zxct1009t8 Zetex Semiconductors plc., zxct1009t8 Datasheet - Page 6

• Manufacturer Part Number: zxct1009t8
• Description: High-side Current Monitor
• Manufacturer: Zetex Semiconductors plc.

APPLICATIONS INFORMATION (Continued)
Charger input
Li-Ion Charger Circuit
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 Zetex
FZT789A high current Super- 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.
R e f e r e n c e :
Development System.
ZXCT1009
Support components omitted for clarity
bq2954
S E M I C O N D U C T O R S
5V
FMMT3904
MOD pin
SNS pin
FMMD914
D V S 2 9 5 4 S 1 H
FZT789A
FMMT451
ZHCS100
L i - I o n
V
I
out
in
ZXCT1009
Load
C h a r g e r
To battery +
6
R (min)
Transient Protection
An additional resistor, Rlim can be added in series
with Rout (figure 1.0), to limit the current from I
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.
Figure 1.0
ZXCT1009 with additional current limiting Resistor
Rlim.
Assuming the worst case condition of V
providing a low impedance to a transient, the
minimum value of R
The maximum value of R
V
characteristic on page 3) of the ZXCT1009 :-
R
lim
out
lim
(max)
(max) and the dropout voltage (see transfer
V
V
I
V
V
V
Voltage
pk
pk
max
in
dp
out
(min) = Minimum Supply Operating Voltage
V
= Peak output current = 40mA
=Dropout Voltage
R [V
pk
= Peak transient voltage to be withstood
(max)= Maximum Operating Output
= Maximum working Voltage = 20V
out
I
pk
V
in
max
(min) (
lim
V
is given by:-
out
(max)
V
lim
dp
is set by V
ISSUE 10 - JULY 2007
V (max)
out
)]
out
in
(min),
= 0V;
out
.