ADP1882-1.0-EVALZ Analog Devices Inc, ADP1882-1.0-EVALZ Datasheet - Page 22

• Manufacturer Part Number: ADP1882-1.0-EVALZ
• Description: 1 MHz Synchronous Current-Mode Buck Controller Eval. Board
• Manufacturer: Analog Devices Inc

Specifications of ADP1882-1.0-EVALZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: PWM Buck Controller
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP1882
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADP1882/ADP1883
SYNCHRONOUS RECTIFIER
The ADP1882/ADP1883 employ an internal lower-side MOSFET
driver to drive the external upper-side and lower-side MOSFETs.
The synchronous rectifier not only improves overall conduction
efficiency but also ensures proper charging to the bootstrap
capacitor located at the upper-side driver input. This is beneficial
during startup to provide a sufficient drive signal to the external
upper-side MOSFET and attain a fast turn on response, which is
essential for minimizing switching losses. The integrated upper-
side and lower-side MOSFET drivers operate in complementary
fashion with built-in anticross conduction circuitry to prevent
unwanted shoot-through current that may potentially damage the
MOSFETs or reduce efficiency as a result of excessive power loss.
POWER SAVING MODE (PSM) VERSION (ADP1883)
The ADP1883 is the power saving mode version of the ADP1882.
The ADP1883 operates in the discontinuous conduction mode
(DCM) and pulse skips at light load to midload currents. It outputs
pulses, as necessary, to maintain output regulation. Unlike the
continuous conduction mode (CCM), DCM operation prevents
negative current, thus allowing improved system efficiency at
light loads. Current in the reverse direction through this pathway,
however, results in power dissipation and, therefore, a decrease
in efficiency.
To minimize the chance of negative inductor current buildup,
an on-board, zero-cross comparator turns off all upper-side and
lower-side switching activities when the inductor current
approaches the zero current line, causing the system to enter
idle mode, where the upper-side and lower-side MOSFETs are
turned off. To ensure idle mode entry, a 10 mV offset, connected
in series at the SW node, is implemented (see Figure 75).
I
LOAD
HS
LS
0A
Figure 75. Zero-Cross Comparator with 10 mV of Offset
Figure 74. Discontinuous Mode of Operation (DCM)
t
ON
COMPARATOR
ZERO-CROSS
t
OFF
LS
10mV
AS THE INDUCTOR
CURRENT APPROACHES
ZERO CURRENT, THE STATE
MACHINE TURNS OFF THE
LOWER-SIDE MOSFET.
SW
Q2
HS AND LS ARE OFF
OR IN IDLE MODE
I
Q2
Rev. 0 | Page 22 of 40
As soon as the forward current through the lower-side
MOSFET decreases to a level where
the zero-cross comparator (or I
turn off the lower-side MOSFET. From this point, the slope of the
inductor current ramping down becomes steeper (see Figure 76)
as the body diode of the lower-side MOSFET begins to conduct
current and continues conducting current until the remaining
energy stored in the inductor has been depleted.
The system remains in idle mode until the output voltage drops
from within regulation. A PWM pulse is then produced, turning
on the upper-side MOSFET to maintain system regulation. The
ADP1883 does not have an internal clock; therefore, it switches
purely as a hysteretic controller as described in this section.
TIMER OPERATION
The ADP1882/ADP1883 employ a constant on-time architecture
that provides a variety of benefits, including improved load and
line transient responses when compared with a constant (fixed)
frequency current-mode control loop of a comparable loop design.
The constant on-time timer, or t
voltage (V
information to produce an adjustable one-shot PWM pulse that
varies the on time of the upper-side MOSFET in response to
dynamic changes in input voltage, output voltage, and load current
conditions to maintain regulation. It then generates an on-time
(t
where K is a constant that is trimmed using an RC timer product
for the 300 kHz, 600 kHz, and 1.0 MHz frequency options.
Figure 76. 10 mV Offset to Ensure Prevention of Negative Inductor Current
ON
) pulse that is inversely proportional to V
10 mV = I
t
ON
I
LOAD
SW
LS
0A
= K ×
IN
) and the output voltage (V
Q2
V
V
OUT
× R
IN
ANOTHER
TRIGGERED WHEN V
FALLS BELOW REGULATION
ON(Q2)
ZERO-CROSS COMPARATOR
DETECTS 10mV OFFSET AND
TURNS OFF LS
10mV = R
t
ON
REV
EDGE IS
ON
ON
comparator) emits a signal to
timer, senses the high input
× I
OUT
LOAD
OUT
IN IDLE MODE
HS AND LS
) using SW waveform
IN
.
t
ON