BQ24040_16 Datasheet, PDF (18/38 Pages) Texas Instruments – Single Cell Li-Ion and Li-Pol Battery Charger With Auto Start

bq24040, bq24041, bq24045
SLUS941F – SEPTEMBER 2009 – REVISED MARCH 2015
www.ti.com
8.4.6 PRE_TERM – Pre-Charge and Termination Programmable Threshold, bq24040/5
Pre-Term is used to program both the pre-charge current and the termination current threshold. The pre-charge
current level is a factor of two higher than the termination current level. The termination can be set between 5
and 50% of the programmed output current level set by ISET. If left floating the termination and pre-charge are
set internally at 10/20% respectively. The pre-charge-to-fast-charge, V_lowv threshold is set to 2.5V.
R_PRE-TERM = %Term × K_TERM = %Pre-CHG × K_PRE-CHG
(2)
Where:
• %Term is the percent of fast charge current where termination occurs;
• %Pre-CHG is the percent of fast charge current that is desired during precharge;
• K_TERM and K_PRE-CHG are gain factors found in the electrical specifications.
8.4.7 ISET2
Is a 3-state input and programs the Input Current Limit/Regulation Threshold. A low will program a regulated fast
charge current via the ISET resistor and is the maximum allowed input/output current for any ISET2 setting, Float
will program a 100mA Current limit and High will program a 500mA Current limit.
Below are two configurations for driving the 3-state ISET2 terminal:
V_CC
To
ISET2
Drive
Logic
V_CC
R1
To ISET2
OR
Q1
R2
Drive
Logic
R1 Divider
set to 0.9 V
Which is the
Float Voltage
Q2
Figure 13. 3-state ISET2 Terminal Circuits
8.4.8 TS (bq24040/5)
The TS function for the bq24040/5 is designed to follow the new JEITA temperature standard for Li-Ion and Li-
Pol batteries. There are now four thresholds, 60°C, 45°C, 10°C, and 0°C. Normal operation occurs between 10°C
and 45°C. If between 0°C and 10°C the charge current level is cut in half and if between 45°C and 60°C the
regulation voltage is reduced to 4.1Vmax, see Figure 11.
The TS feature is implemented using an internal 50μA current source to bias the thermistor (designed for use
with a 10k NTC β = 3370 (SEMITEC 103AT-2 or Mitsubishi TH05-3H103F) connected from the TS terminal to
V_SS. If this feature is not needed, a fixed 10kΩ can be placed between TS and V_SS to allow normal operation.
This may be done if the host is monitoring the thermistor and then the host would determine when to pull the TS
terminal low to disable charge.
The TS terminal has two additional features, when the TS terminal is pulled low or floated/driven high. A low
disables charge (similar to a high on the BAT_EN feature) and a high puts the charger in TTDM.
Above 60°C or below 0°C the charge is disabled. Once the thermistor reaches ≉–10°C the TS current folds back
to keep a cold thermistor (between –10°C and –50°C) from placing the IC in the TTDM mode. If the TS terminal
is pulled low into disable mode, the current is reduce to ≉30μA, see Figure 9. Since the I_TS curent is fixed along
with the temperature thresholds, it is not possible to use thermistor values other than the 10k NTC (at 25°C).
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