Data Sheet ADP197
Rev. C | Page 11 of 13
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 26 shows the
typical ground current when V
EN
= V
IN
, and varies from 1.8 V
to 5.5 V.
0
5
10
15
20
25
30
35
40
45
50
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
GROUND CURRENT (µA)
V
IN
(V)
09298-024
50mA
100mA
200mA
500mA
1000mA
3000mA
Figure 26. Ground Current vs. Input Voltage (V
IN
), Different Load Currents
ENABLE FEATURE
The ADP197 uses the EN pin to enable and disable the VOUT
pin under normal operating conditions. As shown in Figure 27,
when a rising voltage (V
EN
) on the EN pin crosses the active
threshold, VOUT turns on. When a falling voltage (V
EN
) on
the EN pin crosses the inactive threshold, VOUT turns off.
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 0.2 0.4 0.6 0.8 1.0 1.2
V
OUT
(V)
ENABLE VOLTAGE (V)
V
EN
FALLING
V
EN
RISING
V
OUT
AT 3.6V
09298-025
Figure 27. Typical EN Operation
As shown in Figure 27, the EN pin has hysteresis built into it.
This built-in hysteresis 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 and inactive thresholds derive from the V
IN
voltage; therefore, these thresholds vary with the changing input
voltage. Figure 28 shows the typical EN active and inactive
thresholds when the input voltage varies from 1.8 V to 5.5 V.
0
0.2
0.4
0.6
0.8
1.0
1.2
1.82.22.63.03.43.84.24.65.05.4
ENABLE TH
ESHOLD (V)
INPUT VOLTAGE (V)
EN RISE
EN FALL
09298-026
Figure 28. Typical EN Threshold vs. Input Voltage (V
IN
)
