LTC2906/LTC2907
Precision Dual Supply Monitors
with One Pin-Selectable Threshold
and One Adjustable Input
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FEATURES
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DESCRIPTIO
The LTC®2906/LTC2907 are dual supply monitors intended for systems with multiple supply voltages. The
dual supply monitors have a common reset output with
delay (200ms for the LTC2906 and adjustable using an
external capacitor for the LTC2907). These products provide a precise, space-conscious and micropower solution
for supply monitoring.
Monitors Two Inputs Simultaneously
Three Threshold Selections for 5V, 3.3V or 2.5V
Supplies
Low Voltage Adjustable Input (0.5V)
Three Supply Tolerances (5%, 7.5%, 10%)
Guaranteed Threshold Accuracy: ±1.5% of
Monitored Voltage Over Temperature
Internal VCC Auto Select
Power Supply Glitch Immunity
200ms Reset Time Delay (LTC2906 Only)
Adjustable Reset Time Delay (LTC2907 Only)
Open Drain RST Output
Guaranteed RST for V1 ≥ 1V or VCC ≥ 1V
Low Profile (1mm) SOT-23 (ThinSOTTM) and
Plastic (3mm × 2mm) DFN Packages
The LTC2906/LTC2907 feature a tight 1.5% threshold
accuracy over the whole operating temperature range
and glitch immunity to ensure reliable reset operation
without false triggering. The open drain RST output state
is guaranteed to be in the correct state for V1 and/or VCC
down to 1V.
The LTC2906/LTC2907 also feature one adjustable input
with a nominal threshold level at 0.5V, another input with
three possible input threshold levels, and three supply
tolerances for possible margining. These features provide
versatility for any kind of system requiring dual supply
monitors. Two three-state input pins program the threshold and tolerance level without requiring any external
components.
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APPLICATIO S
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Desktop and Notebook Computers
Handheld Devices
Network Servers
Core, I/O Monitor
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
Dual Supply Monitor with Adjustable Tolerance (2.5V, 0.8V)
Supply Selection Programming
V1
2.5V
DC/DC
CONVERTER
SYSTEM
LOGIC
0.8V
49.9k
LTC2907
TMR
S1
GND
TOL
V1
3.3
OPEN
2.5
GND
0.1µF
VCC
Tolerance Programming
100k
TOLERANCE
22nF
TOLERANCE = 10%
5.0
VADJ
V1
0.1µF
S1
RST
29067 TA01
TOL
5%
V1
7.5%
OPEN
10%
GND
29067f
1
LTC2906/LTC2907
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ABSOLUTE
AXI U RATI GS
(Notes 1, 2)
Terminal Voltages
V1, VCC ........................................................ –0.3V to 7V
S1, VADJ, TOL ............................ –0.3V to (VMAX + 0.3V)
RST ............................................................. –0.3V to 7V
RST (LTC2906) ............................................ –0.3V to 7V
TMR (LTC2907) ........................................... –0.3V to 7V
Operating Temperature Range
LTC2906C/LTC2907C .............................. 0°C to 70°C
LTC2906I/LTC2907I ............................–40°C to 85°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
LTC2906CDDB
LTC2906IDDB
LTC2907CDDB
LTC2907IDDB
TOP VIEW
GND 1
8 TOL
RST 2
7 S1
RST/TMR* 3
VCC 4
9
6 VADJ
5 V1
DDB8 PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
EXPOSED PAD IS GND (PIN 9),
MUST BE SOLDERED TO PCB
*RST FOR LTC2906
TMR FOR LTC2907
TJMAX = 125°C, θJA = 250°C/W
ORDER PART
NUMBER
LTC2906CTS8
LTC2906ITS8
LTC2907CTS8
LTC2907ITS8
TOP VIEW
VCC 1
RST/TMR* 2
RST 3
GND 4
DDB8 PART MARKING
LBDC
LBDD
LBDF
LBDG
8 V1
7 VADJ
6 S1
5 TOL
TS8 PART MARKING
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
*RST FOR LTC2906
TMR FOR LTC2907
TJMAX = 125°C, θJA = 250°C/W
LTBCM
LTBCN
LTBCP
LTBCQ
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = V1 = 2.5V, VADJ = 0.55V, S1 = TOL = 0V, unless otherwise noted.
