LTC2905IDDB [Linear]
Precision Dual Supply Monitors with Pin-Selectable Thresholds; 精密双电源监视器与引脚可选门限
| 型号： | LTC2905IDDB |
| 厂家： | 
Linear |
| 描述： | Precision Dual Supply Monitors with Pin-Selectable Thresholds |
| 文件： | 总16页 (文件大小：155K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC2904/LTC2905
Precision Dual Supply Monitors
with Pin-Selectable Thresholds
U
FEATURES
DESCRIPTIO
The LTC®2904/LTC2905 are dual supply monitors in-
tended for systems with two supply voltages. The dual
supply monitors have a common reset output with delay
(200ms for the LTC2904 and adjustable using an external
capacitor for the LTC2905). This product provides a
precise, space-conscious and micropower solution for
supply monitoring.
■
Monitors Two Inputs Simultaneously
■
Nine Threshold Combinations
■
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 (LTC2904 Only)
The LTC2904/LTC2905 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 is
guaranteedtobeinthecorrectstateforinputsdownto1V.
■
Adjustable Reset Time Delay (LTC2905 Only)
■
Open Drain RST Output
■
Guaranteed RST for V1 ≥ 1V or V2 ≥ 1V
Low Profile (1mm) SOT-23 (ThinSOTTM) and Plastic
■
(3mm x 2mm) DUFN Packages
The LTC2904/LTC2905 also feature three programming
input pins, which program the threshold and tolerance
level without requiring any external components. These
three programming pins provide a total of 27 different
voltage level and tolerance combinations, eliminating
the need to have different parts for development and
implementationofdifferentsystemswithdifferentvoltage
levels requiring monitoring function.
APPLICATIO S
■
■
■
■
Desktop and Notebook Computers
Handheld Devices
Network Servers
Core, I/O Monitor
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
U
TYPICAL APPLICATIO
Table 1. Voltage Threshold Programming
5V, 3.3V Dual Supply Monitor with 5% Tolerance
V1
5.0
3.3
3.3
3.3
3.3
2.5
2.5
2.5
2.5
V2
3.3
2.5
1.8
1.5
1.2
1.8
1.5
1.2
1.0
S1
V1
S2
V1
5V
DC/DC
SYSTEM
LOGIC
3.3V
CONVERTER
Open
V1
GND
Open
V1
V1
V2
TMR
GND
RST
LTC2905
0.1µF
0.1µF
Open
Open
GND
GND
GND
V1
S1
Open
GND
Open
V1
22nF
S2
TOL
29045 TA01
GND
sn29045 29045fs
1
LTC2904/LTC2905
W W
U W
ABSOLUTE AXI U RATI GS
(Note 1, 2)
Terminal Voltages
V1, V2 ..................................................... –0.3V to 7V
S1, S2, TOL .............................. –0.3V to (VCC +0.3V)
RST ......................................................... –0.3V to 7V
RST (LTC2904) .......................................–0.3V to 7V
TMR (LTC2905) ...................................... –0.3V to 7V
Operating Temperature Range
LTC2904C/LTC2905C ................................ 0°C to 70°C
LTC2904I/LTC2905I ..............................–40°C to 85°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U
W
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
GND
RST
1
2
3
4
8
7
6
5
TOL
S1
TOP VIEW
LTC2904CDDB
LTC2904IDDB
LTC2905CDDB
LTC2905IDDB
LTC2904CTS8
V2 1
RST/TMR* 2
RST 3
8 V1
7 S2
6 S1
5 TOL
LTC2904ITS8
LTC2905CTS8
LTC2905ITS8
9
RST/TMR*
V2
S2
V1
GND 4
TS8 PACKAGE
DDB8 PACKAGE
DDB8 PART MARKING
TS8 PART MARKING
8-LEAD PLASTIC TSOT-23
8-LEAD (3mm × 2mm) PLASTIC DFN
EXPOSED PAD IS GND (PIN 9),
MUST BE SOLDERED TO PCB
* RST FOR LTC2904
TMR FOR LTC2905
TJMAX = 125°C, θJA = 250°C/W
LTBCJ
LTBCK
LTAJD
LTAJE
LBCZ
LBDB
LTAJF
LBCY
* RST FOR LTC2904
TMR FOR LTC2905
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. V1 = 2.5V, V2 = 1V, S1 = TOL = V1, S2 = 0V, unless otherwise noted.
