOGY CORPORATION 2005
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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