SP3508 Datasheet, PDF (29/36 Pages) Sipex Corporation – Rugged 3.3V, 20Mbps, 8 Channel Multiprotocol Transceiver with Programmable DCE/DTE and Termination Resistors

V _CC = +3V
+6V
+
C_{1 –}
+
C_{2 –}
FEATURES
C _VDD
+ – _{V DD S tora ge C apacitor}
– + _{V SS1 S tora ge C apacitor}
C _VSS1
Figure 48. Charge Pump - Phase 4.
2-phased inverter pump
Phase 1
Please refer to figure below: In the first phase of the clock cycle, switches S2 and S4 are
opened and S1 and S3 closed. This connects the flying capacitor, C3, from Vin to ground.
C3 charge up to the input voltage applied at Vcc.
Phase 2
In the second phase of the clock cycle, switches S2 and S4 are closed and S1 and S3 are
opened. This connects the flying capacitor, C3, in parallel with the output capacitor, C_VSS2.
The Charge stored in C3 is now transferred to C_VSS2. Simultaneously, the negative side of
C_VSS2 is connected to V_ss2 and the positive side is connected to ground. With the voltage
across C_VSS2 smaller than the voltage across C3, the charge flows from C3 to C_VSS2 until the
voltage at the V_ss2 equals -V_cc.
V_SS2 = -V _CC
V _CC
S₁
S₂
C₃ ⁺
+
C _VSS2
S₃
S₄
V _SS2
Figure 49. Circuit for an Ideal Voltage Inverter.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com
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SP3508_100_072208