MIC2007YML datasheet(22/25 Pages) MICREL

22 / 25 page

Micrel, Inc.

MIC20XX Family

January 2009

M9999-012109-A

In this example we have used the nominal value of

VVUVLO_TH. By substituting in the min and max values of

VVUVLO_TH, R1 and R2 the VUVLO trip point window can

be established.

The VUVLO comparator uses no Hysteresis. This is

because the VUVLO blanking timer prevents any

chattering that might otherwise occur if VIN varies about

the trigger point. The timer is reset by upward crossings

of the trip point such that VIN must remain below the trip

point for the full 32ms period for load disengagement to

occur.

In selecting a VTRIP voltage the designer is cautioned to

not make this value less than 2.5V. A minimum of 2.5V

is required for the MIC20X6’s internal circuitry to operate

properly. VUVLO trip points below 2.5V will result in

erratic or unpredictable operation.

Kickstart

2003

2004

2005

2006

2007

2008

2009

2013

2014

2015

2016

2017

2018

2019

Only parts in white boxes have Kickstart.

(Not available in 5-pin SOT-23 packages).

Kickstart allows brief current surges to pass to the load

before the onset of normal current limiting, which

permits dynamic loads to draw bursts of energy without

sacrificing system safety.

Functionally, Kickstart is a forced override of the normal

current limiting function provided by the switch. The

Kickstart period is governed by an internal timer which

allows current to pass up to the secondary current limit

(ILIMIT_2nd) to the load for 128ms and then normal

(primary) current limiting goes into action.

During Kickstart a secondary current limiting circuit is

monitoring output current to prevent damage to the

switch, as a hard short combined with a robust power

supply can result in currents of many tens of amperes.

This secondary current limit is nominally set at 4A and

reacts immediately and independently of the Kickstart

period. Once the Kickstart timer has finished its count

the primary current limiting circuit takes over and holds

IOUT to its programmed limit for as long as the excessive

load persists.

Once the switch drops out of current limiting the

Kickstart timer initiates a lock-out period of 128ms such

that no further bursts of current above the primary

current limit, will be allowed until the lock-out period has

expired.

Kickstart may be over-ridden by the thermal protection

circuit and if sufficient internal heating occurs, Kickstart

will be terminated and IOUT

0A. Upon cooling, if the

load is still present IOUT

ILIMIT, not ILIMIT_2nd.

Figure 10. Kickstart

Automatic Load Discharge

2003

2004

2005

2006

2007

2008

2009

2013

2014

2015

2016

2017

2018

2019

Only parts in white boxes have automatic load discharge.

Automatic discharge is a valuable feature when it is

desirable to quickly remove charge from the VOUT pin.

This allows for a quicker power-down of the load. This

also prevents any charge from being presented to a

device being connected to the VOUT pin, for example,

USB, 1394, PCMCIA, and CableCARD™.

Automatic discharge is performed by a shunt MOSFET

from VOUT pin to GND. When the switch is disabled, a

break before make action is performed turning off the

main power MOSFET and then enabling the shunt

MOSFET. The total resistance of the MOSFET and

internal resistances is typically 126Ω.

Supply Filtering

A minimum 1μF bypass capacitor positioned close to

the VIN and GND pins of the switch is both good design

practice and required for proper operation of the switch.

This will control supply transients and ringing. Without a

bypass capacitor, large current surges or a short may

cause sufficient ringing on VIN (from supply lead

inductance) to cause erratic operation of the switch’s

control circuitry. For best performance good quality, low

ESR capacitors are recommended, preferably ceramic.

When bypassing with capacitors of 10μF and up, it is

good practice to place a smaller value capacitor in

parallel with the larger to handle the high frequency

components of any line transients. Values in the range

of 0.01μF to 0.1μF are recommended. Again, good

quality, low ESR capacitors should be chosen.

MIC2007YML Datasheet(PDF) 22 Page - Micrel Semiconductor

MIC2007YML Datasheet(HTML) 22 Page - Micrel Semiconductor

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

Datasheet Download

Link URL