1.18 x 10

-10

- 1.4 k:

1.18 x 10

-10

+ 67 ns

FB

SW

L1

C2

R1

R2

R3

BST

VCC

D2

C3

C4

D1

LM5010A

VOUT

SGND

ISEN

LM5010A

LM5010A-Q1

www.ti.com

SNVS376E – OCTOBER 2005 – REVISED FEBRUARY 2013

The turn-on sequence is shown in Figure 7. When VCC exceeds the under-voltage lock-out threshold (UVLO) of

5.25V (t1 in Figure 7), the buck switch is enabled, and the SS pin is released to allow the soft-start capacitor (C6)

soft-start voltage increases (t2 in Figure 7).

Figure 8. Self Biased Configuration

Regulation Comparator

The feedback voltage at the FB pin is compared to the voltage at the SS pin (2.5V, ±2%). In normal operation an

on-time period is initiated when the voltage at FB falls below 2.5V. The buck switch conducts for the on-time

remains off until the FB voltage falls below 2.5V. Input bias current at the FB pin is less than 5 nA over

temperature.

Over-Voltage Comparator

The feedback voltage at FB is compared to an internal 2.9V reference. If the voltage at FB rises above 2.9V the

on-time is immediately terminated. This condition can occur if the input voltage, or the output load, changes

suddenly. The buck switch remains off until the voltage at FB falls below 2.5V.

ON-Time Control

calculated as follows:

(5)

(6)

following:

(7)

regulation and the minimum off-time of the LM5010A (260 ns, ±15%). The fixed off-time limits the maximum duty

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