LTC2907 [Linear]
Precision Dual Supply Monitors with One Pin-Selectable Threshold and One Adjustable Input; 精密双电源监视器与一引脚可选门限和一个可调输入
| 型号： | LTC2907 |
| 厂家： | 
Linear |
| 描述： | Precision Dual Supply Monitors with One Pin-Selectable Threshold and One Adjustable Input |
| 文件： | 总16页 (文件大小：195K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC2906/LTC2907
Precision Dual Supply Monitors
with One Pin-Selectable Threshold
and One Adjustable Input
U
FEATURES
DESCRIPTIO
The LTC®2906/LTC2907 are dual supply monitors in-
tended 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 pro-
vide 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
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.
■
■
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
■
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 thresh-
old and tolerance level without requiring any external
components.
Plastic (3mm × 2Umm) DFN Packages
APPLICATIO S
■
Desktop and Notebook Computers
■
Handheld Devices
■
Network Servers
■
Core, I/O Monitor
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATIO
Supply Selection Programming
Dual Supply Monitor with Adjustable Tolerance (2.5V, 0.8V)
V1
5.0
3.3
2.5
S1
V1
2.5V
DC/DC
SYSTEM
LOGIC
0.8V
CONVERTER
OPEN
GND
49.9k
100k
V1
V
V
ADJ
LTC2907
0.1µF
Tolerance Programming
TOLERANCE
TMR
GND
RST
0.1µF
CC
22nF
TOL
V1
S1
5%
7.5%
10%
OPEN
GND
TOL
29067 TA01
TOLERANCE = 10%
29067f
1
LTC2906/LTC2907
W W U W
ABSOLUTE AXI U RATI GS (Notes 1, 2)
Operating Temperature Range
Terminal Voltages
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
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
U
W
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
ORDER PART
NUMBER
LTC2906CTS8
LTC2906ITS8
LTC2907CTS8
LTC2907ITS8
TOP VIEW
NUMBER
GND
RST
1
2
3
4
8
7
6
5
TOL
S1
TOP VIEW
LTC2906CDDB
LTC2906IDDB
LTC2907CDDB
LTC2907IDDB
V
1
8 V1
7 V
6 S1
CC
9
RST/TMR*
V
ADJ
RST/TMR* 2
RST 3
ADJ
V
V1
CC
GND 4
5 TOL
DDB8 PACKAGE
TS8 PACKAGE
DDB8 PART MARKING
TS8 PART MARKING
8-LEAD (3mm × 2mm) PLASTIC DFN
EXPOSED PAD IS GND (PIN 9),
MUST BE SOLDERED TO PCB
*RST FOR LTC2906
8-LEAD PLASTIC TSOT-23
*RST FOR LTC2906
TMR FOR LTC2907
LBDC
LBDD
LBDF
LBDG
LTBCM
LTBCN
LTBCP
LTBCQ
TJMAX = 125°C, θJA = 250°C/W
TMR FOR LTC2907
TJMAX = 125°C, θJA = 250°C/W
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
V
V
V
V
V
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
RT50
RT33
RT25
RTADJ
3.3V, 5% Reset Threshold
3.3V, 7.5% Reset Threshold
3.3V, 10% Reset Threshold
V1 Input 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
2.5V, 5% Reset Threshold
2.5V, 7.5% Reset Threshold
2.5V, 10% Reset Threshold
●
●
●
2.300
2.238
2.175
2.338
2.275
2.213
2.375
2.313
2.250
V
V
V
ADJ, 5% Reset Threshold
ADJ, 7.5% Reset Threshold
ADJ, 10% Reset Threshold
V
ADJ
Input Threshold
●
●
●
0.492
0.479
0.465
0.500
0.487
0.473
0.508
0.495
0.481
V
V
V
Minimum V
Operating Voltage (Note 2) RST, RST in Correct Logic State
MAX
●
1
V
MAX(MIN)
VCC
I
I
I
V
Input Current
V
CC
> V1
●
●
54
100
±1
µA
µA
CC
V1 > V
CC
V1 Input Current
Input Current
V
CC
> V1
●
●
1
55
3
100
µA
µA
V1
V1 > V
CC
V
●
±15
nA
VADJ
ADJ
29067f
2
LTC2906/LTC2907
ELECTRICAL CHARACTERISTICS
(Notes 2, 3, 4)
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.