(Notes 2, 3, 4)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
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
RT18
RT15
RT12
RT10
3.3V, 5% Reset Threshold
3.3V, 7.5% Reset Threshold
3.3V, 10% Reset Threshold
V1, V2 Input Threshold
V1, V2 Input Threshold
V2 Input Threshold
V2 Input Threshold
V2 Input Threshold
V2 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
1.8V, 5% Reset Threshold
1.8V, 7.5% Reset Threshold
1.8V, 10% Reset Threshold
●
●
●
1.656
1.611
1.566
1.683
1.638
1.593
1.710
1.665
1.620
V
V
V
1.5V, 5% Reset Threshold
1.5V, 7.5% Reset Threshold
1.5V, 10% Reset Threshold
●
●
●
1.380
1.343
1.305
1.403
1.365
1.328
1.425
1.388
1.350
V
V
V
1.2V, 5% Reset Threshold
1.2V, 7.5% Reset Threshold
1.2V, 10% Reset Threshold
●
●
●
1.104
1.074
1.044
1.122
1.092
1.062
1.140
1.110
1.080
V
V
V
1V, 5% Reset Threshold
1V, 7.5% Reset Threshold
1V, 10% Reset Threshold
●
●
●
0.920
0.895
0.870
0.935
0.910
0.885
0.950
0.925
0.900
V
V
V
sn29045 29045fs
2
LTC2904/LTC2905
ELECTRICAL CHARACTERISTICS
(Notes 2, 3)
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V1 = 2.5V, V2 = 1V, S1 = TOL = V1, S2 = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
1
UNITS
V
V
Minimum Internal Operating Voltage (Note 2) RST in Correct Logic State
●
●
●
●
●
●
●
CCMIN
I
I
I
I
t
t
t
V1 Input Current
Includes Input Current to Three-State Pins
65
0.4
130
1.0
µA
V1
V2 Input Current
µA
V2
TMR Pull-Up Current
TMR Pull-Down Current
Reset Time-Out Period
Reset Time-Out Period
(LTC2905)
(LTC2905)
(LTC2904)
(LTC2905)
V
V
= 0V
–1.5
1.5
–2.1
2.1
–2.7
2.7
µA
TMR(UP)
TMR(DOWN)
RST
TMR
TMR
= 1.4V
µA
140
140
200
200
150
260
260
ms
ms
µs
C
= 22nF
RST
TMR
Vx Undervoltage Detect to
RST or RST
Vx Less than Reset Threshold V
by More than 1%
UV
RTX
V
V
Output Voltage Low RST, RST
I = 2.5mA
I = 100µA; V1 = 1V (RST Only)
●
●
0.15
0.05
0.4
0.3
V
V
OL
OH
Output Voltage High RST, RST
(Notes 2, 5)
I = –1µA
●
V
–1
V
CC
Three-State Inputs S1, S2, 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 Open 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
Note 5: The output pins RST and RST have an internal pull-up to V of
CC
of a device may be impaired.
typically –6µA. However, an external pull-up resistor may be used when
faster rise time is required or for V voltages greater than V .
Note 2: The greater of V1, V2 is the internal supply voltage (V ).
