LINER LTC1645

LTC4222
Dual Hot Swap Controller
with I2C Compatible
Monitoring
DESCRIPTION
FEATURES
Allows Safe Insertion Into a Live Backplane
n 10-Bit ADC Monitors Currents and Voltages
nI2C/SMBus Interface
n Wide Operating Voltage Range: 2.9V to 29V
n dI/dt Controlled Soft-Start
n High Side Drive for External N-Channel MOSFETs
n No External Gate Capacitors Required
n Input Overvoltage/Undervoltage Protection
n Optional Latchoff or Auto-Retry After Faults
n Alert Host After Faults
n Inrush Current Limit with Foldback
n Available in 32-Pin (5mm × 5mm) QFN
and 36-Pin SSOP Packages
The LTC®4222 Hot Swap™ controller allows two power
paths to be safely inserted and removed from a live backplane. Using external N-channel pass transistors, board
supply voltages and inrush currents are ramped up at an
adjustable rate. An I2C interface and onboard ADC allows
for monitoring of current, voltage and fault status for
each channel.
n
The device features adjustable, analog, foldback current
limit circuits and a soft-start circuit that sets the dI/dt of
the inrush currents. An I2C interface may configure the
part to latch off or automatically restart after the LTC4222
detects a fault on either channel.
The controller has additional features to interrupt the host
when a fault has occurred, notify when output power is
good, detect insertion of a load card and power-up either
automatically upon insertion or wait for an I2C command
to turn on.
APPLICATIONS
n
n
n
n
Live Board Insertion
Electronic Circuit Breakers
Computers, Servers
Platform Management
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Hot
Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of
their respective owners. Protected by U.S. Patents including 7330065.
TYPICAL APPLICATION
Advanced Mezzanine Card Application
6mΩ
12V
Si7336ADP
34k
0.1µF
10Ω
1.02k
3.4k
ON
SDA
SCL
ALERT
NC
0.1µF
3.4k
UV1 VDD1
OV1
ON
SDA
SCL
ALERT
CONFIG
ADR0
ADR1
ADR2
INTVCC
GND
OV2
UV2 VDD2
3.57k
Start-Up Waveform with Sequencing
10k
SENSE1– GATE1 SOURCE1
FB1
GPIO1
EN1
ADIN1
TIMER
LTC4222
SS
ADIN2
EN2
10Ω
10nF
6.55k
VIN1/2
10V/DIV
12PGOOD
1µF
VOUT2
10V/DIV
68nF
VOUT1
10V/DIV
3.57k
50ms/DIV
10k
4.99k
3.3V
300mΩ
Si1046R
4222 TA01a
CONTACT
BOUNCE
GPIO
PGOOD
10V/DIV
AUXPGOOD
GPIO2
FB2
– GATE2 SOURCE2
SENSE2
1.02k
0.1µF
12V
7.4A
10.2k
4222 TA01b
3.3V
150mA
BACKPLANE PLUG-IN
CARD
4222fb
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LTC4222
ABSOLUTE MAXIMUM RATINGS (Notes 1, 2)
Supply Voltages (VDDn)............................... –0.3V to 35V
Supply Voltage (INTVCC)............................ –0.3V to 6.5V
Input Voltages
GATEn – SOURCEn (Note 3)..................... –0.3V to 5V
SENSE+n...........................VDDn – 6.5V to VDDn + 0.3V
SENSE–n..............................–0.3V to SENSE+n + 0.3V
SOURCEn................................................... –5V to 35V
UVn......................................–0.3V to SENSE+n + 0.3V
ENn, FBn, ON, OVn................................. –0.3V to 12V
ADR0-2, TIMER, SS................ –0.3V to INTVCC + 0.3V
ADINn, CONFIG....................................... –0.3V to 12V
ALERT, SCL, SDA, SDAI, SDAO............. –0.3V to 6.5V
Output Voltages
GATEn, GPIOn......................................... –0.3V to 35V
Operating Temperature Range
LTC4222C................................................. 0°C to 70°C
LTC4222I.............................................. –40°C to 85°C
Storage Temperature Range.................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
SSOP................................................................. 300°C
PIN CONFIGURATION
1
36 GATE1
SENSE1+
2
25 SOURCE1
GPIO1
TOP VIEW
SENSE1–
VDD1
3
34 FB1
UV1
4
33 GPIO1
32 31 30 29 28 27 26 25
OV1
5
32 EN1
SS
6
31 ADIN1
CONFIG
7
30 ON1
INTVCC
8
29 ON2
GND
9
28 ALERT
FB1
SOURCE1
GATE1
VDD1
SENSE1–
UV1
OV1
TOP VIEW
SS 1
24 EN1
CONFIG 2
23 ADIN1
INTVCC 3
22 ON
GND 4
21 ALERT
33
ADR0 5
20 SCL
ADR1 6
19 SDA
ADR2 7
18 ADIN2
TIMER 8
17 EN2
GPIO2
FB2
GATE2
SOURCE2
SENSE2–
VDD2
UV2
OV2
9 10 11 12 13 14 15 16
UH PACKAGE
32-LEAD (5mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
EXPOSED PAD (PIN 33), PCB GND CONNECTION OPTIONAL
ADR0 10
27 SCL
ADR1 11
26 SDAI
ADR2 12
25 SDAO
TIMER 13
24 ADIN2
OV2 14
23 EN2
UV2 15
22 GPIO2
VDD2 16
21 FB2
SENSE2+ 17
20 SOURCE2
SENSE2– 18
19 GATE2
G PACKAGE
36-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 95°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4222CG#PBF
LTC4222CG#TRPBF
LTC4222CG
36-Lead Plastic SSOP
0°C to 70°C
LTC4222IG#PBF
LTC4222IG#TRPBF
LTC4222IG
36-Lead Plastic SSOP
–40°C to 85°C
LTC4222CUH#PBF
LTC4222CUH#TRPBF
LTC4222
0°C to 70°C
32-Lead (5mm × 5mm) Plastic QFN
LTC4222IUH#PBF
LTC4222IUH#TRPBF
LTC4222
–40°C to 85°C
32-Lead (5mm × 5mm) Plastic QFN
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
4222fb
2
LTC4222
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD = 12V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supplies
VDDn
Input Supply Range
IDD1
VDD1 Input Supply Current
VDD1 = 12V
l
0.85
1.25
mA
IDD2
VDD2 Input Supply Current
VDD2 = 12V, IINTVCC = 0mA
l
3
4.5
mA
VDDn(UVL)
Input Supply Undervoltage Lockout
VDD Rising
l
2.34
2.43
2.53
V
VDDn(HYST)
Input Supply Undervoltage Lockout
Hysteresis
l
60
80
100
mV
INTVCC
Internal Regulator Voltage
IINTVCC = 0mA
l
3.15
3.3
3.45
V
INTVCC(UVL)
INTVCC Undervoltage Lockout
INTVCC Rising
l
2.55
2.64
2.73
INTVCC(HYST)
INTVCC Undervoltage Lockout Hysteresis
l
35
50
65
mV
l
47.5
48.75
50
50
52.5
51.25
mV
mV
l
2.9
29
V
V
Current Limit and Circuit Breaker (Both Channels)
∆VSENSE(TH)
Circuit Breaker Threshold (VDD – VSENSE)
∆VSENSE
Current Limit Voltage (VDD – VSENSE)
VFB = 1.3V
VFB = 0V
Start-Up Timer Expired
l
l
l
46
14
130
50
16.6
150
54
19
165
mV
mV
mV
tD(OC)
OC Fault Filter
∆VSENSE = 100mV
l
10
20
30
µs
ISENSE(IN)
SENSE+/SENSE– Pin Input Current
VSENSE = 12V
l
0
20
45
µA
∆VGATE
External N-Channel Gate Drive
(VGATE – VSOURCE) (Note 3)
VDD = 2.9V to 29V
l
4.7
5.9
6.5
V
IGATE(UP)
External N-Channel Gate Pull-Up Current
Gate On, VGATE = 0V
l
–8
–12
–18
µA
IGATE(DN)
External N-Channel Gate Pull-Down Current
Gate Off, VGATE = 15V
l
0.8
1
2.0
mA
IGATE(LIM)
Pull-Down Current from GATE to SOURCE
During OC/UVLO
VGATE = 15V, (VDD – VSENSE)n = 200mV
tPHL(SENSE)
(VDD – SENSE) High to GATE Low
VDD – SENSE = 200mV, CGATE = 10nF
l
VGS(POWERBAD)
(GATE-SOURCE) Voltage for Power Bad Fault
VSOURCE = 2.9V to 29V
l
CONFIG, EN, FB, ON, OV and UV Input
Threshold
VIN Rising
Gate Drive
450
mA
0.5
1
µs
3.8
4.3
4.7
V
l
1.215
1.235
1.255
V
l
Comparator Inputs
VINPUT(TH)
∆VCONFIG,EN,ON(HYST) CONFIG, EN, ON Hysteresis
80
128
180
mV
∆VFB(HYST)
FB Power Good Hysteresis
l
2
7
20
mV
∆VOV(HYST)
OV Hysteresis
l
16
24
32
mV
∆VUV(HYST)
UV Hysteresis
l
60
90
110
mV
I(IN)
CONFIG, FB, ON, OV and UV Input Current
VIN = 3V
l
0
±1
µA
IEN(UP)
EN Pull-Up Current
VEN = 0V
l
5
10
20
µA
VUV(RTH)
UV Reset Threshold Voltage
VUV Falling
l
0.36
0.4
0.46
V
∆VUV(RHYST)
UV Reset Threshold Hysteresis
l
60
125
180
mV
VGPIO(TH)
GPIO Input Threshold
l
0.8
1
1.2
V
VGPIO Rising
4222fb
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LTC4222
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD = 12V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VGPIO(OL)
GPIO Output Low Voltage
IGPIO = 5mA
IGPIO(OH)
GPIO Input Leakage Current
ISOURCE
SOURCE Input Current
tP(GATE)
Input (ON, OV, UV, EN) to GATE Off
Propagation Delay
tD(GATE)
GATE Turn-On Delay
VTIMERL(TH)
MIN
TYP
MAX
UNITS
l
0.25
0.4
V
VGPIO = 15V
l
0
±1
µA
SOURCE = 15V
l
115
170
µA
3
5
µs
Other Pin Functions
70
l
ON
UV, OV, EN
Overcurrent Auto-Retry
l
l
l
75
4.2
4
100
5
8
125
6.7
µs
ms
s
TIMER Low Threshold
l
0.18
0.2
0.22
V
VTIMERH(TH)
TIMER High Threshold
l
1.215
1.235
1.260
V
ITIMER(UP)
TIMER Pull-Up Current
