600mA Voltage-Scaling Step-Down Converter
for RF Power Amplifiers with Bypass Switch
Pin Descriptions
Pin #
1
2, 3
AAT1171
Symbol
N/C
VOUT
Function
Not connected.
Feedback input pin. This pin is connected to the converter output. It is used to complete
the control loop, regulating the output voltage to the desired value. When in bypass
mode, a low resistance MOSFET is connected between this pin and VIN.
Bias supply. Supply power for the internal circuitry. Connect to input power via low pass
filter with decoupling to AGND.
Analog ground. Connect the return of all small signal components to this pin.
Control voltage input from a DAC. Input voltage between 0.2V and 1.2V to control output
voltage of the converter. Force pin to 1.3V for bypass switch enable.
Enable DC/DC converter, active high.
Enable control to bypass the DC/DC converter when PA transmitting at full power from
low battery voltage. Active high.
This pin is used to program the device between PWM and LL mode:
HIGH - PWM Mode Only
LOW - LL Mode: PWM operation for loads above 100mA and variable switching frequen-
cy for loads below 100mA
Connecting the SYNC pin to the system clock (19.8MHz) will override the internal clock
and force the switching frequency to the external clock frequency divided by 10.
Input supply voltage for the converter. Must be closely decoupled.
Main power ground. Connect to the output and input capacitor return.
Switching node. Connect the inductor to this pin. It is connected internally to the drain of
both low- and high-side MOSFETs.
Exposed paddle (bottom). Connect to ground directly beneath the package.
4
5
6
7
8
9
VCC
AGND
DAC
EN
BYPASS
MODE/SYNC
10
11
12
EP
VIN
PGND
LX
Pin Configuration
TDFN33-12
(Top View)
N/C
VOUT
VOUT
VCC
AGND
DAC
1
2
3
4
5
6
12
11
10
9
8
7
LX
PGND
VIN
MODE/SYNC
BYPASS
EN
2
1171.2006.06.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
