Linear Technology Analog Devices LT8708 Datasheet page 58

LT8708
APPLICATIONS INFORMATION
48V to 14V Bidirectional Dual Battery System with FHCM & RHCM Details
V Charge Voltage = 48V (FBIN in RHCM)
BAT1
V Charge Voltage = 14.5V (FBOUT in FHCM)
BAT2
V = 21.3V (Falling) or 22.2V (Rising)
BAT1_DEAD
V = 9.25V (Falling) or 9.4V (Rising)
BAT2_DEAD
Table of Operation Modes and Power Flow Directions
CONDITIONS
V
BAT1
<V
BAT1_DEAD
–
<V
BAT1_UV
>V
BAT1_UV
>V
>V >V
BAT1_DEAD BAT2_DEAD
>48V
>V and <48V
BAT1_DEAD
*For use with LT8708-1(s)
Direction Change with
V = 47.5V and V
BAT1 BAT2
DIR
5V/DIV
I
L
20A/DIV
I
IN
10A/DIV
I
OUT
20A/DIV
30ms/DIV
Efficiency
EFFICIENCY
100
97
94
CHARGING V
91
88
85
10 20
58
V to Stop Discharging = 10.5V (VOUTLOMON Falling) or 12.3V (VOUTLOMON Rising)
BAT2_UV
V Charging Current Limit = 4A (IMON_INN)
BAT1
V Charging Current Limit = 15A (IMON_OP)
BAT2
Frequency = 120kHz
V DIR
BAT2
–
–
<V
BAT2_DEAD
> V
BAT2_DEAD
>14.5V
Hi
and <14.5V
BAT2_DEAD
and <V
BAT2_UV
>V
BAT2_UV
Lo
>V
BAT2_UV
Direction Change with
= 14V V
BAT1
DIR
5V/DIV
I
L
20A/DIV
I
OUT
10A/DIV
I
IN
20A/DIV
8708 TA04d
CHARGIN V
BAT2
BAT1
30 40 50 60
VBAT1 (V)
VBAT2 (V)
8708 TA04g
For more information
POWER FLOW
No Power Flow
Power Flows from V
BAT1
(V Charging)
BAT2
No Power Flow
Power Flows from V
BAT2
(V Charging)
BAT1
= 55V and V = 14V
BAT2
30ms/DIV
8708 TA04e
V
V
BAT1
BAT2
15
14
13
12
11
10
0
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RESULTS
CHIP OPERATES IN
Shutdown
No Switching
FHCM
to V
BAT2
RHCM
to V
BAT1
Direction Change with
V = 47.5V and V
BAT1
DIR
5V/DIV
I
L
20A/DIV
I
IN
5A/DIV
I
OUT
20A/DIV
30ms/DIV
Charging Lead Acid Battery V
V
BAT2
I
OUT
5 10 15
CHARGING TIME (HOURS)
8708 TA04h
RVSOFF*
–
Lo
Hi
= 36V
BAT2
8708 TA04f
BAT2
16
13
10
6
3
0
Rev 0