When to start and when to close Charge Pump, how to measure on the chip?
Charge Pump enable or disable is controlled by CPRENB, CPON, CPAUTO buffers, take SN8P1919 for example.
| CPRENB | CPON | CPAUTO | Charge-Pump Status | Regulator Status |
| 0 | X | X | OFF | OFF |
| 1 | 0 | 0 | OFF | ON |
| 1 | 0 | 1 | Auto Mode | ON |
| 1 | 1 | 0 | Always ON | ON |
Auto-Mode Description:
| CPRENB | CPON | CPAUTO | AVDDRENB | VDD | Charge-Pump Status | Regulator Status | AVDDR Output | PGIA, ADC Function |
| 1 | 0 | 1 | 1 | >4.2V | OFF | ON | 3.8V | Available |
| ≦ 4.2V | ON | ON | 3.8V | Available |
When CPON = 1, Charge pump is enabled by force, at this time, AVDDCP voltage is about VDD * 2;
When CPON = 0, Charge pump is forced off, at this time, AVDDCP voltage is approximately VDD;
When set to Auto mode, (CPON = 0, CPAUTO = 1)
VDD<4.2V, Charge Pump enabled automatically, AVDDCP voltage is about VDD * 2
VDD>4.2V, Charge Pump automatically turns off, AVDDCP voltage is approximately VDD
When VDD voltage continue to drop from 4.4V to 3.6V, it can not be set to Auto mode, or it may result in Charge pump damage because of several times instantaneous switch
Reference document: SN8P1900 Series Datasheet