8

AAT1217

600mA, 1.2MHz, Micropower Synchronous Step-Up Converter

DATA SHEET

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

202050B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013

Current Mode Operation

The AAT1217 is based on a slope compensated current

mode PWM control topology. It operates at a fixed fre-

quency of 1.2MHz. At the beginning of each clock cycle,

the main switch (NMOS) is turned on and the inductor

current starts to ramp. After the maximum duty cycle or

the sense current signal equals the error amplifier (EA)

output, the main switch is turned off and the synchro-

nous switch (PMOS) is turned on. This control topology

features cycle-by-cycle current limiting which can pre-

vent the main switch from overstress and the external

inductor from saturating.

Light Load Mode Operation

At very light load, the AAT1217 automatically switches

into light load mode operation to improve efficiency.

During this mode, the PWM control will skip some pulses

to maintain regulation. If the load increases and the out-

put voltage drops, the device will automatically switch

back to normal PWM mode and maintain regulation.

Anti-Ringing Control

An anti-ringing circuitry is included to remove the high

frequency ringing that appears on the SW pin when the

inductor current goes to zero. In this case, a ringing on

the SW pin is induced due to remaining energy stored in

parasitic components of switch and inductor. The anti-

ringing circuitry clamps the voltage internally to the bat-

tery voltage and therefore dampens this ringing.

Device Shutdown

When SHDN is set logic high, the AAT1217 is put into

active mode operation. If SHDN is set logic low, the

device is put into shutdown mode and consumes less

than 1μA of current. After start-up, the internal circuitry

enabled, the internal circuitry will be supplied by the

input source again.

Application Information

Adjustable Output Voltage

An external resistor divider is used to set the output volt-

is determined by the following equation:

⎛⎞

⎝⎠

R1

R2

Table 1 lists the recommended resistor values for par-

ticular output voltage settings.

R1()

R2()

3.3V

1.02M

604k

5.0V

1.02M

332k

Table 1: Resistor Selection for

Output Voltage Setting.

Fixed Output Voltage

The AAT1217 has two fixed output voltage options: 3.3V

and 5V. An internal resistor divider is connected to the

FB pin inside the package which eliminates the need for

external feedback resistors. When designing with the

fixed output voltage option, remember to leave the FB

pin open; otherwise the output voltage will be affected.

However, a feed-forward capacitor can still be added

between the FB and VOUT pins to enhance the control

loop performance.

Inductor Selection

The high switching frequency of 1.2MHz allows for small

surface mount inductors. For most applications, the

AAT1217 operates with inductors from 2.2μH to 10μH.

Use the following equations to select the proper inductor

value for a particular application condition:

2

; D =

=