Detailed description

SPV1020

10/19

Doc ID 17588 Rev 3

5.4

Output voltage sensing and overvoltage protection (OVP)

Another monitoring is carried out on VOUT with the VOUT_SNS pin. This pin is used to

monitor the output voltage in order to regulate it’s maximum value (which cannot exceed 40

V), preventing damage due to overvoltage.

VOUT_SNS (the partitioned VOUT) is checked against a threshold of 1.0 V, generated by an

internal regulated voltage. When VOUT_SNS reaches 1 V, the output feedback loop begins

to regulate and limits the output voltage.

The stability of the loop can be externally regulated by connecting a resistor and a capacitor

(pole-zero compensation) between the PZ_OUT and SGND.

If VOUT_SNS exceeds 1.04 V a fault signal is generated and transmitted to the fault

controller. This stops the drivers and produces a fault signal to an external chip (DIAG = 0).

When VOUT_SNS decreases down to 1.04 V, the boost converter begins to regulate again

and the MPPT restarts from the minimum duty cycle of 5%.

Referring to the schematic shown in

Figure 1, R3 and R4 are the two resistors used to

partition the output voltage.

If VOUT_MAX is the maximum output voltage at the load, R3 and R4 must be selected

according to the following rule:

Also, in order to optimize the efficiency of the whole system, when selecting R3 and R4,

their power dissipation must be taken into account.

Assuming negligible the current flowing through pin VOUT_SNS, maximum power

dissipation in the series R3+R4 is:

As an empirical rule, R3 and R4 should be selected according to:

Note:

R3+R4 should be in the range between 20 µA and 100 µA.

5.5

Overcurrent protection (OCP)

To guarantee safe operation the low-side power switches have overcurrent protection. If LX

is accidentally shorted to VIN or VOUT or when the current flowing through the inductor

exceeds the current limit (~4.5 A), the related low-side power switch is immediately turned

off and the linked synchronous rectifier is turned on. The low-side power switch is turned on

again at the next PWM cycle.

R3

R4

--------

V

outmax

1.02

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

1

–

=

4

R

3

R

)

V

(

P

2

max

_

out

sns

_

vout

+

=

)

I

V

(

x

01

.

P

max

_

out

max

_

out

sns

_

vout

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