LTC4012CUF-3#PBF Linear Technology, LTC4012CUF-3#PBF Datasheet - Page 17

• Manufacturer Part Number: LTC4012CUF-3#PBF
• Description: IC BATT CHRGR MC HI-EFF 20-QFN
• Manufacturer: Linear Technology

Specifications of LTC4012CUF-3#PBF

• Function: Charge Management
• Battery Type: Multi-Chemistry
• Voltage - Supply: 6 V ~ 28 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The value of R
current which can be programmed (Q1 continuously on).
PWM of the Q1 gate voltage changes the value of R
to produce lower currents. The frequency of this modula-
tion should be higher than a few kHz, and C
increased to reduce the ripple caused by switching Q1. In
addition, it may be necessary to increase loop compensa-
tion capacitance connected to ITH to maintain stability or
prevent large current overshoot during start-up. Selecting
a higher Q1 PWM frequency (≈10kHz) will reduce the need
to change C
current will be proportional to the duty cycle of the PWM
input on the gate of Q1.
Programming LTC4012-3 Output Voltage
Figure 5 shows the external circuit for programming the
charger output voltage. The voltage is then governed by
the following equation:
applicaTions inForMaTion
V
BAT
=
1 2085
Figure 5. Programming Output Voltage
*OPTIONAL TRIM RESISTOR
PROG
.
PROG
TYPICAL
85
LTC4012-3
or other compensation values. Charge
(EXPOSED PAD)
V R
controls the maximum value of charge
R
•
2
(
1
FBDIV
+
GND
BAT
V
FB
R
2
11
10
21
)
9
,
R
2
R2A
=
R1
R A R B
R2B*
4012-3 F05
2
C
+
Z
+
PROG
2
must be
PROG
See Table 2 for approximate resistor values for R2.
Selecting R2 to be less than 50k and the sum of R1 and
R2 at least 200k or above, achieves the lowest possible
error at the V
such as R1 and R2 tolerance, FBDIV R
pedance are not included in the specifications given in the
Electrical Characteristics. This leads to the possibility that
very accurate (0.1%) external resistors might be required.
Actually, the temperature rise of the LTC4012-3 will rarely
exceed 50°C at the end of charge, because charge current
will have tapered to a low level. This means that 0.25%
resistors will normally provide the required level of overall
accuracy. Table 2 gives recommended values for R1 and
R2 for popular lithium-ion battery voltages. For values
of R1 above 200k, addition of capacitor C
transient response and loop stability. A value of 10pF is
normally adequate.
Table 2. Programming Output Voltage
*To Obtain Desired Accuracy Requires Series Resistors For R2.
R
1
V
12.3
12.6
16.4
16.8
20.5
24.6
25.2
(V)
4.1
4.2
8.2
8.4
=
21
BAT
R
2



1 2085
.
FB
V
BAT
sense input. Note that sources of error
R1 (0.25%)
(kΩ)
V
165
167
162
169
301
294
284
271
316
298
298
397
– ,
1



R
2
=
R2A (0.25%)
R A R B
(kΩ)
67.3
28.4
32.8
31.2
22.6
19.8
18.2
15.4
2
69
28
21
20
LTC4012-3
+
ON
2
or V
Z
may improve
FB
R2B (1%)*
input im-
200
(Ω)
–
–
–
–
–
–
–
–
–
–
–

40123fb