LTC2921/LTC2922 Series
Power Supply Tracker
with Input Monitors
FEATURES
s
s
s
s
s
s
s
s
s
s
DESCRIPTIO
Tracks Multiple Supplies with MOSFET Switches
Monitors 5 Input Voltages Including V
CC
Guaranteed Threshold Accuracy:
±1%
at 0.5V
Automatic Remote Sense Switching
Adjustable Supply Ramp Rate
Overvoltage Monitor
Adjustable Electronic Circuit Breaker
Adjustable Power-Good Delay
Available for V
CC
Supply Voltages of 5V, 3.3V and 2.5V
Available in 16-Pin Narrow SSOP (LTC2921 Series)
and 20-Pin TSSOP (LTC2922 Series)
The LTC
®
2921 and LTC2922 monitor up to five supplies
and force them to track on power-up in multiple supply
systems. Using external N-channel pass transistors, the
supplies can be ramped up at an adjustable rate. Auto-
matic remote sense switching allows the DC/DC convert-
ers to compensate for series voltage drops in the wiring.
An incorrect level on one or more of the supplies triggers
disconnect of all supplies. Tight 1% accuracy and glitch
immunity on the low 0.5V monitoring level ensure no false
error disconnects.
The LTC2921 and LTC2922 each feature an adjustable
electronic circuit breaker to protect the V
CC
supply against
short circuits. Capacitance at the TIMER pin programs the
delays in the monitoring sequence.
The LTC2921 includes three remote sense switches in a
16-pin narrow SSOP package, while the LTC2922 includes
five remote sense switches in a 20-pin TSSOP package.
Both parts are available for V
CC
supply voltages of 5V,
3.3V, and 2.5V.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
s
Desktop Computers
Plug-In Cards
Telecom Infrastructure
Supply Sequencing
Instruments
TYPICAL APPLICATIO
V
OUT
V
FB
DC/DC
CONVERTER
V
OUT
V
FB
DC/DC
CONVERTER
V
OUT
V
FB
DC/DC
CONVERTER
243k
169k
2.5V SUPPLY
100Ω
3.3V SUPPLY
100Ω
5V SUPPLY
100Ω
Three-Supply Tracker and Monitor (5V, 3.3V, 2.5V)
WSL1206
0.05Ω
Si2316DS
10Ω
3.3V
LOAD
5V
LOAD
Si2316DS
10Ω
2.5V SUPPLY
2V/DIV
5V LOAD
3.3V LOAD
OUTPUTS
2V/DIV
2.5V LOAD
Si2316DS
10Ω
2.5V
LOAD
V
CC
V1
V2
V3
V4
S1
S2
S3
GND
CIRCUIT BREAKER
RESET CONTROL
SENSE
GATE
0.47µF
PG
D1
D2
D3
TIMER
0.22µF
4.7k
PG
2V/DIV
49.9k
Si1012R
CBRST
100k
49.9k
LTC2921
RESET
t
GATE
~ 500ms
t
TIMER
~ 130ms
2921/22 TA01
U
Load Voltage Ramp-Up and
Power-Good Activation
100ms/DIV
5V SUPPLY AT 5V
3.3V SUPPLY AT 3.3V
2921/22 TA01b
U
U
29212fa
1
LTC2921/LTC2922 Series
ABSOLUTE
AXI U RATI GS
(Note 1)
Switch Currents (DC, RMS)
S0, D0, S4, D4 (LTC2922 Series) ..................... 30mA
S1, D1, S2, D2, S3, D3 ..................................... 30mA
Operating Ambient Temperature Range
LTC2921C/LTC2922C .............................. 0°C to 70°C
LTC2921I/LTC2922I ............................–40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
V
CC
Supply Voltage ...................................... –0.3V to 7V
V1, V2, V3, V4 Voltages ............................... –0.3V to 7V
SENSE Voltage ............................................ –0.3V to 7V
TIMER Voltage ............................. –0.3V to (V
CC
+ 0.3V)
Charge Pumped Output Voltages
GATE, PG ............................................ –0.3V to 12.2V
Switch Voltages
S0, D0, S4, D4 (LTC2922 Series) ............ –0.3V to 7V
S1, D1, S2, D2, S3, D3 ............................ –0.3V to 7V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V1 1
V2 2
V3 3
V4 4
S3 5
D3 6
S2 7
D2 8
16 TIMER
15 V
CC
14 SENSE
13 GATE
12 PG
11 GND
10 D1
9
S1
ORDER PART
NUMBER
LTC2921CGN
LTC2921CGN-3.3
LTC2921CGN-2.5
LTC2921IGN
LTC2921IGN-3.3
LTC2921IGN-2.5
GN PART MARKING
2921
292133
292125
2921I
921I33
921I25
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V for LTC2921/LTC2922, V
CC
= 3.3V for
LTC2921-3.3/LTC2922-3.3, and V
CC
= 2.5V for LTC2921-2.5/LTC2922-2.5, unless otherwise noted.