OH
CC
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.
sn29045 29045fs
3
LTC2904/LTC2905
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
2.5V Threshold Voltage vs
Temperature
5V Threshold Voltage vs
Temperature
3.3V Threshold Voltage vs
Temperature
4.75
4.70
4.65
4.60
4.55
4.50
4.45
4.40
4.35
3.120
3.070
3.020
2.970
2.920
2.870
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)
29045 G01
29045 G02
29045 G03
1.2V Threshold Voltage vs
Temperature
1.8V Threshold Voltage vs
Temperature
1.5V Threshold Voltage vs
Temperature
1.705
1.685
1.665
1.645
1.625
1.605
1.585
1.565
1.135
1.125
1.115
1.105
1.095
1.085
1.075
1.065
1.055
1.045
1.425
1.405
1.385
1.365
1.345
1.325
1.305
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)
29045 G04
29045 G05
29045 G06
1V Threshold Voltage vs
Temperature
IV2 vs Temperature
I
V1 vs Temperature
21.5
21.0
20.5
20.0
19.5
19.0
0.950
0.940
0.930
0.920
0.910
0.900
0.890
0.880
0.870
1.8
1.7
1.6
1.5
1.4
1.3
1.2
V1 = 5V
V1 = 5V
V2 = 3.3V
V2 = 3.3V
5%
S1 S2
=
S1 S2
= = TOL = 1.4V
= TOL = 1.4V
7.5%
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)
29045 G07
29045 G08
29045 G09
sn29045 29045fs
4
LTC2904/LTC2905
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
Reset Time Out Period (tRST
vs Capacitance (CTMR
)
Typical Transient Duration vs
IV2 vs Temperature
)
Comparator Overdrive (V1, V2)
700
600
500
400
300
200
100
0
20.0
19.5
19.0
18.5
18.0
17.5
17.0
10000
1000
100
10
V1 = 2.5V
V2 = 3.3V
S1 = S2 = TOL = 1.4V
RESET OCCURS
ABOVE CURVE
1
0.1
25
50
–50
–25
0
75
100
0.1
1
10
100
10p
100p
1n
10n
(FARAD)
100n
1µ
TEMPERATURE (°C)
COMPARATOR OVERDRIVE VOLTAGE (% OF V
)
RTX
C
TMR
29045 G10
29045 G11
29045 G12
Reset Time-Out Period (tRST
vs Temperature
)
RST Output Voltage vs V1
RST Output Voltage vs V1
5
4
5
4
235
230
225
220
215
210
205
200
195
CRT = 22nF
(FILM)
V2 = S1 = S2 = TOL = V1
10k PULL-UP RESISTOR
V2 = S1 = S2 = TOL = V1
10k PULL-UP RESISTOR
3
3
2
2
1
1
0
0
–1
–1
25
50
–50
–25
0
75
100
0
1
2
3
4
5
0
1
2
3
4
5
V1 (V)
V1 (V)
TEMPERATURE (°C)
29045 G13
29045 G15
29045 G14
RST Pull-Down Current (IRST
vs Supply Voltage (VCC
)
RST Pull-Down Current (IRST
)
)
RST Output Voltage vs V1
vs Supply Voltage (VCC
)
5
4
S1
V2 = S1 = S2 = TOL = V1
NO PULL-UP R
= V2 = V1
V2 = S1 = S2 = TOL = V1
10pF CAPACITOR AT RST
5
4
3
2
1
0
5
4
3
2
1
0
TOL = S2 = GND
NO PULL-UP R
3
RST AT 150mV
RST AT 50mV
RST AT 150mV
2
1
RST AT 50mV
0
–1
0
1
2
3
4
5
0
1
2
3
4
5
0
1
2
3
4
5
V1 (V)
SUPPLY VOLTAGE, V (V)
SUPPLY VOLTAGE, V (V)
CC
CC
29045 G16
29045 G17
29045 G18
sn29045 29045fs
5
LTC2904/LTC2905
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
RST Output Voltage Low (VOL) vs
RST Output Voltage Low (VOL) vs
RST Pull-Up Current (IRST) vs
RST Pull-Down Current (IRST
)
RST Pull-Down Current (IRST
)
Supply Voltage (VCC
)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–18
