ISL6146AFUZ-TK Datasheet, PDF (20/28 Pages) Intersil Corporation – Low Voltage OR-ing FET Controller

ISL6146
prevents that when Q1 is on regardless of the V_BATT voltage.
The 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
FLT
BIAS
R1
ISL6146B ADJ
EN
GND
R3
R2
FIGURE 50. ISL6146B EXTERNAL SWITCHOVER SCHEMATIC
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
Figure 51 shows operational scope shots of the above circuit.
BATT SUPPLY
EXT SUPPLY
VOUT
VIN GATE VOUT
FLT
BIAS
R1
ISL6146A ADJ
EN
GND
R2
FIGURE 53. ISL6146A EXTERNAL SWITCHOVER SCHEMATIC
GATE
EXT SUPPLY
BATT SUPPLY
VOUT
FIGURE 51. EXTERNAL SUPPLY < BATT SUPPLY CONNECTED
BATT SUPPLY
EXT SUPPLY
VOUT
GATE
FIGURE 54. EXTERNAL SUPPLY > BATT SUPPLY CONNECTED
GATE
FIGURE 52. EXTERNAL SUPPLY < BATT SUPPLY DISCONNECTED
20
FN7667.4
April 26, 2013