(Notes 2, 3, 4)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT50
5V, 5% Reset Threshold
5V, 7.5% Reset Threshold
5V, 10% Reset Threshold
V1 Input Threshold
●
●
●
4.600
4.475
4.350
4.675
4.550
4.425
4.750
4.625
4.500
V
V
V
VRT33
3.3V, 5% Reset Threshold
3.3V, 7.5% Reset Threshold
3.3V, 10% Reset Threshold
V1 Input Threshold
●
●
●
3.036
2.954
2.871
3.086
3.003
2.921
3.135
3.053
2.970
V
V
V
VRT25
2.5V, 5% Reset Threshold
2.5V, 7.5% Reset Threshold
2.5V, 10% Reset Threshold
V1 Input Threshold
●
●
●
2.300
2.238
2.175
2.338
2.275
2.213
2.375
2.313
2.250
V
V
V
VRTADJ
ADJ, 5% Reset Threshold
ADJ, 7.5% Reset Threshold
ADJ, 10% Reset Threshold
VADJ Input Threshold
●
●
●
0.492
0.479
0.465
0.500
0.487
0.473
0.508
0.495
0.481
V
V
V
VMAX(MIN)
Minimum VMAX Operating Voltage (Note 2) RST, RST in Correct Logic State
●
1
V
IVCC
VCC Input Current
VCC > V1
V1 > VCC
●
●
54
100
±1
µA
µA
IV1
V1 Input Current
VCC > V1
V1 > VCC
●
●
1
55
3
100
µA
µA
IVADJ
VADJ Input Current
±15
nA
●
29067f
2
LTC2906/LTC2907
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = V1 = 2.5V, VADJ = 0.55V, S1 = TOL = 0V, unless otherwise noted.
(Notes 2, 3, 4)
SYMBOL
PARAMETER
CONDITIONS
ITMR(UP)
TMR Pull-Up Current
(LTC2907)
VTMR = 0V
●
ITMR(DOWN)
TMR Pull-Down Current
(LTC2907)
VTMR = 1.4V
●
1.5
2.1
2.7
µA
tRST
Reset Time-Out Period
(LTC2906)
●
140
200
260
ms
tRST
Reset Time-Out Period
(LTC2907)
●
140
200
260
ms
tUV
VX Undervoltage Detect to
RST or RST
VX Less Than Reset Threshold VRTX
by More than 1%
VOL
Output Voltage Low RST, RST
I = 2.5mA
I = 100µA; V1 and/or VCC = 1V (RST Only)
●
●
VOH
Output Voltage High RST, RST
(Notes 2, 5)
I = –1µA
● VMAX – 1
CTMR = 22nF
MIN
TYP
MAX
UNITS
–1.5
–2.1
–2.7
µA
µs
150
0.15
0.05
0.4
0.3
V
V
V
Three-State Inputs S1, TOL
VIL
Low Level Input Voltage
●
VIH
High Level Input Voltage
●
1.4
VZ
Pin Voltage when Left in Hi-Z State
●
0.7
IVPG
I = –10µA
I = 0µA
I = 10µA
V
V
●
1.1
V
V
V
●
±25
µA
0.9
Programming Input Current (Note 6)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The greater of V1, VCC is the internal supply voltage (VMAX).
Note 3: All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
Note 4: For reset thresholds test conditions refer to the voltage threshold
programming table in the Applications Information section.
0.4
Note 5: The output pins RST and RST have an internal pull-up to VMAX of
typically –6µA. However, an external pull-up resistor may be used when
faster rise time is required or for VOH voltages greater than VMAX.
Note 6: The input current to the three-state input pins are the pull-up and
the pull-down current when the pins are either set to V1 or GND
respectively. In the open state, the maximum leakage current to V1 or GND
permissible is 10µA.