l
90
100
110
µA
ITIMER(DOWN)
TIMER Pull-Down Current for OC
Auto-Retry
l
1.6
2.15
2.6
µA
ITIMER(UP/DOWN)
TIMER Pin OC Auto-Retry Duty Cycle
l
38
50
58
N/A
ISS
Soft-Start Ramp Pull-Up Current
l
l
7.5
0.5
10
0.75
12.5
0.95
µA
µA
l
10
Ramping
Waiting for GATE to Slew
ADC
Bits
RES
Resolution (No Missing Codes)
VFS
Full-Scale Voltage (1023 • VLSB)
(VDD – SENSE)
SOURCE
ADIN
64
32
1.28
mV
V
V
LSB
LSB Step Size
(VDD – SENSE)
SOURCE
ADIN
62.5
31.25
1.25
µV
mV
mV
VOS
Offset Error
(VDD – SENSE)
SOURCE
ADIN
l
l
l
±3
±2
±2
LSB
LSB
LSB
INL
Integral Nonlinearity
(Note 5)
l
±0.5
LSB
TUE
Total Unadjusted Error/Full-Scale Error
(VDD – SENSE)
SOURCE
ADIN
l
l
l
±1.5
±1
±1
%
%
%
RADIN
ADIN Sampling Resistance
VADIN = 1.28V
l
IADIN
ADIN Input Current
VADIN = 1.28V
l
Conversion Rate
1
2
0
15
MΩ
±0.1
µA
Hz
4222fb
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LTC4222
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD = 12V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
INTVCC
– 0.8
INTVCC
– 0.4
INTVCC
– 0.2
V
l
5
0
–5
µA
l
0.2
0.4
0.8
V
–80
80
µA
0.4
V
±1
µA
1.7
1.9
V
±1
µA
0.2
0.4
V
I2C Interface
VADR(H)
ADR0, ADR1, ADR2 Input High Voltage
IADR(IN,Z)
ADR0, ADR1, ADR2 Hi-Z Input Current
VADR(L)
ADR0, ADR1, ADR2 Input Low Voltage
IADR(IN)
ADR0, ADR1, ADR2 Input Current
ADR0, ADR1, ADR2 = 0V, INTVCC
l
VALERT(OL)
ALERT Output Low Voltage
IALERT = 3mA
l
IALERT(OH)
ALERT Input Current
ALERT = INTVCC
l
VSDA,SCL(TH)
SDA, SCL Input Threshold
ISDA,SCL(OH)
SDA, SCL Input Current
SCL, SDA = INTVCC
l
VSDA(OL)
SDA Output Low Voltage
ISDA = 3mA
l
fSCL(MAX)
SCL Clock Frequency
Operates with fSCL ≤ fSCL(MAX)
tBUF(MIN)
Bus Free Time Between Stop/Start Condition
0.12
tHD,STA(MIN)
Hold Time After (Repeated) Start Condition
100
600
ns
tSU,STA(MIN)
Repeated Start Condition Set-Up Time
30
600
ns
tSU,STO(MIN)
Stop Condition Set-Up Time
140
600
ns
tHD,DAT(MIN)
Data Hold Time (Input)
30
100
ns
tHD,DATO
Data Hold Time (Output)
300
600
900
ns
tSU,DAT(MIN)
Data Set-Up Time
30
600
ns
tSP
Suppressed Spike Pulse Width
50
110
250
ns
tRST
Stuck-Bus Reset Time
SCL or SDA Held Low
25
32
40
ms
CX
SCL, SDA Input Capacitance
SDAI Tied to SDAO (Note 5)
10
pF
ADR0, ADR1, ADR2 = 0.8V,
INTVCC – 0.8V
l
0.2
1.5
I2C Interface Timing
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
GND unless otherwise specified.
Note 3: An internal clamp limits the GATE pin to a minimum of 5V above
SOURCE. Driving this pin to voltages beyond the clamp may damage the
device.
400
1000
kHz
1.3
µs
Note 4: Integral Nonlinearity is defined as the deviation of a code from a
precise analog input voltage. Maximum specifications are limited by the
LSB step size and the single shot measurement. Typical specifications are
measured from 1/4, 1/2, 3/4 areas of the quantization band.
Note 5: Guaranteed by design and not subject to test.
4222fb
5
LTC4222
TYPICAL PERFORMANCE CHARACTERISTICS
1.0
IDD1 vs VDD1
4.0
TA = 25°C. VDDn = 12V unless otherwise noted.
IDD2 vs VDD2
3.4
0.9
INTVCC vs VDD2
3.3
3.5
0.7
INTVCC (V)
3.2
IDD2 (mA)
IDD1 (mA)
0.8
3.0
3.1
0.6
3.0
2.5
0.5
0.4
2.9
0
5
10
15
20
25
VDD1 (V)
3.50
2.0
30
0
5
10
15
20
25
VDD2 (V)
4222 G01
INTVCC vs ILOAD
1.250
2.8
2.5
30
3.0
4222 G02
VTH(UV) vs Temperature
100
3.5
4.0
VDD2 (V)
4.5
5.0
4222 G03
VHYST(UV) vs Temperature
1.245
95
3.00
1.240
VHYST(UV) (mV)
VDD2 = 2.9V
VDD2 = 3.3V
VDD2 = 5V
VDD2 = 12V
VTH(UV) (V)
INTVCC (V)
3.25
1.235
1.230
2.75
90
85
1.225
2.50
110
0
2.5
5.0
7.5
10.0
ILOAD (mA)
12.5
15.0
1.220
–50
–25
0
50
25
TEMPERATURE (°C)
4222 G04
75
60
–25
0
50
25
TEMPERATURE (°C)
75
100
40
30
20
4222 G07
0
0
0.2
0.4
0.6 0.8
VFB (V)
100
53
10
90
–50
75
VTH Circuit Breaker vs
Temperature
VTH CIRCUIT BREAKER (mV)
CURRENT LIMIT (mV)
ITIMER (µA)
95
0
50
25
TEMPERATURE (°C)
4222 G06
Current Limit vs VFB
50
100
–25
4222 G05
ITIMER vs Temperature
105
80
–50
100
1.0
1.2
1.4
4222 G08
52
51
50
49
48
47
–50
–25
0
50
25
TEMPERATURE (°C)
75
100
4222 G09
4222fb
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LTC4222
TYPICAL PERFORMANCE CHARACTERISTICS
6.1
∆VGATE vs Temperature
6.5
6.0
∆VGATE vs IGATE
6.0
5.6
VDD2 = 2.9V
VDD2 = 3.3V
VDD2 = 5V
VDD2 = 12V
5.5
5.4
–50
–25
25
0
50
TEMPERATURE (°C)
75
5.5
5.0
4.0
0
2
4
4222 G10
ERROR (%)
VGPIO (V)
0.4
VDD2 = 2.9V
0.2
0.1
0
0
2
11.5
–50
14
4
6
IGPIO (mA)
8
10
0.4
0.3
0.7
0.2
0.6
0.1
0.5
0.4
0
–0.2
0.2
–0.3
0.1
–0.4
768
1024
–0.5
0.5
4
0.4
3
FULL-SCALE ERROR (LSB)
0.1
0
–0.1
–0.2
–0.3
256
512
CODE
768
1024
4222 G15
ADC Full-Scale Error vs
Temperature
0.2
0
4222 G14
4222 G13
100
–0.1
0.3
512
CODE
75
ADC INL vs CODE (ADIN1)
0.8
256
25
0
50
TEMPERATURE (°C)
4222 G12
0.9
0
–25
4222 G11
0.5
0
0.3
DNL (LSB)
12
1.0
ADC DNL vs CODE (ADIN1)
100
TPHL VGATE vs VSENSE Overdrive
2
1
0
–1
10
1
–2
–3
–0.4
–0.5
10
INL (LSB)
0.5
VDD2 = 12V
8
6
IGATE (A)
ADC Total Unadjusted Error vs
CODE (ADIN1)
VOL(GPIO) vs IGPIO
0.3
11.7
TPHL VGATE (µs)
0.6
11.8
11.6
4.5
100
IGATE vs Temperature
11.9
IGATE (µA)
∆VGATE (V)
∆VGATE (V)
5.7
12.0
VDD2 = 2.9V
VDD2 = 3.3V
VDD2 = 5V
VDD2 = 12V
5.9
5.8
TA = 25°C. VDDn = 12V unless otherwise noted.
0
256
512
CODE
768
1024
4222 G16
–4
–50
–25
25
0
50
TEMPERATURE (°C)
75
100
4222 G17
0.1
0
50
100 150 200 250 300 350 400
VSENSE (mV)
4222 G18
4222fb
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LTC4222
PIN FUNCTIONS
ADIN: ADC Input. A voltage between 0 and 1.28V applied
to this pin is measured by the on-board ADC. Tie to ground
if unused.
ADR0, ADR1, ADR2: Serial Bus Address Inputs. Tying
these pins to ground, open, or INTVCC configures one
of 27 possible addresses. See Table 1 in Applications
Information.
ALERT: Fault Alert Output. Open-drain logic output that
is pulled to ground when a fault occurs to alert the host
controller. A fault alert is enabled by setting the corresponding bit in the ALERT register as shown in Table 4.
See Applications Information. Tie to ground if unused.
CONFIG: Configuration Input. Configures the part to control
the two channels together or independently. When CONFIG
is tied to GND both channels start up at the same time. A
fault, EN or ON turn-off command on either channel will
shut down both channels. When CONFIG is tied to INTVCC,
either channel can start up independently. A fault, EN or
ON turn-off command will result in the associated channel turning off, while the other channel remains on. If one
channel is commanded to turn on while another channel is
in the turn-on sequence, the LTC4222 waits until the first
channel has finished its turn-on sequence before turning
on the second channel.
EN1, EN2: Enable Input. Ground this pin to indicate a
board is present and enable the N-channel MOSFET to
turn-on. When this pin is high, the MOSFET is not allowed
to turn on. An internal 10µA current source pulls up this
pin. Transitions on this pin are recorded in the FAULT
register. A high-to-low transition activates the logic to read
the state of the ON pin and clear faults. See Applications
Information.
EXPOSED PAD: (Pin 33, QFN Package) Exposed Pad. May
be left open or connected to device ground.
FB1, FB2: Foldback Current Limit and Power-Good Input.
A resistive divider from the output is tied to this pin. When
the voltage at this pin drops below 1.235V, power is not
considered good. The power bad condition may result
in the GPIO pin pulling low or going high impedance
depending on the configuration of CONTROL register
bits 6 and 7. Also a power bad fault is logged when the
FB pin is low, the LTC4222 has finished the startup cycle
and the GATE pin is high. See Applications Information.
The start-up current limit folds back from 50mV sense
voltage to 16.6mV as the FB voltage drops from 0.8V to
0.2V. Foldback is not active once the part leaves startup
and the current limit is increased to 150mV.
