LTC1235
Microprocessor
Supervisory Circuit
FEATURES
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
Guaranteed
Reset Assertion at V
CC
= 1V
1.5mA Maximum Supply Current
Fast (35ns Max.) Onboard Gating of RAM Chip
Enable Signals
Conditional Battery Backup Extends Battery Life
4.65V Precision Voltage Monitor
Power OK/Reset Time Delay: 200ms
External Reset Control
Minimum External Component Count
1µA Maximum Standby Current
Voltage Monitor for Power Fail or Low Battery
Warning
Thermal Limiting
Performance Specified Over Temperature
All the LTC695 Features Plus Conditional Battery
Backup and External Reset Control
The LTC1235 provides complete power supply monitoring
and battery control functions for microprocessor reset,
battery backup, RAM write protection, power failure warn-
ing and watchdog timing. The LTC1235 has all the LTC695
features plus conditional battery backup and external reset
control. When an out-of-tolerance power supply condition
occurs, the reset outputs are forced to active states and the
Chip Enable output write-protects external memory. The
RESET output is guaranteed to remain logic low with V
CC
as
low as 1V. External reset control is provided by a debounced
push-button reset input.
The LTC1235 powers the active CMOS RAMs with a charge
pumped NMOS power switch to achieve low dropout and
low supply current. When primary power is lost, auxiliary
power, connected to the battery input pin, provides backup
power to the RAMs. The LTC1235 can be programmed by
a
µP
signal to either back up the RAMs or not. This extends
the battery life in situations where RAM data need not
always be saved when power goes down.
For an early warning of impending power failure, the
LTC1235 provides an internal comparator with a user-
defined threshold. An internal watchdog timer is also avail-
able, which forces the reset pins to active states when the
watchdog input is not toggled prior to the time-out period.
APPLICATI
s
s
s
s
S
Critical
µP
Power Monitoring
Intelligent Instruments
Battery-Powered Computers and Controllers
Automotive Systems
TYPICAL APPLICATI
V
IN
≥
7.5V
LT1086-5
BATTERY LIFE (NORMALIZED)
+
10µF
V
IN
ADJ
V
OUT
+5V
+
100µF
V
CC
0.1µF
V
OUT
LTC1235
0.1µF
POWER TO
µP
CMOS RAM POWER
I/O LINE
µP RESET
µP NMI
I/O LINE
µP
SYSTEM
V
BATT
51k
+3V
PFI
PB RST
10k
BACKUP
RESET
PFO
WDI
LTC1235 TA1
THE LTC1235 EXTENDS BATTERY LIFE BY PROVIDING BATTERY POWER ONLY WHEN REQUIRED TO BACK UP RAM DATA.
IT SAVES THE BATTERY WHEN NO DATA BACKUP IS NEEDED. THE
µP
REQUESTS BACKUP WITH THE BACKUP PIN.
