33937_09 Datasheet, PDF (31/48 Pages) Freescale Semiconductor, Inc – Three Phase Field Effect Transistor Pre-driver

FUNCTIONAL INTERNAL BLOCK DESCRIPTION
the appropriate mask bit is set. The INT will be held in the
High state until the fault is removed, and the appropriate bit
in the Status Register 0 is cleared by the CLINT1 command.
This fault reporting mechanism is described in detail in the
Logic Commands and Registers section.
HOLD OFF CIRCUIT
The IC guarantees the output FETs are turned off in the
absence of V_DD or V_PWR by means of the Hold off circuit. A
small current source, generated from VSUP, typically
100 µA, is mirrored and pulls all the output gate drive pins low
when V_DD is less than about 3.0 V, RST is active (low), or
when VLS is lower than the VLS_Disable threshold. A
minimum of approximately 3.0 V is required on VSUP to
energize the Hold off circuit.
CHARGE PUMP
The Charge Pump circuit provides the basic switching
elements required to implement a charge pump, when
combined with external capacitors and diodes for enhanced
low voltage operation.
When the 33937 is connected per the typical application
using the charge pump (see Figure 22), the regulation path
for VLS includes the charge pump and a linear regulator. The
regulation set point for the linear regulator is nominally at
15.34 V. As long as VLS output voltage (VLS_OUT) is greater
than the VLS analog regulator threshold (VLS_ATH) minus
V_THREG, the charge pump is not active.
If VLS_OUT < VLS_ATH – V_THREG the charge pump turns ON
until VLS_OUT > VLS_ATH – V_THREG + V_HYST
V_HYST is approximately 200 mV. VLS_ATH will not interfere
with this cycle even when there is overlap in the thresholds,
due to the design of the regulator system.
The maximum current the charge pump can supply is
dependent on the pump capacitor value and quality, the
pump frequency (nominally 130 kHz), and the Rdson of the
pump FETs. The effective charge voltage for the pump
capacitor would be V_SYS – 2 * V_DIODE. The total charge
transfer would then be C_PUMP * (V_SYS – 2*V_DIODE).
Multiplying by the switch frequency gives the theoretical
current the pump can transfer: F_PUMP * C_PUMP * (V_SYS –
2*V_DIODE).
NOTE: There is also another smaller, fully integrated
charge pump (Trickle Charge Pump - see Figure 2), which is
used to maintain the High Side drivers’ gate V_GS in 100
percent duty cycle modes.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33937
31