LTC4000-1 Datasheet, PDF (17/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

LTC4000-1
Applications Information
Input Ideal Diode PMOS Selection
The input external PMOS is selected based on the expected
maximum current, power dissipation and reverse volt-
age drop. The PMOS must be able to withstand a gate to
source voltage greater than V_IGATE(ON) (15V maximum) or
the maximum regulated voltage at the IID pin, whichever
is less. A few appropriate external PMOS for a number of
different requirements are shown at Table 1.
Table 1. PMOS
PART NUMBER
R_DS(ON) AT
V_GS = 10V
(Ω)
SiA923EDJ
0.054
Si9407BDY
0.120
Si4401BDY
0.014
Si4435DDY
0.024
SUD19P06-60
0.060
Si7135DP
0.004
MAX ID
(A)
4.5
4.7
10.5
11.4
18.3
60
MAX VDS
(V) MANUFACTURER
–20
Vishay
–60
Vishay
–40
Vishay
–30
Vishay
–60
Vishay
–30
Vishay
Note that in general the larger the capacitance seen on
the IGATE pin, the slower the response of the ideal diode
driver. The fast turn off and turn on current is limited to
–0.5mA and 0.7mA typical respectively (I_{IGATE(FASTOFF)} and
I_{IGATE(FASTON)}). If the driver can not react fast enough to a
sudden increase in load current, most of the extra current
is delivered through the body diode of the external PMOS.
This increases the power dissipation momentarily. It is
important to ensure that the PMOS is able to withstand
this momentary increase in power dissipation.
Input Current Monitoring
The input current through the sense resistor is available
for monitoring through the IIMON pin. The voltage on
the IIMON pin varies with the current through the sense
resistor as follows:
V_IIMON = 20 • I_RIS • R_IS = 20 • ₍V_IN – V_{CLN )}
If the input current is noisy, add a filter capacitor to the
CLN pin to reduce the AC content. For example, when us-
ing a buck DC/DC converter, the use of a C_CLN capacitor
is strongly recommended. Where the highest accuracy is
important, pick the value of C_CLN such that the AC content
is less than or equal to 50% of the average voltage across
the sense resistor.
The voltage on the IIMON pin can be filtered further by
putting a capacitor on the pin (C_IIMON).
Charge Current Limit Setting and Monitoring
The regulated full charge current is set according to the
following formula:
R_CS
=
20
V_CL
• I_CLIM
where V_CL is the voltage on the CL pin. The CL pin is
internally pulled up with an accurate current source of
50µA. Therefore, an equivalent formula to obtain the
charge current limit is:
R_CL
=
I_CLIM • R_CS
2.5µA
⇒ I_CLIM
=
R_CL
R_CS
• 2.5µA
The charge current through the sense resistor is available
for monitoring through the IBMON pin. The voltage on
the IBMON pin varies with the current through the sense
resistor as follows:
V_IBMON = 20 • I_RCS • R_CS = 20 • ₍V_CSP – V_{CSN )}
The regulation voltage level at the IBMON pin is clamped
at 1V with an accurate internal reference. At 1V on the
IBMON pin, the charge current limit is regulated to the
following value:
I_{CLIM(MAX )}( A)
=
0.050V
R_CS(Ω)
When this maximum charge current limit is desired, leave
the CL pin open or set it to a voltage >1.05V such that
amplifier A5 can regulate the IBMON pin voltage accurately
to the internal reference of 1V.
When the output current waveform of the DC/DC converter
or the system load current is noisy, it is recommended that
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