参数资料
型号: LTC2905ITS8#TRMP
厂商: LINEAR TECHNOLOGY CORP
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8
封装: PLASTIC, MO-193, TSOT-23, 8 PIN
文件页数: 16/16页
文件大小: 152K
代理商: LTC2905ITS8#TRMP
LTC2904/LTC2905
9
29045fb
leakage current allowable from the pin to either GND or V1
is 10μA.
In margining applications, all the 3-state input pins can be
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.
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.
Table 1. Voltage Threshold Programming
V1
V2
S1
S2
5.0
3.3
V1
3.3
2.5
Open
GND
3.3
1.8
V1
Open
3.3
1.5
Open
V1
3.3
1.2
Open
2.5
1.8
GND
2.5
1.5
GND
Open
2.5
1.2
GND
V1
2.5
1.0
V1
GND
Note: Open = open circuit or driven by a three state buffer in high
impedance state with leakage current less than 10μA.
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.
Supply Monitoring
The LTC2904/LTC2905 are low power, high accuracy dual
supply monitors with a common reset output and select-
able thresholds. Reset delay is set to a nominal of 200ms
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.
Power-Up
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.
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.
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.
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).
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.
Programming Pins
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
APPLICATIO S I FOR ATIO
WU
U
Table 2. Tolerance Programming
Tolerance
TOL
5%
V1
7.5%
Open
10%
GND
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