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
5V Threshold Voltage vs
Temperature
3.3V Threshold Voltage vs
Temperature
4.75
2.5V Threshold Voltage vs
Temperature
3.12
2.375
4.65
4.60
7.5%
4.55
4.50
4.45
10%
4.40
4.35
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
29067 G01
THRESHOLD VOLTAGE, VRT25 (V)
5%
THRESHOLD VOLTAGE, VRT33 (V)
THRESHOLD VOLTAGE, VRT50 (V)
5%
4.70
3.07
7.5%
3.02
2.97
10%
2.92
2.87
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
29067 G02
5%
2.325
7.5%
2.275
10%
2.225
2.175
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
29067 G03
29067f
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LTC2906/LTC2907
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
ADJ Threshold Voltage vs
Temperature
19.5
15.8
V1 = 5V
VCC = 3.3V
VADJ =0.55V
S1 =TOL = 1.4V
5%
0.500
19.0
15.4
15.2
7.5%
0.485
18.5
IVCC (µA)
0.490
18.0
0.470
–50
–25
14.2
25
50
0
TEMPERATURE (°C)
75
14.0
17.0
–50
100
–25
25
50
0
TEMPERATURE (°C)
75
29067 G04
100
–50
500
RESET OCCURS
ABOVE CURVE
300
200
100
1000
0
100
10
1
0.1
10p
1
10
100
0.1
COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
100p
1n
10n
CTMR (FARAD)
100n
215
210
205
200
2
1
0
5
V1 (V)
3
2
1
–1
100
S1 = TOL = VCC = V1
VADJ = 0.55V
10pF CAPACITOR AT RST
4
3
2
1
0
0
1
2
3
4
5
V1 (V)
29067 G10
75
5
0
4
25
50
0
TEMPERATURE (°C)
RST Output Voltage vs V1
RST OUTPUT VOLTAGE (V)
RST OUTPUT VOLTAGE (V)
3
–25
29067 G09
S1 = TOL = VCC = V1
VADJ = 0.55V
10k PULL-UP RESISTOR
4
3
220
195
–50
1µ
5
S1 = TOL = VCC = V1
VADJ = 0.55V
10k PULL-UP RESISTOR
2
225
RST Output Voltage vs V1
5
1
CRT = 22nF
230 (FILM)
29067 G08
29067 G07
RST Output Voltage vs V1
100
235
RESET TIME OUT PERIOD, tRST (ms)
RESET TIME OUT PERIOD, tRST (ms)
600
0
75
Reset Time Out Period (t RST)
vs Temperature
10000
4
25
50
0
TEMPERATURE (°C)
29067 G06
Reset Time Out Period (t RST)
vs Capacitance (CTMR)
700
400
–25
29067 G05
Typical Transient Duration vs
Comparator Overdrive (V1, VADJ)
TYPICAL TRANSIENT DURATION (µs)
14.8
14.4
17.5
10%
0.475
RST OUTPUT VOLTAGE (V)
15.0
14.6
0.480
–1
V1 = 2.5V
VCC = 3.3V
VADJ =0.55V
S1 =TOL = 1.4V
15.6
0.495
IV1 (µA)
THRESHOLD VOLTAGE, VRTADJ (V)
IVCC vs Temperature
IV1 vs Temperature
0.505
–1
0
1
2
3
4
5
V1 (V)
29067 G11
29067 G12
29067f
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LTC2906/LTC2907
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
RST Pull-Down Current (IRST)
vs VMAX
4
RST AT 150mV
3
2
1
RST AT 50mV
0
1.8
VCC = V1
S1 = TOL = GND
VADJ = 0.55V
NO PULL-UP R
5
4
RST AT 150mV
3
2
1
RST AT 50mV
1
2
3
VMAX (V)
4
0
5
1
2
3
VMAX (V)
29067 G13
1.0
0.8
0.6
0.4
0.2
0
10
30
40
50
60
20
RST PULL-DOWN CURRENT, IRST (mA)
–12
–10
–8
–6
–4
–2
2.0
VRT33
VRT50
2.5
3.0
3.5
4.0
VMAX (V)
85°C
–40°C
25°C
29067 G19
–8
–6
–4
–2
VRT25
2.5
VRT33
3.0
VRT50
3.5
4.0
VMAX (V)
4.5
5.0
29067 G18
RST Output Voltage High (VOH) vs
RST Output Source Current (IRST)
IS1, ITOL vs Temperature
20
TOL = V1 = 3.3V
VADJ = 0.45V
3.0 S1 = OPEN
NO PULL-UP R
S1 = TOL = V1 = 3.3V
19
18
17
2.5
2.0
–40°C
1.5
16
15
14
13
85°C
12
1.0
25°C
11
0.5
0
–10
2.0
IS1, ITOL (µA)
2.0
–12
0
5.0
4.5
–14
29067G17
RST OUTPUT VOLTAGE HIGH, VOH (V)
RST OUTPUT VOLTAGE HIGH, VOH (V)
TOL = V1 = 3.3V
VADJ = 0.55V
S1 = OPEN
NO PULL-UP R
10
30
40
50
60
20
RST PULL-DOWN CURRENT, IRST (mA)
29067G15
3.5
–8
–6
–4
–2
–10
OUTPUT SOURCE CURRENT, IRST (µA)
0.2
TOL = V1
–14
RST Output Voltage High (VOH)
vs RST Output Source Current (IRST)
0.5
–12
0.4
0
0
1.0
0.6
RST Pull-Up Current (IRST)
vs VMAX
–16
29067 G16
1.5
0.8
–16
VRT25
0
1.0
5
RST PULL-UP CURRENT, IRST (µA)
–40°C
1.2
–40°C
TOL = GND
25°C
RST PULL-UP CURRENT, IRST (µA)
RST OUTPUT VOLTAGE LOW, VOL (V)
1.4
2.5
4
–18
85°C
25°C
85°C
1.2
RST Pull-Up Current (IRST)
vs VMAX
1.8
1.6
1.4
29067 G14
RST Output Voltage Low (VOL)
vs RST Pull-Down Current (IRST)
