LTC3441 datasheet(7/16 Pages) LINER

7 / 16 page

LTC3441

3441fa

OPERATIO

The LTC3441 provides high efficiency, low noise power for

applications such as portable instrumentation. The LTC

proprietary topology allows input voltages above, below or

equal to the output voltage by properly phasing the output

switches. The error amp output voltage on the VC pin de-

termines the output duty cycle of the switches. Since the

VC pin is a filtered signal, it provides rejection of frequen-

cies from well below the switching frequency. The low

RDS(ON), low gate charge synchronous switches provide

high frequency pulse width modulation control at high

efficiency. Schottky diodes across the synchronous switch

D and synchronous switch B are not required, but provide

a lower drop during the break-before-make time (typically

15ns). The addition of the Schottky diodes will improve peak

efficiency by typically 1% to 2%. High efficiency is achieved

at light loads when Burst Mode operation is entered and

when the IC’s quiescent current is a low 25

μA.

LOW NOISE FIXED FREQUENCY OPERATION

Oscillator

The frequency of operation is factory trimmed to 1MHz.

The oscillator can be synchronized with an external clock

applied to the MODE/SYNC pin. A clock frequency of twice

the desired switching frequency and with a pulse width of

at least 100ns is applied. The oscillator sync range is

1.15MHz to 1.7MHz (2.3MHz to 3.4MHz sync frequency).

Error Amp

The error amplifier is a voltage mode amplifier. The loop

compensation components are configured around the

amplifier to obtain stability of the converter. The SHDN/SS

pin will clamp the error amp output, VC, to provide a soft-

start function.

Supply Current Limit

The current limit amplifier will shut PMOS switch A off

once the current exceeds 4A typical. Before the switch

current limit, the average current limit amp (3.2A typical)

will source current into the FB pin to drop the output

voltage. The current amplifier delay to output is typically

50ns.

Reverse Current Limit

The reverse current limit amplifier monitors the inductor

current from the output through switch D. Once a negative

inductor current exceeds – 800mA typical, the IC will shut

off switch D.

Output Switch Control

Figure 1 shows a simplified diagram of how the four

internal switches are connected to the inductor, VIN, VOUT

and GND. Figure 2 shows the regions of operation for the

LTC3441 as a function of the internal control voltage, VCI.

The VCI voltage is a level shifted voltage from the output of

the error amp (VC pin) (see Figure 5). The output switches

are properly phased so the transfer between operation

modes is continuous, filtered and transparent to the user.

When VIN approaches VOUT the Buck/Boost region is

reached where the conduction time of the four switch

region is typically 150ns. Referring to Figures 1 and 2, the

various regions of operation will now be described.

SW1

SW2

PMOS A

NMOS B

PVIN

PMOS D

NMOS C

3441 F01

VOUT

75%

DMAX

BOOST

DMIN

BOOST

DMAX

BUCK

DUTY

CYCLE

V4 (

≈2.05V)

V3 (

≈1.65V)

BOOST REGION

BUCK REGION

BUCK/BOOST REGION

V2 (

≈1.55V)

V1 (

≈0.9V)

3441 F02

A ON, B OFF

PWM CD SWITCHES

D ON, C OFF

PWM AB SWITCHES

FOUR SWITCH PWM

INTERNAL

CONTROL

VOLTAGE, VCI

Figure 1. Simplified Diagram of Output Switches

Figure 2. Switch Control vs Internal Control Voltage, VCI

LTC3441 Datasheet(PDF) 7 Page - Linear Technology

LTC3441 Datasheet(HTML) 7 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL