LTC4010_15 Datasheet, PDF (12/24 Pages) Linear Technology – High Efficiency Standalone Nickel Battery Charger

LTC4010
Operation (Refer to Figure 1)
Status Outputs
The LTC4010 open-drain status outputs provide valuable
information about the IC’s operating state and can be
used for a variety of purposes in applications. Table 1
summarizes the state of the three status outputs and the
V_CDIV pin as a function of LTC4010 operation. The status
outputs can directly drive current-limited LEDs terminated
to the DC input. The V_CDIV column in Table 1 is strictly
informational. V_CDIV should only be used to terminate the
V_CELL resistor divider, as previously discussed.
Table 1. LTC4010 Status Pins
READY FAULT CHRG
Off
Off
Off
On
Off
Off
On
Off
On
On
On On or Off
Off
On
Off
V_CDIV
Off
On
On
On
On
CHARGER STATE
Off
Ready to Charge
(V_TEMP Held Low)
or Automatic Recharge
Precharge, Fast or Top Off
Charge (May be Paused)
Temperature Limits
Exceeded
Fault State (Latched)
PWM Current Source Controller
An integral part of the LTC4010 is the PWM current source
controller. The charger uses a synchronous step-down
architecture to produce high efficiency and limited thermal
dissipation. The nominal operating frequency of 550kHz
allows use of a smaller external inductor. The TGATE and
BGATE outputs have internally clamped voltage swings.
They source peak currents tailored to smaller surface-
mount power FETs likely to appear in applications providing
an average charge current of 3A or less. During the various
charging states, the LTC4010 uses the PWM controller to
regulate an average voltage between SENSE and BAT that
ranges from 10mV to 100mV.
A conceptual diagram of the LTC4010 PWM control loop
is shown in Figure 2.
The voltage across the external current programming
resistor R_SENSE is averaged by integrating error amplifier
EA. An internal programming current is also pulled from
input resistor R1. The I_PROG • R1 product establishes the
desired average voltage drop across R_SENSE, and hence,
V_CC
LTC4010
TGATE
14
R_SENSE
BGATE
12
SENSE
9
BAT
10
R1
R2
QS
R
PWM CLOCK
R3
CC
R4
–
I_TH
EA
+
I_PROG
4010 F02
Figure 2. LTC4010 PWM Control Loop
4010fb
12