GATE1, GATE2: Gate Drive for External N-Channel MOSFET.
An internal 12µA current source charges the gate of the
MOSFET. No compensation capacitor is required on the
GATE pin, but a resistor and capacitor network from this
pin to ground may be used to set the turn-on output voltage slew rate. During turn-off there is a 1mA pull-down
current. During a short circuit or undervoltage lockout (VDD
or INTVCC), a 450mA pull-down current source between
GATE and SOURCE is activated.
GND: Device Ground.
GPIO1, GPIO2: General Purpose Input/Output. Open-drain
logic output or logic input. Defaults to an output set to pull
low to indicate power is not good. Configure according
to Table 3.
INTVCC: Low Voltage Supply Decoupling Output. Connect
a 0.1µF capacitor from this pin to ground.
ON: (QFN Package) On Control Input. Formed by internally
tying the ON1 and ON2 lines together.
ON1, ON2: (SSOP Package) On Control Inputs. A rising
edge turns on the external N-channel FET and a falling edge
turns it off. This pin also configures the state of the FET
ON register bit (and hence the external FET) at power up.
For example, if the ON pin is tied high, then the FET ON bit
(Control bit 3 in Table 3) goes high 100ms after power-up.
Likewise if the ON pin is tied low then the channel remains
off after power-up until the FET ON bit is set high using
the I2C bus. A high-to-low transition on this pin clears the
fault register for the related channel. The two ON pins are
tied together internally on the QFN package.
OV1, OV2: Overvoltage Comparator Input. Connect this pin
to an external resistive divider from VDD. If the voltage at
this pin rises above 1.235V, an overvoltage fault is detected
and the GATE turns off. Tie to GND if unused.
4222fb
8
LTC4222
PIN FUNCTIONS
SCL: Serial Bus Clock Input. Data at the SDA pin is shifted
in or out on rising edges of SCL. This is a high impedance
pin that is generally driven by an open-collector output
from a master controller. An external pull-up resistor or
current source is required.
SOURCE1, SOURCE2: N-Channel MOSFET Source and
ADC Input. Connect this pin to the source of the external
N-channel MOSFET switch for gate drive return. This pin
also serves as the ADC input to monitor output voltage.
The pin provides a return for the gate pull-down circuit.
SDAO: (SSOP Package) Serial Bus Data Output. Opendrain output for sending data back to the master controller or acknowledging a write operation. Normally tied to
SDAI to form the SDA line. An external pull-up resistor
or current source is required. Internally tied to SDAI in
QFN package.
SS: Soft-Start Input. Sets the inrush current slew rate at
start-up. Connect a 68nF capacitor to provide 5mV/ms as
the slew rate for the sense voltage in start-up. This corresponds to 1A/ms with a 5mΩ sense resistor. Note that
a large soft-start capacitor and a small TIMER capacitor
may result in a condition where the timer expires before
the inrush current has started. Allow an additional 2nF of
timer capacitance per 1nF of soft-start capacitor to ensure
proper start-up.
SDAI: (SSOP Package) Serial Bus Data Input. A high impedance input for shifting in address, command or data
bits. Normally tied to SDAO to form the SDA line. Internally
tied to SDAO in QFN package.
SDA: (QFN Package) Serial Bus Data Input/Output Line.
Formed by internally tying the SDAO and SDAI lines
together. An external pull-up resistor or current source
is required.
SENSE1–, SENSE2–: Negative Current Sense Input. Connect this pin to the output of the current sense resistor. The
current limit circuit controls the corresponding GATE pin
voltage to limit the sense voltage between the SENSE+ and
SENSE– pins to the level set by the soft-start and foldback
characteristic, with a maximum of 50mV during start-up
and to 150mV independent of soft-start and foldback after
the start-up timer has expired. A circuit breaker, enabled
after start-up, trips when the sense voltage exceeds 50mV
for 20µs.
SENSE1+, SENSE2+: (SSOP Package) Positive Current
Sense Input. Connect this pin to the input of the current
sense resistor. It must be connected to the same trace as
VDDn. Internally tied to VDDn in the QFN package.
TIMER: Start-Up Timer Input. Connect a capacitor between this pin and ground to set a 12.3ms/µF duration
for start-up, after which an overcurrent fault is logged if
the inrush is still current limited. The duration of the off
time is 600ms/µF when overcurrent auto-retry is enabled,
resulting in a 1:50 duty cycle. An internal timer provides
a 100ms start-up time and 5 second auto-retry time if
this pin is tied to INTVCC. Allow an additional 2nF of timer
capacitance per 1nF of soft-start (SS) capacitor to ensure
proper start-up.
UV1, UV2: Undervoltage Comparator Input. Connect this
pin to an external resistive divider from VDD. If the voltage at this pin falls below 1.145V, an undervoltage fault
is detected and the GATE turns off. Pulling this pin below
0.4V resets the fault register for that channel except for
the UV fault bit. Tie to INTVCC if unused.
VDD1, VDD2: Supply Voltage Input and Positive Current
Sense Input. This pin has an undervoltage lockout threshold
of 2.43V. In the QFN package this pin is also the positive
current sense input.
4222fb
9
LTC4222
FUNCTIONAL DIAGRAM
SENSE–
FB
0.2V
0.6V
UV
CB
–
UV
UVS
–
0.4V
+
RST
OV1
1.235V
+
1.235V
EN
EN
–
SOURCE
PG
OVS
1.235V
–
GPIO
+
+
+
10µA
CS
+
GATE
FAULT
–
INTVCC
+–
CHARGE
PUMP
AND
GATE
DRIVER
–
FET ON
RESET
OV
50mV
0mV TO
150mV
+–
+
FOLDBACK
and DIDT
+
1.235V
SENSE+ (SSOP)
GP
PWRGD
–
–
1V
EN
2.43V
+
ONS
UVLO1
VDD
–
ON
LOGIC
VDD UVLO
ON
+
–
1.235V
2x
1x
SS
0.2V
SOFT-START
CONFIG
+
1.235V
+
INTVCC
TM1
–
100µA
TIMER
COUPLE
2µA
+
–
VDD2
TM2
1.235V
SDAI (SSOP)
SDAO (SSOP)
SDA (QFN)
I2C ADDR
–
5
+
I2C
SCL
VCC UVLO
ALERT
ADIN1
INTVCC
3.3V
GEN
A/D CONVERTER
UVLO2
–
2.64V
10 BIT
SOURCE1
ADR0
VDDA – SENSE1
ADIN2
1 OF 27
SOURCE2
ADR1
ADR2
VDDB – SENSE2
4222 BD
4222fb
10
LTC4222
TIMING DIAGRAM
SDAI/SDAO
tSU, DAT
tSU, STA
tHD, DATO,
tHD, DATI
tSP
tHD, STA
tSP
tBUF
tSU, STO
4222 TD01
SCL
tHD, STA
START
CONDITION
REPEATED START
CONDITION
STOP
CONDITION
START
CONDITION
OPERATION
The LTC4222 is designed to turn two supply voltages
on and off in a controlled manner, allowing boards to be
safely inserted or removed from a live backplane. During
normal operation, the charge pump and gate drivers turn
on external N-channel MOSFET gates to pass power to
the loads. The gate driver circuits use a charge pump that
derives its power from the VDD1 or VDD2 pin, whichever is
higher. Also included in the gate driver circuits are internal
6.5V GATE-to-SOURCE clamps to protect the oxide of
logic-level MOSFETs. During start-up the inrush currents
are tightly controlled by using current limit foldback, softstart dI/dt limiting and output dI/dt limiting. The LTC4222
is capable of controlling both channels independently, or
coupling control signals so that both channels start up
and turn off together.
The current sense (CS) amplifiers monitor the load currents using the difference between the SENSE+ (VDD for
QFN) and SENSE– pin voltages. A CS amplifier limits the
current in the load by pulling back on the GATE-to-SOURCE
voltage in an active control loop when the sense voltage
exceeds the commanded value. The CS amplifiers require
20µA input bias current from both the SENSE+ and the
SENSE– pins.
A short circuit on an output to ground results in excessive
power dissipation during active current limiting. To limit this
power, the corresponding CS amplifier regulates the voltage
between the SENSE+ and SENSE– pins at 150mV.
If an overcurrent condition persists, the internal circuit
breaker (CB) registers a fault when the sense voltage
exceeds 50mV for more than 20µs. This indicates to
the logic that it is time to turn off the GATE to prevent
overheating. At this point the TIMER capacitor starts to
discharge with the 2µA current source until the voltage
drops below 0.2V (comparator TM1) which tells the logic
that the pass transistor has cooled and it is safe to turn
on again if overcurrent auto-retry is enabled. If the TIMER
pin is tied to INTVCC, the cool-down time defaults to
5 seconds using an internal system timer.
The output voltages are monitored using the FB resistive
divider and the power good (PG) comparators to determine
when output voltages are acceptable for the loads. The
power good conditions are signaled by the GPIO1 and
GPIO2 pins using open-drain pull-down transistors. The
GPIO pins may also be independently configured to signal
power bad, or as general purpose inputs (GP comparators),
or general purpose open-drain outputs.
The Functional Diagram shows the monitoring blocks of
the LTC4222. The group of comparators on the left side
includes the undervoltage (UV), overvoltage (OV), reset
(RST), enable (EN) and on (ON) comparators for channel 1 or 2. These comparators determine if the external
conditions are valid prior to turning on their corresponding GATE. The two undervoltage lockout circuits, UVLO1
and UVLO2, validate the input supplies and the internally
generated 3.3V supply, INTVCC. UVLO2 also generates
the power-up initialization to the logic circuits as INTVCC
crosses this rising threshold.
The CONFIG pin is used to select the desired start-up
behavior of the LTC4222. When the CONFIG pin is low,
both channels will start up and turn off simultaneously
and a fault on either channel will result in both channels
turning off, or prevent both channels from starting up.
4222fb
11
LTC4222
OPERATION
When the CONFIG pin is high the two channels work
completely independently and ignore the behavior of the
other channel. This allows for the channels to start up in
sequence by connecting the GPIO (power good) output of
one channel to the UV pin of the other channel.
The two channels share the TIMER and SS (soft-start)
pins that control start-up behavior. If the CONFIG pin is
high and one channel is enabled while the other channel
is starting up, the LTC4222 will wait for the start-up cycle
to end before starting up the second channel to ensure
that it gets a full timer cycle. The exception to this is the
ON pins, which turn on the corresponding channel immediately. When both channels start up simultaneously, the
inrush current for both channels is limited by whichever
FB pin is lowest.
Included in the LTC4222 is a 10-bit A/D signal. The 6-input
multiplexer ahead of the A/D converter allows to select
between the two ADIN pins, the two SOURCE pins and
the two current sense devices.