SYMBOL
PARAMETER
CONDITIONS
MIN
–1.5
1.5
TYP
–2.1
2.1
MAX
–2.7
2.7
UNITS
µA
I
I
t
t
t
TMR Pull-Up Current
TMR Pull-Down Current
Reset Time-Out Period
Reset Time-Out Period
(LTC2907)
(LTC2907)
(LTC2906)
(LTC2907)
V
V
= 0V
●
●
●
●
TMR(UP)
TMR(DOWN)
RST
TMR
TMR
= 1.4V
µA
140
140
200
200
150
260
260
ms
ms
µs
C
= 22nF
RST
TMR
V Undervoltage Detect to
X
V Less Than Reset Threshold V
X
UV
RTX
RST or RST
by More than 1%
V
V
Output Voltage Low RST, RST
I = 2.5mA
●
●
0.15
0.05
0.4
0.3
V
V
OL
OH
I = 100µA; V1 and/or V = 1V (RST Only)
CC
Output Voltage High RST, RST
(Notes 2, 5)
I = –1µA
●
V
– 1
V
MAX
Three-State Inputs S1, TOL
V
V
V
Low Level Input Voltage
●
●
●
0.4
V
V
IL
IH
Z
High Level Input Voltage
1.4
0.7
Pin Voltage when Left in Hi-Z State
I = –10µA
I = 0µA
I = 10µA
V
V
V
0.9
●
●
1.1
I
Programming Input Current (Note 6)
±25
µA
VPG
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 5: The output pins RST and RST have an internal pull-up to V
of
MAX
typically –6µA. However, an external pull-up resistor may be used when
faster rise time is required or for V voltages greater than V
.
MAX
OH
Note 2: The greater of V1, V is the internal supply voltage (V
).
MAX
CC
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.
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.
U W
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
2.5V Threshold Voltage vs
Temperature
4.75
4.70
4.65
4.60
4.55
4.50
4.45
4.40
4.35
3.12
3.07
3.02
2.97
2.92
2.87
2.375
2.325
2.275
2.225
2.175
5%
5%
5%
7.5%
7.5%
10%
7.5%
10%
10%
25
50
25
50
25
50
–50
–25
0
75
100
–50
–25
0
75
100
–50
–25
0
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
29067 G01
29067 G02
29067 G03
29067f
3
LTC2906/LTC2907
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
ADJ Threshold Voltage vs
Temperature
IVCC vs Temperature
IV1 vs Temperature
0.505
0.500
0.495
0.490
0.485
0.480
0.475
0.470
19.5
19.0
18.5
18.0
17.5
17.0
15.8
15.6
V1 = 5V
V1 = 2.5V
5%
V
V
= 3.3V
V
V
= 3.3V
CC
ADJ
CC
ADJ
=0.55V
=0.55V
S1 =TOL = 1.4V
15.4 S1 =TOL = 1.4V
15.2
15.0
14.8
14.6
14.4
14.2
14.0
7.5%
10%
25
50
–50
–25
0
75
100
25
50
25
50
–50
–25
0
75
100
–50
–25
0
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
29067 G04
29067 G05
29067 G06
Reset Time Out Period (tRST
vs Temperature
)
Reset Time Out Period (tRST
vs Capacitance (CTMR
)
Typical Transient Duration vs
Comparator Overdrive (V1, VADJ
)
)
10000
1000
100
10
235
230
225
220
215
210
205
200
195
700
600
500
400
300
200
100
0
CRT = 22nF
(FILM)
RESET OCCURS
ABOVE CURVE
1
0.1
25
50
–50
–25
0
75
100
10p
100p
1n
10n
(FARAD)
100n
1µ
0.1
1
10
100
C
COMPARATOR OVERDRIVE VOLTAGE (% OF V
)
TMR
TEMPERATURE (°C)
RTX
29067 G08
29067 G09
29067 G07
RST Output Voltage vs V1
RST Output Voltage vs V1
RST Output Voltage vs V1
5
4
5
4
5
4
S1 = TOL = V = V1
S1 = TOL = V = V1