–16
–14
–12
–10
–8
V1 = 5V
V2 = 3V
S1 = S2 = TOL = V1
NO PULL-UP R
V1 = 5V
TOL = GND
25°C
V2 = 3.3V
85°C
25°C
85°C
S1 = S2 = TOL = V1
NO PULL-UP R
–40°C
–40°C
–6
–4
–2
V
RT25
V
V
RT50
RT33
0
0
10
30
40
50
(mA)
60
0
10
30
40
50
60
2.0
2.5
3.0
3.5
5.0
20
20
4.0
4.5
RST PULL-DOWN CURRENT, I
RST PULL-DOWN CURRENT, I
(mA)
SUPPLY VOLTAGE, V (V)
CC
RST
RST
29045 G19
29045 G20
29045 G21
RST Pull-Up Current (IRST) vs
RST Output Voltage High (VOH) vs
RST Output Voltage High (VOH) vs
RST Output Source Current (IRST)
Supply Voltage (VCC
)
RST Output Source Current (IRST
)
–16
–14
–12
–10
–8
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
V1 = 3.3V
V1 = 3.3V
V2 = 1.8V
V2 = 1.5V
S1 = TOL =V1
S2 = OPEN
NO PULL-UP R
S1 = TOL = V1
S2 = OPEN
NO PULL-UP R
–40°C
–6
85°C
85°C
–4
–40°C
25°C
25°C
–2
V
RT25
V
V
RT33
RT50
0
2.0
2.5
3.0
3.5
5.0
4.0
4.5
–12
–8
–6
–4
–2
(µA)
0
–8 –7 –6 –5 –4 –3 –2
OUTPUT SOURCE CURRENT, I
0
–10
–1
SUPPLY VOLTAGE, V (V)
OUTPUT SOURCE CURRENT, I
(µA)
CC
RST
RST
29045 G22
29045 G23
29045 G24
IS1, IS2, ITOL vs Temperature
IS1, IS2, ITOL vs Temperature
20
19
18
17
16
15
14
13
12
11
10
–20
S1 = S2 = TOL = 3.3V
S1 = S2 = TOL = GND
–19
–18
–17
–16
–15
–14
–13
–12
–11
–10
25
50
–50
–25
0
75
100
25
50
–50
–25
0
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
29045 G25
29045 G26
sn29045 29045fs
6
LTC2904/LTC2905
U
U
U
PI FU CTIO S
(TS8 Package/DDB8 Package)
V2 (Pin 1/Pin 4): Voltage Input 2. Input for V2 monitor.
Select from 3.3V, 2.5V, 1.8V, 1.5V, 1.2V or 1.0V. Refer to
Table1fordetails. ThegreaterofV1, V2isalsotheinternal
supplyvoltage,VCC.Bypassthispintogroundwitha0.1µF
(or greater) capacitor.
inputs are above threshold. This pin has a weak pull-up
to VCC and may be pulled above VCC using an external
pull-up.
GND (Pin 4/Pin 1, Pin 9): Ground.
TOL (Pin 5/Pin 8): Three-state Input for Supply Tolerance
Selection (5%, 7.5% or 10%). See the Applications Infor-
mation section for tolerance selection chart (Table 2).
RST (Pin 2/Pin 3): (LTC2904 Only) Reset Logic Output.
When all voltage inputs are above the reset threshold for
atleasttheprogrammeddelaytime,thispinpullslow.This
pin has a weak pull-up to VCC and may be pulled above VCC
using an external pull-up.
S1 (Pin 6/Pin 7): Voltage Threshold Select Three-State
Input. Connect to V1, GND or leave unconnected in open
state (See Table 1).
TMR (Pin 2/Pin 3): (LTC2905 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.
S2 (Pin 7/Pin 6): The Second Voltage Threshold Select
Three-State Input. Connect to V1, GND or leave uncon-
nected in open state (See Table 1).
V1 (Pin 8/Pin 5): Voltage Input 1. Input for V1 monitor.
Select from 5V, 3.3V, or 2.5V. See Table 1 for details. The
greater of V1, V2 is also the internal supply voltage, VCC.
Bypass this pin to ground with a 0.1µF (or greater)
capacitor.
