Compared to LowR, buffers offer a higher drive capability with relatively fixed operating current, which
achieve a better performance (waveform quality versus power consumption) when the panel represents a
big capacitive load (i.e. 10nF).
Figure 43-18. LowR and Buffer Illustration
VLCD
Bias1
Bias2
Bias3
buf
LowR_en
Buffer_en
buf
buf
43.6.1.11. Reference Refresh and Power Refresh
There are two refresh signals for SLCD:
•
Reference refresh, which is used to periodically sample the bias current and target VLCD voltage.
•
Power refresh, which is used to charge the external VLCD capacitor to the target VLCD level. This
is usually due to the fact that the LCD panel driving waveform will need to charge the panel
segment capacitors.
The reference refreshment rate is defined by the leakage of the circuit. The bias current and reference
voltage start to drift slowly due to parasitic effects. A high frequency refresh rate can tolerate higher
leakage at cost of higher power consumption. User can configure the reference refresh rate by writing the
Reference Refresh Frequency bits in the Control A register (CTRLA.RRF).
The power refreshment rate is defined by the leakage of the circuit. High frequency could result in bit
higher power but can tolerate higher load current on VLCD, which means driving a bigger panel at higher
frequency. User can configure the power refresh rate by writing the Power Refresh Frequency bits in the
Control A register (CTRLA.PRF)
Figure 43-19. Reference and Power Refresh System Behavior
CTRLA.ENABLE
32k clock
Reference refresh signal
Reference refrefresh period defined by CTRLA.RRF
STATUS.LCDR
LCD bias status,
just for software
Power refresh signal
Power refrefresh period defined by CTRLA.PRF
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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