参数资料
型号: LM5046MHX
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 稳压器
英文描述: SWITCHING CONTROLLER, 540 kHz SWITCHING FREQ-MAX, PDSO28
封装: TSSOP-28
文件页数: 16/32页
文件大小: 888K
代理商: LM5046MHX
30147830
FIGURE 13. Input Transient Protection
30147837
FIGURE 14. Start-up Regulator for VPWR>100V
UVLO AND OVP VOLTAGE DIVIDER SELECTION
Two dedicated comparators connected to the UVLO and OVP
pins are used to detect under voltage and over voltage con-
ditions. The threshold values of both these comparators are
set at 1.25V. The two functions can be programmed inde-
pendently with two separate voltage dividers from VIN to
AGND as shown in Figure 15 and Figure 16, or with a three-
resistor divider as shown in Figure 17. Independent UVLO
and OVP pins provide greater flexibility for the user to select
the operational voltage range of the system. When the UVLO
pin voltage is below 0.4V, the controller is in a low current
shutdown mode. For a UVLO pin voltage greater than 0.4V
but less than 1.25V the controller is in standby mode. Once
the UVLO pin voltage is greater than 1.25V, the controller is
fully enabled. Two external resistors can be used to program
the minimum operational voltage for the power converter as
shown in Figure 15. When the UVLO pin voltage falls below
the 1.25V threshold, an internal 20A current sink is enabled
to lower the voltage at the UVLO pin, thus providing threshold
hysteresis. Resistance values for R
1 and R2 can be deter-
mined from the following equations:
Where V
PWR is the desired turn-on voltage and VHYS is the
desired UVLO hysteresis at V
PWR.
For example, if the LM5046 is to be enabled when VPWR
reaches 33V, and disabled when V
PWR is decreased to 31V,
R
1 should be 100k, and R2 should be 4.2k. The voltage at
the UVLO pin should not exceed 7V at any time.
Two external resistors can be used to program the maximum
operational voltage for the power converter as shown in Fig-
ure 16. When the OVP pin voltage rises above the 1.25V
threshold, an internal 20A current source is enabled to raise
the voltage at the OVP pin, thus providing threshold hystere-
sis. Resistance values for R
1 and R2 can be determined from
the following equations:
If the LM5046 is to be disabled when V
PWR-OFF reaches 80V
and enabled when it is decreased to 78V. R
1 should be
100k
, and R
2 should be 1.5 k. The voltage at the OVP pin
should not exceed 7V at any time.
23
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LM5046
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