ZL2106ALCF datasheet(14/29 Pages) RENESAS

14 / 29 page

ZL2106

FN6852 Rev 6.00

Page 14 of 29

February 20, 2013

The soft-start delay period begins when the EN pin is asserted

and ends when the delay time expires. The soft-start delay period

is set using the SS pin. Precise ramp delay timing mode reduces

the delay time variations and is available when the appropriate

bit in the MISC_CONFIG register had been set. Please refer to

Application Note AN2033 for details.

The soft-start ramp timer enables a precisely controlled ramp to

the nominal VOUT value that begins once the delay period has

expired. The ramp-up is guaranteed monotonic and its slope may

be precisely set using the SS pin. Using the pin-strap method, the

soft-start delay and ramp times can be set to one of three

standard values according to Table 5.

If the desired soft-start delay and ramp times are not one of the

values listed in Table 5, the times can be set to a custom value by

connecting a resistor from the SS pin to SGND using the

appropriate resistor value from Table 6. The value of this resistor

is measured upon start-up or Restore and will not change if the

resistor is varied after power has been applied to the ZL2106

(see Figure 15).

The soft-start delay and ramp times can also be set to custom

values via the I2C/SMBus interface. When the SS delay time is

set to 0ms, the device will begin its ramp-up after the internal

circuitry has initialized (~2ms). When the soft-start ramp period

is set to 0ms, the output will ramp up as quickly as the output

load capacitance and loop settings will allow. It is generally

recommended to set the soft-start ramp to a value greater than

500µs to prevent inadvertent fault conditions due to excessive

inrush current.

TABLE 5. SOFT-START DELAY AND RAMP SETTINGS

SS PIN SETTING

DELAY AND

RAMP TIME

(ms)

UVLO

LOW

7.5V

OPEN

HIGH

RSS

FIGURE 15. SS PIN RESISTOR CONNECTIONS

TABLE 6. DELAY AND RAMP CONFIGURATION

RSS

)

DELAY

TIME

(ms)

RAMP

TIME

(ms)

UVLO

(V)

4.5

12.1

13.3

14.7

16.2

17.8

5.5

19.6

21.5

23.7

26.1

28.7

31.6

34.8

38.3

42.2

46.4

51.1

56.2

7.5

61.9

68.1

82.5

90.9

100

110

121

133

147

162

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