A5975AD datasheet(41/50 Pages) STMICROELECTRONICS

41 / 50 page

A5975AD

Application information

Doc ID 018761 Rev 1

41/50

The switch peak current must be lower than the minimum current limit of the overcurrent

protection (see Table 4 for details) while the average current must be lower than the rated

DC current of the device.

As a consequence, the maximum output current is:

Equation 46

where ISW MAX represents the rated current of the device.

Figure 29 shows a tested circuit to implement a boost current source for high current LED

driving (350 mA). To implement a boost conversion the LED string must be composed of a

minimum device number having a total voltage drop larger than maximum input voltage.

The input voltage can be either a DC or AC thanks to the input bridge rectifier. In the case of

a DC voltage source D1, D2, D3, D4, C1, and C2 can be removed from the circuit and 1µF

capacitor value can be used for C5.

8.10

Synchronization example

See Section 5.3 for details.

Figure 30.

Synchronization example

8.11

Compensation network with MLCC at the output

The A5975AD standard compensation network (please refer to Figure 1 and Section 7)

introduces a single zero and a low frequency pole in the system bandwidth, so a high ESR

output capacitor must be selected to compensate the 180-degree phase shift given by the

LC double pole.

The selection of the output capacitor must guarantee that the zero introduced by this

component is inside the designed system bandwidth and close to the frequency of the

double pole introduced by the LC filter. A general rule for the selection of this compound for

the system stability is provided in Equation 47.

OUT MAX

SW MAX

–

()

⋅

≅

AM09673v1

A5975AD

A5975AD Datasheet(PDF) 41 Page - STMicroelectronics