U
Battery Life vs
Backup Duty Cycle
10
9
8
7
6
5
4
3
2
1
0
0
20
60
80
40
BACKUP DUTY CYCLE (%)
100
LTC695
(WITHOUT
CONDITIONAL
BATTERY
BACKUP)
LTC1235
LTC1235 TA02
UO
UO
1
LTC1235
ABSOLUTE
AXI U
RATI GS
U
W W
RESET
RESET
WDO
CE IN
CE OUT
WDI
PFO
PFI
S PACKAGE
16-LEAD PLASTIC SOL
T
JMAX
= 110°C,
θ
JA
= 130°C/W
CONDITIONS: PCB MOUNT ON FR4 MATERIAL,
STILL AIR AT 25°C, COPPER TRACE
Terminal Voltage
V
CC
.................................................... –0.3V to 6.0V
V
BATT
................................................. –0.3V to 6.0V
All Other Inputs .................... –0.3V to (V
CC
+ 0.3V)
Input Current
V
CC
.............................................................. 200mA
V
BATT
............................................................. 50mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
BATT
V
OUT
V
CC
GND
BATT ON
LOW LINE
PB RST
BACKUP
1
2
3
4
5
6
7
8
LTC1235
16
15
14
13
12
11
10
9
ORDER PART
NUMBER
LTC1235CN
N PACKAGE
16-LEAD PLASTIC DIP
T
JMAX
= 110°C,
θ
JA
= 130°C/W
PRODUCT SELECTIO GUIDE
PINS
LTC1235
LTC690
LTC691
LTC694
LTC695
LTC699
LTC1232
16
8
16
8
16
8
8
RESET
X
X
X
X
X
X
X
WATCHDOG
TIMER
X
X
X
X
X
X
X
BATTERY
BACKUP
X
X
X
X
X
POWER FAIL
WARNING
X
X
X
X
X
RAM WRITE
PROTECT
X
X
X
X
PUSH-BUTTON
RESET
X
CONDITIONAL
BATTERY
BACKUP
X
2
U
W
U
U
W
(Notes 1 and 2)
V
OUT
Output Current .................. Short Circuit Protected
Power Dissipation ............................................. 500mW
Operating Temperature Range
LTC1235C ............................................ 0°C to 70°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
(Note 3)
TOP VIEW
V
BATT
V
OUT
V
CC
GND
BATT ON
LOW LINE
PB RST
BACKUP
1
2
3
4
LTC1235
5
6
7
8
12
11
10
9
16 PRESET
15
14
13
PRESET
WDO
CE IN
CE OUT
WDI
PFO
PFI
ORDER PART
NUMBER
LTC1235CS
LTC1235
ELECTRICAL CHARACTERISTICS
V
CC
= Full Operating Range, V
BATT
= 2.8V, Backup = No Connection, T
A
= 25°C, unless otherwise noted.
PARAMETER
Battery Backup Switching
Operating Voltage Range
V
CC
V
BATT
V
OUT
Output Voltage
I
OUT
= 1mA
q
CONDITONS
MIN
TYP
MAX
UNITS
4.75
2.00
V
CC
– 0.05
V
CC
– 0.1
V
CC
– 0.5
V
CC
– 0.005
V
CC
– 0.005
V
CC
– 0.25
5.50
4.25
V
V
I
OUT
= 50mA
BACKUP Input Threshold
V
CC
> Reset Voltage Threshold
Logic Low
Logic High
I
OUT
= 250µA, V
CC
< V
BATT
V
CC
< V
BATT
1MΩ Pulldown on V
OUT
I
OUT
≤
50mA
q
0.8
2.0
3
V
BATT
– 0.1
V
BATT
– 0.02
0
0.6
0.6
0.04
0.04
–0.1
–1.0
70
50
20
0.4
0.5
35
1
25
0.8
2.0
q
V
µA
V
V
BACKUP Pullup Current (Note 4)
V
OUT
in Battery Backup Mode (Note 5)
V
OUT
in Battery Saving Mode (Note 5)
V
CC
Supply Current (excluding I
OUT
)
Battery Supply Current in Battery Backup Mode and
Battery Saving Mode (Note 5)
Battery Standby Current
(+ = Discharge, – = Charge)
Battery Switchover Threshold
