LTC4417_15 Datasheet, PDF (22/32 Pages) Linear Technology – Prioritized PowerPat Controller

LTC4417
Applications Information
12V SUPPLY
+
7.4V Li-Ion
BATTERY
(2 × 3.7V)
+
C_IN
2700µF
IRF7324
M1
M2
C_S
6.8nF
IRF7324
M3
M4
7.4V Li-Ion
BATTERY
(2 × 3.7V)
+
D_S
BAT54
R_S
2.21k
IRF7324
M5
M6
C_V3
0.1µF
C_V2
0.1µF
R9
768k
R8
53.6k
R7
113k
C_VS1
68nF
C_V1
0.1µF
R3
806k
R2
41.2k
R1
60.4k
VS1
V1
UV1
OV1
V2
R6
768k 140k
UV2
R5
53.6k
OV2
R4
113k
V3
140k
UV3
OV3
C_VS2
0.1µF
G1
C_VS3
0.1µF
VS2 G2
VS3 G3
V_OUT
+ _CL
100µF
V_OUT
R10 R11 R12
1M 1M 1M
LTC4417
VALID1
VALID2
VALID3
V1 INVALID
V2 INVALID
V3 INVALID
GND
EN
SHDN
HYS
CAS
4417 F13
R_HYS
255k
1%
Figure 13. Industrial Hand Held Computer
electrolytic capacitors, add 20% to C_L and for ceramic
NP0 C_S capacitors subtract 5%.
R_S
=
(6V
–
1.8V) • 120µF • 20mΩ
6.5nF • 700mV
(22)
R_S = 2.22kΩ
The standard value of 2.21kΩ is chosen for R_S and C_VS1
is chosen to be ten times C_S or 68nF. Although 1.8V is a
typical value for V_GS, there is sufficient margin – even if
V_GS = 0V, the resulting I_DM is lower than the 71A rating.
22
With R_S and C_S known, the desired load capacitance with
inrush current limiting is checked with Equation (14)
as shown in Equation (23). Because the required load
capacitance of 90µF is lower than the chosen load ca-
pacitor of 100µF, the initial choice of 100µF is suitable.
C_L
≥
2A
•
(3µs
+
12µs
+ 0.79 •
600mV
2.21kΩ
•
6.8nF)
(23)
C_L ≥ 90µF
4417f