ZXCT1009 Просмотр технического описания (PDF) - Diodes Incorporated.

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ZXCT1009

HIGH-SIDE CURRENT MONITOR

Diodes Incorporated. 

ZXCT1009

HIGH-SIDE CURRENT MONITOR

Application Information (cont.)

Li-Ion Charger Circuit

Transient Protection

An additional resistor, RLIM can be added in series with ROUT

(as below), to limit the current from IOUT. Any circuit

connected to VOUT will be protected from input voltage

transients. This can be of particular use in automotive

applications where load dump and other common transients

need to be considered.

VIN

RSENSE

To load

The above figure shows the ZXCT1009 supporting the

Benchmarq bq2954 Charge Management IC. Most of the

support components for the bq2954 are omitted for clarity.

This design also uses the Diodes FZT789A high current

Super-ß PNP as the switching transistor in the DC-DC step

down converter and the FMMT451 as the drive NPN for the

FZT789A. The circuit can be configured to charge up to four

Li-Ion cells at a charge current of 1.25A. Charge can be

terminated on maximum voltage, selectable minimum

current, or maximum time out. Switching frequency of the

PWM loop is approximately 120kHz.

The ZXCT1009 is intended as a direct functional

replacement for the ZDS1009, which is featured in a

complete design from Unitrode/Texas Instruments on the

Li-Ion charger circuit shown above. Reference:

DVS2954S1H Li-Ion Charger Development System.

2

VSENSE+

3

VSENSE-

ZXCT1009

IOUT

1

RLIM

VOUT

ROUT

ZXCT1009 with additional current limiting Resistor RLIM.

Assuming the worst case condition of VOUT = 0V; providing a

low impedance to a transient, the minimum value of RLIM is

given by:-

RLIM(min) = (VPK – VMAX)/IPK

VPK = Peak transient voltage to be withstood

VMAX = Maximum working voltage = 20V

IPK = Peak output current = 40mA

The maximum value of RLIM is set by VIN(MIN), VOUT(MAX) and

the dropout voltage (see transfer characteristic on page 3) of

the ZXCT1009 :-

RLIM(MAX) = ROUT[VIN(MIN) – (VDP + VOUT(MAX))]/VOUT(MAX)

VIN(MIN) = Minimum Supply Operating Voltage

VDP = Dropout Voltage

VOUT(MAX) = Maximum Operating Output Voltage

ZXCT1009

Document number: DS33441 Rev. 12 - 2

5 of 8

www.diodes.com

April 2011

© Diodes Incorporated

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