V
CC
– V
BATT
Battery Switchover Hysteresis
BATT ON Output Voltage (Note 6)
BATT ON Output Short Circuit Current (Note 6)
Push-Button Reset
PB RST Input Threshold
PB RST Input Low Time (Notes 4, 7)
Reset and Watchdog Timer
Reset Voltage Threshold
Reset Threshold Hysteresis
Reset Active Time
Watchdog Time-out Period
Reset Active Time PSRR
Watchdog Time-out Period PSRR
Minimum WDI Input Pulse Width
RESET Output Voltage At V
CC
= 1V
RESET and LOW LINE Output Voltage
(Note 6)
V
IL
= 0.4V, V
IH
= 3.5V
I
SINK
= 10µA, V
CC
= 1V
I
SINK
= 1.6mA, V
CC
= 4.25V
I
SOURCE
= 1µA, V
CC
= 5V
3.5
q
q
1.5
2.5
1
5
+0.02
+0.10
mA
µA
µA
mV
mV
V
mA
µA
V
ms
V
CC
= 0V, V
BATT
= 2.8V
q
5.5 > V
CC
> V
BATT
+ 0.2V
q
Power Up
Power Down
I
SINK
= 3.2mA
BATT ON = V
OUT
Sink Current
BATT ON = 0V Source Current
Logic Low
Logic High
40
4.5
160
140
1.2
1.0
4.65
40
200
200
1.6
1.6
1
8
200
4
200
0.4
4.75
240
280
2.00
2.25
V
mV
ms
sec
ms/V
ms/V
ns
mV
V
V
CC
= 5V
q
V
CC
= 5V
q
3
LTC1235
ELECTRICAL CHARACTERISTICS
V
CC
= Full Operating Range, V
BATT
= 2.8V, Backup = No Connection, T
A
= 25°C, unless otherwise noted.
PARAMETER
RESET and WDO Output Voltage
(Note 6)
RESET, RESET, WDO, LOW LINE
Output Short Circuit Current (Note 6)
WDI Input Threshold
WDI Input Current
Power Fail Detector
PFI Input Threshold
PFI Input Threshold PSRR
PFI Input Current
PFO Output Voltage (Note 6)
PFO Short Circuit Source Current
(Note 6)
PFI Comparator Response Time (falling)
PFI Comparator Response Time (rising)
(Note 6)
Chip Enable Gating
CE IN Threshold
CE IN Pullup Current (Note 4)
CE OUT Output Voltage
I
SINK
= 3.2mA
I
SOURCE
= 3.0mA
I
SOURCE
= 1µA, V
CC
= 0V
V
CC
= 5V, C
L
= 20pF
q
CONDITONS
I
SINK
= 1.6mA, V
CC
= 5V
SOURCE
= 1µA, V
CC
= 4.25V
Output Source Current
Output Sink Current
Logic Low
Logic High
WDI = V
OUT
WDI = 0V
V
CC
= 5V
q
q
MIN
3.5
1
TYP
MAX
0.4
UNITS
V
µA
mA
V
µA
3
25
25
0.8
2.0
–50
1.25
4
–8
1.3
0.3
±0.01
±25
0.4
3.5
1
3
30
2
40
8
0.8
2.0
3
0.4
V
OUT
– 1.50
V
OUT
– 0.05
20
20
30
35
35
45
ns
mA
µA
V
25
µA
mA
µs
µs
50
q
1.35
V
mV/V
nA
V
I
SINK
= 3.2mA
I
SOURCE
= 1µA
PFI = HIGH, PFO = 0V
PFI = LOW, PFO = V
OUT
∆V
IN
= –20mV, V
OD
= 15mV
∆V
IN
= 20mV, V
OD
= 15mV
with 10kΩ Pullup
V
IL
V
IH
V
CE Propagation Delay
CE OUT Output Short Circuit Current
Output Source Current
Output Sink Current
The
q
denotes specifications which apply over the operating temperature
range.
Note 1:
Absolute maximum ratings are those values beyond which the life
of device may be impaired.
Note 2:
All voltage values are with respect to GND.
Note 3:
For military temperature range parts, consult the factory.
Note 4:
The input pins of PB RST, BACKUP and CE IN, have weak internal
pullups which pull to the supply when the input pins are floating.
