L6919C Просмотр технического описания (PDF) - STMicroelectronics
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L6919C Datasheet PDF : 32 Pages
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L6919C
The BOOTx and VCCDR pins are separated from IC's power supply (VCC pin) as well as signal ground (SGND
pin) and power ground (PGND pin) in order to maximize the switching noise immunity. The separated supply
for the different drivers gives high flexibility in mosfet choice, allowing the use of logic-level mosfet. Several com-
bination of supply can be chosen to optimize performance and efficiency of the application. Power conversion
is also flexible; 5V or 12V bus can be chosen freely.
The peak current is shown for both the upper and the lower driver of the two phases in figure 3. A 10nF capac-
itive load has been used. For the upper drivers, the source current is 1.9A while the sink current is 1.5A with
VBOOT -VPHASE = 12V; similarly, for the lower drivers, the source current is 2.4A while the sink current is 2A with
VCCDR = 12V.
CURRENT READING AND OVER CURRENT
The current flowing trough each phase is read using the voltage drop across the low side mosfets RdsON or
across a sense resistor (RSENSE) and internally converted into a current. The Tran conductance ratio is issued
by the external resistor Rg placed outside the chip between ISENx and PGNDSx pins toward the reading points.
The full differential current reading rejects noise and allows to place sensing element in different locations with-
out affecting the measurement's accuracy. The current reading circuitry reads the current during the time in
which the low-side mosfet is on (OFF Time). During this time, the reaction keeps the pin ISENx and PGNDSx
at the same voltage while during the time in which the reading circuitry is off, an internal clamp keeps these two
pins at the same voltage sinking from the ISENx pin the necessary current (Needed if low-side mosfet RdsON
sense is implemented to avoid absolute maximum rating overcome on ISENx pin).
The proprietary current reading circuit allows a very precise and high bandwidth reading for both positive and
negative current. This circuit reproduces the current flowing through the sensing element using a high speed
Track & Hold Tran conductance amplifier. In particular, it reads the current during the second half of the OFF
time reducing noise injection into the device due to the mosfet turn-on (See fig. 5). Track time must be at least
200ns to make proper reading of the delivered current
Figure 5. Current Reading Timing (Left) and Circuit (Right)
ILS1
ILS2
Total current
information
Track & Hold
LGATEX
ISENX
PGNDSX
Rg
IISENx
Rg
50µA
This circuit sources a constant 50µA current from the PGNDSx pin and keeps the pins ISENx and PGNDSx at
the same voltage. Referring to figure 4, the current that flows in the ISENx pin is then given by the following
equation:
IISENx
=
50µA + -R----S----E---N----S----E-----⋅---I-P----H----A----S---E--
Rg
=
50µ A + IINFOx
Where RSENSE is an external sense resistor or the rds,on of the low side mosfet and Rg is the transconductance
resistor used between ISENx and PGNDSx pins toward the reading points; IPHASE is the current carried by each
phase and, in particular, the current measured in the middle of the oscillator period
The current information reproduced internally is represented by the second term of the previous equation as
11/32
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