V1 = VCC = 5V
VADJ = 0.55V
S1 = TOL = V1
NO PULL-UP R
V1 = VCC = 5V
VADJ = 0.45V
S1 = TOL = V1
NO PULL-UP R
1.6
0
0
0
3.0
RST Output Voltage Low (VOL)
vs RST Pull-Down Current (IRST)
RST OUTPUT VOLTAGE LOW, VOL (V)
S1 = TOL = VCC = V1
VADJ = 0.55V
NO PULL-UP R
5
RST PULL-DOWN CURRENT, IRST (mA)
RST PULL-DOWN CURRENT, IRST (mA)
RST Pull-Down Current (IRST)
vs VMAX
–8
–7 –6 –5 –4 –3 –2
–1
OUTPUT SOURCE CURRENT, IRST (µA)
0
290467 G20
10
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
29067 G21
29067f
5
LTC2906/LTC2907
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TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
IS1, ITOL vs Temperature
–20
–19
S1 = TOL = GND
V1 = 3.3V
–18
IS1, ITOL (µA)
–17
–16
–15
–14
–13
–12
–11
–10
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
29067 G22
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PI FU CTIO S
(TS8 Package/DDB8 Package)
VCC (Pin 1/Pin 4): Optional Power Supply Pin. VCC powers
and maintains the correct operation of the RST and RST
pins in the complete absence of V1. If V1 is present, the
greater of VCC or V1 (VMAX) powers the internal circuitry
and the reset outputs. Bypass this pin to ground with a
0.1µF (or greater) capacitor. Tie to V1 when no optional
power is available.
RST (Pin 2/Pin 3): (LTC2906 Only) Reset Logic Output.
When all voltage inputs are above the reset threshold for
at least the programmed delay time, this pin pulls low. This
pin has a weak pull up to VMAX and may be pulled above
VMAX using an external pull-up.
TMR (Pin 2/Pin 3): (LTC2907 Only) Reset Delay Time
Programming Pin. Attach an external capacitor (CTMR) to
GND to set a reset delay time of 9ms/nF. Leaving the pin
open generates a minimum delay of approximately 200µs.
A 22nF capacitor will generate a 200ms reset delay time.
RST (Pin 3/Pin 2): Inverted Reset Logic Output. Pulls low
when either V1 or VADJ is below the reset threshold and
holds low for programmed delay time after all voltage
inputs are above threshold. This pin has a weak pull up to
VMAX and may be pulled above VMAX using an external
pull-up.
GND (Pin 4/Pin 1 and Pin 9): Ground.
TOL (Pin 5/Pin 8): Three-State Input for Supply Tolerance
Selection (5%, 7.5% or 10%). Refer to Applications Information for tolerance selection chart (Table 3).
S1 (Pin 6/Pin 7): The Voltage Threshold Select ThreeState Input. Connect to V1, GND or leave unconnected in
open state to select one of three possible input threshold
levels (refer to Table 1).
VADJ (Pin 7/Pin 6): Adjustable Voltage Input. Bypass this
pin to ground with a 0.1µF (or greater) capacitor in a noisy
environment.
V1 (Pin 8/Pin 1): Voltage Input 1. Select from 5V, 3.3V or
2.5V. Refer to Table 1 for details. The greater of (V1, VCC)
is also the internal VCC (VMAX). Bypass this pin to ground
with a 0.1µF (or greater) capacitor.
29067f
6
LTC2906/LTC2907
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BLOCK DIAGRA
VMAX
LTC2906
6µA
–
RST
V1
+
VMAX
RESISTOR
NETWORK
POWER
DETECT
200ms
RESET PULSE
GENERATOR
VMAX
6µA
+
VCC
–
VADJ
RST
BAND GAP
REFERENCE
THREE-STATE DECODER
GND
2906 BD
S1
TOL
LTC2907
–
V1
TMR
VMAX
POWER
DETECT
VMAX
RESISTOR
NETWORK
+
6µA
200ms
RESET PULSE
GENERATOR
VCC
+
RST
–
VADJ
BAND GAP
REFERENCE
THREE-STATE DECODER
GND
2907 BD
S1
TOL
29067f
7
LTC2906/LTC2907
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TI I G DIAGRA
Vx Monitor Timing
VRTX
VX
tRST
tUV
RST
1V
RST
1V
29067 TD
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APPLICATIO S I FOR ATIO
Supply Monitoring
The LTC2906/LTC2907 are low power, high accuracy dual
supply monitoring circuits with an adjustable input and
another input with selectable threshold. Reset delay is set
to a nominal of 200ms for LTC2906 and is adjustable using
an external capacitor for LTC2907.