Note 5:
The LTC1235 can be programmed either to provide or not to
provide battery backup power to the V
OUT
pin during power failure. The
power down condition of V
OUT
is selected by the logic level of the BACKUP
pin which is latched internally when V
CC
falls through the reset voltage
threshold. If the latched logic level of the BACKUP pin is high, V
OUT
will be
in Battery Backup Mode and will be switched to V
BATT
when V
CC
falls
below V
BATT
. If the latched logic level of the BACKUP pin is low, V
OUT
will
be in Battery Saving Mode when V
CC
falls below V
BATT
.
Note 6:
The output pins of BATT ON, LOW LINE, PFO, WDO, RESET and
RESET have weak internal pullups of typically 3µA. However, external
pullup resistors may be used when higher speed is required.
Note 7:
The push-button reset input requires an active low signal.
Internally, this input signal is debounced and timed for a minimum of
40ms. When this condition is satisfied, the reset outputs go to the active
states. The reset outputs will remain in active states for a minimum of
140ms from the moment the push-button reset input is released from
logic low level.
4
LTC1235
TYPICAL PERFOR A CE CHARACTERISTICS
V
OUT
vs I
OUT
5.00
V
CC
= 5V
V
BATT
= 2.8V
T
A
= 25
°
C
2.80
V
CC
= 0V
V
BATT
= 2.8V
T
A
= 25
°
C
BACKUP MODE
SELECTED
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
2.78
SLOPE = 125Ω
2.76
PFI INPUT THRESHOLD (V)
4.95
4.90
SLOPE = 5Ω
4.85
4.80
4.75
0
10
30
40
20
LOAD CURRENT (mA)
RESET Output Voltage vs Supply
Voltage
5
T
A
= 25°C
EXTERNAL PULLUP = 10µA
V
BATT
= 0V
232
RESET VOLTAGE THRESHOLD (V)
RESET OUTPUT VOLTAGE (V)
RESET ACTIVE TIME (ms)
4
3
2
1
0
0
1
3
4
2
SUPPLY VOLTAGE (V)
Power Fail Comparator
Response Time
PFO OUTPUT VOLTAGE (V)
PFO OUTPUT VOLTAGE (V)
PFO OUTPUT VOLTAGE (V)
6
5
4
3
2
1
0
V
PFI
1.3V
+
–
PFO
30pF
V
CC
= 5V
T
A
= 25
°
C
1.305V
1.285V
0
1
V
PFI
= 20mV STEP
2
3 4 5
TIME (µs)
6
U W
50
LTC1235 G01
V
OUT
vs I
OUT
1.308
1.306
1.304
1.302
1.300
1.298
1.296
2.72
Power Failure Input Threshold
vs Temperature
V
CC
= 5V
2.74
0
100
300
400
200
LOAD CURRENT (µA)
500
1.294
–50 –25
50
25
75
0
TEMPERATURE (
˚
C)
100
125
LTC1235 G02
LTC1235 G03
Reset Active Time vs
Temperature
4.66
V
CC
= 5V
224
216
208
200
192
184
–50 –25
4.65
4.64
4.63
4.62
4.61
Reset Voltage Threshold
vs Temperature
5
LTC1235 G04
50
25
75
0
TEMPERATURE (
°
C)
100
125
4.60
–50 –25
50
25
75
0
TEMPERATURE (
°
C)
100
125
LTC1235 G05
LTC1235 G06
Power Fail Comparator
Response Time
6
5
4
3
2
1
0
V
PFI
1.3V
+
–
PFO
30pF
Power Fail Comparator Response
Time with Pullup Resistor
6
5
4
3
2
1
0
+5V
V
PFI
1.3V
+
–
PFO
10k
30pF
V
CC
= 5V
T
A
= 25
°
C
V
CC
= 5V
T
A
= 25
°
C
1.315V
1.295V
7
8
0
V
PFI
= 20mV STEP
1.315V
1.295V
0
2
V
PFI
= 20mV STEP
20 40
60 80 100 120 140 160 180
TIME (µs)
LTC1235 G08
4
6
8 10 12 14 16 18
TIME (µs)
LTC1235 G09
LTC1235 G07
5
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