L6919E

10/33

Figure 3. Drivers peak current: High Side (left) and Low Side (right)

To allow the turning on of the low-side mosfet even in this case, a watchdog controller is enabled: if the source

of the high-side mosfet don't drop for more than 240ns, the low side mosfet is switched on so allowing the neg-

ative current of the inductor to recirculate. This mechanism allows the system to regulate even if the current is

negative.

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

VCCDR = 12V.

CURRENT READING AND OVER CURRENT

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

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. 4). Track time must be at least

200ns to make proper reading of the delivered current

This circuit sources a constant 50

µA 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:

CH3 = HGATE1; CH4 = HGATE2

CH3 = LGATE1; CH4 = LGATE2

I

ISENx

50

µA

R

SENSE

I

PHASE

⋅

R

g

----------------------------------------------

+

50

µAI

IN FO x

+

==