RST (Pin 3/Pin 2): Inverted Reset Logic Output. Pulls low
when any voltage input is below the reset threshold and is
held low for programmed delay time after all voltage
W
BLOCK DIAGRA
V
LTC2904
CC
6µA
–
RST
V1
+
V
CC
200ms
RESET PULSE
GENERATOR
POWER
DETECT
RESISTOR
NETWORK
V
CC
6µA
–
+
V2
RST
GND
BAND GAP
REFERENCE
THREE-STATE DECODER
2904 BD
S1
S2
TOL
sn29045 29045fs
7
LTC2904/LTC2905
W
BLOCK DIAGRA
LTC2905
–
+
TMR
RST
GND
V
CC
V1
V
CC
6µA
POWER
DETECT
RESISTOR
NETWORK
RESET PULSE
GENERATOR
–
+
V2
BAND GAP
REFERENCE
THREE-STATE DECODER
2905 BD
S1
S2
TOL
W U
W
TI I G DIAGRA
VX Monitor Timing
V
RTX
V
X
t
t
UV
RST
RST
RST
1V
1V
29045 TD
sn29045 29045fs
8
LTC2904/LTC2905
U
W
U U
APPLICATIO S I FOR ATIO
Supply Monitoring
leakage current allowable from the pin to either GND or V1
is 10µA.
The LTC2904/LTC2905 are low power, high accuracy dual
supply monitors with a common reset output and select- In margining applications, all the 3-state input pins can be
able thresholds. Reset delay is set to a nominal of 200ms driven using a tri-state buffer. Note however the low and
high output of the tri-state buffer has to satisfy the VIL and
VIH of the 3-state pin listed in the Electrical Characteristics
Table. Moreover, when the tri-state buffer is in the high
impedance state, the maximum leakage current allowed
from the pin to either GND or V1 is 10µA.
for the LTC2904 and is adjustable using an external
capacitor for the LTC2905.
The two three-state input pins (S1 and S2) select one of
nine possible threshold voltage combinations. Another
three-state input pin sets the supply tolerance (5%, 7.5%
or 10%). Both input voltages (V1 and V2) must be above
predetermined thresholds for the reset not to be invoked.
The LTC2904/LTC2905 assert the reset outputs during
power-up, power-down and brownout conditions on
either of the voltage inputs.
Monitor Programming
Connecting S1 and S2 to GND, V1 or leaving them open
selects the LTC2904/LTC2905 input voltage combina-
tions. Table 1 shows the nine possible combinations of
nominal input voltages and their corresponding S1, S2
connections.
Power-Up
Table 1. Voltage Threshold Programming
The greater of V1, V2 is the internal supply voltage (VCC).
VCC powers the drive circuits for the RST pin. Therefore as
soon as V1 or V2 reaches 1V during power-up, the RST
output asserts low.
V1
5.0
3.3
3.3
3.3
3.3
2.5
2.5
2.5
2.5
V2
3.3
2.5
1.8
1.5
1.2
1.8
1.5
1.2
1.0
S1
V1
S2
V1
Open
V1
GND
Open
V1
VCC also powers the drive circuits for the RST pin in the
LTC2904. Therefore, RST weakly pulls high when V1 or V2
reaches at least 1V.
Open
Open
GND
GND
GND
V1
Open
GND
Open
V1
Threshold programming is complete when V1 reaches at
least 2.17V. After programming, if either V1 or V2 falls
below its programmed threshold, RST asserts low (RST
weakly pulls high) as long as VCC is at least 1V.
GND
Note: Open = open circuit or driven by a three state buffer in high
impedance state with leakage current less than 10µA.
Once V1 and V2 rise above their thresholds, an internal
timer is started. After the programmed delay time, RST
weakly pulls high (RST asserts low).
Tolerance Programming
The three-state input pin, TOL programs the common
supply tolerance for both V1 and V2 input voltages (5%,
7.5% or 10%). The larger the tolerance the lower the trip
threshold. Table 2 shows the tolerances selection corre-
sponding to a particular connection at the TOL pin.
