The JTMA7120 ,JTMA7120A is a fixed 300kHz frequency, voltage(2)

BOOT (Pin 1)

This pin provides ground referenced bias voltage to the high-side MOSFET driver. A bootstrap circuit with
a diode connected to 5~12V is used to create a voltage suitable to drive a logic-level N-channel
MOSFET.
UGATE (Pin 2)
Connect this pin to the high-side N-channel MOSFET’s gate. This pin provides gate drive for the high-side
MOSFET.
GND (Pin 3)
The GND terminal provides return path for the IC’s biascurrent and the low-side MOSFET driver’s pull-low
current. Connect the pin to the system ground via very low impedance layout on PCBs.
LGATE (Pin 4)
Connect this pin to the low-side N-channel MOSFET’s gate. This pin provides gate drive for the low-side
MOSFET.

VCC (Pin 5)
Connect this pin to a 5~12V supply voltage. This pin provides bias supply for the control circuitry and the
low-side MOSFET driver. The voltage at this pin is monitored for the Power-On-Reset (POR) purpose.

FB (Pin 6)
This pin is the inverting input of the internal Gm amplifier.Connect this pin to the output (VOUT) of the converter
via an external resistor divider for closed-loop operation.The output voltage set by the resistor divider is deter-
mined using the following formula :
where R1 is the resistor connected from VOUT to FB ,and R2 is the resistor connected from FB to GND. The
FB pin is also monitored for under and over-voltage events.

OCSET (Pin 7)
The OCSET is a dual-function input pin for over-current protection and shutdown control. Connect a
resistor (ROCSET) from this pin to the Drain of the low-side MOSFET. This resistor, an internal 40µA current
source (IOCSET), and the MOSFET’s on-resistance(RDSON) set the converter over-current trip level (IPEAK)
according to the following formula:
Pulling and holding this pin below 0.15V with an open drain device, with very low parasitic capacitor, shuts
down the IC with floating output and also resets the over-current counter. Releasing OCSET pin initiates a
new soft-start and the converter works again.

PHASE (Pin 8)

The pin provides return path for the high-side MOSFETdriver’s pull-low current. Connect this pin to the high-
side MOSFET’s source.

六.电路原理图

七,功能概述
Power-On-Reset (POR)
The JTMA7120 monitors the VCC voltage (V CC) for Power-On-Reset function, preventing wrong logic
operation during powering on. When the VCC voltage is ready, the JTMA7120 starts a start-up process and
then ramps the output voltage up to the target voltage.
Soft-Start
The JTMA7120 has a built-in digital soft-start to control the output voltage rise and limit the current surge at
the start-up. During the soft-start, an internal ramp con-nected to the one of the positive inputs of the Gm
amplifier rises up from 0V to 2V to replace the reference voltage (0.8V) until the ramp voltage reaches the refer-
ence voltage. The soft-start interval is about 3.2mstypical, independent of the converter’s input and out-
put voltages.

Over-Current Protection (OCP)
The over-current function protects the switching c o nverter against over-current or short-circuit
conditions. The controller senses the inductor current by detecting the drain-to-source voltage, product of
the inductor’s current and the on-resistance, of the low-side MOSFET during it’s on-state. This method
enhances the converter’s efficiency and reduces cost by eliminating a current sensing resistor.
A resistor (ROCSET), connected from the OCSET to the
Over-Current Protection (OCP) (Cont.)
low-side MOSFET’s drain, programs the over-current trip level. An internal 40µA (typical) current source
flowing through the ROCSET develops a voltage (VROCSET) across the ROCSET. When the VOCSET (VROCSET+ VDS of (责任编辑：oumao18)