Owner manual

MAX8728
Low-Cost, Multiple-Output
Power Supply for LCD Monitors/TVs
______________________________________________________________________________________ 13
Pin Description (continued)
PIN
NAME
FUNCTION
21 DRN
High-Voltage Switch Control Input. DRN is the drain of the internal high-voltage p-channel MOSFET connected
to GON. See the High-Voltage Switch Control section for details.
22 THR
GON Falling Regulation Adjustment Input. Connect THR to the center of a resistive voltage-divider between a
reference supply and GND to adjust the GON falling regulation set point. CTL and MODE allow GON to
disconnect from SRC and be discharged through DRN; discharge stops when GON reaches 10 x V
THR
. See
the High-Voltage Switch Control section for details.
23 FB2
Step-Up Regulator Feedback Input. Connect FB2 to the center of a resistive voltage-divider between the step-
up regulator output and GND to set the step-up regulator output voltage. Place the resistive voltage-divider
close to FB2.
24 FBN
Negative Charge-Pump Regulator Feedback Input. Connect FBN to the center of a resistive voltage-divider
between the negative output and REF to set the negative charge-pump regulator output voltage. Place the
resistive voltage-divider close to FBN.
25
GND2
Step-Down Regulator Power Ground
26 LX2
Step-Up Regulator Switching Node. Connect the inductor and the Schottky diode to LX2 and minimize the
trace area for low EMI.
27
GATE
Input MOSFET Gate-Driver Output. GATE controls an external p-channel MOSFET between the input voltage
and the step-up regulator’s inductor. The switch is off when the step-up regulator is turned off, so that the
regulator’s output discharges to ground. During startup, the step-up regulator’s soft-start begins when V
GATE
falls below the GATE done threshold.
28 EN
Enable Input. Pulling EN high or leaving EN unconnected enables the step-up regulator and the negative
charge pump. Connecting EN to GND disables the above blocks and puts the step-down regulator in skip
mode. EN sources 5µA to allow a capacitor-controlled startup delay.
29
MODE
High-Voltage Switch-Control Block Mode Selection Input and Timing-Adjustment Input. See the High-Voltage
Switch Control section for details.
30 DEL
Positive Charge-Pump Regulator and High-Voltage Switch-Control Delay Input. Connect a capacitor between
DEL and GND to set the delay time. A 5µA current source charges C
DEL
. DEL is internally pulled to GND
through a 20Ω internal resistor in shutdown.
31
COMP
Step-Up Regulator Error Amplifier Compensation Pin. See the Loop Compensation section for details.
32 FB1
Step-Down Regulator Feedback Input. Connect FB1 to the center of a resistive voltage-divider between the
step-down regulator output and GND to set the step-down regulator output voltage.
—EP
Exposed Pad. Connect the exposed backside pad to GND and provide adequate thermal path to cool the IC.
See the PC Board Layout and Grounding section.