Power-Down
On power-down, once either V1 or V2 inputs drops below
its threshold, RST asserts logic low and RST weakly pulls
high. VCC of at least 1V guarantees a logic low of 0.4V at
RST.
Table 2. Tolerance Programming
Tolerance
5%
TOL
V1
Programming Pins
7.5%
Open
GND
The three 3-state input pins: S1, S2 and TOL should be
connected to GND, V1 or left unconnected during normal
operation. Note that when left unconnected, the maximum
10%
sn29045 29045fs
9
LTC2904/LTC2905
W U U
U
APPLICATIO S I FOR ATIO
Threshold Accuracy
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.
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 LTC2904/
LTC2905 inputs have the same relative threshold accu-
racy. The specification for LTC2904/LTC2905 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
tRST (200ms for LTC2904 and using an external capacitor
for LTC2905). 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 V2 drops below its programmed
threshold, the RST pin asserts low (RST weakly pulls
high). Then when the supply recovers above the pro-
grammedthreshold,thereset-pulse-generatortimerstarts
counting.
Forexample,whentheLTC2904/LTC2905areprogrammed
to handle a 5V input with 10% tolerance (S1 = S2 = V1 and
TOL = GND, refer to Table 1 and Table 2), 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 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 it
starts fresh when the supply next rises above the pro-
grammed threshold.
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.
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.
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 ±1.0% hysteresis is equivalent to a ±3.5%
monitor with no hysteresis.
Selecting the Reset Timing Capacitor
The reset time-out period for LTC2905 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:
TheLTC2904/LTC2905takesadifferentapproachtosolve
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
C
TMR = tRST • 110 • 10–9 [F/s]
For example, using a standard capacitor value of 22nF
would give a 22000/110 = 200ms delay.
sn29045 29045fs
10
LTC2904/LTC2905
W U U
APPLICATIO S I FOR ATIO
U
Figure 1 shows the desired delay time as a function of the
value of the timer capacitor that should be used:
As noted in the Power-Up and Power-Down sections the
circuits that drive RST and RST are powered by VCC.
During fault condition, VCC of at least 1V guarantees a
maximum VOL = 0.4V at RST. However, at VCC = 1V the
weak pull-up current on RST is barely turned on. There-
fore, 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 VCC.
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.
1
0.1
10p
100p
1n
10n
100n
1µ
C
(FARAD)
TMR
Output Rise and Fall Time Estimation
29045 F01
The RST and RST outputs have strong pull-down capabil-
ity. The following formula estimates the output fall time
(90% to 10%) for a particular external load capacitance
(CLOAD):
Figure 1. 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
large value capacitor with low leakage. The TMR capacitor
will never charge if the leakage current exceeds the mini-
mum TMR charging current of 2.1µA (typical).
tFALL ≈ 2.2 • RPD • CLOAD
where RPD is the on-resistance of the internal pull-down
transistor estimated to be typically 40Ω at room tempera-
ture (25°C) and CLOAD is the external load capacitance on
the pin. Assuming a 150pF load capacitance, the fall time
is about 13ns.
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 VCC = Max (V1, V2) and a strong pull-
down to ground.
The rise time, on the RST and RST pins is limited by weak
internal pull-up current sources to VCC. The following
formulaestimatestheoutputrisetime(10%to90%)atthe
RST and RST pins:
tRISE ≈ 2.2 RPU • CLOAD
Theweakpull-upandstrongpull-downarrangementallow
thesetwopinstohaveopen-drainbehaviorwhilepossess-
ing several other beneficial characteristics.
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 represen-
tation.
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.
The on-resistance as a function of the VCC = Max (V1, V2)
voltage (for VCC > 1V) at room temperature is estimated as
sn29045 29045fs
11
LTC2904/LTC2905
W U U
U
APPLICATIO S I FOR ATIO
follow:
capacitance, the rise time is 86µs. An external pull-up
resistor may be used if the output needs to pull up faster
and/or to a higher voltage, for example: the rise time
reducesto3.3µsfora150pFloadcapacitance,whenusing
a 10k pull-up resistor.
