ADP2119-EVALZ Analog Devices Inc, ADP2119-EVALZ Datasheet - Page 16

• Manufacturer Part Number: ADP2119-EVALZ
• Description: Step-Down Regulator Eval. Board
• Manufacturer: Analog Devices Inc

Specifications of ADP2119-EVALZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: Step Down DC/DC Converter
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP2119
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 0.6V ~ Vin
• Current - Output: 2A
• Voltage - Input: 2.3 ~ 5.5 V
• Regulator Topology: Buck
• Frequency - Switching: 1.2MHz
• Board Type: Fully Populated
• Utilized Ic / Part: ADP2119
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADP2119/ADP2120
THEORY OF OPERATION
The ADP2119/ADP2120 are step-down, dc-to-dc regulators
that use a fixed frequency, peak current mode architecture with
integrated high-side switch and low-side synchronous rectifier.
The high switching frequency and tiny 10-lead, 3 mm × 3 mm
LFCSP_WD 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 at medium-to-full loads while light load efficiency
is improved using the PFM mode.
The ADP2119/ADP2120 support input voltages from 2.3 V
to 5.5 V and regulate the output voltage down to 0.6 V. The
ADP2119/ADP2120 are 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.
CONTROL SCHEME
The ADP2119/ADP2120 use a fixed frequency, peak current
mode PWM control architecture and operate in PWM mode
for medium-to-full loads but shift to PFM mode (if enabled) at
light loads to maintain high efficiency. When operating in fixed
frequency PWM mode, the duty cycle of the integrated switches
is adjusted to regulate the output voltage. When operating in
PFM mode at light loads, the switching frequency is adjusted
to regulate the output voltage.
The ADP2119/ADP2120 operate in PWM mode when the load
current is greater than the pulse-skipping threshold current. At
load currents below this value, the regulator smoothly transitions
to the PFM mode of operation.
PWM MODE OPERATION
In PWM mode, the ADP2119/ADP2120 operate at a fixed
frequency. At the start of each oscillator cycle, the P-channel
MOSFET switch is turned on, putting 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 puts a negative voltage
across the inductor, causing the inductor current to decrease.
The synchronous rectifier stays on for the rest of the cycle or
until the inductor current reaches zero, which causes the zero-
crossing comparator to turn off the N-channel MOSFET as well.
The peak inductor current level is set by V
of a transconductance error amplifier that compares the feedback
voltage with an internal 0.6 V reference.
COMP
. V
COMP
is the output
Rev. 0 | Page 16 of 24
PFM MODE OPERATION
When PFM mode is enabled, the regulator smoothly transitions
to the variable frequency PFM mode of operation when the load
current decreases below the pulse-skipping threshold current.
Switching continues only as necessary to maintain the output
voltage within regulation. When the output voltage drops below
regulation, the part enters PWM mode for a few oscillator cycles to
increase the output voltage back to regulation. During the wait
time between bursts, both power switches are off, and the output
capacitor supplies the load current. Because the output voltage
dips and recovers occasionally, the output voltage ripple in this
mode is larger than the ripple in the PWM mode of operation.
SLOPE COMPENSATION
Slope compensation stabilizes the internal current control loop
of the ADP2119/ADP2120 when operating close to and beyond
the 50% duty cycle to prevent subharmonic oscillations. Slope
compensation is implemented by summing an artificial voltage
ramp to 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, there is more slope
compensation. The slope compensation ramp value determines
the minimum inductor that can be used to prevent subharmonic
oscillations.
ENABLE/SHUTDOWN
The EN input pin has a precision analog threshold of 1.2 V (typical)
with 100 mV of hysteresis. When the enable voltage exceeds 1.2 V,
the regulator turns on, and when it falls below 1.1 V (typical),
the regulator turns off. To force the part to automatically start
when input power is applied, connect EN to VIN.
When the ADP2119/ADP2120 are shut down, the soft start
capacitor is discharged. This causes a new soft start cycle to
begin when the part is reenabled.
An internal pull-down resistor (1 MΩ) prevents an accidental
enable if EN is left floating.
INTEGRATED SOFT START
The ADP2119/ADP2120 include integrated soft start circuitry
to limit the output voltage rise time and reduce inrush current
at startup. The soft start time is fixed at 1024 clock cycles.
If the output voltage is precharged prior to turn-on, the part
prevents reverse inductor current (which would discharge the
output capacitor) by keeping both MOSFETs turned off until
the soft start voltage exceeds the voltage on the FB pin.