An I2C interface is provided to read the A/D registers. It
also allows the host to poll the device and determine if
faults have occurred. If the ALERT line is configured as
an interrupt, the host is enabled to respond to faults in
real time. The SDA line is divided into an SDAI (input)
and SDAO (output). This simplifies applications using an
optoisolator driven directly from the SDAO output. The
I2C device address is forwarded to the address decoder
from the ADR0, ADR1 and ADR2 pins. These inputs have
three states each that decode into a total of 27 device
addresses.
APPLICATIONS INFORMATION
A typical LTC4222 application is in a high availability system
in which two positive voltage supplies are distributed to
one or more cards. The device measures card voltages
and currents and records past and present fault conditions
for both channels. The system queries each LTC4222 over
the I2C periodically and reads status and measurement
information.
A basic LTC4222 application circuit is shown in Figure 1.
The following sections cover turn-on, turn-off and acts
upon various faults that the LTC4222 detects. External
component selection is discussed in detail in the Design
Example section.
Turn-On Sequence
The power supplies on a board are controlled by using
external N-channel pass transistors (Q1 and Q2) placed
in the power path. Note that resistor RSn provides current
detection. Resistors R1n, R2n and R3n define undervoltage
and overvoltage levels for the two channels. R5n prevents
high frequency oscillations in Qn and R6n. C1n forms an
optional network that may be used to provide an output
dV/dt limited start-up.
Several conditions must be present before the external
MOSFET for a given channel turns on. First the external
supplies, VDDn, must exceed their 2.44V undervoltage
lockout levels. Next the internally generated supply, INTVCC,
must cross its 2.64V undervoltage threshold. This generates a 60µs to 120µs power-on-reset pulse. During reset
the fault registers are cleared and the control registers are
set or cleared as described in the register section.
After a power-on-reset pulse, the LTC4222 goes through the
following turn-on sequence for one or both channels. First
the UV and OV comparators indicate that input power is
within the acceptable range, which is indicated by STATUS
bits 0 to 1 in Table 5. Second, the EN pin is externally pulled
low. Finally, all of these conditions must be satisfied for
the duration of 100ms to ensure that any contact bounce
during insertion has ended. Additionally, if the CONFIG pin
is low all initial conditions for both channels must be met
before the pair are allowed to turn on together.
When these initial conditions are satisfied, the ON pin
is checked and its state written to bit 3 in the CONTROL
register (Table 3). If it is high, the external MOSFET is
turned on. If the ON pin is low, the external MOSFET is
turned on when the ON pin is brought high or if a serial bus
turn-on command is sent by setting CONTROL bit 3. If the
CONFIG pin is low, either both ON pins must be high or
both CONTROL registers third bits must be set in order for
the external MOSFETs to be turned on simultaneously.
4222fb
12
LTC4222
APPLICATIONS INFORMATION
RS1
0.01Ω
VIN1
12V
Z1
SA14A
CF1
0.1µF
R11
140k
R5-1
10Ω
UV1 VDD1
OV1
ON
SDA
SCL
ALERT
NC
C3
0.1µF
GND
R32
13.7k
SENSE1– GATE1
CONFIG
ADR0
ADR1
ADR2
INTVCC
VIN2
3.3V
BACKPLANE PLUG-IN
CARD
R81
3.57k
ADIN2
EN2
GND
OV2
UV2 VDD2
SENSE2– GATE2
RG2
15k
R5-2
10Ω
R12
23.7k
Z2
SA14A
SOURCE1
FB1
GPIO1
EN1
ADIN1
TIMER
RS2
0.01Ω
CG2
3.9nF
R41
100k
CTIMER
0.68µF
SS
LTC4222
R22
3.32k
CF2
0.1µF
R71
10.2k
RG1
15k
CG1
3.9nF
R21
4.53k
R31
13.7k
ON
SDA
SCL
ALERT
Q1
FDD3706
CSS
68nF
GPIO2
FB2
SOURCE2
R82
3.57k
R42
100k
R72
4.99k
Q2
FDD3706
4222 TA01a
Figure 1. Typical Application
A MOSFET is turned on by charging up the GATE with a
12µA current source. When the GATE voltage reaches the
MOSFET threshold voltage, the MOSFET begins to turn on
and the SOURCE voltage then follows the GATE voltage
as it increases.
pin reaches threshold of 1.235V, the part checks to see if
it is in current limit. If this is the case, the overcurrent fault
bit, FAULT bit 2 in Table 6, is set and the part turns off. If
the part is not in current limit, the 50mV circuit breaker is
armed and the current limit is switched to 150mV. Alternately an internal 100ms start-up timer may be selected
by tying the TIMER pin to INTVCC.
While the MOSFET is turning on, the inrush current increases linearly at a dI/dt rate selected by capacitor CSS.
This is accomplished using the current limit amplifier
controlling the GATE pin voltage. Once the inrush current
reaches the limit set by the FB pin, the dI/dt ramp stops and
the inrush current follows the foldback profile as shown
in Figure 2. When both channels turn on simultaneously,
the foldback current limit is set by the lower of the two
FB pins.
As the SOURCE voltage rises, the FB pin voltage follows as
set by R7 and R8. Once FB crosses its 1.235V threshold,
and the start-up timer has expired, the corresponding GPIO
pin, in the default power good configuration, ceases to
pull low and indicates that power is now good. Alternately
STATUS bit 3 can be read to check power-good status,
where a zero indicates that power is good.
A start-up timer is used to prevent damaging the MOSFET
when starting up into a short-circuit. The TIMER capacitor
integrates at 100µA during start-up and once the TIMER
If a series resistor and capacitor from GATE to GROUND
(R6 and C1) are employed to provide a constant inrush
current during start-up, which provides a constant dV/dt at
4222fb
13
LTC4222
APPLICATIONS INFORMATION
VDD + 6V
VGATE
VDD
VOUT
GPIO
(POWER GOOD)
VSENSE
tSTARTUP
50mV
17mV
ILOAD • RSENSE
4222 F02
SS
LIMITED
FB
LIMITED
TIMER
EXPIRES
Figure 2. Power-Up Waveform
the output, a 12µA pull-up current (IGATE) from the GATE
pin slews the gate upwards and resulting current is less
than the current limit. Because the inrush current is less
than the current limit, the start-up timer can expire without
producing an overcurrent fault and a small timer capacitor
may be used. After the timer has expired power good will
not be signaled until the FB pin crosses its threshold and
the GATE-to-SOURCE voltage crosses the 4.3V threshold
that indicates the MOSFET is fully enhanced. When both
those conditions are met the output voltage is suitable
for the load to be turned on and the impedance back to
the supply through the MOSFET is low. Power good is
then asserted with the GPIO pin or read via the interface,
signaling that it is safe to turn on downstream loads. A
power-bad fault is not generated when starting up in this
manner because the FB pin will cross its threshold before
the GATE-to-SOURCE threshold is crossed. RG should be
chosen such that IGATE • RG is less than the threshold of
the MOSFET to avoid a current spike at the beginning of
startup. Reducing RG degrades the stability of the current
limit circuit, see applications information on current limit
stability.
GATE Pin Voltage
A curve of GATE-to-SOURCE voltage vs VDD is shown in
the Typical Performance Characteristics. At minimum input
supply voltage of 2.9V, the minimum GATE-to-SOURCE
drive voltage is 4.7V. The GATE-to-SOURCE voltage is
clamped below 6.5V to protect the gates of logic-level
N-channel MOSFETs.
Turn-Off Sequence
One or both GATE pins are turned off by a variety of conditions. A normal turn-off is initiated by an ON pin going
low or a serial bus turn-off command. Additionally, several
fault conditions cause a GATE to turn off. These include an
input overvoltage (OV pin), input undervoltage (UV pin),
overcurrent circuit breaker (SENSE– pin), or EN transitioning
high. Writing a logic one into the UV, OV or OC fault bits
(FAULT register bits 0 to 2 in Table 6) also latches off the
associated GATE if their auto-retry bits are set to false.
A MOSFET is turned off with a 1mA current pulling down
the GATE pin to ground. With the MOSFET turned off, the
SOURCE and FB voltages drop as CL discharges. When
the FB voltage crosses below its threshold, GPIO may be
configured to pull low to indicate that the output power
is no longer good.
If the INTVCC pin drops below 2.60V for greater than 1µs,
or the associated VDD pin falls below 2.35V for greater than
2µs, a fast shut down of the MOSFET is initiated. In this
case the GATE pin is pulled down with a 450mA current
to the SOURCE pin.
Overcurrent Fault
The LTC4222 has different current limiting behavior during
start-up, when the output supply ramps up under TIMER,
SS and FB control, and normal operation. As such it can
generate an overcurrent fault during both phases of operation. Both set the faulting supply’s overcurrent fault bit
(FAULT register bit 2) and shut off the faulting GATE, or
both GATEs if the CONFIG pin is low.
During start-up when both TIMER and SS are ramping,
the current limit is a function of SS pin voltage and the
voltage on the FB pins. A supply could power up entirely
in current limit depending on the bypass capacitor at the
outputs of the ramping supplies. The TIMER pin sets
the time duration for current limit during start-up, either
12.3ms/µF when using a timer capacitor, or 100ms when
the TIMER pin is tied to INTVCC. If the supply is still in
current limit at the end of the timing cycle, an overcurrent
4222fb
14
LTC4222
APPLICATIONS INFORMATION
fault is declared for that supply and the MOSFET is turned
off. If the CONFIG pin is low, then both channels will turn
off together. After the switch has turned off due to an
OC fault the part will wait for a cool-down period before
allowing the switch to turn on again. If the TIMER pin is
tied to VCC the cool-down period will be 5 seconds on the
internal timer. Otherwise if using a TIMER capacitor, the
capacitor will discharge at 2µA and the internal 100ms timer
is started, when the 100ms timer expires and the TIMER
pin reaches its 0.2V lower threshold the part is allowed to
restart if the overcurrent fault bit (FAULT register bit 2) has
been cleared or the overcurrent auto-retry bit (CONTROL
register bit 2) has been set.
Overvoltage Fault
After start-up, a supply has dual-level glitch-tolerant protection against overcurrent faults. The sense resistor voltage
drop is monitored by a 50mV electronic circuit breaker and
a 150mV active current limit. In the event that a supply’s
current exceeds the circuit breaker threshold, an internal
20µs timer is started. If the supply is still overcurrent after
20µs the circuit breaker trips and the switch is turned off.
An analog current limit loop prevents the supply current
from exceeding the 150mV current limit in the event of a
short circuit. The 20µs filter delay and the higher current
limit threshold prevent unnecessary resets of the board
due to minor current surges. The LTC4222 will stay in
the latched off state unless the overcurrent auto-retry bit
(CONTROL register bit 2) is set, in which case the switch
turns on again after 100ms when using the external TIMER
capacitor to set the start-up time, or 5 seconds when using
the internal timer. Note that current limit foldback is not
active after start-up.
