MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER

MP2351 Rev. 1.5

www.MonolithicPower.com

3

1/6/2006

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© 2006 MPS. All Rights Reserved.

TM

Parameter

Symbol Condition

Min

Typ

Max

Units

Maximum Duty Cycle

70

%

Minimum On Time

70

ns

EN Shutdown Threshold Voltage

0.7

1.0

1.3

V

Enable Pull Up Current

1.15

1.50

µA

EN UVLO Threshold Rising

2.37

2.50

2.62

V

EN UVLO Threshold Hysteresis

210

mV

Supply Current (Shutdown)

20

36

µA

Supply Current (Quiescent)

1.1

1.3

mA

Thermal Shutdown

160

°C

Note:

4) Equivalent output current = 1.5A ≥ 50% Duty Cycle

2.0A ≤ 50% Duty Cycle

Assumes ripple current = 30% of load current.

Slope compensation changes current limit above 40% duty cycle.

PIN FUNCTIONS

Pin #

Name

Description

1

NC

No Connect.

2

BS

Bootstrap (C5). This capacitor is needed to drive the power switch’s gate above the supply

voltage. It is connected between SW and BS pins to form a floating supply across the power

switch driver. The voltage across C5 is about 5V and is supplied by the internal +5V supply

when the SW pin voltage is low.

3

NC

No Connect.

4

IN

Supply Voltage. The MP2351 operates from a +4.75V to +23V unregulated input. C1 is needed

to prevent large voltage spikes from appearing at the input.

5

SW

Switch. This connects the inductor to either IN through M1 or to GND through M2.

6

GND

Ground. This pin is the voltage reference for the regulated output voltage. For this reason care

must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to

prevent switching current spikes from inducing voltage noise into the part.

7

FB

Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets the

output voltage. To prevent current limit run away during a short circuit fault condition the

frequency foldback comparator lowers the oscillator frequency when the FB voltage is below

700mV.

8

COMP Compensation. This node is the output of the transconductance error amplifier and the input to the

current comparator. Frequency compensation is done at this node by connecting a series R-C to

ground. See the compensation section for exact details.

9

EN

Enable/UVLO. A voltage greater than 2.62V enables operation. Leave EN unconnected for

automatic startup. An Under Voltage Lockout (UVLO) function can be implemented by the

pin voltage needs to be less than 700mV.

10

SYNC Synchronization Input. This pin is used to synchronize the internal oscillator frequency to an

external source. There is an internal 11kΩ pull down resistor to GND, therefore leave SYNC

unconnected if unused.