33486A Datasheet, PDF (11/30 Pages) Freescale Semiconductor, Inc – Dual High-Side Switch for H-Bridge Applications

damage (low-side MOSFETs ON). The overtemperature
protection circuitry incorporates hysteresis.
Overtemperature fault condition is reported on the status
output.
High-Side Overcurrent Protection
The 33486A incorporates a current shutdown threshold of
35 A typical. When this limit is reached due to an overload
condition or a short to ground, the faulty output is tri-stated.
To clear the fault, the input (INn) line needs to return low, then
on the next high transition the output will be enabled.
This information is reported on the status output.
Low-Side Block
The low-side block has control circuitry for two external
N-channel power MOSFETs. The low-side control circuitry is
PWM capable and protects the low-side MOSFETs in case of
overcurrent (short to V_BAT). This information is reported on
the status output.
The low-side gate controls are clamped at 14 V maximum
to protect the gates of the low-side MOSFETs. Figures 13,
page 15, and 14, page 15, depict the characteristics of the
low-side block when a current is sourced from the GLS pin or
sinked from the GLS pin, respectively.
During normal operation, the outputs OUT1 and OUT2 are
driven by the high side. The low-side gate driver will only turn
on when the voltage (same connection as OUT1 or OUT2) of
the internal high sides is less than 2.0 V, which prevents any
cross-conduction in the bridge.
Low-Side Overcurrent Protection
Unlike the high-side overcurrent circuitry, this overcurrent
protection does not measure the current; rather, it measures
the effect of current on the low-side power MOSFETs through
a condition: V_GS > 4.3 V and V_DS > 1.0 V. When this set of
conditions occurs for 3.0 µs typical (blanking time), both
outputs OUT1 and OUT2 are tri-stated. The full bridge is tri-
stated to prevent the motor running in case of short to V_BAT.
Once the fault is removed, the input INn of the OUTn that
experienced the fault must be reset in order to recover normal
mode operation.
The 33486A can be used without the external low-side
MOSFETs only if the overcurrent protection condition is not
reached. If the external low-side power MOSFETs are not
used, a 470 pF capacitor in parallel with a 100 kΩ resistor
can be connected at the GLSn pin to prevent the activation of
the low-side MOSFET overcurrent protection.
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
As V_GS and V_DS are measured in respect to the 33486A
ground terminal, it is essential that the low-side source is
connected to this same ground in order to prevent false
overcurrent detection due to ground shifts.
Thermal Management
The high-side block is assembled into a power surface
mount package. This package offers high thermal
performances and high current capabilities. It offers
10 terminals on each package side and one additional
connection, which is the package heat sink (called terminal
21). The heatsink acts as the device power VBAT connection.
The junction-to-case thermal resistance is 2.0°C/W
maximum. The junction-to-ambient thermal resistance is
dependant on the mounting technology and if an additional
heat sink is used. One of the most commonly used mounting
technique consists of using the printed circuit board and the
copper lines as heatsink.
Figure 7 is an example of printed circuit board layout. It
has a total of 10 cm² additional copper on two sides (2.5 cm²
on the top side and 7.5 cm² on the down side).
Bottom-side PCB
8.0 cm²
Top-side PCB
2.0 cm²
33486A
Thermal
via from
top to down-
side PCB
External PCB (4 x 4 cm)
Figure 7. Printed Board Layout Example (not to scale)
With the above layout, thermal resistance junction-to-
ambient of 25°C/W can be achieved. This value is split into:
•Junction to case (R_θJC) = 2.0°C/W
•Case to ambient (R_θCA) = 23°C/W
Lower value can be reached with the help of larger and
thicker copper metal, higher number of thermal via from top
to bottom side PCB, and the use of additional thermal via
from the circuit board to the module case.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33486A
11