Chapter 1 Device Overview MC9S12ZVM-Family
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor
79
The device supports the use of an external PNP to supplement the VDDX supply, for reducing on chip
power dissipation. In this configuration, most of the current flowing from VRBATP to VDDX, flows
through the external PNP. This configuration, using the BCTL pin, can be enabled by register bits
EXTXON and INTXON.
A supply for an external CANPHY is offered via external device pins BCTLC and VDDC, whereby
BCTLC provides the base current of an external PNP and VDDC is the CANPHY supply (output voltage
of the external PNP). This is only available in the CANPHY package option. This configuration can be
enabled by the register bit EXTCON.
The LINPHY pull-up resistor is internally connected to the HD voltage. This is chosen as opposed to
VSUP to ensure that the LINPHY is not disturbed by the internal VSUP boost circuit. The external
connections for the HD pin must ensure a reverse battery protection.
The ADC register bit VRH_SEL maps the ADC reference VRH to VDDA or to the device pad PAD8.
1.13.7.1
Voltage Domain Monitoring
The BATS module monitors the voltage on the VSUP pin, providing status and flag bits, an interrupt and
a connection to the ADC, for accurate measurement of the scaled VSUP level.
The POR circuit monitors the VDD and VDDA domains, ensuring a reset assertion until an adequate
voltage level is attained. The LVR circuit monitors the VDD, VDDF and VDDX domains, generating a
reset when the voltage in any of these domains drops below the specified assert level. The VDDX LVR
monitor is disabled when the VREG is in reduced power mode. A low voltage interrupt circuit monitors
the VDDA domain.
The GDU high side drain voltage, pin HD, is monitored within the GDU and mapped to an interrupt. A
connection to the ADC is provided for accurate measurement of a scaled HD level.
1.13.7.2
FET-Predriver (GDU) Supplies
A dedicated low drop regulator is used to generate the VLS_OUT voltage from VSUP. The VLS_OUT
voltage is used to supply the low side drivers and can be directly connected to the VLS inputs of each low
side driver. For FET-predriver operation at lower VSUP levels, a boost circuit can be enabled by the GBOE
register bit. The boost circuit requires Shottky diodes, a coil and capacitors, as shown in
. More
detailed information is included in the GDU module description.
1.13.7.2.1
Bootstrap Precharge
The FET-predriver high side driver must provide a sufficient gate-source voltage and sufficient charge for
the gate capacitance of the external FETs. A bootstrap circuit is used to provide sufficient charge, whereby
the capacitor C
BS
is first charged to VLS_OUT via an external diode, when the low side driver is active
. When the high side driver switches on, the charge on this capacitor, supplies the FET-
predriver via the VBSx pin. The C
BS
capacitor can only be charged if the low side driver is active, so after
a long period of inactivity of the low side driver, the C
BS
capacitor becomes discharged. In this case, the
low side driver must be switched on to charge C
BS
before commencing high side driving. The time it takes
to discharge the bootstrap capacitor C
BS
can be calculated from the size of the bootstrap capacitor C
BS
and
the leakage current on VBSx pin.