ADP2164 Data Sheet
Rev. 0 | Page 14 of 20
THEORY OF OPERATION
INTEGRATED SOFT START
The ADP2164 is a step-down dc-to-dc regulator that uses
a fixed-frequency, peak current mode architecture with an
integrated high-side switch and low-side synchronous rectifier.
The high switching frequency and tiny, 16-lead, 4 mm × 4 mm
LFCSP package provide a small, step-down dc-to-dc regulator
solution. The integrated high-side switch (P-channel MOSFET)
and synchronous rectifier (N-channel MOSFET) yield high
efficiency.
The ADP2164 has integrated soft start circuitry to limit the
output voltage rise time and reduce inrush current at startup.
The soft start time is set at 2048 clock cycles.
If the output voltage is precharged before the part is turned
on, the ADP2164 prevents a reverse inductor current—which
would discharge the output capacitor—until the soft start
voltage exceeds the voltage on the FB pin.
The ADP2164 operates with an input voltage from 2.7 V to 6.5 V
and regulates the output voltage down to 0.6 V. The ADP2164 is
also available with preset output voltage options of 3.3 V, 2.5 V,
1.8 V, 1.5 V, 1.2 V, and 1.0 V.
OSCILLATOR AND SYNCHRONIZATION
The ADP2164 switching frequency is controlled by the RT pin.
If the RT pin is connected to GND, the switching frequency is
set to 600 kHz. If the RT pin is connected to VIN, the switching
frequency is set to 1.2 MHz.
CONTROL SCHEME
The ADP2164 uses a fixed-frequency, peak current mode
PWM control architecture. At the start of each oscillator cycle,
the P-channel MOSFET switch is turned on, placing a positive
voltage across the inductor. Current in the inductor increases
until the current sense signal crosses the peak inductor current
level, turns off the P-channel MOSFET switch, and turns on the
N-channel MOSFET synchronous rectifier. This action places a
negative voltage across the inductor, causing the inductor current
to decrease. The synchronous rectifier stays on for the rest of
the cycle.
Connecting a resistor from RT to GND allows programming
of the switching frequency from 500 kHz to 1.4 MHz. Use the
following equation to set the switching frequency:
(kHz)
000,54
)(k
S
f
RT =Ω
Figure 37 shows the typical relationship between the switching
frequency and the RT resistor.
1600
1400
1200
1000
800
600
400
200
20 40 60 80 100 120 140 160 180
RT RESISTOR (kΩ)
FREQUENCY (kHz)
09944-037
The peak inductor current level is set by the compensation
(COMP) voltage. The COMP voltage is the output of a transcon-
ductance error amplifier that compares the feedback voltage
with an internal 0.6 V reference (see Figure 36).
SLOPE COMPENSATION
To prevent subharmonic oscillations, slope compensation
stabilizes the internal current control loop of the ADP2164
when the part operates at or beyond a 50% duty cycle. Slope
compensation is implemented by summing an artificial voltage
ramp with the current sense signal during the on time of the
P-channel MOSFET switch. This voltage ramp depends on the
output voltage. When operating at high output voltages, slope
compensation increases. The slope compensation ramp value
determines the minimum inductor value that can be used to
prevent subharmonic oscillations.
Figure 37. Switching Frequency vs. RT Resistor
To synchronize the ADP2164, drive an external clock at the
SYNC pin. The frequency of the external clock can be in the
range of 500 kHz to 1.4 MHz.
PRECISION ENABLE/SHUTDOWN
The EN pin is a precision analog input that enables the device
when the voltage exceeds 1.2 V (typical); this pin has 100 mV
hysteresis. When the enable voltage falls below 1.1 V (typical),
the part turns off. To force the ADP2164 to start automatically
when input power is applied, connect the EN pin to the VIN pin.
When the SYNC pin is driven by an external clock, the user
can configure the switching frequency to be in phase with the
external clock or 180° out of phase with the external clock, as
follows:
• If the RT pin is connected to GND or to a resistor, the
switching frequency is in phase with the external clock.
When the ADP2164 is shut down, the soft start capacitor is
discharged. This causes a new soft start cycle to begin when
the part is reenabled.
•
If the RT pin is connected to VIN, the switching frequency
is 180° out of phase with the external clock.
An internal pull-down resistor (1 MΩ) prevents accidental
enabling of the part if the EN input is left floating.
