ADP1610(Rev0) データシートの表示（PDF） - Analog Devices
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ADP1610 Datasheet PDF : 16 Pages
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ADP1610
THEORY OF OPERATION
The ADP1610 current-mode step-up switching converter
converts a 2.5 V to 5.5 V input voltage up to an output voltage as
high as 12 V. The 1.2 A internal switch allows a high output
current, and the high 1.2 MHz switching frequency allows tiny
external components. The switch current is monitored on a
pulse-by-pulse basis to limit it to 2 A.
CURRENT-MODE PWM OPERATION
The ADP1610 uses current-mode architecture to regulate the
output voltage. The output voltage is monitored at FB through a
resistive voltage divider. The voltage at FB is compared to the
internal 1.23 V reference by the internal transconductance error
amplifier to create an error current at COMP. A series resistor-
capacitor at COMP converts the error current to a voltage. The
switch current is internally measured and added to the stabiliz-
ing ramp, and the resulting sum is compared to the error
voltage at COMP to control the PWM modulator. This current-
mode regulation system allows fast transient response, while
maintaining a stable output voltage. By selecting the proper
resistor-capacitor network from COMP to GND, the regulator
response is optimized for a wide range of input voltages, output
voltages, and load conditions.
FREQUENCY SELECTION
The ADP1610’s frequency is user-selectable to operate at either
700 kHz to optimize the regulator for high efficiency or to
1.2 MHz for small external components. Connect RT to IN for
1.2 MHz operation, or connect RT to GND for 700 kHz
operation. To achieve the maximum duty cycle, which might be
required for converting a low input voltage to a high output
voltage, use the lower 700 kHz switching frequency.
SOFT START
To prevent input inrush current at startup, connect a capacitor
from SS to GND to set the soft start period. When the ADP1610
is in shutdown (SD is at GND) or the input voltage is below the
2.4 V undervoltage lockout voltage, SS is internally shorted to
GND to discharge the soft start capacitor. Once the ADP1610 is
turned on, SS sources 3 µA to the soft start capacitor at startup.
As the soft start capacitor charges, it limits the voltage at COMP.
Because of the current-mode regulator, the voltage at COMP is
proportional to the switch peak current, and, therefore, the
input current. By slowly charging the soft start capacitor, the
input current ramps slowly to prevent it from overshooting
excessively at startup.
ON/OFF CONTROL
The SD input turns the ADP1610 regulator on or off. Drive SD
low to turn off the regulator and reduce the input current to
10 nA. Drive SD high to turn on the regulator.
When the dc-dc step-up switching converter is turned off, there
is a dc path from the input to the output through the inductor
and output rectifier. This causes the output voltage to remain
slightly below the input voltage by the forward voltage of the
rectifier, preventing the output voltage from dropping to zero
when the regulator is shut down. Figure 28 shows the applica-
tion circuit to disconnect the output voltage from the input
voltage at shutdown.
SETTING THE OUTPUT VOLTAGE
The ADP1610 features an adjustable output voltage range of VIN
to 12 V. The output voltage is set by the resistive voltage divider
(R1 and R2 in Figure 2) from the output voltage (VOUT) to the
1.230 V feedback input at FB. Use the following formula to
determine the output voltage:
VOUT = 1.23 × (1 + R1/R2)
(1)
Use an R2 resistance of 10 kΩ or less to prevent output voltage
errors due to the 10 nA FB input bias current. Choose R1 based
on the following formula:
R1
=
R2
×
⎜⎜⎝⎛
VOUT − 1.23
1.23
⎟⎟⎠⎞
(2)
INDUCTOR SELECTION
The inductor is an essential part of the step-up switching
converter. It stores energy during the on-time, and transfers that
energy to the output through the output rectifier during the off-
time. Use inductance in the range of 1 µH to 22 µH. In general,
lower inductance values have higher saturation current and
lower series resistance for a given physical size. However, lower
inductance results in higher peak current that can lead to
reduced efficiency and greater input and/or output ripple and
noise. Peak-to-peak inductor ripple current at close to 30% of
the maximum dc input current typically yields an optimal
compromise.
For determining the inductor ripple current, the input (VIN) and
output (VOUT) voltages determine the switch duty cycle (D) by
the following equation:
D = VOUT − VIN
(3)
VOUT
Rev. 0 | Page 10 of 16
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