MAX3221: Maximum voltage applied to both ends of C1, C2, C3, C4

Hi Masanori,

These capacitors are part of the charge pump that generates the output voltage for the driver. The "flying" capacitor C1 is used to charge V+. The inverting capacitor C2 inverts V+ to charge V-. C3 and C4 are storage capacitors that hold the charges V+ and V- while the switching and charging of C1 an C2 occur. See image below.

During the switching, each capacitor should typically see voltages as described below:

C1: Vcc to GND  (5-V or 3.3-V)

C2: V+ to GND    (5.4-V typical)

C3: V+ to GND    (5.4-V typical)

C4: GND to V-     (5.4-V typical)

External capacitors should have a voltage rating of at least 10-V (recommended closer to 16-V) to account for variances and noise.

Let me know if this makes sense.

Regards,

Eric

Hi Eric-san,

Thank you very much for the easy-to-understand explanation.
I understood the operation principle of the charge pump circuit and the voltages applied to C1, C2, C3 and C4 respectively.

By the way, the MAX value of V +, V- is not specified in the datasheet.
How much are these MAX values as actually?

Sincerely,
M. Tachibana

Hi Masanoroi-san,

V+ and V- hold the charge that is used for the driver output which has a typical value of +-5.4-V. The values at V+ and V- can be expected to be marginally higher. The MAX values are not specified on the datasheet but theoretically the maximum voltage amplitude the charge pump could push these to is 2*Vcc with respect to GND.

Regards,
Eric