An undervoltage fault occurs when a UV pin falls below
its 1.235V threshold for more than 2µs. This turns off the
corresponding GATE with a 1mA current to ground and
sets undervoltage present STATUS bit 1 and undervoltage
FAULT bit 1. If the UV pin subsequently rises above the
threshold for 100ms, the GATE is turned on again unless
undervoltage auto-retry has been disabled by clearing
CONTROL bit 1. When power is applied to the device, if
UV is below its 1.235V threshold after INTVCC crosses its
2.64V undervoltage lockout threshold, an undervoltage
fault is logged in the FAULT register. If the CONFIG pin is
tied low, an UV fault on either channel will shut off both
channels simultaneously.
LOAD CURRENT
5A/DIV
VGATE
10V/DIV
VSOURCE
10V/DIV
VGPIO
5V/DIV
CL = 0F
RSHORT = 5mΩ
RS = 20mΩ
RG = 1k
CG = 1µF
10µs/DIV
4222 F03
An overvoltage fault occurs when an OV pin rises above
its 1.235V threshold for more than 2µs. This shuts off
the corresponding GATE with a 1mA current to ground
and sets the overvoltage present STATUS bit 0 and the
overvoltage FAULT bit 0. If the pin subsequently falls back
below the threshold for 100ms, the GATE is allowed to turn
on again unless overvoltage auto-retry has been disabled
by clearing CONTROL bit 0. If the CONFIG pin is tied low,
an OV fault on either channel will shut off both channels
simultaneously.
Undervoltage Fault
ON Signals and the CONFIG Pin
Turn-on commands are issued from the ON pins or the I2C
interface. Internally, rising and falling edges of the ON pins
set and reset the FET_ON register bits. Unlike the other
control signals such as UV, OV and EN, the rising edge of
the ON signal is not filtered by the 100ms internal timer and
instead turns on the corresponding channel immediately.
Cycling an ON signal cancels the corresponding channel’s
overcurrent auto-retry cool-down period, allowing the
channel to restart after a 100ms delay.
To start up and shut down both channels at the same time
set the CONFIG pin low. Both channels then start up when
all the UV, OV, EN and ON signals are in the correct state
to turn on both channels, and when any of these signals
turns one channel off, both channels turn off.
Figure 3. Short-Circuit Waveform
4222fb
15
LTC4222
APPLICATIONS INFORMATION
Setting the CONFIG pin high allows the two channels to
start up and turn off independently. When both ON signals
are brought high sequentially, the channel turned on first
immediately begins to start up and the second channel
has a 200ns window to assert it’s ON signal in order to
start up in the same timer period. If the second ON signal
is asserted after the 200ns window but before the end of
the first channel’s start-up time, the second channel startup is delayed. The second channel will then start 100ms
after the first channel’s start-up timer has expired and the
TIMER pin, if used, reaches its 200mV low threshold.
When an external TIMER capacitor is used, the TIMER
capacitor voltage ramps up with a 100µA current. Once the
TIMER pin reaches its 1.235V threshold the TIMER begins
to discharge. While the TIMER capacitor is discharging, the
ON signal for the second channel should not be asserted
for 2ms/µF of TIMER capacitance. This allows the TIMER
capacitor to return to its low state and ensures that the next
channel to start receives a full timer cycle. This wait time
is unnecessary when using the internal 100ms timer.
is reinserted the fault register is cleared except for FAULT
bit 4. After 100ms the state of the ON pin is latched into
bit 3 of the CONTROL register. At this point the channel
starts up again.
If a connection sense on the plug-in card is driving an EN
pin, insertion or removal of the card may cause the pin
voltage to bounce. This results in clearing the fault register
when the card is removed. The pin may be debounced
using a filter capacitor, CEN, on the EN pin as shown in
Figure 4. The filter time is given by:
tFILTER = CEN • 123 (ms/µF)
OUT
LTC4222
SOURCE
10µA
EN
+
–
1.235V
GND
Board Present Change of State
The EN pins may be used to detect the presence of one or
two downstream cards. Whenever an EN pin toggles, FAULT
bit 4 is set to indicate a change of state. When the EN pin
goes high, indicating board removal, the corresponding
GATE turns off immediately (with a 1mA current to ground)
and the board present STATUS bit 4, is cleared. If the EN
pin is pulled low, indicating a board insertion, all fault bits
for that channel except FAULT bit 4 are cleared and enable
STATUS bit 4, is set. If the EN pin remains low for 100ms
the state of the ON pin is captured in ‘FET On’ CONTROL
bit 3. This turns the switch on if the ON pin is tied high.
There is an internal 10µA pull-up current source on the
EN pin. If the CONFIG pin is tied low, both EN pins must
be low for 100ms for the two channels to be enabled and
if either EN pin goes high both channels will turn off.
If a channel shuts down due to a fault, it may be desirable
to restart that channel simply by removing and reinserting
the related load card. In cases where the LTC4222 and the
switch reside on a backplane or midplane and the load
resides on a plug-in card, the EN pin detects when the
plug-in card is removed. Figure 4 shows an example where
the EN pin is used to detect insertion. Once the plug-in card
16
LOAD
CEN
4222 F04
MOTHERBOARD
CONNECTOR
PLUG-IN
CARD
Figure 4. Plug-In Card Insertion/Removal
FET Short Fault
A FET short fault is reported if the data converter measures
a current sense voltage greater than or equal to 2mV while
the corresponding GATE is turned off. This condition sets
FET short bit, Fault bit 5.
Power-Bad Fault
A power-bad fault is reported if a FB pin voltage drops
below its 1.235V threshold for more than 2µs when the
corresponding GATE is above the 4.3V gate to source
threshold. This pulls the GPIO pin low immediately in the
default power good configuration, and sets power-bad
present bit, STATUS bit 3, and power-bad bit, FAULT bit 3.
A circuit prevents power-bad faults if the GATE-to-SOURCE
voltage is low, eliminating false power-bad faults during
power-up or power-down. If the FB pin voltage subsequently
rises back above the threshold, a power good configured
GPIO pin returns to a high impedance state and STATUS
bit 3 is reset.
4222fb
LTC4222
APPLICATIONS INFORMATION
Fault Alerts
When any of the fault bits in a FAULT register (see Table 4)
are set, an optional bus alert is generated if the appropriate bit in the ALERT register has been set. This allows
only selected faults to generate alerts. At power-up the
default state is to not alert on faults and the ALERT pin
is high. If an alert is enabled, the corresponding fault
causes the ALERT pin to pull low. After the bus master
controller broadcasts the Alert Response Address, the
LTC4222 responds with its address on the SDA line and
releases ALERT as shown in Table 7. If there is a collision
between two LTC4222s responding with their addresses
simultaneously, then the device with the lower address
wins arbitration and responds first. The ALERT line is also
released if the device is addressed by the bus master if
ALERT is pulled low due to an alert.
Once the ALERT signal has been released for one fault, it
is not 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 do not generate alerts until the associated FAULT register bit has been cleared.
Resetting Faults
Faults are reset with any of the following conditions on a
given channel. First, a serial bus command writing zeros
to the FAULT register bits 0 to 5 clears the associated
faults. Second, FAULT register bits 0 to 5 are cleared when
the corresponding switch is turned off by the ON pin or
STATUS bit 3 going from high to low, if the corresponding
UV pin is brought below its 0.4V reset threshold for 2µs,
or if INTVCC falls below its 2.64V undervoltage lockout
threshold. Finally, when EN is brought from high to low,
only corresponding FAULT bits 0-3 and 5 are cleared, and
bit 4, which indicates a EN change of state, is set. Note
that faults that are still present, as indicated in the STATUS
registers, cannot be cleared.
The FAULT registers are not cleared when auto-retrying.
When auto-retry is disabled the existence of an overvoltage,
undervoltage, or overcurrent fault keeps the switch off.
As soon as the fault is cleared, the switch turns on. If
auto-retry is enabled, then a high value in STATUS register
bits 0 or 1 holds the switch off and the fault register is
ignored. Subsequently, when STATUS register bits 0 and
1 are cleared by removal of the fault condition, the switch
is allowed to turn on again. The LTC4222 will set FAULT
bit 2 and turn off in the event of an overcurrent fault,
preventing it from remaining in an overcurrent condition.
If configured to auto-retry, the LTC4222 will continually
attempt to restart after cool-down cycles until it succeeds
in starting up without generating an overcurrent fault. Note
that if a switch is on after an auto-retry and the FAULT bit
has not been reset, clearing the corresponding auto-retry
bit will turn the channel off.
Data Converter
The LTC4222 incorporates a 10-bit A/D converter that
continuously scans six different voltages. The SOURCE
pins have a 1/24 resistive divider to monitor a full-scale
voltage of 32V with 31.25mV resolution. The ADIN pins are
monitored with a 1.28V full scale and 1.25mV resolution,
and the voltage between the VDD and SENSE pins is monitored with a 64mV full scale and 62.5µV resolution.
Results from each conversion are stored, left justified, in
registers as seen in Tables 7 and 8, and are updated 15
times per second. Setting ADC_CONTROL register bit 0
invokes a test mode that halts the data converter so that
the data converter result registers may be written to and
read from for software testing.
The data converter also has a direct address mode that
allows the user to take a specific measurement at a specific time and hold that value for later readback. Direct
address mode is entered by setting the Halt bit, bit 0, in
the ADC_CONTROL register (see Table 9). Then when
the channel address bits, ADC_CONTROL bits 1 to 3, are
written to, the ADC will make a single measurement on
the channel indicated by those bits, then stop. Setting the
ADC Alert bit, ADC_CONTROL bit 4, will enable an interrupt
when the data converter finishes the conversion, resulting in the ALERT pin pulling low when the data is ready.
Alternately, the ADC Busy bit, ADC_CONTROL bit 5, can
be polled to check for the end of the conversion, after a
direct address conversion the ADC Busy bit will go low. In
normal mode ADC Busy is always high. Resetting the Halt
bit returns the data converter to the scan mode.
4222fb
17
LTC4222
APPLICATIONS INFORMATION
Configuring the GPIO Pins
Table 3 describes the possible states of the GPIO pins using
the CONTROL registers bits 6 and 7. At power-up, the default
state is for a GPIO pin to go high impedance when power is
good (FB pin greater than 1.235V). Other applications for a
GPIO pin are to pull down when power is good, a general
purpose output and a general purpose input.
A simple application of the GPIO pin in the power good
configuration is to connect it to the UV pin of the other
channel with the CONFIG pin high. This will result in the
second channel being turned on after the first channel has
started up and signaled power good.
