ADuM5000

Rev. 0 | Page 13 of 16

derating the output current. However, following the recommen-

dations in the PCB Layout section decreases the thermal resistance

to the PCB allowing increased thermal margin at high ambient

temperatures.

CURRENT LIMIT AND THERMAL OVERLOAD

PROTECTION

The ADuM5000 is protected against damage due to excessive

power dissipation by thermal overload protection circuits. Thermal

overload protection limits the junction temperature to a maximum

of 150°C (typical). Under extreme conditions (that is, high am-

bient temperature and power dissipation), when the junction

temperature starts to rise above 150°C, the PWM is turned off,

reducing the output current to zero. When the junction temper-

ature drops below 130°C (typical), the PWM turns on again,

restoring the output current to its nominal value.

occurs. At first, the ADuM5000 reaches its maximum current,

dissipates on the primary side of the converter (see Figure 7). If

self-heating of the junction becomes great enough to cause its

temperature to rise above 150°C, thermal shutdown activates,

turning off the PWM and reducing the output current to zero.

As the junction temperature cools and drops below 130°C, the

PWM turns on and power dissipates again on the primary side

of the converter, causing the junction temperature to rise to

150°C again. This thermal oscillation between 130°C and 150°C

causes the part to cycle on and off as long as the short remains

at the output.

Thermal limit protections are intended to protect the device

against accidental overload conditions. For reliable operation,

externally limit device power dissipation to prevent junction

temperatures from exceeding 130°C.

POWER CONSIDERATIONS

The ADuM5000 converter primary side is protected from pre-

mature operation by undervoltage lockout (UVLO) circuitry.

Below the minimum operating voltage, the power converter

holds its oscillator inactive.

When the primary side oscillator begins to operate, it transfers

starts below its UVLO limit making it inactive and unable to

generate a regulation control signal. The primary side power

oscillator is allowed to free run under this condition, supplying

the maximum amount of power to the secondary. As the sec-

ondary voltage rises to its regulation setpoint, a large inrush

is reached, the regulation control circuit produces the regulation

control signal that modulates the oscillator on the primary side.

current. The inrush current is less than the short-circuit current

shown in Figure 7. The duration of the inrush depends on the

INCREASING AVAILABLE POWER

The ADuM5000 device is designed with the capability of

running in combination with other compatible isoPower devices.

pin acting as a master. It can also receive a PWM signal from

a master or slave device. When the ADuM5000 is acting as a

slave, its power is regulated by the master device allowing mul-

tiple isoPower parts to be combined in parallel while sharing the

load equally. When the ADuM5000 is configured as a master/

standalone unit, it generates its own PWM feedback signal to

regulate itself and slave devices.

The ADuM5000 can act as a master or a slave device, the

ADuM5401 through the ADuM5404 devices can only serve as

master/standalone, and the ADuM520x can only be a

slave/standalone device. This means that the ADuM5000,

ADuM520x, and ADuM5401, ADuM5402, ADuM5403, and

ADuM5404 can only be used in certain master slave

combinations as listed in Table 14.

Table 14. Allowed Combinations of isoPower Parts

Master

Slave

ADuM5000

ADuM520x

ADuM5401 to

ADuM5404

ADuM5000

Yes

Yes

No

ADuM520x

No

No

No

ADuM5401 to

ADuM5404

Yes

Yes

No

The allowed combinations of master and slave configured parts

listed in Table 14 is sufficient for any combination of power and

channel count. Table 15 illustrates how isoPower devices can pro-

vide many combinations of data channel count and multiples of

the single unit power.