參數(shù)資料
型號(hào): TPS54350MPWPREP
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: 7.2 A SWITCHING REGULATOR, 700 kHz SWITCHING FREQ-MAX, PDSO16
封裝: GREEN, PLASTIC, HTSSOP-16
文件頁數(shù): 35/36頁
文件大?。?/td> 1057K
代理商: TPS54350MPWPREP
www.ti.com
DETAILED DESCRIPTION
Undervoltage Lockout (UVLO)
320 k
125 k
R1
R2
Input Voltage Supply
1 k
R1 +
VIN(start)
1 kW
1.24 V
* 1kW
(1)
VIN(stop) +
(R1 ) 1 kW)
1.02 V
1 kW
(2)
Enable (ENA) and Internal Slow Start
T
SS_INTERNAL(ms) +
1.15k
s(kHz)
(3)
TPS54350-EP
SGLS308 – OCTOBER 2005
The undervoltage lockout (UVLO) system has an internal voltage divider from VIN to AGND. The defaults for the
start/stop values are labeled VIN and given in Table 1. The internal UVLO threshold can be overridden by
placing an external resistor divider from VIN to ground. The internal divider values are approximately 320 k
for
the high side resistor and 125 k
for the low side resistor. The divider ratio (and therefore the default start/stop
values) is quite accurate, but the absolute values of the internal resistors may vary as much as 15%. If high
accuracy is required for an externally adjusted UVLO threshold, select lower value external resistors to set the
UVLO threshold. Using a 1-k
resistor for the low side resistor (R2 see Figure 1) is recommended. Under no
circumstances should the UVLO pin be connected directly to VIN.
Table 1. Start/Stop Voltage Threshold
START VOLTAGE THRESHOLD
STOP VOLTAGE THRESHOLD
VIN (Default)
4.49
3.69
UVLO
1.24
1.02
Figure 1. Circuit Using External UVLO Function
The equations for selecting the UVLO resistors are:
For applications which require an undervoltage lock out (UVLO) threshold greater than 4.49 V, external resistors
may be implemented, see Figure 1, to adjust the start voltage threshold. For example, an application needing an
UVLO start voltage of approximately 7.8 V using the Equation 1, R1 is calculated to the nearest standard resistor
value of 5.36 k
. Using Equation 2, the input voltage stop threshold is calculated as 6.48 V.
Once the ENA pin voltage exceeds 0.5 V, the TPS54350 starts operation. The TPS54350 has an internal digital
slow start that ramps the reference voltage to its final value in 1150 switching cycles. The internal slow start time
(10%–90%) is approximated by the following expression:
Once the TPS54350 device is in normal regulation, the ENA pin is high. If the ENA pin is pulled below the stop
threshold of 0.5 V, switching stops and the internal slow start resets. If an application requires the TPS54350 to
be disabled, use open drain or open collector output logic to interface to the ENA pin (see Figure 2). The ENA
pin has an internal pullup current source. Do not use external pullup resistors.
8
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