The three-state input pin (S1) selects one of three possible
threshold voltage levels for V1. Another three-state input
pin sets the supply tolerance (5%, 7.5% or 10%). Both
input voltages (V1 and VADJ) must be above predetermined thresholds for the reset not to be invoked. The
LTC2906/LTC2907 assert the reset outputs during powerup, power-down and brownout conditions on any one of
the voltage inputs.
Power-Up
The greater of V1, VCC is the internal supply voltage
(VMAX). VMAX powers the drive circuits for the RST pin.
Therefore, as soon as V1 or VCC reaches 1V during power
up, the RST output asserts low.
VMAX also powers the drive circuits for the RST pin in the
LTC2906. Therefore, RST weakly pulls high when either
V1 or VCC reaches at least 1V.
Threshold programming is complete, when V1 reaches at
least 2.17V. After programming, if any one of the Vx inputs
falls below its programmed threshold, RST asserts low
(RST weakly pulls high) as long as VMAX is at least 1V.
Once both V1 and VADJ inputs rise above their thresholds,
an internal timer is started. After the programmed delay
time, RST weakly pulls high (RST asserts low).
Power-Down
On power-down, once either V1 or VADJ drops below its
threshold, RST asserts logic low and RST weakly pulls
high. VMAX of at least 1V guarantees a logic low of 0.4V
at RST.
Auxiliary Power
If an auxiliary power is available it can be connected to the
VCC pin. Since the internal supply voltage (VMAX) is the
greater of V1, VCC; a VCC of at least 1V guarantees logic low
of 0.4V at RST for voltage inputs (V1 and/or VADJ) down
to 0V.
Programming Pins
The two three-state input pins, S1 and TOL, should be
connected to GND, V1 or left unconnected during normal
operation. Note that when left unconnected, the maximum
leakage current allowable from the pin to either GND or V1
is 10µA.
29067f
8
LTC2906/LTC2907
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APPLICATIO S I FOR ATIO
In margining application, the three-state input pins can be
driven using a three-state buffer. Note however, the low
and high output of the three-state buffer has to satisfy the
VIL and VIH of the three-state pin listed in the Electrical
Characteristics Table. Moreover, when the three-state
buffer is in the high impedance state, the maximum
leakage current allowed from the pin to either GND or V1
is 10µA.
Monitor Programming
R2 =100kΩ is recommended. Once the resistor divider is
set in the 5% tolerance mode, there is no need to change
the divider for the other tolerance modes (7.5%, 10%)
because the internal reference at the noninverting input on
the VADJ comparator is scaled accordingly, moving the trip
point in 2.5% decrements.
Table 2 shows suggested 1% resistor values for various
adjustable applications.
Table 2. Suggested 1% Resistor Values for the VADJ Inputs
Connecting S1 to either GND, or V1, or leaving it in open
state selects the LTC2906/LTC2907 V1 input voltage
threshold. Table 1 shows the three possible selections of
V1 nominal input voltage and their corresponding S1
connection.
Table 1. Supply Selection Programming
VSUPPLY (V)
VTRIP (V)
R1 (kΩ)
R2 (kΩ)
12
11.25
2150
100
10
9.4
1780
100
8
7.5
1400
100
7.5
7
1300
100
6
5.6
1020
100
V1
S1
5
4.725
845
100
5.0
V1
3.3
3.055
511
100
3.3
OPEN
3
2.82
464
100
GND
2.5
2.325
365
100
Note: Open = open circuit or driven by a three-state buffer
in high impedance state with leakage current less than 10µA.
1.8
1.685
237
100
1.5
1.410
182
100
The noninverting input on the VADJ comparator is set
to 0.5V when the TOL pin is set high (5% tolerance)
(Figure␣ 1) and the high impedance inverting input directly
ties to the VADJ pin.
