MP2162A – 2A, 6V, 1.5MHz SYNCHRONOUS STEP-DOWN CONVERTER

MP2162A Rev. 1.03

www.MonolihicPower.com

11

6/30/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2016 MPS. All Rights Reserved.

OPERATION

The MP2162A uses constant-on-time control with

an input voltage feed-forward to stabilize the

switching frequency over a full input voltage

range. During light loads, the MP2162A employs

proprietary control of the low-side switches and

inductor currents to eliminate ringing on the

switching node and improve efficiency.

Constant-On-Time Control

Compared to the fixed frequency PWM control,

the constant-on-time control offers the advantage

of a simpler control loop and a faster transient

response. By using input voltage feed-forward,

the MP2162A maintains a near constant

switching frequency across the input and output

voltage ranges. The on time of the switching

pulse can be estimated with Equation (1):

OUT

ON

IN

V

T0.667 s

V





(1)

To prevent inductor current runaway during the

load transient, the MP2162A has a fixed

minimum off time of 60ns. However, this

minimum off time limit does not affect the

operation of the MP2162A in its steady state in

any way.

Light-Load Operation

In light-load conditions, the MP2162A uses a

proprietary control scheme to save power and

improve efficiency. The MP2162A uses a zero

current cross circuit to detect if the inductor

current is starting to reverse. The low-side switch

turns off when the inductor current starts to

reverse and then begins working in discontinuous

conduction mode (DCM).

The delay for the internal circuit propagation time

is typically 50ns. This means that the inductor

current continues falling after the ZCD is

triggered in this delay. If the inductor current

inductor current may be negative, and the

MP2162A will not be able to enter DCM

operation. If DCM mode is required, the off time

of the low-side MOSFET in CCM should be

longer than 100ns (2x the propagation delay).

time in CCM is 55ns. It is difficult to enter DCM at

a light load. Using a smaller inductor can help the

MP2162A enter DCM more easily.

Enable (EN)

When the input voltage is greater than the under-

voltage lockout (UVLO) threshold (typically 2.3V),

the MP2162A is enabled by pulling EN higher

than 1.2V. Leaving EN floating or grounded

disables the MP2162A. There is an internal 1MΩ

resistor from EN to ground.

Soft Start

The MP2162A has a built-in soft start that ramps

up the output voltage at a controlled slew rate to

avoid overshooting at start-up. The soft-start time

is typically about 1.15ms.

Power Good Indicator

The MP2162A uses an open drain with a 550kΩ

pull-up resistor as a power good indicator (PG).

When the FB voltage is within +/-10% of the

regulation voltage (i.e. 0.6V), PG is pulled up to

VIN by an internal resistor. If the FB voltage is

out of the +/-10% window, PG is pulled down to

ground by an internal MOSFET. The MOSFET

Current Limit

The MP2162A has a typical 3.2A current limit for

the high-side switch. When the high-side switch

hits its current limit, the MP2162A enters hiccup

mode until the current drops. This prevents the

inductor

current

from

rising

and

possibly

damaging the components.

Short Circuit and Recovery

The MP2162A enters short-circuit protection

mode when the current limit is hit; it tries to

recover from the short circuit by entering hiccup

mode. In short-circuit protection, the MP2162A

disables the output power stage, discharges a

soft-start capacitor, and automatically tries to soft

start. If the short-circuit condition still holds after

the soft start ends, the MP2162A repeats this

operation until the short circuit disappears, and

the output rises back to regulation levels.