ISL6146_15 Datasheet, PDF (20/28 Pages) Intersil Corporation – Low Voltage OR-ing FET Controller

ISL6146
ISL6146 bias is pulled from the common drain node to ensure an
always adequate bias from either source when the other is
absent.
Q1
V_EXT
3.3V-24V
SWITCHED
OUTPUT
V_BATT
3.3V-20V
Q2 Q3
Use when V_BATT > V_EXT
Q3 disconnects V_BATT from
output when GATE is off.
VIN GATE VOUT
BIAS
FLT
R₁
ISL6146B ADJ
EN
GND
R₃
R₂
FIGURE 50. ISL6146B EXTERNAL SWITCHOVER SCHEMATIC
Figure 51 shows operational scope shots of the above circuit.
BATT SUPPLY
EXT SUPPLY
VOUT
GATE
All of the scope shots were taken with a 5A load and 100µF of
bulk load capacitance.
Figure 52 is a ISL6146A switchover circuit to use where the
preferred V_EXT source is always greater than the V_BATT. Because
this is so, there is no need for a 3rd FET for blocking as in
Figure 50. Additionally, the preferred V_EXT source when present
or at a programmed minimum threshold voltage via R₁ and R₂
divider, will turn on Q2/turn-off Q1 but when absent or not
minimally adequate, will do the opposite. In this circuit, with the
ISL6146A not connected to the battery, and thus no constant I_VIN
load on it, which allows for longer battery life.
Bias voltage is pulled from the common output to ensure an
always adequate IC bias from either source.
Q1
V_BATT
SWITCHED
OUTPUT
V_EXT
Q2
Use when V_BATT < V_EXT
VIN GATE VOUT
BIAS
FLT
R₁
ISL6146A ADJ
EN
GND
R₂
FIGURE 53. ISL6146A EXTERNAL SWITCHOVER SCHEMATIC
EXT SUPPLY
BATT SUPPLY
VOUT
FIGURE 51. EXTERNAL SUPPLY < BATT SUPPLY CONNECTED
BATT SUPPLY
EXT SUPPLY
GATE
VOUT
FIGURE 54. EXTERNAL SUPPLY > BATT SUPPLY CONNECTED
GATE
FIGURE 52. EXTERNAL SUPPLY < BATT SUPPLY DISCONNECTED
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FN7667.5
August 17, 2015