LC75857E 데이터 시트보기 (PDF) - ON Semiconductor

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LC75857E

1/3, 1/4 Duty LCD Driver with Key Input Function

ON Semiconductor 

LC75857E, LC75857W

Voltage Detection Type Reset Circuit (VDET)

This circuit generates an output signal and resets the system when logic block power is first applied and when the voltage

drops, i.e., when the logic block power supply voltage is less than or equal to the power down detection voltage VDET,

which is 2.2V, typical. To assure that this function operates reliably, a capacitor must be added to the logic block power

supply line so that the logic block power supply voltage VDD rise time when the logic block power is first applied and the

logic block power supply voltage VDD fall time when the voltage drops are both at least 1 ms. (See Figure 5 and Figure 6.)

Power Supply Sequence

The following sequences must be observed when power is turned on and off. (See Figure 5 and Figure 6.)

• Power on :Logic block power supply(VDD) on → LCD driver block power supply(VLCD) on

• Power off:LCD driver block power supply(VLCD) off → Logic block power supply(VDD) off

However, if the logic and LCD driver block use a shared power supply, then the power supplies can be turned on and off

at the same time.

System Reset

The LC75857E/W supports the reset methods described below. When a system reset is applied, display is turned off, key

scanning is stopped, and all the key data is reset to low. When the reset is cleared, display is turned on and key scanning

become possible.

1. Reset methods

If at least 1 ms is assured as the logic block supply voltage VDD rise time when logic block power is applied, a system

reset will be applied by the VDET output signal when the logic block supply voltage is brought up. If at least 1 ms is

assured as the logic block supply voltage VDD fall time when logic block power drops, a system reset will be applied

in the same manner by the VDET output signal when the supply voltage is lowered. Note that the reset is cleared at

the point when all the serial data (1/3 duty: the display data D1 to D126 and the control data, 1/4 duty: the display

data D1 to D164 and the control data) has been transferred, i.e., on the fall of the CE signal on the transfer of the last

direction data, after all the direction data has been transferred. (See Figure 5 and Figure 6.)

No. 7980-25/39

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