Current Limit Stability
For many applications the LTC4222 current limit will be
stable without additional components. However there are
certain conditions where additional components may be
needed to improve stability. The dominant pole of the current limit circuit is set by the capacitance and resistance at
the gate of the external MOSFET, and larger gate capacitance makes the current limit loop more stable. Usually
a total of 8nF gate to source capacitance is sufficient for
stability and is typically provided by inherent MOSFET CGS,
however the stability of the loop is degraded by increasing
RSENSE or by reducing the size of the resistor on a gate RC
network if one is used, which may require additional gate
to source capacitance. Board level short-circuit testing
is highly recommended as board layout can also affect
transient performance, for stability testing the worst-case
condition for current limit stability occurs when the output
is shorted to ground after a normal start-up.
There are two possible parasitic oscillations when the
MOSFET operates as a source follower when ramping
at power-up or during current limiting. The first type of
oscillation occurs at high frequencies, typically above
1MHz. This high frequency oscillation is easily damped
with R5 as shown in Figure 1. In some applications, one
may find that R5 helps in short-circuit transient recovery
as well. However, too large of an R5 value will slow down
the turn-off time. The recommended R5 range is between
5Ω and 500Ω.
The second type of source follower oscillation occurs at
frequencies between 200kHz and 800kHz due to the load
18
capacitance being between 0.2µF and 9µF, the presence
of R5 resistance, the absence of a drain bypass capacitor,
a combination of bus wiring inductance and bus supply
output impedance. To prevent this second type of oscillation
avoid load capacitance below 10µF, alternately connect an
external capacitor from the MOSFET gate to ground with
a value greater than 1.5nF.
Supply Transients
The LTC4222 is designed to ride through supply transients
caused by load steps. If there is a shorted load and the
parasitic inductance back to the supply is greater than
0.5µH, there is a chance that the supply collapses before
the active current limit circuit brings down the GATE pin.
If this occurs, the undervoltage monitors pull the corresponding GATE pin low. The undervoltage lockout circuit
has a 2µs filter time after VDD drops below 2.35V. The UV
pin reacts in 2µs to shut the GATE off, but it is recommended to add a filter capacitor, CF , to prevent unwanted
shutdown caused by a transient. Eventually either the UV
pin or undervoltage lockout responds to bring the current
under control before the supply completely collapses.
Supply Transient Protection
The LTC4222 is safe from damage with supply voltages up
to 35V. However, spikes above 35V may damage the part.
During a short-circuit condition, large changes in current
flowing through power supply traces may cause inductive voltage spikes which exceed 35V. To minimize such
spikes, the power trace inductance should be minimized
by using wider traces or heavier trace plating. Also, a
snubber circuit dampens inductive voltage spikes. Build
a snubber by using a 100Ω resistor in series with a 0.1µF
capacitor between VDD and GND. A surge suppressor, Z1
in Figure 1, at the input can also prevent damage from
voltage surges.
Design Example
As a design example, take the following specifications for
channel 1: VIN = 12V, IMAX = 5A, IINRUSH = 1A, dI/dtINRUSH
= 10A/ms, CL = 330µF, VUV(RISING) = 10.75V, VOV(FALLING)
=  14.0V, VPWRGD(UP) = 11.6V, and I2C ADDRESS = 1000111.
This completed design is shown in Figure 1.
4222fb
LTC4222
APPLICATIONS INFORMATION
Selection of the sense resistor, RS, is set by the overcurrent
threshold of 50mV:
Energy in CL = Energy in Q1
This uses:
Energy in CL =
1
1
CV 2 = (0.33mF)(12)2
2
2
or 0.024 joules. Calculate the time it takes to charge up
COUT:
C •V I
0.33mF •12V
t STARTUP = L DD INRUSH =
= 4ms
I
1A
INRUSH
The power dissipated in the MOSFET:
CSS =
50mV
RS =
= 0.01Ω
IMAX
The MOSFET is sized to handle the power dissipation during inrush when output capacitor COUT is being charged.
A method to determine power dissipation during inrush
is based on the principle that:
The inrush dI/dt is set to 10A/ms using CSS:
PDISS =
Energy in CL
= 6W
t STARTUP
The SOA (safe operating area) curves of candidate MOSFETs
must be evaluated to ensure that the heat capacity of the
package tolerates 6W for 4ms. The SOA curves of the
Fairchild FDC653N provide for 2A at 12V (24W) for 10ms,
satisfying this requirement. Since the FDC653N has less
than 8nF of gate capacitance and we are using a GATE
RC network, the short-circuit stability of the current limit
should be checked and improved by adding a capacitor
from GATE to SOURCE if needed.
The inrush current is set to 1A using C1:
C •I
C1= L GATE
IINRUSH
0.33mF •12µA
C1=
or C1= 3.9nF
1A
=
ISS
1
• 0.0429 •
 A
RSENSE
dl/dt  
 s
10µA • 0.0429 •1
= 4.3nF choose 4.7nF
10000 • 0.01Ω
For a start-up time of 4ms with a 2x safety margin we
choose:
2 • t STARTUP
+CSS • 2
12.3ms/µF
8ms
+ 4.7nF • 2 = 0.68µF
CTIMER =
12.3ms/µF
CTIMER =
Note the minimum value of CTIMER is 10nF.
The UV and OV resistor string values can be solved in the
following method. First pick R3 based on ISTRING being
1.235V/R3 at the edge of the OV rising threshold. Then
solve the following equations:
R2 =
R1=
VOV(OFF)
VUV(ON)
•R3 •
UVTH(RISING)
OVTH(FALLING)
VUV(ON) •(R3+R2)
UVTH(RISING)
–R3
–R3 –R2
In our case we choose R3 to be 3.4k to give a resistor
string current below 100µA.
Then solving the equations results in R2 = 1.16k and
R1 = 34.6k.
The FB divider is solved by picking R8 and solving for R7,
choosing 3.57k for R8 we get:
R7 =
VPWRGD(UP) •R8
FBTH(RISING)
–R8
Resulting in R7 = 30k
A 0.1µF capacitor, CF, is placed on the UV pins to prevent
supply glitches from turning off the GATE via UV or OV.
4222fb
19
LTC4222
APPLICATIONS INFORMATION
The address is set with the help of Table 1, which indicates binary address 1000111 corresponds to address
4. Address 4 is set by setting ADR2 low, ADR1 open and
ADR0 high.
Next the value of R5 and R6 are chosen to be the default
values 10Ω and 15kΩ as discussed previously.
In addition a 0.1µF ceramic bypass capacitor is placed on
the INTVCC pin.
Layout Considerations
To achieve accurate current sensing, a Kelvin connection
is required. The minimum trace width for 1oz copper
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
resistance of about 530µΩ. Small resistances add up
quickly in high current applications. To improve noise
immunity, put the resistive dividers to the UV, OV and FB
pins close to the device and keep traces to VDD and GND
short. It is also important to put the bypass capacitor for
the INTVCC pin, C3, as close as possible between INTVCC
and GND. 0.1µF capacitors from the UV pins (and OV pins
through resistor R2) to GND also helps reject supply noise.
Figure 5 shows a layout that addresses these issues. Note
that surge suppressor, Z1 is placed between supply and
ground using wide traces.
SENSE RESISTOR RS
ILOAD
R1
Z1
CF
VIAS TO
GROUND
PLANE
C3
INTVCC
SENSE–
VDD
SENSE+
CONFIG
UV
OV
SS
The LTC4222 communicates with a bus master using a
2-wire interface compatible with I2C Bus and SMBus, an
I2C extension for low power devices. The LTC4222 is a
read-write slave device and supports SMBus bus Read
Byte, Write Byte, Read Word and Write Word commands.
A complete list of the resistors of the LTC4222 is shown
in Table 2. The second word in a Read Word command is
the contents of the subsequent 8-bit register. The second
word in a Write Word command is ignored. Data formats
for these commands are shown in Figures 6 to 11.
The LTC4222 interface also features a 25ms timeout feature
to prevent the bus being stuck low if a communication
error occurs. If either the SCL or SDA lines remain low
for more than 25ms the LTC4222 will reset it’s interface
and release the SDAO pin, freeing the bus to resume
communication.
The LTC4222 also features PMBus compatibility, the interface will not acknowledge unsupported commands and
the internal addresses are in the manufacturer specified
address space under the PMBus specification.
START and STOP Conditions
When the bus is idle, both SCL and SDA are high. A bus
master signals the beginning of a transmission with a start
condition by transitioning SDA from high to low while SCL
is high, as shown in Figure 6. When the master has finished
communicating with the slave, it issues a STOP condition
by transitioning SDA from low to high while SCL is high.
The bus is then free for another transmission.
I2C Device Addressing
R2
R3
CSS
Digital Interface
LTC4222UHD
GND
VIA TO
GROUND
PLANE
4222 F05
Figure 5. Recommended Layout
Twenty seven distinct bus addresses are available using
three 3-state address pins, ADR0, ADR1 and ADR2. Table  1
shows the correspondence between pin states and addresses. In addition, the LTC4222 responds to two special
addresses. Address (1100 0110) is a mass write address
that writes to all LTC4222s, regardless of their individual
address settings. Mass write can be disabled by setting
register bit 4 in the CONTROL register of channel 2 to zero.
Address (0001 100) is the SMBus Alert Response Address.
If the LTC4222 is pulling low on the ALERT pin due to an
4222fb
20
LTC4222
APPLICATIONS INFORMATION
SDA
a6 - a0
SCL
1-7
b7 - b0
8
9
1-7
b7 - b0
8
9
1-7
8
9
S
P
START
CONDITION
ADDRESS
R/W
ACK
DATA
ACK
DATA
ACK
STOP
CONDITION
4222 F06
Figure 6. Data Transfer Over I2C or SMBus
alert, it acknowledges this address by broadcasting its
address and releasing the ALERT pin.
Acknowledge
The acknowledge signal is used in handshaking between
transmitter and receiver to indicate that the last byte of
data was received. The transmitter always releases the
SDA line during the acknowledge clock pulse. When the
slave is the receiver, it pulls down the SDA line so that it
remains LOW during this pulse to acknowledge receipt
of the data. If the slave fails to acknowledge by leaving
SDA high, then the master may abort the transmission by
generating a STOP condition. When the master is receiving
data from the slave, the master pulls down the SDA line
during the clock pulse to indicate receipt of the data. After
the last byte has been received the master leaves the SDA
line HIGH (not acknowledge) and issues a stop condition
to terminate the transmission.
Write Protocol
The master begins communication with a START condition followed by the seven bit slave address and the
R/W bit set to zero, as shown in Figure 7. The addressed
LTC4222 acknowledges this and then the master sends
a command byte which indicates which internal register
the master wishes to write. The LTC4222 acknowledges
this and then latches the lower three bits of the command
byte into its internal Register Address pointer. The master
then delivers the data byte and the LTC4222 acknowledges
once more and latches the data into its control 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
is acknowledged by the LTC4222 but ignored, as shown
in Figure 8.