S1 = TOL = V = V1
CC
CC
CC
V
= 0.55V
V
= 0.55V
V
= 0.55V
ADJ
ADJ
ADJ
10k PULL-UP RESISTOR
10k PULL-UP RESISTOR
10pF CAPACITOR AT RST
3
3
3
2
2
2
1
1
1
0
0
0
–1
–1
–1
0
1
2
3
4
5
0
1
2
3
4
5
0
1
2
3
4
5
V1 (V)
V1 (V)
V1 (V)
29067 G12
29067 G10
29067 G11
29067f
4
LTC2906/LTC2907
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
RST Pull-Down Current (IRST
vs VMAX
)
RST Output Voltage Low (VOL
)
RST Pull-Down Current (IRST
vs VMAX
)
vs RST Pull-Down Current (IRST
)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
V
= V1
V1
V
S1 = TOL = V = V1
CC
ADJ
NO PULL-UP R
= V = 5V
CC
ADJ
CC
S1 = TOL = GND
= 0.55V
5
4
3
2
1
0
5
4
3
2
1
0
V
= 0.55V
= 0.45V
25°C
85°C
V
S1 = TOL = V1
NO PULL-UP R
ADJ
NO PULL-UP R
–40°C
RST AT 150mV
RST AT 150mV
RST AT 50mV
RST AT 50mV
0
1
2
3
4
5
0
1
2
V
3
4
5
0
10
30
40
50
(mA)
60
20
V
MAX
(V)
(V)
RST PULL-DOWN CURRENT, I
RST
MAX
29067 G13
29067 G14
29067G15
RST Output Voltage Low (VOL
)
RST Pull-Up Current (IRST
vs VMAX
)
RST Pull-Up Current (IRST
vs VMAX
)
vs RST Pull-Down Current (IRST
)
–16
–14
–12
–10
–8
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–18
TOL = V1
V1
V
TOL = GND
= V = 5V
CC
ADJ
= TOL = V1
25°C
85°C
–16
–14
–12
–10
–8
= 0.55V
S1
NO PULL-UP R
–40°C
–6
–6
–4
–4
–2
–2
V
RT25
V
V
RT50
V
RT25
V
RT33
V
RT50
RT33
0
0
2.0
2.5
3.0
3.5
(V)
5.0
4.0
4.5
0
10
30
40
50
(mA)
60
2.0
2.5
3.0
3.5
(V)
5.0
20
4.0
4.5
V
RST PULL-DOWN CURRENT, I
V
MAX
MAX
RST
29067G17
29067 G16
29067 G18
RST Output Voltage High (VOH
)
RST Output Voltage High (VOH) vs
vs RST Output Source Current (IRST
)
RST Output Source Current (IRST
)
IS1, ITOL vs Temperature
20
19
18
17
16
15
14
13
12
11
10
3.0
2.5
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
TOL = V1 = 3.3V
TOL = V1 = 3.3V
S1 = TOL = V1 = 3.3V
V
= 0.55V
V
= 0.45V
ADJ
ADJ
S1 = OPEN
S1 = OPEN
NO PULL-UP R
NO PULL-UP R
–40°C
25°C
85°C
85°C
–40°C
25°C
25
50
–50
–25
0
75
100
–12
–8
–6
–4
–2
(µA)
0
–8 –7 –6 –5 –4 –3 –2
OUTPUT SOURCE CURRENT, I
0
–10
–1
(µA)
OUTPUT SOURCE CURRENT, I
TEMPERATURE (°C)
RST
RST
29067 G21
290467 G20
29067 G19
29067f
5
LTC2906/LTC2907
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
IS1, ITOL vs Temperature
–20
S1 = TOL = GND
–19
–18
–17
–16
–15
–14
–13
–12
–11
–10
V1 = 3.3V
25
50
–50
–25
0
75
100
TEMPERATURE (°C)
29067 G22
U
U
U
(TS8 Package/DDB8 Package)
PI FU CTIO S
VCC (Pin 1/Pin 4): Optional Power Supply Pin. VCC powers holds low for programmed delay time after all voltage
and maintains the correct operation of the RST and RST inputs are above threshold. This pin has a weak pull up to
pins in the complete absence of V1. If V1 is present, the VMAX and may be pulled above VMAX using an external
greater of VCC or V1 (VMAX) powers the internal circuitry pull-up.
and the reset outputs. Bypass this pin to ground with a
GND (Pin 4/Pin 1 and Pin 9): Ground.
