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Data Sheet

ADP5600

Rev. 0 | Page 17 of 25

PRECISION ENABLE/SHUTDOWN

The EN input pin has a precision analog threshold of 1.2 V

(typical) with 70 mV of hysteresis. When the enable voltage

exceeds 1.2 V, the regulator turns on; when it falls below 1.13 V

(typical), the regulator turns off. To force the regulator to auto-

matically start when input power is applied, connect EN to VIN.

Through an internal switch, the precision EN pin has an internal

pull-down resistor of approximately 1 MΩ, providing a default

turn-off if the EN pin is open. However, it is not recommended

to leave EN open. EN should be pulled high or low to enable or

disable the device, respectively.

When the EN pin voltage exceeds 0.8 V (typical), the ADP5600

starts up and enables its housekeeping block. Below this voltage,

the device operates in a deep shutdown mode for minimum

current consumption. As EN voltage rises to 1.2 V, the precision

enable is triggered, turning on the oscillator, charge pump, and

LDO blocks.

Figure 48. ISW vs. EN Voltage

ADP5600 also includes an output discharge resistor to force the

CPOUT and LDO output voltages to zero when the ADP5600 is

disabled. This procedure ensures that the outputs of CPOUT and

the LDO are always in a well-defined state, whether enabled or not.

OSCILLATOR

The oscillator frequency, fOSC, of the ADP5600 can be set to a value

from 100 kHz to 1 MHz by connecting a resistor, RT, from the

FREQ pin to ground. The oscillator frequency can be estimated

using the following equation:

fOSC [kHz] = 64,700/RT [kΩ]

If RT is approximately 50 kΩ or less, the oscillator frequency clamps

at near 1 MHz.

Figure 49 shows the typical relationship between fOSC and RT.

The adjustable frequency allows the user to make decisions based

on the trade-off between efficiency and solution size.

Figure 49. fOSC vs. RT

SYNCHRONIZATION

To synchronize the ADP5600, connect an external clock to the

SYNC pin. The frequency of the external clock can be in the

range of 180 kHz to 2.2 MHz. The ADP5600 uses the rising

edge of this signal to create the 50% duty cycle charge pump

oscillator. Therefore, each of the two charge pumps operates at

one half of the SYNC frequency, and the input and output

voltage ripple frequency is exactly at the original SYNC input

frequency.

If this external clock is applied to the SYNC pin prior to EN,

then the ADP5600 starts up with the SYNC signal running the

oscillator. If the external clock is applied after the ADP5600

starts up, then the ADP5600 uses the oscillator set by the

condition of the FREQ pin until the SYNC signal becomes

available. In this way, the charge pump starts up normally even

if there is some delay between the enable of the ADP5600 and

the application of the synchronization clock.

02.0

1.8

0.6

1.4

0.4

1.0

1.6

1.2

0.8

0.2

EN VOLTAGE (V)

TJ = +125ºC

TJ = +25ºC

TJ = –40ºC

1000

100

300

600

500

200

400

800

700

900

01000

900

300

700

200

500

800

600

400

100

RT (kΩ)

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