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# Schottky Diode Free Mode in charge pump circuit(DC/DC)

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#### 020170

##### Full Member level 4
charge pump circuit

Nowadays I analyzed Charge Pump DC/DC circuits.

This DC/DC Charge Pump has current limit block that was consist of PMOS and series Resistors.

However, This DC/DC Charge Pump has mode that was called in "Schottky Diode Free Mode"

If DC/DC was in "Schottky Diode Free Mode", the connection between Input Supply Voltage and DC/DC was opened.

I don't know how this circuit works and what is the purpose.

thanks

charge pump circuits

I don't understand it either. Can you provide more details?

charge pump circuit design

The Nmos and Pmos are the Pull-Down and the Pull-Up af a CMOS inverter. If the control signal is low, the pmos is on, and the DC/DC input power voltage is 3V. If the control signal is high the nmos is on and the DC/DC input power voltage is connected to ground through the resistors.

I try to guess the situation: charge pumps multiply the amplitude of a clock signal and they can add (or not) a voltage as input (which adds to the output). So maybe this circuit adds (or not) the input initial voltage.

charge pump

Why Schottky Diode used in DC/DC Charge pump?
What characteririsc of Schottky diode are effect on DC/DC?

Could you explain in a point of layout & Latch-up ?

thanks

pump circuit

Use of Schottky diodes is preferable in charge pump circuits because their threshold voltage [tex:178e22369f]V_{\gamma}[/tex:178e22369f] is sensibly lower. Consider that [tex:178e22369f]V_{\gamma}[/tex:178e22369f] affects the voltage pumping gain of the charge pump: the output voltage of such a circuit is

$V_{\text{out}}=V_{\text{in}}+N\left[ \frac{C}{C+C_p} V_{\phi} - V_{\gamma} - \frac{I_{\text{out}}}{f(C+C_p)} \right]-V_{\gamma}$

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### 020170

Points: 2
diode charge pump

I think maybe this nomenclature refers to a synchronous "reset switch" in a
buck converter; an NMOS low side switch can recirculate the inductor current
with lower conduction losses (up to the point that Rds(on)*Iinductor exceeds
the Schottky Vf for the same current). The cost is the gate charge of the
low side switch, which goes to switching losses instead. The cheap way is a
Schottky and this design is "Schottky-free".

Schottky forward losses loom larger, as the output voltage goes lower; your
efficiency cannot exceed (Vout-Vf)/Vout. Or something close to that.

charge pump schottky

Why Schottky Diode used in DC/DC Charge pump?
It isn't in the presented circuit.
I think maybe this nomenclature refers to a synchronous "reset switch" in a
buck converter
Sounds reasonable. Unfortunately, a charge pump uses no inductor and can't work without push-pull synchronous switches at the driver side, as far as I see. So related to the presented circuit and particularly the control signal, the term seems completely meaningless.

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