0.1µF (or greater) capacitor. Tie to V1 when no optional
TOL (Pin 5/Pin 8): Three-State Input for Supply Tolerance
Selection (5%, 7.5% or 10%). Refer to Applications Infor-
mation for tolerance selection chart (Table 3).
power is available.
RST (Pin 2/Pin 3): (LTC2906 Only) Reset Logic Output.
When all voltage inputs are above the reset threshold for
atleasttheprogrammeddelaytime,thispinpullslow.This
pin has a weak pull up to VMAX and may be pulled above
S1 (Pin 6/Pin 7): The Voltage Threshold Select Three-
State Input. Connect to V1, GND or leave unconnected in
open state to select one of three possible input threshold
levels (refer to Table 1).
V
MAX 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
opengeneratesaminimumdelayofapproximately200µs.
A 22nF capacitor will generate a 200ms reset delay time.
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.
RST (Pin 3/Pin 2): Inverted Reset Logic Output. Pulls low
when either V1 or VADJ is below the reset threshold and
29067f
6
LTC2906/LTC2907
W
BLOCK DIAGRA
V
LTC2906
MAX
6µA
–
+
RST
V1
V
MAX
RESISTOR
NETWORK
POWER
200ms
RESET PULSE
GENERATOR
DETECT
V
MAX
6µA
+
–
V
CC
RST
GND
V
ADJ
BAND GAP
REFERENCE
THREE-STATE DECODER
2906 BD
S1
TOL
LTC2907
V1
–
+
TMR
RST
GND
V
MAX
V
MAX
POWER
DETECT
RESISTOR
NETWORK
6µA
200ms
RESET PULSE
GENERATOR
V
CC
+
–
V
ADJ
BAND GAP
REFERENCE
THREE-STATE DECODER
2907 BD
S1
TOL
29067f
7
LTC2906/LTC2907
W U
W
TI I G DIAGRA
Vx Monitor Timing
V
RTX
V
X
t
t
RST
UV
RST
RST
1V
1V
29067 TD
U
W
U U
APPLICATIO S I FOR ATIO
Supply Monitoring
falls below its programmed threshold, RST asserts low
(RST weakly pulls high) as long as VMAX is at least 1V.
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
toanominalof200msforLTC2906andisadjustableusing
an external capacitor for LTC2907.
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
Thethree-stateinputpin(S1)selectsoneofthreepossible
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 predeter-
mined thresholds for the reset not to be invoked. The
LTC2906/LTC2907asserttheresetoutputsduringpower-
up, power-down and brownout conditions on any one of
the voltage inputs.
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
greaterofV1, VCC;aVCC ofatleast1Vguaranteeslogiclow
of 0.4V at RST for voltage inputs (V1 and/or VADJ) down
to 0V.
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.
Programming Pins
The two three-state input pins, S1 and TOL, should be
connected to GND, V1 or left unconnected during normal
operation. Notethatwhenleftunconnected, themaximum
leakage current allowable from the pin to either GND or V1
is 10µA.
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
least2.17V. Afterprogramming, ifanyoneoftheVxinputs
29067f
8
LTC2906/LTC2907
W U U
APPLICATIO S I FOR ATIO
U
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.
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%)
becausetheinternalreferenceatthenoninvertinginputon
theVADJ comparatorisscaledaccordingly,movingthetrip
point in 2.5% decrements.
Table 2 shows suggested 1% resistor values for various
adjustable applications.
Monitor Programming
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.
V
(V)
V
(V)
TRIP
R1 (kΩ)
2150
1780
1400
1300
1020
845
R2 (kΩ)
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
SUPPLY
12
11.25
9.4
10
8
7.5
7.5
6
7
Table 1. Supply Selection Programming
5.6
5
4.725
3.055
2.82
V1
5.0
3.3
2.5
S1
V1
3.3
3
511
464
OPEN
2.5
1.8
1.5
1.2
1
2.325
1.685
1.410
1.120
0.933
0.840
0.750
0.655
0.561
365
GND
Note: Open = open circuit or driven by a three-state buffer
in high impedance state with leakage current less than 10µA.
