33997 查看數據表（PDF） - Freescale Semiconductor

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33997

Switching Power Supply with Linear Regulators

Freescale Semiconductor 

Freescale Semiconductor, Inc.

Power-On Reset Timer

This timer starts to time out at the end of the soft-start period

if the VDDH and VDDL outputs are in the valid regulation range.

If the timer “times out”, then the open-drain PWROK signal is

released, indicating that “power is ON”.

Supervisory Circuits PWROK and VKAMOK

The 33997 has two voltage monitoring open-drain outputs,

the PWROK and the VKAMOK pins. PWROK is "active high".

This output is pulled low when either of the regulator outputs

(VDDH or VDDL) are below their regulation windows. If both

regulator outputs are above their respective lower thresholds,

and the Power-On Reset Timer has expired, the output driver is

turned off and this pin is at high-impedance state (see

Figure 6).

The VKAMOK signal indicates a severe fault condition on

the keep-alive regulator output VKAM. The VKAM output voltage

is compared to the internal bandgap reference voltage. When

the VKAM falls below the bandgap reference voltage level, the

VKAMOK signal is pulled low.

33997

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