Read Protocol
The master begins a read operation with a START condition followed by the seven bit slave address and the
R/W bit set to zero, as shown in Figure 9. The addressed
LTC4222 acknowledges this and then the master sends
a command byte which indicates which internal register
the master wishes to read. The LTC4222 acknowledges
this and then latches the lower three bits of the command
byte into its internal Register Address pointer. The master
then sends a repeated START condition followed by the
S
S
ADDRESS W A
a7:a0
0 0
COMMAND
b7:b0
FROM MASTER TO SLAVE
FROM SLAVE TO MASTER
a7:a0
A DATA A P
0 b7:b0 0
A: ACKNOWLEDGE (LOW)
A: NOT ACKNOWLEDGE (HIGH)
R: READ BIT (HIGH)
W: WRITE BIT (LOW)
S: START CONDITION
P: STOP CONDITION
4222 F07
Figure 7. LTC4222 Serial Bus SDA Write Byte Protocol
ADDRESS W A
0 0
COMMAND
A DATA A
DATA
b7:b0
0 b7:b0 0
XXXXXXXX
A P
0
4222 F08
Figure 8. LTC4222 Serial Bus SDA Write Word Protocol
S
ADDRESS W A
a7:a0
0 0
COMMAND
b7:b0
A S
0
ADDRESS
a7:a0
R A DATA A P
1 0 b7:b0 1
4222 F09
Figure 9. LTC4222 Serial Bus SDA Read Byte Protocol
4222fb
21
LTC4222
APPLICATIONS INFORMATION
same seven bit address with the R/W bit now set to one.
The LTC4222 acknowledges 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,
Figure 10, the LTC4222 repeats the requested register as
the second data byte.
Alert Response Protocol
When any of the fault bits in the FAULT register are set,
an optional bus alert is generated if the appropriate bit in
the ALERT register is also set. If an alert is enabled, the
S
ADDRESS W A
a7:a0
0 0
COMMAND
b7:b0
A S
0
corresponding fault causes the ALERT pin to pull low. After
the bus master controller broadcasts the Alert Response
Address, the LTC4222 responds with its address on the
SDA line and then release ALERT as shown in Figure 11.
The ALERT line is also released if the device is addressed
by the bus master. The ALERT signal is not 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
do not generate alerts until the associated FAULT register
bit has been cleared.
ADDRESS
a7:a0
R A DATA A DATA A P
1 0 b7:b0 0 b7:b0 1
4222 F10
Figure 10. LTC4222 Serial Bus SDA Read Word Protocol
ALERT
S RESPONSE R A
ADDRESS
0001100 1 0
DEVICE
ADDRESS
a7:a0
A P
1
4222 F11
Figure 11. LTC4222 Serial Bus SDA Alert Response Protocol
4222fb
22
LTC4222
APPLICATIONS INFORMATION
Table 1. LTC4222 I2C Device Addressing
DESCRIPTION
DEVICE
ADDRESS
LTC4222
ADDRESS PINS
DEVICE ADDRESS
h
7
6
5
4
3
2
1
0
ADR2
ADR1
ADR0
Mass Write
C6
1
1
0
0
0
1
1
0
X
X
X
Alert Response
19
0
0
0
1
1
0
0
1
X
X
X
0
88
1
0
0
0
1
0
0
X
L
NC
L
1
8A
1
0
0
0
1
0
1
X
L
H
NC
2
8C
1
0
0
0
1
1
0
X
L
NC
NC
3
8E
1
0
0
0
1
1
1
X
L
NC
H
4
98
1
0
0
1
1
0
0
X
L
L
L
5
9A
1
0
0
1
1
0
1
X
L
H
H
6
9C
1
0
0
1
1
1
0
X
L
L
NC
7
9E
1
0
0
1
1
1
1
X
L
L
H
8
A8
1
0
1
0
1
0
0
X
NC
NC
L
9
AA
1
0
1
0
1
0
1
X
NC
H
NC
10
AC
1
0
1
0
1
1
0
X
NC
NC
NC
11
AE
1
0
1
0
1
1
1
X
NC
NC
H
12
B8
1
0
1
1
1
0
0
X
NC
L
L
13
BA
1
0
1
1
1
0
1
X
NC
H
H
14
BC
1
0
1
1
1
1
0
X
NC
L
NC
15
BE
1
0
1
1
1
1
1
X
NC
L
H
16
C8
1
1
0
0
1
0
0
X
H
NC
L
17
CA
1
1
0
0
1
0
1
X
H
H
NC
18
CC
1
1
0
0
1
1
0
X
H
NC
NC
19
CE
1
1
0
0
1
1
1
X
H
NC
H
20
D8
1
1
0
1
1
0
0
X
H
L
L
21
DA
1
1
0
1
1
0
1
X
H
H
H
22
DC
1
1
0
1
1
1
0
X
H
L
NC
23
DE
1
1
0
1
1
1
1
X
H
L
H
24
E8
1
1
1
0
1
0
0
X
L
H
L
25
EA
1
1
1
0
1
0
1
X
NC
H
L
26
EC
1
1
1
0
1
1
0
X
H
H
L
4222fb
23
LTC4222
APPLICATIONS INFORMATION
Table 2. LTC4222 Register Addresses and Contents
REGISTER ADDRESS
Decimal
Hex
REGISTER NAME
208
D0h
Control1 (A1)
DESCRIPTION
209
D1h
Alert1 (B1)
210
D2h
Status1 (C1)
Displays the Status of Channel 1
211
D3h
Fault1 (D1)
Fault Log for Channel 1
212
D4h
Control2 (A2)
213
D5h
Alert2 (B2)
214
D6h
Status2 (C2)
Displays the Status of Channel 2
215
D7h
Fault2 (D2)
Fault Log for Channel 2
216
D8h
SOURCE1 MSB
ADC SOURCE1 MSB data
217
D9h
SOURCE1 LSB
ADC SOURCE1 LSB data
218
DAh
SOURCE2 MSB
ADC SOURCE2 MSB data
219
DBh
SOURCE2 LSB
ADC SOURCE2 LSB data
220
DCh
ADIN1 MSB
ADC ADIN1 MSB
221
DDh
ADIN1 LSB
ADC ADIN1 LSB
222
DEh
ADIN2 MSB
ADC ADIN2 MSB
223
DFh
ADIN2 LSB
224
E0h
SENSE1 MSB
Sets Behavior for Channel 1
Selects Which Channel 1 Faults Generate Alerts
Sets Behavior for Channel 2
Selects which Channel 2 Faults Generate Alerts
ADC ADIN2 LSB
ADC SENSE1 MSB
225
E1h
SENSE1 LSB
ADC SENSE1 LSB
226
E2h
SENSE2 MSB
ADC SENSE2 MSB
227
E3h
SENSE2 LSB
ADC SENSE2 LSB
228
E4h
ADC CONTROL
Configures Behavior of the ADC
+ Set bit ADC_CONTROL(0) before writing
4222fb
24
LTC4222
APPLICATIONS INFORMATION
Table 3. CONTROL Registers A – Read/Write
BIT CONTROL 1 (D0h)
CONTROL 2 (D4h)
OPERATION
7:6 GPIO1 Configure
GPIO2 Configure
FUNCTION
A6
A7
GPIO PIN
Power Good (Default)
0
0
GPIO = C3
PowerGood
0
1
GPIO = C3
General Purpose Output
1
0
GPIO = A5
General Purpose Input
1
1
C6 = GPIO
5
GPIO1 Output
GPIO2 Output
Output Data for GPIO Pins When Configured as General Purpose Output
4
Reserved
Mass Write Enable
Allows Mass Write Addressing
3
Channel 1 FET On Control
Channel 2 FET On Control
On Control Bit, Latches the State of the On Pin at the End of the
Debounce Delay
1 = High Impedance, 0 = Pulled Low
1 = Mass Write Enabled (Default), 0 = Mass Write Disabled
1 = FET On, 0 = FET Off
2
Channel 1 Overcurrent Auto-Retry
Channel 2 Overcurrent Auto-Retry
Overcurrent Auto-Retry Bit
1 = Auto-Retry After Overcurrent, 0 = Latch Off After Overcurrent
(Default)
1
Channel 1 Undervoltage Auto-Retry Channel 2 Undervoltage Auto-Retry Undervoltage Auto-retry
1 = Auto-Retry After Undervoltage (Default), 0 = Latch Off After
Undervoltage
0
Channel 1 Overvoltage Auto-Retry
Channel 2 Overvoltage Auto-Retry
Overvoltage Auto-retry
1 = Auto-Retry After Overvoltage (Default), 0 = Latch Off After
Overvoltage
Table 4. ALERT Registers B – Read/Write
BIT ALERT 1 (D1h)
ALERT 2 (D5h)
OPERATION
7
Reserved
Reserved
Not Used
6
Reserved
Reserved
Not Used
5
Channel 1 FET Short Alert
Channel 2 FET Short Alert
Enables Alert for FET Short Condition
1 = Enable Alert, 0 = Disable Alert (Default)
4
EN1 State Change Alert
EN2 State Change Alert
Enables Alert When EN Changes State
1 = Enable Alert, 0 = Disable Alert (Default)
3
Channel 1 Power Bad Alert
Channel 2 Power Bad Alert
Enables Alert When Output Power is Bad
1 = Enable Alert, 0 = Disable Alert (Default)
2
Channel 1 Overcurrent Alert
Channel 2 Overcurrent Alert
Enables Alert for Overcurrent Condition
1 = Enable Alert, 0 = Disable Alert (Default)
1
Channel 1 Undervoltage Alert
Channel 2 Undervoltage Alert
Enables Alert for Undervoltage Condition
1 = Enable Alert, 0 = Disable Alert (Default)
0
Channel 1 Overvoltage Alert
Channel 2 Overvoltage Alert
Enables Alert for Overvoltage Condition
1 = Enable Alert, 0 = Disable Alert (Default)
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25
LTC4222
APPLICATIONS INFORMATION
Table 5. STATUS Registers C – Read
BIT STATUS 1 (D2h)
STATUS 2 (D6h)
OPERATION
7
FET On
FET On
1 = FET On, 0 = FET Off
6
GPIO1 Input
GPIO2 Input
Reports the State of the GPIO1
Pin 1 = GPIO1 High, 0 = GPIO1 Low
5
Channel 1 FET Short Status
Channel 2 FET Short Status
Reports the State of the GPIO2
Pin 1 = GPIO2 High, 0 = GPIO2 Low
4
EN1 Status
EN2 Status
Indicates If the Channel is Enabled When EN is Low
1 = EN pin Low, 0 = EN pin High
3
Channel 1 Power Bad
Channel 2 Power Bad
Indicates Power is Bad When FB is Low
1 = FB Low, 0 = FB High
2
Channel 1 Overcurrent
Channel 2 Overcurrent
Indicates Overcurrent Condition; 1 = Overcurrent, 0 = Not Overcurrent
1
Channel 1 Undervoltage
Channel 2 Undervoltage
Indicates Input Undervoltage When UV is Low
0
Channel 1 Overvoltage
Channel 2 Overvoltage
1 = UV Low, 0 = UV High
Indicates Input Overvoltage When OV is High
1 = OV High, 0 = OV Low