SYMBOL
Supply Pin
V
CC
Supply Voltage
Typical Operating Range
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
LTC2921-2.5/LTC2922-2.5
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
LTC2921-2.5/LTC2922-2.5
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
LTC2921-2.5/LTC2922-2.5
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
I
CC
V
CC(MON)
Supply Current
Supply Monitor Threshold Voltage
4.285
2.828
2.265
5.82
3.84
3.08
V
CC(OV)
Supply Overvoltage Threshold
2
U
U
W
W W
U
W
TOP VIEW
SO 1
TIMER 2
V1 3
V2 4
V3 5
V4 6
S4 7
D4 8
S3 9
D3 10
20 D0
19 V
CC
18 SENSE
17 GATE
16 PG
15 GND
14 D1
13 S1
12 D2
11 S2
ORDER PART
NUMBER
LTC2922CF
LTC2922CF-3.3
LTC2922CF-2.5
LTC2922IF
LTC2922IF-3.3
LTC2922IF-2.5
F PACKAGE
20-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 90°C/W
MIN
TYP
MAX
UNITS
4.50
2.97
2.37
5.00
3.30
2.50
2
4.350
2.871
2.300
6.13
4.04
3.24
5.50
3.63
2.63
4.415
2.914
2.335
6.43
4.24
3.40
V
V
V
mA
V
V
V
V
V
V
29212fa
LTC2921/LTC2922 Series
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC(UVLO)
V
CC(UVH)
∆V
SENSE
I
SENSE
t
V1(DLY)
PARAMETER
Supply Undervoltage Lockout
Supply Undervoltage Hysteresis
Circuit Breaker Trip Voltage
SENSE Pin Input Current
Circuit Breaker Trip Delay Time
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V for LTC2921/LTC2922, V
CC
= 3.3V for
LTC2921-3.3/LTC2922-3.3, and V
CC
= 2.5V for LTC2921-2.5/LTC2922-2.5, unless otherwise noted.
CONDITIONS
V
CC
Rising
V
CC
Falling
∆V
SENSE
= V
CC
- V
SENSE
V
CC
- V
SENSE
= 150mV
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
LTC2921-2.5/LTC2922-2.5
Guaranteed Not to Reset
Guaranteed to Reset
q
q
q
q
q
MIN
2.08
TYP
2.20
120
MAX
2.30
UNITS
V
mV
Electronic Circuit Breaker
45
50
150
0.5
0.5
0.5
150
0.490
0.495
0.492
0.665
0.500
0.500
0.500
0.700
0.510
0.505
0.508
0.735
±0.1
q
55
500
3.0
3.0
6.0
50
mV
nA
µs
µs
µs
µs
µs
V
V
V
V
µA
V
µA
µA
mV
V
V
V
µA
mA
1.5
1.5
1.5
t
V1(RST)
V
V1(RST)
Monitor Inputs
V
MON
V
OV
I
MON
TIMER Pin
V
TIMER(TH)
I
TIMER(PU)
I
TIMER(PD)
V
TIMER(CLR)
GATE Pin
V
GATE
Circuit Breaker Reset Pulse Width
Circuit Breaker Reset Threshold Voltage
V1-V4 Monitor Threshold Voltages
q
V1-V4 Overvoltage Thresholds
V1-V4 Input Currents
TIMER Ramp Threshold Voltage
TIMER Pull-Up Current
TIMER Pull-Down Current
TIMER Cleared Threshold Voltage
GATE Drive Output Voltage
V
TIMER
= 1V
V
CC
= 2.35V, V
TIMER
= 0.4V
V
TIMER
Falling
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
LTC2921-2.5/LTC2922-2.5
V
GATE
= V
CC
V
CC
= 2.35V, V
GATE
= 2.35V
V
D
= V
CC
V
PG
= V
CC
V
CC
= 2.35V, V
PG
= 2.35V
V
CC
= 2.35V, I
PG
= 5mA
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
LTC2921-2.5/LTC2922-2.5
q
1.15
–1.3
100
1.20
–2.0
150
1.25
–2.5
250
12.2
9.8
7.5
–12.5
q
q
q
q
q
10.0
8.4
6.1
–6.5
10
11.1
9.1
6.8
–10.0
I
GATE(PU)
I
GATE(PD)
R
DS(FB)
PG Pin
I
PG(PU)
I
PG(PD)
V
PG(OL)
V
PG
GATE Pull-Up Current
GATE Pull-Down Current
Feedback Switch Resistances (Note 3)
PG Pull-Up Current
PG Pull-Down Current
PG Output Low Voltage
PG Output Voltage (Note 4)
Remote Sense Switches
q
2
–2.6
10
–4.0
10
–5.0
0.4
Ω
µA
mA
V
V
V
V
q
q
q
q
q
10.0
8.4
6.1
11.1
9.1
6.8
12.2
9.8
7.5
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
LTC2921 Series: T
J
= T
A
+ (P
D
• 110°C/W)
LTC2922 Series: T
J
= T
A
+ (P
D
• 90°C/W)
Note 3:
This specification applies to all switches, and is measured with
V
S
< V
D
.
Note 4:
The PG pin will rise to approximately the same voltage as the
GATE pin when not pulled up or pulled down by external resistance.
