ADP1613ARMZ-R7 datasheet(11/28 Pages) AD

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ADP1612/ADP1613

Rev. A | Page 11 of 28

THEORY OF OPERATION

FREQ

PWM

COMPARATOR

UVLO

COMPARATOR

TSD

COMPARATOR

OSCILLATOR

COMPARATOR

DREF

VIN

CURRENT

SENSING

5µA

DRIVER

BAND GAP

RESET

1.1M

Ω

AGND

VIN

UVLOREF

TSENSE

TREF

ERROR

AMPLIFIER

VBG

SOFT

START

5µA

VSS

RCOMP

CCOMP

COMP

CSS

CIN

VOUT

VIN

VOUT

COUT

GND

AGND

>1.6V

ADP1612/AD1613

VIN

<0.3V

>1.6V

<0.3V

Figure 34. Block Diagram with Step-Up Regulator Application Circuit

The ADP1612/ADP1613 current-mode step-up switching

converters boost a 1.8 V to 5.5 V input voltage to an output

voltage as high as 20 V. The internal switch allows a high

output current, and the high 650 kHz/1.3 MHz switching

frequency allows for the use of tiny external components.

The switch current is monitored on a pulse-by-pulse basis to

limit it to 1.4 A typical (ADP1612) or 2.0 A typical (ADP1613).

CURRENT-MODE PWM OPERATION

The ADP1612/ADP1613 utilize a current-mode PWM control

scheme to regulate the output voltage over all load conditions.

The output voltage is monitored at FB through a resistive voltage

divider. The voltage at FB is compared to the internal 1.235 V

reference by the internal transconductance error amplifier to

create an error voltage at COMP. 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 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 frequency of the ADP1612/ADP1613 is pin-selectable

to operate at either 650 kHz to optimize the regulator for high

efficiency or at 1.3 MHz for use with small external components.

If FREQ is left floating, the part defaults to 650 kHz. Connect

FREQ to GND for 650 kHz operation or connect FREQ to VIN

for 1.3 MHz operation. When connected to VIN for 1.3 MHz

operation, an additional 5 μA, typical, of quiescent current is

active. This current is turned off when the part is shutdown.

SOFT START

To prevent input inrush current to the converter when the part is

enabled, connect a capacitor from SS to GND to set the soft start

period. Once the ADP1612/ADP1613 are turned on, SS sources

5 μA, typical, to the soft start capacitor (CSS) until it reaches

1.2 V at startup. As the soft start capacitor charges, it limits the

peak current allowed by the part. By slowly charging the soft

start capacitor, the input current ramps slowly to prevent it

from overshooting excessively at startup. When the ADP1612/

ADP1613 are in shutdown mode (EN ≤ 0.3 V), a thermal shut-

down event occurs, or the input voltage is below the falling

undervoltage lockout voltage, SS is internally shorted to GND

to discharge the soft start capacitor.

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