ADP1823-EVAL Analog Devices Inc, ADP1823-EVAL Datasheet - Page 24

• Manufacturer Part Number: ADP1823-EVAL
• Description: BOARD EVAL FOR ADP1823
• Manufacturer: Analog Devices Inc

Specifications of ADP1823-EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.2V
• Current - Output: 15A
• Voltage - Input: 5.5 ~ 20V
• Regulator Topology: Buck
• Frequency - Switching: 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ADP1823
• Silicon Manufacturer: Analog Devices
• Application Sub Type: Step Down DC/DC Converter
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP1823
• Kit Contents: Board
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

ADP1823
Setting the Channel 2 Undervoltage Threshold for
Ratiometric Tracking
If FB2 is regulated to a voltage lower than 0.6 V by configuring
TRK2 for ratiometric tracking, the Channel 2 undervoltage
threshold can be set appropriately by splitting the top resistor
in the voltage divider, as shown in Figure 33. R
calculated for the compensation in Equation 52, and
The current in all the resistors is the same.
where:
V
V
tracking calculations.
V
Solving for R
UV2
FB2
OUT2
is the feedback voltage value set during the ratiometric
R
is 600 mV.
POK2
R
R
R
V
is the Channel 2 output voltage.
TOP
A
B
BOT
FB
Figure 33. Setting the Channel 2 Undervoltage Threshold
=
=
2
= R
R
R
=
BOT
BOT
A
A
V
+ R
and R
UV
TO ERROR
AMPLIFIER
(
(
V
V
2
B
UV
OUTA
R
B
−
B
V
B
2
V
,
B
V
FB
−
2
FB
FB
2
V
−
2
2
FB
V
=
2
UV
)
V
2
)
OUT
2
R
−
550mV
750mV
A
V
UV
2
UV2
FB2
BOT
CHANNEL 2
VOLTAGE
OUTPUT
is the same as
R
R
R
A
B
BOT
(53)
(54)
(55)
(56)
Rev. D | Page 24 of 32
THERMAL CONSIDERATIONS
The current required to drive the external MOSFETs comprises
the vast majority of the power dissipation of the ADP1823. The
on-chip LDO regulates down to 5 V, and this 5 V supplies the
drivers. The full gate drive current passes through the LDO and
is then dissipated in the gate drivers. The power dissipated on
the gate drivers on the ADP1823 is
where:
V
f
Q numbers are the total gate charge specifications from the
selected MOSFET data sheets.
The power dissipation heats the ADP1823. As the switching
frequency, the input voltage, and the MOSFET size increase, the
power dissipation on the ADP1823 increases. Care must be taken
not to exceed the maximum junction temperature. To calculate
the junction temperature from the ambient temperature and
power dissipation
The thermal resistance, θ
depending on board layout, and the maximum specified junction
temperature is 125°C, which means that at a maximum ambient
temperature of 85°C without airflow, the maximum dissipation
allowed is about 1 W.
A thermal shutdown protection circuit on the ADP1823 shuts
off the LDO and the controllers if the die temperature exceeds
approximately 145°C, but this is a gross fault protection only
and should not be relied upon for system reliability.
SW
IN
is the switching frequency.
is the voltage applied to IN.
P
T
D
J
= T
= V
A
IN
+ P
f
SW
D
(Q
θ
DH1
JA
+ Q
JA
DL1
, of the package is typically 40°C/W
+ Q
DH2
+ Q
DL2
)
(57)
(58)