1.2
1.120
124
100
2.5
VTRIP
LTC2906/LTC2907
R1
1%
1
0.933
86.6
100
0.9
0.840
68.1
100
0.8
0.750
49.9
100
0.7
0.655
30.9
100
0.6
0.561
12.1
100
–
VADJ
Tolerance Programming
R2
1%
+
+
–
0.5V
29067 F01
Figure 1. Setting the Adjustable Trip Point
In a typical application, the VADJ pin connects to a tap point
on an external resistive divider between the positive voltage being monitored and ground. The following formula
obtains R1 resistor value for a particular value of R2 and
a desired trip voltage at 5% tolerance:
VTRIP(5%)
– 1 R2
R1 =
0.5V
The three-state input pin TOL, programs the common
supply tolerance for both V1 and VADJ input voltages (5%,
7.5% or 10%). The larger the tolerance the lower the trip
threshold. Table 3 shows the tolerances selection corresponding to a particular connection at the TOL pin.
Table 3. Tolerance Programming
TOLERANCE
TOL
5%
V1
7.5%
OPEN
10%
GND
29067f
9
LTC2906/LTC2907
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APPLICATIO S I FOR ATIO
Threshold Accuracy
Reset threshold accuracy is of the utmost importance in a
supply sensitive system. Ideally such a system should not
reset while supply voltages are within a specified margin
below the rated nominal level. Both of the LTC2906/
LTC2907 inputs have the same relative threshold accuracy. The specification for LTC2906/LTC2907 is ±1.5% of
the programmed nominal input voltage (over the full
operating temperature range).
For example, when the LTC2906/LTC2907 are programmed
to handle a 5V input with 10% tolerance (S1 = V1 and TOL
= GND, refer to Table 1 and Table 3), it does not issue a
reset command when V1 is above 4.5V. The typical 10%
trip threshold is at 11.5% below the nominal input voltage
level. Therefore, the typical trip threshold for the 5V input
is 4.425V. With ±1.5% accuracy, the trip threshold range
is 4.425V ±75mV over temperature (i.e. 10% to 13%
below 5V). This implies that the monitored system must
operate reliably down to 4.35V or 13% below 5V over
temperature.
The same system using a supervisor with only ±2.5%
accuracy needs to work reliably down to 4.25V (4.375V
±125mV) or 15% below 5V, requiring the monitored
system to work over a much wider operating voltage
range.
In any supervisory application, supply noise riding on the
monitored DC voltage can cause spurious resets, particularly when the monitored voltage is near the reset threshold. A less desirable but common solution to this problem
is to introduce hysteresis around the nominal threshold.
Notice however, this hysteresis introduces an error term
in the threshold accuracy. Therefore, a ±2.5% accurate
monitor with ±1% hysteresis is equivalent to a ±3.5%
monitor with no hysteresis.
The LTC2906/LTC2907 take a different approach to solve
this problem of supply noise causing spurious reset. The
first line of defense against this spurious reset is a first
order low pass filter at the output of the comparator. Thus,
the comparator output goes through a form of integration
before triggering the output logic. Therefore, any kind of
transient at the input of the comparator needs to be of
sufficient magnitude and duration before it can trigger a
change in the output logic.
The second line of defense is the programmed delay time
tRST (200ms for LTC2906 and adjustable using an external
capacitor for LTC2907). This delay will eliminate the effect
of any supply noise, whose frequency is above 1/ tRST, on
the RST and RST output.
When either V1 or VADJ drops below its programmed
threshold, the RST pin asserts low (RST weakly pulls
high). When the supply recovers above the programmed
threshold, the reset-pulse-generator timer starts
counting.
If the supply remains above the programmed threshold
when the timer finishes counting, the RST pin weakly pulls
high (RST asserts low). However, if the supply falls below
the programmed threshold any time during the period
when the timer is still counting, the timer resets and starts
fresh when the supply next rises above the programmed
threshold.
Note that this second line of defense is only effective for a
rising supply and does not affect the sensitivity of the
system to a falling supply. Therefore, the first line of
defense that works for both cases of rising and falling is
necessary. These two approaches prevent spurious reset
caused by supply noise without sacrificing the threshold
accuracy.
Selecting the Reset Timing Capacitor
The reset time-out period for LTC2907 is adjustable in
order to accommodate a variety of microprocessor applications. Connecting a capacitor, CTMR, between the TMR
pin and ground sets the reset time-out period, tRST. The
following formula determines the value of capacitor needed
for a particular reset time-out period:
CTMR = tRST • 110 • 10–9 [F/s]
For example, using a standard capacitor value of 22nF
gives a 200ms delay.