237
182
124
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.
86.6
68.1
49.9
30.9
12.1
0.9
0.8
0.7
0.6
V
TRIP
LTC2906/LTC2907
R1
1%
V
ADJ
–
R2
1%
Tolerance Programming
+
+
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 corre-
sponding to a particular connection at the TOL pin.
–
0.5V
29067 F01
Figure 1. Setting the Adjustable Trip Point
Inatypicalapplication, theVADJ pinconnectstoatappoint
on an external resistive divider between the positive volt-
age 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:
Table 3. Tolerance Programming
TOLERANCE
5%
TOL
V1
7.5%
OPEN
GND
10%
VTRIP(5%)
R1=
– 1 R2
0.5V
29067f
9
LTC2906/LTC2907
W U U
U
APPLICATIO S I FOR ATIO
Threshold Accuracy
sufficient magnitude and duration before it can trigger a
change in the output logic.
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 accu-
racy. The specification for LTC2906/LTC2907 is ±1.5% of
the programmed nominal input voltage (over the full
operating temperature range).
The second line of defense is the programmed delay time
t
RST (200msforLTC2906andadjustableusinganexternal
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.
Forexample,whentheLTC2906/LTC2907areprogrammed
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.
If the supply remains above the programmed threshold
whenthetimerfinishescounting, theRSTpinweaklypulls
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.
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, particu-
larly when the monitored voltage is near the reset thresh-
old. 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.
Selecting the Reset Timing Capacitor
The reset time-out period for LTC2907 is adjustable in
order to accommodate a variety of microprocessor appli-
cations. Connecting a capacitor, CTMR, between the TMR
pin and ground sets the reset time-out period, tRST. The
followingformuladeterminesthevalueofcapacitorneeded
for a particular reset time-out period:
CTMR = tRST • 110 • 10–9 [F/s]
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 attheoutputofthe 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
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
W U U
APPLICATIO S I FOR ATIO
U
10000
1000
100
10
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.
Output Rise and Fall Time Estimation
TheRSTandRSToutputhavestrongpull-downcapability.
The following formula estimates the output fall time (90%
to 10%) for a particular external load capacitance (CLOAD):
1
0.1
10p
100p
1n
10n
100n
1µ
C
(FARAD)
TMR
tFALL ≈ 2.2 • RPD • CLOAD
29067 F02
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 capaci-
tance, the fall time is about 13ns.
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 capaci-
tor will never charge if the leakage current exceeds the
TMR charging current of 2.1µA (typical).
The rise time on the RST and RST pins is limited by weak
internal pull-up current sources to VMAX. The following
formulaestimatestheoutputrisetime(10%to90%)atthe
RST and RST pins:
RST and RST Output Characteristics
t
RISE ≈ 2.2 • RPU • CLOAD
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
internalpull-uptoVMAX andastrongpull-downtoground.
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 weak pull-up and strong pull-down arrangement
allows these two pins to have open-drain behavior while
possessing several other beneficial characteristics.
The on-resistance as a function of the VMAX = MAX (V1,
VCC) voltage (for VMAX > 1V) at room temperature is
estimated as follows:
The weak pull-ups eliminate the need for external pull-up
resistorswhentherisetimeonthesepinsisnotcritical.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.
6•105
RPU
=
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 pull-
upresistormaybeusediftheoutputneedstopullupfaster
and/or to a higher voltage. For example, the rise time
reducesto3.3µsfora150pFloadcapacitance,whenusing
a 10k pull-up resistor.
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 =1Vtheweakpull-upcurrentonRSTisbarelyturned
on. Therefore, an external pull-up resistor of no more than
100k is recommended on the RST pin if the state and pull-
up strength of the RST pin is crucial at very low VMAX
.
