BQ500101 Datasheet, PDF (11/20 Pages) Texas Instruments – NexFET Power Stage

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bq500101
SLPS585 – MARCH 2016
T_J = 125°C, unless stated otherwise
8.3 System Example
8.3.1 Power Loss Curves
MOSFET centric parameters such as ON-resistance and gate charges are primarily needed by engineers to
estimate the loss generated by the devices. In an effort to simplify the design process for engineers, Texas
Instruments has provided measured power loss performance curves. Figure 3 plots the power loss of the
bq500101 as a function of load current. This curve is measured by configuring and running the bq500101 as the
circuit shown in Figure 10. The measured power loss is the bq500101 device power loss which consists of both
input conversion loss and gate drive loss. Equation 1 is used to generate the power loss curve.
Power Loss = (V_IN x I_IN) + (V_DD x I_DD) – (V_{SW_AVG} x I_OUT)
(1)
The power loss curve in Figure 3 is measured at the maximum recommended junction temperature of
T_J = 125°C under isothermal test conditions.
Gate Drive
Current (IDD)
VDD
A
Gate Drive _V
Voltage (VDD)
bq500101
VDD
BST
DRVH
HSgate
LL
Vsw
Boot
VIN
Control
FET
VSW
CBoot
Boot_R
Input Current (IIN)
Vin
A
Cin
Input Voltage
V
(VIN)
LO
VO
A
PWM
PWM
GND
DRVL
LSgate
Sync
FET
PGND
Co
Output Current
(IOUT)
Averaging
V
Circuit
Averaged Switched
Node Voltage
(VSW_AVG)
Figure 10. Power Loss Test Circuit
8.3.2 Safe Operating Area (SOA) Curves
The SOA curves in the bq500101 datasheet give engineers guidance on the temperature boundaries within an
operating system by incorporating the thermal resistance and system power loss. Figure 5 and Figure 6 outline
the temperature and airflow conditions required for a given load current. The area under the curve dictates the
safe operating area. All the curves are based on measurements made on a PCB design with dimensions of 4.0"
(W) x 3.5" (L) x 0.062" (T) and 6 copper layers of 1-oz. copper thickness.
8.3.3 Normalized Curves
The normalized curves in the bq500101 data sheet give engineers guidance on the Power Loss and SOA
adjustments based on their application specific needs. These curves show how the power loss and SOA
boundaries will adjust for a given set of systems conditions. The primary Y-axis is the normalized change in
power loss and the secondary Y-axis is the change is system temperature required in order to comply with the
SOA curve. The change in power loss is a multiplier for the Power Loss curve and the change in temperature is
subtracted from the SOA curve.
Copyright © 2016, Texas Instruments Incorporated
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