ADP5600ACPZ-R7 datasheet(20/25 Pages) AD

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ADP5600

Data Sheet

Rev. 0 | Page 20 of 25

APPLICATIONS INFORMATION

CAPACITOR SELECTION

Charge Pump Input and Output Capacitor Selection

The input and output capacitors dictate the amount of ripple

voltage present in their respective nodes. The minimum effective

capacitance that is required to keep the input and output ripple at

a reasonable level is 4.7 μF. A 10 μF 10% X7R ceramic capacitor

with twice the voltage rating compared to the intended input

voltage is recommended for CIN and CCPOUT.

Charge Pump Flying Capacitor Selection

The flying capacitance affects the output resistance of the charge

pump, as seen in Figure 56. A low flying capacitance causes a

voltage drop from the input to output transfer due to the small

charge storage capacity and higher reactance. In general, higher

flying capacitance improves both the load transient response

and the steady state ripple.

Figure 56. ROUT vs. ICPOUT at Different CFLY Values, fOSC = 500 kHz

LDO Capacitor Selection

ADP5600 is designed to operate with small space-saving

ceramic capacitors, as long as its ESR value is taken into

consideration. The ESR of the output capacitor affects the

stability of the LDO control loop. A minimum of 2.2 μF

capacitance with an ESR of 0.1 Ω or less is recommended to

ensure the stability of the ADP5600. Transient response to

changes in load current is also affected by output capacitance.

Using a larger value of output capacitance improves the transient

response of the ADP5600 to large changes in load current.

Figure 57 shows the transient response at CLDO_OUT = 10 μF.

Figure 57. Output Transient Response,

CLDO_OUT = 10 μF

OUTPUT VOLTAGE SETTINGS

The inverting charge pump provides a voltage on CPOUT that

is approximately equal to the negative of its input voltage and

some loss, depending on the output current, ICPOUT, and output

resistance, ROUT. More specifically, the CPOUT voltage is given

by the equation

VCPOUT = −(VIN + ICPOUT × ROUT)

where:

VCPOUT is the voltage at CPOUT.

VIN is the voltage at VIN.

ICPOUT is the load current at CPOUT.

ROUT is the charge pump output resistance.

The LDO output voltage of the ADP5600 can be configured for

preprogrammed, fixed ,output voltages or adjusted using feedback

resistors. Setting the SEL1 and SEL2 pins changes the LDO

fixed output voltage, according to Table 8.

Table 8. LDO Fixed Output Voltage Configurations

SEL1

SEL2

VLDO_OUT

GND

−0.505 V

Floating

GND

−1.5 V

GND

Floating

−2.5 V

Floating

−5.0 V

If the desired output voltage of the LDO is −0.505 V, −1.5 V, −2.5 V,

or −5.0 V, set the SEL1 and SEL2 pins as shown in Table 8 and

connect the FB pin directly to LDO_OUT. To obtain any other

voltage between −0.505 V and –VIN, use a resistor divider on the

FB pin, as shown in Figure 58.

Figure 58. LDO Output Voltage Setup

–100 –90

–30

–70

–20

–50

–80

–60

–40

–10

ICPOUT (mA)

C1, C2 = 0.47µF

C1, C2 = 1µF

C1, C2 = 10µF

10.9

8.5

9.1

9.5

10.1

9.9

9.3

9.7

8.9

8.7

10.5

10.3

10.7

CH1 50mA BW

CH2 2.00V BW

CH3 10.0mV Ω BW CH4 10.0V BW

M20.0ms A CH1

–49mA

60.20000ms

ILDO_OUT

VLDO_OUT

VCPOUT

C1+

VLDO_OUT

VIN

CPOUT

SEL1

SEL2

INVERTING

CHARGE PUMP

NEGATIVE

LDO

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