2s

10

ON

FB

SW

L1

VOUT

LM5019

+

VOUT

(low ripple)

LM5019

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SNVS788E – JANUARY 2012 – REVISED DECEMBER 2013

At high input voltages, the power dissipated in the high voltage regulator is significant and can limit the overall

voltage is driven externally by an alternate voltage source, between 8 V and 13 V, the internal regulator is

disabled. This reduces the power dissipation in the IC.

Figure 13. Low Ripple Output Configuration

Regulation Comparator

The feedback voltage at FB is compared to an internal 1.225 V reference. In normal operation, when the output

voltage is in regulation, an on-time period is initiated when the voltage at FB falls below 1.225 V. The high side

switch will stay on for the on-time, causing the FB voltage to rise above 1.225 V. After the on-time period, the

high side switch will stay off until the FB voltage again falls below 1.225 V. During start-up, the FB voltage will be

below 1.225 V at the end of each on-time, causing the high side switch to turn on immediately after the minimum

forced off-time of 144 ns. The high side switch can be turned off before the on-time is over, if the peak current in

the inductor reaches the current limit threshold.

Overvoltage Comparator

The feedback voltage at FB is compared to an internal 1.62 V reference. If the voltage at FB rises above 1.62 V

the on-time pulse is immediately terminated. This condition can occur if the input voltage and/or the output load

changes suddenly. The high side switch will not turn on again until the voltage at FB falls below 1.225 V.

On-Time Generator

LM5019 is:

(4)

Current Limit

The LM5019 contains an intelligent current limit off-timer. If the current in the buck switch exceeds 240mA the

present cycle is immediately terminated, and a non-resetable off-timer is initiated. The length of off-time is

maximum off-time is set to 16

μs. This condition occurs when the output is shorted, and during the initial part of

start-up. This amount of time ensures safe short circuit operation up to the maximum input voltage of 100 V.

In cases of overload where the FB voltage is above zero volts (not a short circuit) the current limit off-time is

reduced. Reducing the off-time during less severe overloads reduces the amount of foldback, recovery time, and

start-up time. The off-time is calculated from the following equation:

(5)

The current limit protection feature is peak limited. The maximum average output will be less than the peak.

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