6•105
MAX(V1,V2)– 1V
RPU
=
Ω
At VCC = 3.3V, RPU is about 260k. Using 150pF for load
U
TYPICAL APPLICATIO S
2.5V, 1.2V Supply Monitor, 10% Tolerance
V2
V1
S2
1.2V
2.5V
LTC2904
RST
RST
GND
0.1µF
0.1µF
SYSTEM
RESET
S1
TOL
2904 TA02
3.3V, 1.2V Dual Supply Monitor with LED Power Good Indicator,
7.5% Tolerance and Adjustable Timer
3.3V
510Ω
V2
V1
RST
RST
TOL
1.2V
LTC2904
LED
S2
0.1µF
0.1µF
SYSTEM
RESET
S1
GND
2905 TA03
sn29045 29045fs
12
LTC2904/LTC2905
U
TYPICAL APPLICATIO S
5V, 3.3V Dual Supply Monitor with Voltage
Margining for Automated On-Board Testing
5V
DC/DC
CONVERTER
SYSTEM
LOGIC
3.3V
V1
V2
TMR
GND
RST
LTC2905
V
IN
0.1µF
S1
SUPPLY
CONTROLLER
0.1µF
22nF
THREE-STATE
S2
TOL
29045 TA06
3.3V, 1.2V Dual Supply Monitor with Asymmetric Hysteresis, 5%
Tolerance (Supplies Rising), 10% Tolerance (After RST Goes Low)
V2
V1
RST
TOL
RST
1.2V
3.3V
LTC2904
10k
0.1µF
S2
0.1µF
S1
SYSTEM
RESET
GND
2904 TA04
sn29045 29045fs
13
LTC2904/LTC2905
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
sn29045 29045fs
14
LTC2904/LTC2905
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
sn29045 29045fs
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
LTC2904/LTC2905
U
TYPICAL APPLICATIO
Quad Supply Monitor with LED Undervoltage Indicator,
5% Tolerance, 3.3V, 2.5V, 1.8V, 1.2V
3.3V 1.8V
2.5V
V2
V1
V2
V1
1.2V
LTC2905
LTC2905
0.1µF
TMR
S2
0.1µF
TOL
0.1µF
510Ω
TMR
GND
RST
TOL
22nF
0.1µF
22nF
S2
S1
S1
LED
GND
RST
2905 TA05
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690
5V Supply Monitor, Watchdog Timer and Battery Backup
3.3V Supply Monitor, Watchdog Timer and Battery Backup
5V Supply Monitor and Watchdog Timer
4.65V Threshold
2.9V Threshold
4.65V Threshold
4.37V/4.62V Threshold
LTC694-3.3
LTC699
LTC1232
5V Supply Monitor, Watchdog Timer and Push-Button Reset
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
Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Open-Drain Reset
Micropower Triple Supply Monitor with Push-Pull Reset Output
Programmable Quad Supply Monitor
Meets PCI t Timing Specifications
FAIL
LTC1726-2.5/LTC1726-5
LTC1727-2.5/LTC1727-5
LTC1728-1.8/LTC1728-3.3
LTC1728-2.5/LTC1728-5
LTC1985-1.8
Adjustable RESET and Watchdog Time-Outs
Individual Monitor Outputs in MSOP
5-Lead SOT-23 Package
5-Lead SOT-23 Package
5-Lead SOT-23 Package
LTC2900
Adjustable RESET, 10-Lead MSOP, DFN Packages
LTC2901
Programmable Quad Supply Monitor
Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
LTC2902
Programmable Quad Supply Monitor
Precision Quad Supply Monitor
Selectable Tolerance, RESET Disable for Margining
Functions, 16-Lead SSOP Package
LTC2903-1
Ultra Low Voltage RESET, 6-Lead SOT-23 Package
sn29045 29045fs
LT/TP 01/04 1K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
©LINEAR TECHNOLOGY CORPORATION 2003
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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