adum5000 Analog Devices, Inc., adum5000 Datasheet - Page 12

• Manufacturer Part Number: adum5000
• Description: Isolated Dc/dc Converter
• Manufacturer: Analog Devices, Inc.

ADuM5000
APPLICATION INFORMATION
THEORY OF OPERATION
The DC/DC converter section of the ADuM5000 works on
principles that are common to most modern power supply
designs. It is implemented as a secondary side controller with
isolated PWM feedback. V
circuit that switches current into a chip-scale air core
transformer. Power is transferred to the secondary side where it
is rectified to a DC voltage. The power is then regulated to
either 3.3or 5V and supplied to the secondary side data section
and to the V
implemented by a digital feedback path. The output regulator
creates a pulse width modulated signal which is coupled to the
input side and switches the oscillator on and off regulating the
power. Feedback allows for significantly higher power,
efficiency, and synchronization of multiple supplies.
The ADuM5000 provides its Regulation Control output
(RCout) signal that can be connected to other isoPower devices.
This allows a single regulator to control multiple power
modules without contention. When auxiliary power modules
are present, the V
single supply. Since there is only one feedback control path, the
supplies will work together seamlessly. The ADuM5000 can
only be a source of Regulation Control, other devices
There is hysteresis into the input V
circuit. Once the DC/DC converter is active, the input voltage
must be decreased below the turn on threshold to disable the
converter. This feature ensures that the converter does not go
into oscillation due to noisy input power.
PC BOARD LAYOUT
The ADuM5000 digital isolator with a
DC/DC converter requires no external interface circuitry for
the logic interfaces. Power supply bypassing is required at the
input and output supply pins (Figure 11). The power supply
section of the ADuM5000 uses a very high oscillator frequency
to efficiently pass power through its chip scale transformers. In
addition, the normal operation of the data section of the
iCoupler introduces switching transients on the power supply
pins. Bypass capacitors are required for several operating
frequencies. Noise suppression requires a low inductance high
frequency capacitor, ripple suppression and proper regulation
require a large value capacitor. These are most conveniently
connected between Pins 1 and 2 for V
and 16 for V
combination of at least two capacitors is required. The
recommended capacitor values are 0. 1 μF, and 6.6μF. It is
strongly recommended that a very low inductance ceramic or
equivalent capacitor be used for the smaller value. The total lead
length between both ends of the capacitor and the input power
supply pin should not exceed 20 mm. Bypassing between Pins 1
ISO
ISO
. To suppress noise and reduce ripple, a parallel
pin for external use. Active feedback is
SIO
pins can be connected together to work as a
DD1
power is supplied to an oscillating
DD
input voltage detect
DD1
½
W isoPower integrated
and between Pins 15
Rev. PrA| Page 12 of 15
and 8 and between Pins 9 and 16 should also be considered
unless the both of the common ground pins are connected
together close to the package.
In applications involving high common-mode transients, care
should be taken to ensure that board coupling across the isolation
barrier is minimized. Furthermore, the board layout should be
designed such that any coupling that does occur equally affects
all pins on a given component side. Failure to ensure this could
cause voltage differentials between pins exceeding the device’s
Absolute Maximum Ratings, specified in Table 9 thereby
leading to latch-up and/or permanent damage.
The ADuM5000 is a power device that dissipates about 1W of
power when fully loaded and running at maximum speed.
Since it is not possible to apply a heat sink to an isolation
device, the device primarily depends on heat dissipation into
the PCB through the GND pins. If the device will be used at
high ambient temperatures, care should be taken to provide a
thermal path from the GND pins to the PCB ground plane.
The board layout in Figure 11 shows enlarged pads for pins 2, 8,
9, and 15. Multiple vias should be implemented from the pad to
the ground plane. This will significantly reduce the
temperatures inside of the chip. The dimensions of the
expanded pads are left to discretion of the designer and the
available board space.
THERMAL ANALYSIS
The ADuM5000 parts consist of four internal die, attached to a
split lead frame with two die attach paddles. For the purposes
of thermal analysis it is treated as a thermal unit with the
highest junction temperature reflected in the θ
The value of θ
mounted on a JEDEC standard 4 layer board with fine width
traces and still air. Under normal operating conditions the
ADuM5000 will operate at full load across the full temperature
range without derating the output current. However, following
the recommendations in the PC Board Layout section will
decrease the thermal resistance to the PCB allowing increased
thermal margin it high ambient temperatures.
CURRENT LIMIT AND THERMAL OVERLOAD
PROTECTION
Figure 11. Recommended Printed Circuit Board Layout
JA
is based on measurements taken with the part
Preliminary Technical Data
JA
from Table 4.