SLVA504A February 2012 – July 2021 DRV8243-Q1 , DRV8244-Q1 , DRV8245-Q1 , DRV8800 , DRV8801 , DRV8802 , DRV8803 , DRV8804 , DRV8805 , DRV8806 , DRV8811 , DRV8812 , DRV8813 , DRV8814 , DRV8818 , DRV8821 , DRV8823 , DRV8824 , DRV8825 , DRV8828 , DRV8829 , DRV8830 , DRV8832 , DRV8832-Q1 , DRV8833 , DRV8834 , DRV8835 , DRV8836 , DRV8837 , DRV8840 , DRV8841 , DRV8842 , DRV8843 , DRV8844 , DRV8870 , DRV8871 , DRV8872

There are **two** fundamental sources of power
dissipation on the power FETs in a driver IC.

- Power dissipation from
conduction loss of each FET due to its on-resistance is given by:Equation 1. P
_{RON }[W] = R_{ON}× I_{L}^{2}, where,- R
_{ON}= FET on-resistance [ohm] - I
_{L}= Load current [A]

_{ON}increases with temperature. So as the device heats up, the power dissipation also increases. This must be considered when calculating the total device power dissipation. Typically, the R_{ON}approximately doubles its value at 150 Cº compared to room temperature at 25 Cº. - R
- Power dissipation due to
switching losses associated with PWM based current regulation can be
**approximated**with the following expressions:- Power dissipation due to
output slewing during rising and falling edges is given
by:Equation 2. P
_{SW1}[W] = (0.5 x V_{M}x I_{L}x V_{M}/ SR_{rise}x f_{PWM}) + (0.5 x V_{M}x I_{L}x V_{M}/ SR_{fall}x f_{PWM}), where,- f
_{PWM}= PWM switching frequency [Hz] - V
_{M}= Supply voltage to the driver [V] - I
_{L}= Load current [A] - SR
_{rise}= Output voltage slew rate during rise [V/sec] - SR
_{fall}= Output voltage slew rate during fall [V/sec]

- f
- Power dissipation due to
the dead times between switching FETs is given by:Equation 3. P
_{SW2}[W] = (V_{D}x I_{L}x tDEAD_{rise}x f_{PWM}) + (V_{D}x I_{L}x tDEAD_{fall}x f_{PWM}), where,- f
_{PWM}= PWM switching frequency [Hz] - V
_{D}= FET body diode forward bias voltage [V] - I
_{L}= Load current [A] - tDEAD
_{rise}= dead time during rise [sec] - tDEAD
_{fall}= dead time during fall [sec]

- f
- Power dissipation due to
OUTPUT slewing during FET turn ON in the recirculation path is given
by:Equation 4. P
_{SW3}[W] = (0.5 x V_{D}x I_{L}x V_{D}/ SR_{rise}x f_{PWM}) + (0.5 x V_{D}x I_{L}x V_{D}/ SR_{fall}x f_{PWM}), where,- f
_{PWM}= PWM switching frequency [Hz] - V
_{D}= FET body diode forward bias voltage [V] - I
_{L}= Load current [A] - SR
_{rise}= Output voltage slew rate during rise [V/sec] - SR
_{fall}= Output voltage slew rate during fall [V/sec]

**not**considered as it is quite insignificant. - f
- Power dissipation also
occurs due to reverse recovery losses of switching FET. This occurs due
to change in current direction of the forward biased body diode of a
typically large power FETs (R
_{DSON}< ~100 mΩ). These losses typically limit the power dissipation savings at the higher slew rates (> 25 V/μsec). This dissipation is also typically**not**considered as it is quite insignificant.

- Power dissipation due to
output slewing during rising and falling edges is given
by:
- Power dissipation due to device
current consumption, given by,Equation 5. P
_{IVM}[W] = V_{M}x I_{VM}, where,- V
_{M}= Supply voltage to the driver [V] - I
_{VM}= Device operating supply current [A]

**not**considered as it is quite insignificant, given that I_{VM}is typically ~5 - 10 mA. - V
- Some driver devices have an
external LDO regulator output available that is used to provide some reference
current, or current to power external loads. Power dissipation due to this
external load current is given by,Equation 6. P
_{LDO}[W] = (V_{M}– V_{LDO})x I_{LDO}, where,- V
_{M}= Supply voltage to the driver [V] - V
_{LDO}= LDO output voltage [V] - I
_{LDO}= External load current [A]

- V

This dissipation is typically **not** considered as it is quite insignificant.

In summary, power dissipation total is given by:

Equation 7. P_{TOT} = P_{RON} +
P_{SW1} + P_{SW2} + P_{SW3} + P_{IVM} +
P_{LDO}

Typically, this can be approximated to just three sources, given by:

Equation 8. P_{TOT} = ~(P_{RON} +
P_{SW1} + P_{SW2})

The next set of sub-sections show the power dissipation in each power FET for conduction and switching losses based on the application configuration (H-bridge or Half bridge driver using high-side or low-side recirculation).