LTC4100 Linear Technology, LTC4100 Datasheet - Page 15

• Manufacturer Part Number: LTC4100
• Description: Smart Battery Charger Controller
• Manufacturer: Linear Technology

OPERATIO
ues, when there is sufficient DCIN voltage to charge the
battery.
10. Writing a zero value to ChargingVoltage() function.
11. Writing a zero value to ChargingCurrent() function.
The SafetySignal Decoder Block
This block measures the resistance of the SafetySignal
and features high noise immunity at critical trip points. The
low power standby mode supports only battery presence
SMB charger reporting requirements when AC is not
present. The SafetySignal decoder is shown in Figure 4.
The value of R
SafetySignal sensing is accomplished by a state machine
that reconfigures the switches of Figure 4 using THA_SELB
and THB_SELB, a selectable reference generator, and two
comparators. This circuit has two modes of operation
based upon whether AC is present.
When AC is present, the LTC4100 samples the value of the
SafetySignal and updates the ChargerStatus register ap-
proximately every 32ms. The state machine successively
samples the SafetySignal value starting with the RES_OR
threshold, RES_IDEAL RES_HOT threshold, and finally
the RES_HOT RES_UR threshold. Once the SafetySignal
RES_COLD threshold, then RES_C0LD
C
SS
R
1.13k
54.9k
R
R
SafetySignal
THA
THB
Figure 4. SafetySignal Decoder Block
THA
THB
THA
V
V
U
DD
DD
is 1.13k and R
THB_SELB
THA_SELB
SafetySignal
CONTROL
THB
LATCH
MUX
REF
is 54.9k.
HI_REF
LO_REF
RES_OR
RES_COLD
RES_H0T
RES_UR
RES_IDEAL
+
–
+
–
TH_LO
TH_HI
4100 F04
range is determined, the lower value thresholds are not
sampled. The SafetySignal decoder block uses the previ-
ously determined SafetySignal value to provide the appro-
priate adjustment in threshold to add hysteresis. The R
resistor value is used to measure the RES_OR RES_COLD
and RES_COLD RES_IDEAL thresholds by connecting
the THB pin to V
the THA pin. The R
the RES_IDEAL
thresholds by connecting the THA pin to V
ing the voltage resultant on the THB pin.
The SafetySignal decoder block uses a voltage divider
network between V
range thresholds. Since the THA and THB inputs are
sequentially connected to V
immunity during SafetySignal measurement.
When AC power is not available the SafetySignal block
supports the following low power operating features:
1. The SafetySignal is sampled every 250ms or less,
2. A full SafetySignal status is sampled every 30s or less,
The SafetySignal impedance is interpreted according to
Table 4.
instead of 32ms.
instead of every 32ms
Figure 5. Simplified V
V
LIM
R
VLIM
33k
DD
12.5k
12.5k
25k
25k
25k
and measuring the voltage resultant on
DD
THA
RES_HOT and RES_HOT
V
DD
and GND to determine SafetySignal
LIM
resistor value is used to measure
Circuit Concept (I
+
–
+
–
+
+
–
–
DD
, this provides V
AC_PRESENT
ENCODER
LTC4100
LIM
DD
4
is Similar)
and measur-
V
LIM
4100 F05
[3:0]
DD
sn4100 4100is
RES_UR
15
noise
THB