CS5111

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7

Figure 8. Timing Diagram When WDI Fails to

RESET

WDI

AB

50% Duty

Cycle

A: Watchdog waiting for low–going transition on WDI

The RESET signal frequency is given by:

fRESET +

1

2(tWDI)

The Power On Reset (POR) and low voltage RESET use

the same circuitry and issue a reset when the linear output

the minimum specified value, RESET remains low for a

RESET

4.45 V

4.25 V

Figure 10. RESET Signal Is Issued Whenever

RESET

5.0 V

5.0 V

4.25 V

tPOR + 1.353

CDelayRBIAS

CURRENT MODE PWM SWITCHING CIRCUITRY

The current mode PWM switching voltage regulator

contains an error amplifier with selectable feedback inputs,

a current sense amplifier, an adjustable oscillator and a 1.4 A

output power switch with antisaturation control. The

switching regulator and external components, connected in

a boost configuration, are shown in Figure 11.

switching supply’s control circuitry is powered through

transistor.

The output transistor turns on when the oscillator starts to

develop a voltage drop across the internal sense resistor

the output of the current sense amplifier, which is compared

to the output of the error amplifier. The error amplifier

generates an output voltage which is proportional to the

difference between the scaled down output boost voltage

Once the current sense amplifier output exceeds the error

amplifier’s output voltage, the output transistor is turned off.

The energy stored in the inductor during the output

transistor on time is transferred to the load when the output

transistor is turned off. The output transistor is turned back

on at the next rising edge of the oscillator. On a cycle by

cycle basis, the current mode controller in a discontinuous

mode of operation charges the inductor to the appropriate

amount of energy, based on the energy demand of the load.

Figure 12 shows the typical current and voltage waveforms

for a boost supply operating in the discontinuous mode.

Notes:

1. Refer to Figure 5 to determine oscillator frequency.

2. The switching regulator can be disabled by providing

a logic high at the ENABLE input.

3. The boost output voltage can be controlled

dynamically by the feedback select input. If select is

selected.