SNAD01B Datasheet, PDF (29/31 Pages) SONiX Technology Company – 8-CHANNEL 8-BIT ADC

SNAD01B
8-CHANNEL 8-BIT ADC
Program 5: Battery Low Detection
SNC520
VDD
VDD
P22
P21
P20
VSS
VDD
SNAD01B _VDD
AVDD
REF
START
CLK
DIO
VSS
AVSS
VDD
0.1uF
Battery:
1.5Vx3
CH[7]
VDD
An application uses three 1.5V batteries for power supply. During operation, the
power of batteries keeps consumed and the voltage of battery keeps going down.
Now, voltage lower than 3.6V is treated as “Battery Low”. The ADC and bandgap
reference circuit in SNAD01B can be utilized to detect “Battery Low”.
The voltage through channel 7 to ADC is reduced to 1/6*VDD (Figure10). Thus, when
VDD=3.6V, the voltage into ADC is around 0.6V. And bandgap is chosen for
reference voltage (approximately 1.17V within the whole operation voltage range).
The value acquired from ADC is about (0.6/1.17)*256=131. For simplification
consideration, we choose “ADC’s readout < 128” as “Battery Low” condition.
;; Inherit from program 1
;; Enter Power-down Mode (0)
CheckBattery:
@Set_Control_Reg #0, #1, #1, #0
;; Set rf=1, turn-on bandgap
@Set_Attrib #1, #1, #1, #0, #0, #0, #1, #1 ;; Switch Ch7 to Analog
mov m15 #0
CheckAgain:
@Read_ADC #1, #1, #1
mov a
#1000b
and a
ad_out_h
caje #1000b Battery_Low_No
mov a
m15
inca
mov m15 a
caje #3 Battery_Low_Yes
jmp CheckAgain
Battery_Low_Yes:
mov m14 #1
;; Read Ch7
;; if (Value>=128) then Not Battery Low
;; if (Value<128) for 3 times, then
;; battery low.
Version: 1.3
29
July 31, 2003