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Chapter 17 Gate Drive Unit (GDUV4)
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor
658
17.4.10 Boost Converter
The GDU module integrates the necessary hardware to build a boost converter with external components
in case of low voltage condition. The external components needed are two Schottky diodes, one coil, and
capacitors. See
. The boost converter clock which is driving the transistor T1 (see
) is derived from the bus clock. This clock can be divided down as described in
converter also includes a circuit to limit the current through coil. This current limit can be adjusted with
the bits GBCL[3:0] in the GDUBCL register. See GDU electrical parameters.
The output voltage of the boost converter on VSUP pin is divided down and compared with a reference
voltage V
ref
. As long as the divided voltage V
VSUP
is below V
ref
the boost converter clock is enabled
assuming that GBOE (GDU Boost Option Enable) is set.
Figure 17-24. Boost Converter Option with external Components
1
1. Diode D2 shown is optional if coil is connected behind reverse battery protection.
GBCL[3:0]
+
-
V
refcl
=
R1
R2
+
-
VSSB
BST
=
VSUP
V
ref
GBOCD[4:0]
GBOE
Clock Frequency
&
Duty Cycle
Bus Clock Input
Boost Converter Clock
Disable
Enable
C1
D1
V
BAT
D2
L
R
T1
Current Limitation
I
COIL
C2
Output Voltage Control
GBODC[1:0]