MP1400 – NEGATIVE DCDC POWER CONVERTER

MP1400 Rev.1.1

www.MonolithicPower.com

10

5/27/2015

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OPERATION

The MP1400 is a monolithic negative DCDC

power converter with built-in internal power

MOSFET. The DC-DC IC has a tiny surface

mount 0.8mm x 1.6mm 8-ball CSP package and

is optimized for low voltage powered applications

where small size are critical. It achieves up to

600mA peak output current from a 2.7V to 7V

input voltage. The output voltage can be

regulated from -0.9V to -6V. The built-in 300m Ω

PFET can provide high efficiency and eliminates

an external boost capacitor. The duty cycle D of

negative converter is defined as:

OUT

ON

OSC

IN

OUT

V

D T

f

100%

100%

VV













Current Mode PWM Control

Slope compensated current mode PWM control

provides stable switching and cycle-by-cycle

current limit for superior load and line response

and protection of the internal main switch and

rectifier diode. The MP1400 switches at a

constant frequency (1.5MHz) and regulates the

output voltage. During each cycle the PWM

comparator modulates the power transferred to

the load by changing the inductor peak current

based on the feedback error voltage. During

normal operation, the main switch is turned on for

a certain time to ramp the inductor current at

each rising edge of the internal oscillator, and

switched off when the peak inductor current is

above the error voltage. When the main switch is

off, the rectifier diode will supply the current on

immediately.

Light Load Operation

In light load condition, the load requires less

energy so the charged current to inductor is

smaller than heavy load. The rectifier diode

discharges the inductor current. If the inductor

current hit the zero, MP1400 will works in

discontinuous conduction mode (DCM) operation.

Startup and Shutdown

When input voltage is greater than the under-

voltage lockout threshold (UVLO), typically 2.5V,

MP1400 can be enabled by pulling EN pin to

higher than 1.2V. Leaving EN pin float or pull

down to ground will disable MP1400. There is an

internal 1Meg Ohm resistor from EN pin to

ground.

When the device is disabled, the part goes into

output discharge mode automatically and its

internal discharge MOSFET provides a resistive

discharge path for the output capacitor.

For the load capability is depending on the input

voltage to output voltage ratio. It’s strongly

recommending to power on VIN quick enough

when load is high.

Soft Start

MP1400 has built-in soft start that ramps up the

output voltage in a controlled slew rate. During

power up, internal soft-start circuitry will limit the

amount of in-rush current that drawn from the

power supply. The soft start time is about 0.5ms

typical.

Current Limit

MP1400 has a typical 1.6A current limit for the

main PFET switch. When the PFET hits current

limit, MP1400 will touch the hiccup threshold until

the current lower down. This will prevent inductor

current from continuing to build up which will

result in damage of the components.

Output Over Voltage Protection

MP1400 has a built-in output voltage protection

block. If the output voltage is lower than -6.5V,

the PFET will be turned off immediately. After the

output voltage status is removed, the part will re-

switches automatically.