The JTMA7237 is a fixed switching frequency (1.5MHz typical)(2)

六.电路原理图

七,功能概述
Main Control Loop
The JTMA7237 is a constant frequency and current-mode switching regulator. In normal operation, the internal N-
channel power MOSFET is turned on each cycle when the oscillator sets an internal RS latch, and then turned off
when an internal comparator (ICMP) resets the latch. The peak inductor current at which ICMP resets the RS latch
is controlled by the voltage on the COMP node which is the output of the error amplifier (EAMP). An external resis-
tive divider connected between VOUT and ground allows the EAMP to receive an output feedback voltage VFB at FB
pin. When the load current increases, it causes a slightly to decrease in VFB associated with the 1.23V reference,
which in turn, it causes the COMP voltage to increase until the average inductor current matches the new load
current.

VIN Under-Voltage Lockout (UVLO)
The Under-Voltage Lockout (UVLO) circuit compares the input voltage at VIN with the UVLO threshold to ensure
the input voltage is high enough for reliable operation.The 100mV (typ) hysteresis prevents supply transients
from causing a restart. Once the input voltage exceeds the UVLO rising threshold, startup begins. When the in-
put voltage falls below the UVLO falling threshold, the controller turns off the converter.
Soft-Start
The JTMA7237 has a built-in soft-start to control the output voltage rise during start-up. During soft-start, an internal
ramp voltage, connected to the one of the positive inputs of the error amplifier, raises up to replace the reference
voltage (1.23V typical) until the ramp voltage reaches the reference voltage.
Current-Limit Protection
The JTMA7237 monitors the inductor current, flows through the N-channel MOSFET, and limits the current peak at
current-limit level to prevent loads and the JTMA7237 from damaging during overload or short-circuit conditions.

Over-Temperature Protection (OTP)
The over-temperature circuit limits the junction tempera-ture of the JTMA7237. When the junction temperature ex-
ceeds 150 oC, a thermal sensor turns off the power MOSFET allowing the devices to cool. The thermal sen-
sor allows the converters to start a soft-start process and regulates the output voltage again after the junction tem-
perature cools by 40oC. The OTP is designed with a 40oC hysteresis to lower the average Junction Temperature
(TJ) during continuous thermal overload conditions in-creasing the lifetime of the device.

Enable/Shutdown
Driving EN to the ground places the JTMA7237 in shut-down mode. When in shutdown, the internal power
MOSFET turns off, all internal circuitry shuts down, and the quiescent supply current reduces to 1µA maximum.

八,相关产品

Part_No	Package & Pins	Topology	Architecture	Input Voltage (V)		Max Adj. Output Voltage(V)		Switch Current Limit (max)(A)	Fixed Output Voltage (V)	Switching Frequency (kHz)	Internal Power Switch	Sync. Rectifier
				min	max	min	max
JTMA7079	SOT-89	Boost	VM Hysteresis	0.9	5.5	2.5	5.5	0.5	1.8	-	No	Yes
									2.6
									2.8
									3
									3.3
									3.8
									4.5
									5
JTMA7078	MSOP-8	Boost	VM	2.5	5.5	2.5	-	-	-	200 ~ 1000	No	No
	TSSOP-8
	SOP-8
JTMA7075	TSSOP-8	Boost	VM	1	5.5	2.5	5	1	2.5	300	Yes	Yes
	SOP-8P								3.3
JTMA34063	SOP-8	Boost	CM	3	40	1.25	40	1.5	-	33 ~ 100	Yes	No
		Buck
JTMA7130/1/2	TQFN5x5-32	Boost	CM	2.5	6.5	2.5	18	3	No	1200	Yes	No
JTMA7237	TSOT-23-5	Boost	CM	2.5	6	2.5	20	2	-	1500	Yes	No
	TDFN2x2-6
JTMA7277	TQFN4x4-16	Boost	CM	1.8	5.5	2.7	5.5	5	-	1.2	Yes	Yes
	TDFN3x3-12
JTMA7137	SOT-23-5	Boost	CM	2.5	6	2.5	32	1	-	1000	Yes	No

(责任编辑：oumao18)