NCP3121
PIN DESCRIPTION
Pin
1, 31, 32
2
−
7
8 – 10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Symbol
SW1
V
IN
SW2
GND2
SS2
COMP2
AGND
FB2
RT
TRACK 2
TRACK 1
SEQ2
EN2
SEQ1
EN1
PG2
PG1
AV
IN
FB1
AGND
COMP1
SS1
GND1
Exposed Pad
(GND)
Description
Switch node of Channel 1. Connect an inductor between SW1 and the regulator output.
Input power supply voltage pins. These pins should be connected together to the input signal supply
voltage pin.
Switch node of Channel 2. Connect an inductor between SW2 and the regulator output.
Power ground for Channel 2
Soft−start control input for Channel 2. An internal current source charges an external capacitor connected
to this pin to set the soft−start time.
Compensation pin of Channel 2. This is the output of the error amplifier and inverting input of the PWM
comparator.
Analog ground; connect to GND1 and GND2.
Feedback Pin. Used to set the output voltage of Channel 2 with a resistive divider from the output.
Resistor select for the oscillator frequency. Connect a resistor from the RT pin to AGND to set the fre-
quency of the master oscillator. Leave this pin floating, for 200 kHz operation.
Tracking input for Channel 2. This pin allows the user to control the rise time of the second output. This pin
must be tied high in the normal operation (except in the tracking mode).
Tracking input for Channel 1. This pin allows the user to control the rise time of the first output. This pin
must be tied high in the normal operation (except in the tracking mode).
Sequence pin for Channel 2. I/O used in power sequencing. Connect SEQ to EN for normal operation of a
standalone device.
Enable input for Channel 2.
Sequence pin for Channel 1. I/O used in power sequencing. Connect SEQ to EN for normal operation of a
standalone device.
Enable input for Channel 1.
Power good, open−drain output of Channel 2. Output logic is pulled to ground when the output is less than
90% of the desired output voltage. Tied to an external pull−up resistor. Leave this pin floating, if not used.
Power good, open−drain output of Channel 1. Output logic is pulled to ground when the output is less than
90% of the desired output voltage. Tied to an external pull−up resistor. Leave this pin floating, if not used.
Input signal supply voltage pin.
Feedback Pin. Used to set the output voltage of Channel 1 with a resistive divider from the output.
Analog ground. Connect to GND1 and GND2.
Compensation pin of Channel 1. This is the output of the error amplifier and inverting input of the PWM
comparator.
Soft−start/stop control input for Channel 1. An internal current source charges an external capacitor con-
nected to this pin to set the soft−start time.
Power ground for Channel 1.
The exposed pad at the bottom of the package is the electrical ground connection of the NCP3121. This
node must be tied to ground.
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