Stand-by power for non-volatile cmos rams
#CMOS RAM
#stand-by power
#data retention
#voltage switching
#Vcc
#VBAT
#chip select
#decoupling capacitor
#non-volatile memory
Description: To prevent data loss when a CMOS RAM transitions from normal operation (Vcc = 5 volts) to standby mode (Vcc = VBAT), it is crucial to maintain the CS pin close to the Vcc rail at all times. This is achieved by using capacitor C for AC coupling to the chip select, which interrupts the DC current path between Vqq (and consequently VBAT) and the decoder output. Regardless of the impedance state of the decoder during power down, the battery will supply current solely to the RAM, ensuring that the voltage at the CS pin remains near Vcc.
In this circuit, the CMOS RAM operates under two distinct conditions: normal operation and standby mode. During normal operation, the RAM is powered by a standard supply voltage of 5 volts (Vcc). However, when transitioning to standby mode, the power supply switches to a backup battery voltage (VBAT), which is typically lower than Vcc. The critical aspect of this transition is to ensure that the chip select (CS) pin remains sufficiently biased to prevent any unintended data loss.
The AC coupling capacitor (C) plays a vital role in this circuit configuration. It effectively isolates the DC components of the signal from the decoder output, which may exhibit varying impedance levels when the system enters power-down mode. By doing so, the capacitor prevents any DC current from flowing directly from Vqq or VBAT to the decoder's output, which may otherwise lead to incorrect CS pin voltage levels.
The design ensures that the battery provides just enough current to maintain the required voltage at the CS pin, regardless of the impedance state of the decoder. This careful management of current flow is essential for maintaining data integrity in the RAM during the transition between operational states. The result is a reliable system that safeguards against data loss, allowing for seamless power management in battery-operated devices.To prevent loss of data when a CMOS RAM is switched from normal operation (Vcc = 5 volts) to stand-by mode (Vcc = VBAT) it must be ensured that the CS pin goes near the Vcc rail at all times. Ac coupling to the chip select is made through capacitor C, breaking the dc current path between Vqq (and hence VBAT) and the decoder output.
So, whatever the impedance state of the decoder in power down, the battery will provide current only for the RAM, low enough to keep the voltage at CS near to V^.
In this circuit, the CMOS RAM operates under two distinct conditions: normal operation and standby mode. During normal operation, the RAM is powered by a standard supply voltage of 5 volts (Vcc). However, when transitioning to standby mode, the power supply switches to a backup battery voltage (VBAT), which is typically lower than Vcc. The critical aspect of this transition is to ensure that the chip select (CS) pin remains sufficiently biased to prevent any unintended data loss.
The AC coupling capacitor (C) plays a vital role in this circuit configuration. It effectively isolates the DC components of the signal from the decoder output, which may exhibit varying impedance levels when the system enters power-down mode. By doing so, the capacitor prevents any DC current from flowing directly from Vqq or VBAT to the decoder's output, which may otherwise lead to incorrect CS pin voltage levels.
The design ensures that the battery provides just enough current to maintain the required voltage at the CS pin, regardless of the impedance state of the decoder. This careful management of current flow is essential for maintaining data integrity in the RAM during the transition between operational states. The result is a reliable system that safeguards against data loss, allowing for seamless power management in battery-operated devices.To prevent loss of data when a CMOS RAM is switched from normal operation (Vcc = 5 volts) to stand-by mode (Vcc = VBAT) it must be ensured that the CS pin goes near the Vcc rail at all times. Ac coupling to the chip select is made through capacitor C, breaking the dc current path between Vqq (and hence VBAT) and the decoder output.
So, whatever the impedance state of the decoder in power down, the battery will provide current only for the RAM, low enough to keep the voltage at CS near to V^.
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