29212fa
3
LTC2921/LTC2922 Series
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at T
A
= 25°C unless otherwise noted.
Monitor Trip Delay vs
Monitor Input Overdrive
100
Supply Current vs Supply Voltage
3.00
2.75
2.4
2.50
I
CC
(mA)
I
CC
(mA)
PG SIGNAL ASSERTED
LTC2921
LTC2922
LTC2921-3.3
LTC2922-3.3
MONITOR TRIP DELAY (µs)
LTC2921-3.3
2.25
LTC2922-3.3
2.00
1.75
1.50
LTC2921-2.5
LTC2922-2.5
LTC2921
LTC2922
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
V
CC
(V)
2921/2 G01
Monitor Input Threshold vs
Temperature
0.505
MONITOR INPUT THRESHOLD (V)
BREAKER TRIP (mV)
0.500
50
I
SENSE
(nA)
0.495
–50
–30
30
–10 10
50
TEMPERATURE (°C)
TIMER Trip Voltage
vs Temperature
1.21
2.5
2.4
TIMER TRIP VOLTAGE (V)
2.2
CURRENT (µA)
PULL-DOWN CURRENT (µA)
1.20
1.19
–50
–30
30
–10 10
50
TEMPERATURE (°C)
4
U W
70
2921/2 G04
Supply Current vs Temperature
2.6
PG SIGNAL ASSERTED
80
60
LTC2921-2.5
LTC2922-2.5
40
LTC2921/LTC2922
LTC2921-3.3/LTC2922-3.3
20
2.2
2.0
LTC2921-2.5
LTC2922-2.5
1.8
–50 –30
0
30
50
–10 10
TEMPERATURE (°C)
70
90
0
80
40
100 120
60
20
MONITOR INPUT OVERDRIVE (mV)
140
2921/2 G02
2921/2 G03
Circuit Breaker Trip Voltage vs
Temperature
55
250
SENSE Input Current
vs Temperature
V
SENSE
= V
CC
200
150
100
50
90
45
–50
–30
30
10
–10
50
TEMPERATURE (°C)
70
90
0
–50
–30
30
–10 10
50
TEMPERATURE (°C)
70
90
2921/2 G05
2921/2 G06
TIMER Pull-Up Current
vs Temperature
V
TIMER
= 1V
170
165
160
155
150
145
140
TIMER Pull-Down Current
vs Supply Voltage
V
TIMER
= 0.4V
2.3
2.1
2.0
1.9
1.8
1.7
1.6
70
90
1.5
–50
–30
–10
10
30
50
70
90
TEMPERATURE (°C)
2921/2 G07
2921/2 G08
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
V
CC
(V)
2921/2 G09
29212fa
LTC2921/LTC2922 Series
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at T
A
= 25°C unless otherwise noted.
Gate Voltage vs Supply Voltage
12
GATE LOAD = 1000pF || 10MΩ
PG LOAD = 2kΩ TO V
CC
11 V
CC
BYPASS CAP = 1µF
LTC2921
LTC2922
10
9
8
7
6
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
V
CC
(V)
2921/2 G10
GATE VOLTAGE (V)
GATE VOLTAGE (V)
10
LTC2921-3.3
LTC2922-3.3
9
8
7
6
–50 –30
GATE LOAD = 1000pF || 10MΩ
PG LOAD = 2kΩ TO V
CC
V
CC
BYPASS CAP = 1µF
LTC2921-2.5
LTC2922-2.5
GATE VOLTAGE (V)
LTC2921-3.3
LTC2922-3.3
LTC2921-2.5
LTC2922-2.5
GATE Pull-Up Current
vs Temperature
11.5
11.0
CURRENT (µA)
V
GATE
= V
CC
PG (V)
10.0
9.5
9.0
8.5
–50 –30
9
8
7
6
LTC2921-3.3
LTC2922-3.3
CURRENT (µA)
10.5
30
50
–10 10
TEMPERATURE (°C)
U W
70
Gate Voltage vs Temperature
12
11
LTC2921
LTC2922
12
10
8
6
4
2
0
Gate Voltage vs Load Current
LTC2921
LTC2922
LTC2921-3.3
LTC2922-3.3
LTC2921-2.5
LTC2922-2.5
GATE LOAD = 1000pF || 10MΩ
PG LOAD = 2kΩ TO V
CC
V
CC
BYPASS CAP = 1µF
0
1
2
3 4 5 6 7 8
LOAD CURRENT (µA)
9
10
30
50
–10 10
TEMPERATURE (°C)
70
90
2921/2 G11
2921/2 G12
PG Voltage vs Supply Voltage
12
GATE LOAD = 1000pF || 10MΩ
PG LOAD = 1000pF || 10MΩ
11 V
CC
BYPASS CAP = 1µF
LTC2921
LTC2922
10
5.5
5.0
4.5
4.0
3.5
3.0
PG Pull-Up Current vs
Temperature
V
PG
= V
CC
LTC2921-2.5
LTC2922-2.5
90
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
V
CC
(V)
2921/2 G14
2.5
–50 –30
30
50
–10 10
TEMPERATURE (°C)
70
90
2921/2 G13
2921/2 G15
29212fa
5
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