ADP1610 データシートの表示（PDF） - Analog Devices

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ADP1610

1.2 MHz DC-to-DC Step-Up Switching Converter

Analog Devices 

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 stabilizing

ramp. 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 main-

taining 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 frequency of the ADP1610 is selectable to operate at either

700 kHz to optimize the regulator for high efficiency or at 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 may 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. When 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 the current

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-to-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 application 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. To calculate the output voltage

use the following equation:

VOUT = 1.23 × (1 + R1/R2)

(1)

To prevent output voltage errors due to the 10 nA FB input bias

current, an R2 resistance of 10 kΩ or less is to be used. Choose

R1 based on the following equation:

R1 = R2 × ⎜⎛ VOUT − 1.23 ⎟⎞

(2)

⎝ 1.23 ⎠

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. A peak-to-peak

inductor ripple current at approximately 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. A | Page 10 of 20

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