ADP5063ACPZ-1-R7 datasheet(39/44 Pages) AD

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Data Sheet

ADP5063

Rev. 0 | Page 39 of 44

POWER DISSIPATION AND THERMAL CONSIDERATIONS

CHARGER POWER DISSIPATION

When the ADP5063 charger operates at high ambient tempera-

tures and at maximum current charging and loading conditions,

the junction temperature can reach the maximum allowable

operating limit of 125°C.

When the junction temperature exceeds 140°C, the ADP5063 turns

off, allowing the device to cool down. When the die temperature

falls below 110°C and the TSD 140°C fault bit in Register 0x0D

is cleared by an I2C write, the ADP5063 resumes normal operation.

This section provides guidelines to calculate the power dissipated

in the device to ensure that the ADP5063 operates below the

maximum allowable junction temperature.

To determine the available power dissipation in different

operating modes under various operating conditions, use

Equation 1 through Equation 4:

PD = PLDOFET + PISOFET

(1)

where:

PLDOFET is the power dissipated in the input LDO FET.

PISOFET is the power dissipated in the battery isolation FET.

Calculate the power dissipation in the LDO FET and the battery

isolation FET using Equation 2 and Equation 3.

PLDOFET = (VIN – VISO_Sx) × (ICHG + ILOAD)

(2)

PISOFET = (VISO_Sx – VISO_Bx) × ICHG

(3)

where:

VIN is the input voltage at the VINx pins.

VISO_Sx is the system voltage at the ISO_Sx pins.

ICHG is the battery charge current.

ILOAD is the system load current from the ISO_Sx pins.

VISO_Bx is the battery voltage at the ISO_Bx pins.

LDO Mode

The system regulation voltage is user-programmable from 4.3 V

to 5.0 V. In LDO mode (charging disabled, EN_CHG = low),

calculation of the total power dissipation is simplified, assuming

that all current is drawn from the VINx pins and the battery is

not shared with ISO_Sx.

PD = (VIN – VISO_Sx) × ILOAD

Charging Mode

In charging mode, the voltage at the ISO_Sx pins depends on

the battery level. When the battery voltage is lower than VISO_SFC

(typically 3.4 V), the voltage drop over the battery isolation FET

is higher and the power dissipation must be calculated using

Equation 3. When the battery voltage level reaches VISO_SFC, the

power dissipation can be calculated using Equation 4.

PISOFET = RDSON_ISO × ICHG

(4)

where:

RDSON_ISO is the on resistance of the battery isolation FET

(typically 110 mΩ during charging).

ICHG is the battery charge current.

The thermal control loop of the ADP5063 automatically limits

the charge current to maintain a die temperature below TLIM

(typically 115°C).

The most intuitive and practical way to calculate the power

dissipation in the ADP5063 device is to measure the power

dissipated at the input and all of the outputs. Perform the

measurements at the worst-case conditions (voltages, currents,

and temperature). The difference between input and output

power is the power that is dissipated in the device.

JUNCTION TEMPERATURE

In cases where the board temperature, TA, is known, the thermal

resistance parameter, θJA, can be used to estimate the junction

temperature rise. TJ is calculated from TA and PD using the formula

TJ = TA + (PD × θJA)

(5)

The typical θJA value for the 20-lead LFCSP is 35.6°C/W (see

Table 5). A very important factor to consider is that θJA is based

on a 4-layer, 4 in × 3 in, 2.5 oz. copper board as per JEDEC

standard, and real-world applications may use different sizes

and layers. It is important to maximize the copper to remove

the heat from the device. Copper exposed to air dissipates heat

better than copper used in the inner layers.

If the case temperature can be measured, the junction

temperature is calculated by

TJ = TC + (PD × θJC)

(6)

where TC is the case temperature and θJC is the junction-to-case

thermal resistance provided in Table 5.

The reliable operation of the charger can be achieved only if the

estimated die junction temperature of the ADP5063 (Equation 5)

is less than 125°C. Reliability and mean time between failures

(MTBF) are greatly affected by increasing the junction temperature.

Additional information about product reliability can be found

in the ADI Reliability Handbook located at the following URL:

http://www.analog.com/reliability_handbook.

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