The graph in Figure 2 shows the desired delay time as a
function of the value of the timer capacitor that should be
used:
29067f
10
LTC2906/LTC2907
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APPLICATIO S I FOR ATIO
Note however, by adding an external pull-up resistor, the
pull-up strength on the RST pin is increased. Therefore, if
it is connected in a wired-OR connection, the pull-down
strength of any single device needs to accommodate this
additional pull-up strength.
RESET TIME OUT PERIOD, tRST (ms)
10000
1000
100
10
Output Rise and Fall Time Estimation
1
0.1
10p
100p
1n
10n
CTMR (FARAD)
100n
1µ
29067 F02
Figure 2. Reset Time-Out Period vs Capacitance
Leaving the TMR pin open with no external capacitor
generates a reset time-out of approximately 200µs. For
long reset time-out, the only limitation is the availability of
a large value capacitor with low leakage. The TMR capacitor will never charge if the leakage current exceeds the
TMR charging current of 2.1µA (typical).
RST and RST Output Characteristics
The DC characteristics of the RST and RST pull-up and
pull-down strength are shown in the Typical Performance
Characteristics section. Both RST and RST have a weak
internal pull-up to VMAX and a strong pull-down to ground.
The weak pull-up and strong pull-down arrangement
allows these two pins to have open-drain behavior while
possessing several other beneficial characteristics.
The weak pull-ups eliminate the need for external pull-up
resistors when the rise time on these pins is not critical. On
the other hand, the open-drain RST configuration allows
for wired-OR connections and can be useful when more
than one signal needs to pull-down on the RST line.
As noted in the Power-Up and Power-Down sections, the
circuits that drive RST and RST are powered by VMAX =
MAX (V1, VCC). During fault condition, VMAX of at least 1V
guarantees a maximum VOL = 0.4V at RST. However, at
VMAX = 1V the weak pull-up current on RST is barely turned
on. Therefore, an external pull-up resistor of no more than
100k is recommended on the RST pin if the state and pullup strength of the RST pin is crucial at very low VMAX.
The RST and RST output have strong pull-down capability.
The following formula estimates the output fall time (90%
to 10%) for a particular external load capacitance (CLOAD):
tFALL ≈ 2.2␣ •␣ RPD␣ •␣ CLOAD
where RPD is the on-resistance of the internal pull-down
transistor estimated to be typically 40Ω at VMAX >1V, at
room temperature (25°C), and CLOAD is the external load
capacitance on the pin. Assuming a 150pF load capacitance, the fall time is about 13ns.
The rise time on the RST and RST pins is limited by weak
internal pull-up current sources to VMAX. The following
formula estimates the output rise time (10% to 90%) at the
RST and RST pins:
tRISE ≈ 2.2 • RPU • CLOAD
where RPU is the on-resistance of the pull-up transistor.
Notice that this pull-up transistor is modeled as a
6µA current source in the Block Diagram as a typical
representation.
The on-resistance as a function of the VMAX = MAX (V1,
VCC) voltage (for VMAX > 1V) at room temperature is
estimated as follows:
RPU =
6 • 105
Ω
MAX(V1, VCC ) – 1V
At VMAX = 3.3V, RPU is about 260k. Using 150pF for load
capacitance, the rise time is 86µs. A smaller external pullup resistor maybe used if the output needs to pull up faster
and/or to a higher voltage. For example, the rise time
reduces to 3.3µs for a 150pF load capacitance, when using
a 10k pull-up resistor.
