MCP1602 datasheet(12/26 Pages) MICROCHIP

12 / 26 page

MCP1602

DS22061A-page 12

4.0

DETAILED DESCRIPTION

4.1

Device Overview

The MCP1602 is a synchronous buck regulator with a

power-good signal. The device operates in a Pulse

Frequency Modulation (PFM) mode or a Pulse Width

Modulation

(PWM)

mode

maximize

system

efficiency over the entire operating current range.

Capable of operating from a 2.7V to 5.5V input voltage

source,

the

MCP1602

can

deliver

500 mA

continuous output current.

When using the MCP1602, the PCB area required for

a complete step-down converter is minimized since

both the main P-Channel MOSFET and the synchro-

nous N-Channel MOSFET are integrated. Also while in

PWM mode, the device switches at a constant

frequency of 2.0 MHz (typical) which allow for small fil-

tering components. Both fixed and adjustable output

voltage options are available. The fixed voltage options

(1.2V, 1.5V, 1.8V, 2.5V, 3.3V) do not require an external

voltage divider which further reduces the required

circuit board footprint. The adjustable output voltage

options allow for more flexibility in the design, but

require an external voltage divider.

Additionally the device features undervoltage lockout

(UVLO),

overtemperature

shutdown,

overcurrent

protection, and enable/disable control.

4.2

Synchronous Buck Regulator

The MCP1602 has two distinct modes of operation that

allow the device to maintain a high level of efficiency

throughout the entire operating current and voltage

range. The device automatically switches between

PWM mode and PFM mode depending upon the output

load requirements.

4.2.1

FIXED FREQUENCY, PWM MODE

During heavy load conditions, the MCP1602 operates

at a high, fixed switching frequency of 2.0 MHz (typi-

cal). This minimizes output ripple (10 - 15 mV typically)

and noise while maintaining high efficiency (88% typi-

cal with VIN = 3.6V, VOUT = 1.8V, IOUT = 300 mA).

During normal PWM operation, the beginning of a

switching cycle occurs when the internal P-Channel

MOSFET is turned on. The ramping inductor current is

sensed and tied to one input of the internal high-speed

comparator. The other input to the high-speed compar-

ator is the error amplifier output. This is the difference

between the internal 0.8V reference and the sensed

output voltage. When the sensed current becomes

equal to the amplified error signal, the high-speed

comparator

switches

states

and

the

P-Channel

MOSFET is turned off. The N-Channel MOSFET is

turned on until the internal oscillator sets an internal RS

latch initiating the beginning of another switching cycle.

PFM-to-PWM mode transition is initiated for any of the

following conditions:

• Continuous device switching

• Output voltage has dropped out of regulation

4.2.2

LIGHT LOAD, PFM MODE

During light load conditions, the MCP1602 operates in

a PFM mode. When the MCP1602 enters this mode, it

begins to skip pulses to minimize unnecessary

quiescent current draw by reducing the number of

switching cycles per second. The typical quiescent

current draw for this device is 45 µA.

PWM-to-PFM mode transition is initiated for any of the

following conditions:

• Discontinuous inductor current is sensed for a set

duration

• Inductor peak current falls below the transition

threshold limit

4.3

Power-Good (PG)

The open-drain power-good (PG) circuitry monitors the

regulated output voltage. A fixed delay time of

approximately 262 ms is generated once the output

voltage is above the power-good high threshold,

VTH_H, (typically 94% of VOUT). As the output voltage

falls below the power-good low threshold, VTH_L,

(typically 92% of VOUT) the PG signal transitions to a

low state indicating that the output is out of regulation.

The PG circuitry has a typical 165 µs delay when

detecting a falling output voltage. This helps to

increase the noise immunity of the power-good output,

avoiding false triggering of the PG signal during line

and load transients.

FIGURE 4-1:

Power-Good Timing.

VTH_H

VOUT

tRPU

tRPD

VOL

VOH

VTH_L

MCP1602 Datasheet(PDF) 12 Page - Microchip Technology

MCP1602 Datasheet(HTML) 12 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL