LTC4367 datasheet(13/30 Pages) AD

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LTC7000A

Rev. 0

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OPERATION

Internal Charge Pump

The LTC7000A/LTC7000A-1 contains an internal charge

pump that enables the MOSFET gate drive to have 100%

duty cycle. The charge pump regulates the BST-TS volt-

age to 12V reducing external power losses associated

with external MOSFET on-resistance. The charge pump

uses the higher voltage of TS or VCC as the source for

the charge.

Start-Up and Shutdown

If the voltage on the RUN pin (LTC7000A only) is less than

0.7V, the LTC7000A enters a shutdown mode in which

all internal circuitry is disabled, reducing the DC supply

current to approximately 1µA. When the voltage on the

RUN pin exceeds 0.7V, the internal LDO connected to VIN

is enabled and regulates VCC to 10V. At VIN voltages less

than 10V, the LDO will operate in drop-out and VCC will fol-

low VIN. When the voltage on the RUN pin exceeds 1.21V,

the input circuitry is enabled allowing TGUP and TGDN to

be driven high with respect to TS. The LTC7000A-1 does

not include the RUN pin. The internal LDO connected to

VIN and the input circuitry for the LTC7000A-1 become

enabled when VIN is higher than 3.5V.

Protection Circuitry

When using the LTC7000A/LTC7000A-1, care must

be taken not to exceed any of the ratings specified in

the Absolute Maximum Ratings section. As an added

safeguard, the LTC7000A/LTC7000A-1 incorporates an

overtemperature shutdown feature. If the junction tem-

perature reaches approximately 180°C, the LTC7000A/

LTC7000A-1 will enter thermal shutdown mode and TGDN

will be pulled to TS. After the part has cooled below 160°C,

TGDN will be allowed to go back high. The overtem-

perature level is not production tested. The LTC7000A/

LTC7000A-1 is guaranteed to start a temperatures below

150°C.

The LTC7000A/LTC7000A-1 additionally implements

protection features which prohibit TGUP being pulled to

BST when VIN, VCC or (VBST–VTS) are not within proper

operating ranges. By using a resistive divider from VIN to

ground (LTC7000A only), the RUN and OVLO pins can

serve as a precise input supply overvoltage/undervolt-

age lockouts. TGDN is pulled to TS when either RUN falls

below 1.11V or OVLO rises above 1.21V, which can be

configured to limit switching to a specific range on input

supply voltages. Furthermore, if VIN falls below 3.5V, an

internal undervoltage detector pulls TGDN to TS.

VCC contains an undervoltage lockout feature that will

pull TGDN to TS and is configured by the VCCUV pin. If

VCCUV is open, TGDN is pulled to TS until VCC is greater

than 7.0V. By using a resistor from VCCUV to ground, the

rising undervoltage lockout on VCC can be adjusted from

3.5V to 10.5V.

An additional internal undervoltage lockout is included

that will pull TGDN to TS when the floating voltage from

BST to TS is less than 3.1V (typical).

(Refer to Block Diagram)

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