29067f
11
LTC2906/LTC2907
U
TYPICAL APPLICATIO S
5V, 3.3V Supply Monitor, 5% Tolerance
with LED Power Good Indicator
VCC
V1
3.3V
499Ω
0.1µF
5V
LTC2906
845k
TOL
P0WER
GOOD
LED
S1
100k
RST
SYSTEM
RESET
RST
0.1µF
VADJ
GND
2906 TA02
3.3V, 1.8V Monitor, 7.5% Tolerance
with an Auxiliary 5V Supply (5V Not Monitored)
VCC
V1
3.3V
LTC2906
0.1µF
TOL
S1
237k
SYSTEM
RESET
RST
0.1µF
VADJ
100k
TMR
22nF
5V
1.8V
GND
2907 TA03
29067f
12
LTC2906/LTC2907
U
TYPICAL APPLICATIO S
2.5V, 1V Monitor, 10% Tolerance with LED Undervoltage Indicator
and 5V High Availability Auxiliary Supply (5V Not Monitored)
1V
86.6k
VADJ
V1
2.5V
LTC2907
0.1µF
100k
VCC
TMR
RST
TOL
S1
GND
22nF
499Ω
5V
0.1µF
0.1µF
LED
2907 TA04
Dual Supply Monitor with Hysteresis, 5% Tolerance
(Supplies Rising), 10% Tolerance (After RST Goes Low)
3.3V
511k
VADJ
5V
V1
LTC2906
100k
0.1µF
VCC
GND
S1
10k
RST
SYSTEM
RESET
TOL
RST
2906 TA05
Dual Supply Monitor for Tracked/Sequenced Supply
3.3V
0.1µF
CGATE
10nF
RONB
154k
RONA
100k
VCC GATE
ON
IN
DC/DC
RAMP
FB1
FB
OUT
2.5V
SYSTEM
LTC2923
RFA1
RAMPBUF
RFB1
0.1µF
RTB1
TRACK1
RTA1
RTB2
FB2
TRACK2
RTA2
VCC
IN
DC/DC
FB
V1
OUT
GND
LTC2907
1.8V
TOL
RST
VADJ
TMR
237k
RFA2
RFB2
22nF
100k
S1
GND
292067 TA06
29067f
13
LTC2906/LTC2907
U
PACKAGE DESCRIPTIO
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 ±0.05
(2 SIDES)
R = 0.115
TYP
5
0.56 ± 0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
0.675 ±0.05
2.50 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.38 ± 0.10
8
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0 – 0.05
4
0.25 ± 0.05
1
PIN 1
CHAMFER OF
EXPOSED PAD
(DDB8) DFN 1103
0.50 BSC
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
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
29067f
14
LTC2906/LTC2907
U
PACKAGE DESCRIPTIO
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
29067f
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.
15
LTC2906/LTC2907
U
TYPICAL APPLICATIO
Quad Supply Monitor with LED Undervoltage
Indicator, 5% Tolerance, 3.3V, 2.5V, 0.8V, 0.6V
0.8V
3.3V
49.9k
LTC2907
VADJ
V1
V1
TOL
22nF
0.1µF
0.1µF
499Ω
VCC
VADJ
S1
100k
TMR
S1
GND
12.1k
TOL LTC2907
VCC
TMR
100k
0.6V
2.5V
LED
RST
GND
22nF
RST
2907 TA07
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690
5V Supply Monitor, Watchdog Timer and Battery Backup
4.65V Threshold
LTC694-3.3
3.3V Supply Monitor, Watchdog Timer and Battery Backup
2.9V Threshold
LTC699
5V Supply Monitor and Watchdog Timer
4.65V Threshold
LTC1232
5V Supply Monitor, Watchdog Timer and Push-Button Reset
4.37V/4.62V Threshold
LTC1326/LTC1326-2.5
Micropower Precision Triple Supply Monitor for
5V/2.5V, 3.3V and ADJ
4.725V, 3.118V, 1V Threshold (±0.75%)
LTC1536
Precision Triple Supply Monitor for PCI Applications
Meets PCI tFAIL Timing Specifications
LTC1726-2.5/LTC1726-5
Micropower Triple Supply Monitor for
2.5V/5V, 3.3V and ADJ
Adjustable RESET and Watchdog Time-Outs
LTC1727-2.5/ LTC1727-5
Micropower Triple Supply Monitor with Open-Drain Reset
Individual Monitor Outputs in MSOP
LTC1728-1.8/ LTC1728-3.3
Micropower Triple Supply Monitor with Open-Drain Reset
5-Lead SOT-23 Package
LTC1728-2.5/ LTC1728-5
Micropower Triple Supply Monitor with Open-Drain Reset
5-Lead SOT-23 Package
LTC1985-1.8
Micropower Triple Supply Monitor with
Push-Pull Reset Output
5-Lead SOT-23 Package
LTC2900
Programmable Quad Supply Monitor
Adjustable RESET, 10-Lead MSOP and
3mm X 3mm 10-Lead DFN Packages
LTC2901
Programmable Quad Supply Monitor
Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
LTC2902
Programmable Quad Supply Monitor
Selectable Tolerance, RESET Disable for Margining
Functions, 16-Lead SSOP Package
LTC2903
Precision Quad Supply Monitor
Ultralow Voltage RESET, 6-Lead SOT-23 Package
LTC2904
Three-State Programmable Precision Dual Supply Monitor
Adjustable Tolerance, 8-Lead SOT-23 and
3mm × 2mm DFN Packages
LTC2905
Three-State Programmable Precision Dual Supply Monitor
Adjustable RESET and Tolerance, 8-Lead SOT-23 and
3mm × 2mm DFN Packages
29067f
16
Linear Technology Corporation
LT/TP 0304 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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