29067f
11
LTC2906/LTC2907
U
TYPICAL APPLICATIO S
5V, 3.3V Supply Monitor, 5% Tolerance
with LED Power Good Indicator
V1
V
CC
3.3V
5V
LTC2906
499Ω
0.1µF
TOL
S1
845k
100k
P0WER
GOOD
LED
0.1µF
V
ADJ
RST
RST
SYSTEM
RESET
GND
2906 TA02
3.3V, 1.8V Monitor, 7.5% Tolerance
with an Auxiliary 5V Supply (5V Not Monitored)
5V
V1
V
CC
3.3V
1.8V
237k
LTC2906
0.1µF
TOL
S1
0.1µF
V
ADJ
TMR
RST
100k
22nF
SYSTEM
RESET
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
V1
V
ADJ
2.5V
LTC2907
0.1µF
100k
V
TMR
TOL
CC
22nF
0.1µF
499Ω
5V
RST
S1
0.1µF
LED
GND
2907 TA04
Dual Supply Monitor with Hysteresis, 5% Tolerance
(Supplies Rising), 10% Tolerance (After RST Goes Low)
3.3V
511k
5V
V
V1
ADJ
LTC2906
0.1µF
100k
V
CC
GND
RST
S1
10k
RST
TOL
SYSTEM
RESET
2906 TA05
Dual Supply Monitor for Tracked/Sequenced Supply
3.3V
0.1µF
C
GATE
10nF
IN
DC/DC
R
ONB
V
GATE
RAMP
CC
154k
2.5V
FB
OUT
OUT
ON
FB1
FB2
SYSTEM
R
ONA
LTC2923
100k
R
FB1
R
FA1
0.1µF
RAMPBUF
TRACK1
TRACK2
R
R
TB1
TA1
V
CC
IN
V1
R
R
TB2
LTC2907
DC/DC
1.8V
237k
100k
FB
RST
TOL
GND
TA2
TMR
V
R
FB2
ADJ
22nF
R
FA2
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
0.38 ± 0.10
3.00 ±0.10
(2 SIDES)
TYP
5
8
0.56 ± 0.05
(2 SIDES)
0.675 ±0.05
2.50 ±0.05
1.15 ±0.05
2.00 ±0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
PIN 1
CHAMFER OF
PACKAGE
OUTLINE
EXPOSED PAD
4
1
(DDB8) DFN 1103
0.25 ± 0.05
0.25 ± 0.05
0.75 ±0.05
0.200 REF
0.50 BSC
2.20 ±0.05
(2 SIDES)
0.50 BSC
2.15 ±0.05
(2 SIDES)
0 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
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)
2.90 BSC
(NOTE 4)
0.52
MAX
0.65
REF
1.22 REF
1.50 – 1.75
(NOTE 4)
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
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
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.95 BSC
0.09 – 0.20
(NOTE 3)
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
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
2.5V
0.6V
12.1k
V1
V1
49.9k
LTC2907
LTC2907
V
CC
TOL
V
ADJ
V
0.1µF
0.1µF
499Ω
LED
TOL
V
ADJ
CC
TMR
S1
S1
100k
22nF
100k
22nF
TMR
GND
RST
GND
RST
2907 TA07
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690
5V Supply Monitor, Watchdog Timer and Battery Backup
4.65V Threshold
2.9V Threshold
4.65V Threshold
LTC694-3.3
LTC699
3.3V Supply Monitor, Watchdog Timer and Battery Backup
5V Supply Monitor and Watchdog Timer
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 t Timing Specifications
FAIL
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
LTC1728-1.8/ LTC1728-3.3
LTC1728-2.5/ LTC1728-5
LTC1985-1.8
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Open-Drain Reset
Individual Monitor Outputs in MSOP
5-Lead SOT-23 Package
5-Lead SOT-23 Package
Micropower Triple Supply Monitor with
Push-Pull Reset Output
5-Lead SOT-23 Package
LTC2900
LTC2901
LTC2902
Programmable Quad Supply Monitor
Programmable Quad Supply Monitor
Programmable Quad Supply Monitor
Adjustable RESET, 10-Lead MSOP and
3mm X 3mm 10-Lead DFN Packages
Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
Selectable Tolerance, RESET Disable for Margining
Functions, 16-Lead SSOP Package
LTC2903
LTC2904
Precision Quad Supply Monitor
Ultralow Voltage RESET, 6-Lead SOT-23 Package
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
LT/TP 0304 1K • PRINTED IN USA
16 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 2004
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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