ADP197ACBZ-R7 datasheet(11/16 Pages) AD

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ADP197

Rev. 0 | Page 11 of 16

APPLICATIONS INFORMATION

CAPACITOR SELECTION

Output Capacitor

The ADP197 is designed for operation with small, space-saving

ceramic capacitors but functions with most commonly used capa-

citors when the effective series resistance (ESR) value is carefully

considered. The ESR of the output capacitor affects the response

to load transients. A typical 1 μF capacitor with an ESR of 0.1 Ω

or less is recommended for good transient response. Using a larger

value of output capacitance improves the transient response to

large changes in load current.

Input Bypass Capacitor

Connecting at least 1 μF of capacitance from VIN to GND reduces

the circuit sensitivity to the printed circuit board (PCB) layout,

especially when high source impedance or long input traces are

encountered. When greater than 1 μF of output capacitance is

required, increase the input capacitor to match it.

GROUND CURRENT

The major source for ground current in the ADP197 is the internal

charge pump for the FET drive circuitry. Figure 24 shows the

typical ground current when VEN = VIN, and varies from 1.8 V

to 5.5 V.

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

VIN (V)

50mA

100mA

200mA

500mA

1000mA

3000mA

Figure 24. Ground Current vs. Load Current, Different Input Voltages (VIN)

ENABLE FEATURE

The ADP197 uses the EN pin to enable and disable the VOUT

pin under normal operating conditions. As shown in Figure 25,

when a rising voltage (VEN) on the EN pin crosses the active

threshold, VOUT turns on. When a falling voltage (VEN) on

the EN pin crosses the inactive threshold, VOUT turns off.

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.2

0.4

0.6

0.8

1.0

1.2

ENABLE VOLTAGE (V)

VEN FALLING

VEN RISING

VOUT AT 3.6V

Figure 25. Typical EN Operation

As shown in Figure 25, the EN pin has hysteresis built into it.

This prevents on/off oscillations that can occur due to noise on

the EN pin as it passes through the threshold points.

The EN pin active/inactive thresholds derive from the VIN voltage;

therefore, these thresholds vary with the changing input voltage.

Figure 26 shows the typical EN active/inactive thresholds when

the input voltage varies from 1.8 V to 5.5 V.

0.2

0.4

0.6

0.8

1.0

1.2

1.82.22.63.03.43.8

4.24.65.05.4

INPUT VOLTAGE (V)

EN RISE

EN FALL

Figure 26. Typical EN Thresholds vs. Input Voltage (VIN)

TIMING

Turn-on delay is defined as the interval between the time that

VEN exceeds the rising threshold voltage and when VOUT rises to

~10% of its final value. The ADP197 includes circuitry that has a

typical 1 ms turn-on delay and a controlled rise time to limit the

VIN inrush current. As shown in Figure 27 and Figure 28, the turn-

on delay is nearly independent of the input voltage.

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