LTC7000ARMSEPBF datasheet(19/30 Pages) AD

19 / 30 page

LTC7000A

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

of 0.1µF for CB will be sufficient. However, the following

relationship for CB should be maintained:

CB >

External MOSFET QG

The internal charge pump that charges the BST-TS supply

outputs approximately 30µA to the BST pin. If the time

to charge the external bootstrapped capacitor, CB from

initial power-up with the internal charge pump is not suf-

ficient for the application, a low reverse leakage external

silicon diode, D1, with a reverse voltage rating greater

than VIN connected between VCC and BST should be used

as shown in Figure 10. An external silicon diode between

VCC and BST should be used if the following relationship

cannot be met:

BST diode required if

power-up to INP going high < CB •12V

30µA

≅ 40ms

Figure 10. External BST Diode

7000A F10

LTC7000A/

LTC7000A-1

BST

VCC

Another reason to use an external silicon diode between

VCC and BST is if the external MOSFET is switched at a

frequency so high that the BST-TS supply collapses. An

external silicon diode between VCC and BST should be

used if the following relationship cannot be met:

BST diode required

if switching frequency >

30µA

2 •MOSFET QG

≅ 500Hz

A Schottky diode should not be used between VCC and

BST, as the reverse leakage of the Schottky diode at hot

will be more current than the charge pump can overcome.

Some example silicon diodes with low leakage include:

• MMBD1501A - Fairchild Semiconductor

• CMPD3003 - Central Semiconductor

VCC Generation

The VCC pin provides the power for the MOSFET gate

drivers and internal circuitry. The LTC7000A/LTC7000A-1

features an internal P-channel low dropout regulator

(LDO) that can supply power at VCC from the VIN supply

pin or VCC can be driven from an external power supply.

If the internal P-channel LDO is used to power VCC, it

must have a minimum 1.0µF low ESR ceramic capacitor

to ensure stability and should not be connected to any

other circuitry other than optionally biasing some pins

on the LTC7000A/LTC7000A-1 (FAULT, INP or TIMER).

If the internal P-channel LDO is used to power VCC and an

external silicon diode is used between VCC and BST, care

must be taken not to switch an external MOSFET at too

high a frequency that can collapse the internal LDO. The

internal LDO can only supply 1mA with a 200mV drop-out.

In order to keep the internal LDO supply from collapsing

when an external silicon diode is used from VCC to BST,

the following relationship should be maintained:

Maximum switching

frequency with internal LDO<

1mA

2 •MOSFET QG

≅ 20kHz

For higher gate charge applications, an external silicon

diode between VCC and BST should be used and VCC

can be driven from a high efficiency external supply. VCC

should never be driven higher than VIN or permanent

damage to the LTC7000A/LTC7000A-1 could occur.

VCC Undervoltage Comparator

The LTC7000A/LTC7000A-1 contains an adjustable

undervoltage lockout (UVLO) on the VCC voltage that

pulls TGDN to TS and can be easily programmed using a

resistor (RVCCUV) between the VCCUV pin and ground. The

voltage generated on VCCUV by RVCCUV and the internal

10µA current source set the VCC UVLO. The rising VCC

UVLO is internally limited within the range of 3.5V and

10.5V. If VCCUV is open the rising VCC UVLO is set internally

to 7.0V. The typical value of resistor for a particular rising

VCC UVLO can be selected using Figure 11 or the following

equation:

RVCCUV =

Rising VCC UVLO

70µA

LTC7000ARMSEPBF bảng dữ liệu(PDF) 19 Page - Analog Devices

LTC7000ARMSEPBF bảng dữ liệu(HTML) 19 Page - Analog Devices

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 27 28 29 30

bảng dữ liệu tải về

Link URL