参数资料
型号: TPS2311IPW
厂商: TEXAS INSTRUMENTS INC
元件分类: 电源管理
英文描述: 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO20
封装: PLASTIC, TSSOP-20
文件页数: 9/24页
文件大小: 644K
代理商: TPS2311IPW
www.ti.com
SETTING THE CURRENT-LIMIT CIRCUIT-BREAKER THRESHOLD
I
LMT1 +
R
ISET1
50
10–6
R
ISENSE1
(2)
SETTING THE POWER-GOOD THRESHOLD VOLTAGE
R
VSENSE1_TOP +
V
O1_min * 1.225
1.225
R
VSENSE1_BOT
(3)
UNDERVOLTAGE LOCKOUT (UVLO)
SLVS275G – FEBRUARY 2000 – REVISED NOVEMBER 2006
During an overcurrent fault condition, the external MOSFET transistor that exhibited an over-current condition
is rapidly turned off by an internal pulldown circuit capable of pulling in excess of 400 mA (at 4 V) from the
pin. Once the gate has been pulled below approximately 1.5 V, this driver is disengaged and the UVLO
driver is enabled instead. If any channel experiences an overcurrent condition, then both channels are turned
off rapidly.
Using channel 1 as an example, the current sensing resistor RISENSE1 and the current limit setting resistor RISET1
determine the current limit of the channel, and can be calculated by the following equation:
Typically RISENSE1 is usually very small (0.001 to 0.1 ). If the trace and solder-junction resistances between
the junction of RISENSE1 and ISENSE1 and the junction of RISENSE1 and RISET1 are greater than 10% of the
RISENSE1 value, then these resistance values should be added to the RISENSE1 value used in the calculation
above.
The above information and calculation also apply to channel 2. Table 3 shows some of the current sense
resistors available in the market.
Table 3. Some Current Sense Resistors
CURRENT
PART NUMBER
DESCRIPTION
MANUFACTURER
RANGE (A)
0 to 1
WSL-1206, 0.05 1%
0.05
, 0.25 W, 1% resistor
1 to 2
WSL-1206, 0.025 1%
0.025
, 0.25 W, 1% resistor
2 to 4
WSL-1206, 0.015 1%
0.015
, 0.25 W, 1% resistor
Vishay Dale
4 to 6
WSL-2010, 0.010 1%
0.010
, 0.5 W, 1% resistor
6 to 8
WSL-2010, 0.007 1%
0.007
, 0.5 W, 1% resistor
8 to 10
WSR-2, 0.005 1%
0.005
, 0.5 W, 1% resistor
The two feedback resistors RVSENSEx_TOP and RVSENSEx_BOT connected between VOx and ground form a resistor
divider setting the voltage at the VSENSEx pins. VSENSE1 voltage equals:
VI(SENSE1) = VO × RVSENSE1_BOT/(RVSENSE1_TOP + RVSENSE1_BOT)
This voltage is compared to an internal voltage reference (1.225 V
±2%) to determine whether the output voltage
level is within a specified tolerance. For example, given a nominal output voltage at VO1, and defining VO1_min as
the minimum required output voltage, then the feedback resistors are defined by:
Start the process by selecting a large standard resistor value for RVSENSE1_BOT to reduce power loss. Then
RVSENSE1_TOP can be calculated by inserting all of the known values into the equation above. When VO1 is lower
than VO1_min, PWRGD1 is low as long as the controller is enabled.
The TPS2310/11 includes an undervoltage lockout (UVLO) feature that monitors the voltage present on the
VREG pin. This feature disables both external MOSFETs if the voltage on VREG drops below 2.78 V (nominal)
and re-enables normal operation when it rises above 2.85 V (nominal). Since VREG is fed from IN1 through a
low-dropout voltage regulator, the voltage on VREG tracks the voltage on IN1 within 50 mV. While the
undervoltage lockout is engaged, both GATE1 and GATE2 are held low by internal PMOS pulldown transistors,
ensuring that the external MOSFET transistors remain off at all times, even if all power supplies have fallen to
0 V.
17
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