Table 6. FAULT Registers D – Read/Write
BIT FAULT 1 (D3h)
FAULT 2 (D7h)
OPERATION
7
Reserved
Reserved
Reserved
6
Reserved
Reserved
Reserved
5
Channel 1 FET Short Fault
Occurred
Channel 2 FET Short Fault
Occurred
Indicates Potential FET Short was Detected When Measured Current
Sense Voltage Exceeded 1mV While FET was Off
1 = FET was Shorted, 0 = FET is Good
4
Channel 1 EN Changed State
Channel 2 EN Changed State
Indicates That the LTC4215-1 was Enabled or Disabled When EN
Changed State
3
Channel 1 Power Bad Fault
Occurred
Channel 2 Power Bad Fault
Occurred
Indicates Power was Bad When FB Went Low
2
Channel 1 Overcurrent Fault
Occurred
Channel 2 Overcurrent Fault
Occurred
Indicates Overcurrent Fault Occurred
Channel 1 Undervoltage Fault
Occurred
Channel 2 Undervoltage Fault
Occurred
Indicates Input Undervoltage Fault Occurred When UV Went Low
Channel 1 Overvoltage Fault
Occurred
Channel 2 Overvoltage Fault
Occurred
Indicates Input Overvoltage Fault Occurred When OV Went High
1 = EN Changed State, 0 = EN Unchanged
1
0
1 = FB was Low, 0 = FB was High
1 = Overcurrent Fault Occurred, 0 = No Overcurrent Faults
1 = UV was Low, 0 = UV was High
1 = OV was High, 0 = OV was Low
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26
LTC4222
APPLICATIONS INFORMATION
Table 7. ADC Register Data Format: ADINn, SOURCEn, SENSEn MSB Bytes – Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (9)
Data (8)
Data (7)
Data (6)
Data (5)
Data (4)
Data (3)
Data (2)
*Set bit ADC­_CONTROL(0) before writing
Table 8. ADC Register Data Format: ADINn, SOURCEn, SENSEn LSB Bytes – Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (1)
Data (0)
Reserved**
Reserved**
Reserved**
Reserved**
Reserved**
Reserved**
*Set bit ADC­_CONTROL(0) before writing
**Read as zero
Table 9. ADC CONTROL Register E – Read/Write
BIT ADC_CONTROL (E4h)
OPERATION
7
Reserved
Reserved
6
Reserved
Reserved
5
ADC Busy
Status Bit That is High When the ADC is Converting. Always High in Free-Run Mode, Low When ADC is
Halted or After a Point and Shoot Conversion. Read Only
4
ADC Alert
Enables the ALERT Pin to Pull Low When the ADC Finishes a Measurement
3
ADC Channel Address
These Bits May Be Written to Cause the ADC to Make a Single Measurement of the Desired Channel
When the Halt Bit is High
2
1
0
Halt
FUNCTION
SF2-0
SOURCE1
000
SOURCE2
001
ADIN1
010
ADIN2
011
SENSE1
100
SENSE2
101
Stops the Data Converter and Enables Point and Shoot Mode
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27
LTC4222
TYPICAL APPLICATIONS
RS1
0.01Ω
VIN1
12V
INTVCC
R10
3.3k
5V
5V
2
8
Z1
SA14A
R9
10k
6
SDA
CF1
0.1µF
UV1 VDD1
OV1
SDA1
SDA0
SCL
ALERT
R3-1
3.4k
5
8
2
BAT
254
HCPL-0300
5
5V
2
SCL
3
INTVCC
R10
3.3k
NC
8
C3
0.1µF
R12
10k
R3-2
3.4k
6
SENSE1– GATE1
LTC4222
GND
VIN2
3.3V
BACKPLANE PLUG-IN
CARD
CF2
0.1µF
SOURCE1
FB1
GPIO1
EN1
ADIN1
INTVCC
ON1
GND
OV2
UV2 VDD2
SENSE2– GATE2
R6-2
15k
R5-2
10Ω
R1-2
6.55k
Z2
SA14A
R4-1
100k
SS
HCPL-0300
5
R8-1
3.57k
TIMER
ON2
CONFIG
ADR0
ADR1
ADR2
INTVCC
R2-2
1.02k
3
R7-1
10.2k
R6-1
15k
C1-1
22nF
R2-1
1.02k
INTVCC
6
R5-1
10Ω
470Ω
HCPL-0300
3
R1-1
34k
Q1
FDD3706
RS2
0.01Ω
C1-2
22nF
ADIN2
EN2
GPIO2
FB2
SOURCE2
CSS
68nF
R8-2
3.57k
R7-2
4.99k
Q2
FDD3706
4222 TA03
Figure 12. 3.3V and 12V Application with Sequenced Turn-On Optically Isolated I2C Communication
and 5A Current Limits. Schottky Diode Allows 3.3V Switch to Turn On When 12V is Absent
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28
LTC4222
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UH Package
32-Lead Plastic QFN (5mm × 5mm)
(Reference LTC DWG # 05-08-1693 Rev D)
0.70 ±0.05
5.50 ±0.05
4.10 ±0.05
3.50 REF
(4 SIDES)
3.45 ± 0.05
3.45 ± 0.05
PACKAGE OUTLINE
0.25 ± 0.05
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
5.00 ± 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.75 ± 0.05
R = 0.05
TYP
0.00 – 0.05
R = 0.115
TYP
PIN 1 NOTCH R = 0.30 TYP
OR 0.35 × 45° CHAMFER
31 32
0.40 ± 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
3.50 REF
(4-SIDES)
3.45 ± 0.10
3.45 ± 0.10
(UH32) QFN 0406 REV D
0.200 REF
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-220 VARIATION WHHD-(X) (TO BE APPROVED)
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 0.20mm 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
0.25 ± 0.05
0.50 BSC
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29
LTC4222
PACKAGE DESCRIPTION
G Package
36-Lead Plastic SSOP (5.3mm)
(Reference LTC DWG # 05-08-1640)
12.50 – 13.10*
(.492 – .516)
1.25 ±0.12
7.8 – 8.2
36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19
5.3 – 5.7
0.42 ±0.03
7.40 – 8.20
(.291 – .323)
0.65 BSC
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
RECOMMENDED SOLDER PAD LAYOUT
2.0
(.079)
MAX
5.00 – 5.60**
(.197 – .221)
0° – 8°
0.09 – 0.25
(.0035 – .010)
0.55 – 0.95
(.022 – .037)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
MILLIMETERS
2. DIMENSIONS ARE IN
(INCHES)
0.65
(.0256)
BSC
0.22 – 0.38
(.009 – .015)
TYP
0.05
(.002)
MIN
G36 SSOP 0204
3. DRAWING NOT TO SCALE
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED .152mm (.006") PER SIDE
**DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
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30
LTC4222
REVISION HISTORY
(Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
3/12
Updated Typical Application
Revised Electrical Characteristics limits
Revised Figure 2 and Figure 12
Corrected Comments for LTC4215 in Related Parts
1
3, 4
15, 29
32
4222fb
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
31
LTC4222
TYPICAL APPLICATION
6mΩ
12V
Si7336ADP
12V
93.1k
93.1k
10Ω
0.1µF
12.1k
2k
UV1 VDD1
OV1
10.2k
NC
0.1µF
10.2k
FB1
ON
SDA
SCL
ALERT
CONFIG
ADR0
ADR1
ADR2
INTVCC
GPIO1
EN1
ADIN1
TIMER
LTC4222
SS
ADIN2
EN2
GPIO2
GND
OV2
µTCA
PLUG-IN
CARD 1
FB2
PWR GOOD 1
2k
68nF
PWR GOOD 2
12.1k
10Ω
93.1k
LOAD
1
1µF
µTCA
PLUG-IN
CARD 2
SENSE2– GATE2 SOURCE2
UV2 VDD2
0.1µF
100k
SENSE1– GATE1 SOURCE1
100k
LOAD
2
93.1k
12V
6mΩ
Si7336ADP
12V
BACKPLANE
4222 TA02a
Figure 13. µTCA Application Supplying 12V Payload Power to Two µTCA Slots
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1642A
Single Channel, Hot Swap Controller
Operates from 3V to 16.5V, Overvoltage Protection up to 33V, SSOP-16
LTC1645
Dual Channel, Hot Swap Controller
Operates from 3V to 12V, Power Sequencing, SO-8 or SO-14
LTC1647-1/LTC1647-2/ Dual Channel, Hot Swap Controller
LTC1647-3
Operates from 2.7V to 16.5V, SO-8 or SSOP-16
LTC4210
Single Channel, Hot Swap Controller
Operates from 2.7V to 16.5V, Active Current Limiting, SOT23-6
LTC4211
Single Channel, Hot Swap Controller
Operates from 2.5V to 16.5V, Multifunction Current Control, MSOP-8 or MSOP-10
LTC4212
Single Channel, Hot Swap Controller
Operates from 2.5V to 16.5V, Power-Up Timeout, MSOP-10
LTC4214
Negative Voltage, Hot Swap Controller
Operates from –6V to –16V, MSOP-10
LTC4215
Single Channel, Hot Swap Controller with I2C
Monitoring
Operates from 2.9V to 15V, 8-Bit ADC Monitors Current and Voltage
LTC4216
Single Channel, Hot Swap Controller
Operates from 0V to 6V, MSOP-10 or 12-Lead (4mm × 3mm) DFN
LTC4217
Single Channel, Hot Swap Controller
Operates from 2.9V to 26.5V, Integrated MOSFET, TSSOP-20 or DFN-16
LTC4218
Single Channel, Hot Swap Controller
Operates from 2.9V to 26.5V, 5% Accurate Current Limit, SSOP-16 or DFN-16
LT4220
Positive and Negative Voltage, Dual Channel,
Hot Swap Controller
Operates from ±2.7V to ±16.5V, SSOP-16
LTC4221
Dual Hot Swap Controller/Sequencer
Operates from 1V to 13.5V, Multifunction Current Control, SSOP-16
LTC4224
Dual Channel, Hot Swap Controller
Operates from 1V to 6V, Compact, MSOP-10 or (3mm × 2mm) DFN-10
4222fb
32 Linear Technology Corporation
LT 0312 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2008