ADP5600ACPZ-R7 datasheet(15/25 Pages) AD

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Data Sheet

ADP5600

Rev. 0 | Page 15 of 26

In Figure 41, an oscillator generating antiphase signals (φ1 and

φ2) controls the S1, S2, and S3, S4 switches. During the charging

phase, φ1, the S1 and S2 switches are closed, charging CFLY up to

the voltage at VIN. During output phase, φ2, S1 and S2 open

and S3 and S4 close. The positive terminal of CFLY is connected

to GND via S3 and the negative terminal of CFLY connects to

OUT via S4. The charge on CFLY is transferred to COUT during φ2.

The net result at steady state is voltage inversion at OUT with

respect to GND. Ideally, capacitor COUT maintains its voltage

during φ1. However, due to limited storage capacity, this voltage

drops due to the load (IOUT) until φ2 arrives. This discharging

and charging action of COUT is the output ripple. The charge

transfer efficiency depends on the on-resistance of the switches,

the frequency at which they are being switched, and on the

equivalent series resistance (ESR) of the external capacitors. For

minimum losses and maximum efficiency, capacitors with low

ESR are, therefore, recommended.

The charging and discharging current are always discontinuous

and the output voltage ripple for the charge pumps is always

OUT

OSC

OUT





Similarly, the input voltage ripple is always

OUT

OSC





where:

ΔVOUT is the output voltage ripple.

ΔVIN is the input voltage ripple.

IOUT

is the charge pump load current.

fOSC

is the charge pump switching frequency.

CIN

is the charge pump input capacitor.

COUT

is the charge pump output capacitor.

Therefore, the voltage ripple (noise) can only be improved by

decreasing IOUT (impractical), increasing the switching frequency

(less efficient), or increasing the capacitance (costly).

By adding another charge pump of the opposite phase, the

ADP5600 offers a solution with an almost continuous current

flowing at the input and output nodes, greatly reducing the

voltage ripple.

INTERLEAVED INVERTING CHARGE PUMP

OPERATION

The ADP5600 has two inverting charge pumps that operate in

an interleaving manner, requiring the use of two small flying

capacitors (CC1 and CC2), which are typically of the same value.

Each fly capacitor operates on a separate charge pump inverter that

runs out of phase with each other. The output is then combined at

CPOUT as shown in Figure 42. The interleaving operation

results in a periodic ripple that is twice the frequency of the

oscillator.

Figure 42. Interleaved Operation

This approach provides a roughly constant input and output

current that dramatically reduces the voltage ripple. For an

interleaved inverting charge pump, the output voltage ripple is

given by



CPOUT

OUT

OSC

CPOUT









 









where:

ΔVCPOUT is the ripple voltage in CPOUT.

ICPOUT

is the load current in CPOUT.

fOSC

is the charge pump switching frequency.

CCPOUT

is the output capacitor in CPOUT.

CC1

is the fly capacitor.

ROUT

is the effective output resistance of the charge pump.

RON

is the average on resistance of the four switches.

β =

OSC





A comparison of the conventional charge pump topology and the

interleaving approach is shown in Figure 43 and Figure 44.

Figure 43. Noninterleaved Charge Pump Operation (fOSC = 500 kHz,

CIN = 10 μF, C1 = 1 μF, C2 = Float, CCPOUT = 10 μF)

CCPOUT

CPOUT = –VIN

VIN

C2+

C2–

OSCILLATOR

Ф1

Ф2

CC2

VIN

CIN

CPH1

CPH2

CPG1

CPG2

FNG1

FNG2

FNO1

FNO2

C1+

C1–

CC1

CH1 2.00mVΩBW CH2 2.00mVΩBW

CH3 10V BW

M1.00µs A CH4

6.80V

VIN

C+

CPOUT

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