七,功能概述
Main Control Loop
The JTMA7179 has dual independent constant frequency,current-mode PWM step-down converters. During nor-
mal operation, the internal P-channel power MOSFET is turned on each cycle when the oscillator sets an internal
RS latch and is 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, which is the output of the error amplifier
(EAMP). An external resistive 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 decrease in VFB associated
with the 0.6V reference, which in turn causes the COMP voltage to increase until the average inductor current
matches the new load current.
 
Soft-Start
Each channel in the JTMA7179 has a built-in soft-start to control the output voltage rise during start-up. During soft-
start, an internal ramp, connected to the one of the posi- tive inputs of the error amplifier, raise up to replace the
reference voltage (0.6V typical) until the ramp voltage reaches the reference voltage.
 
Short Circuit Protection
For each channel, when the output is shortened to the ground, the frequency of the oscillator will be reduced to
210kHz. This lower frequency allows the inductor current to safely discharge, thereby preventing current runaway.
The oscillator’s frequency will gradually increase to its designed rate when the feedback voltage on the FB again
approaches 0.6V.
 
Over-Temperature Protection (OTP)
 
For each channel, the over-temperature circuit limits the junction temperature of the JTMA7179. When the junction
temperature exceeds 150oC, a thermal sensor turns off the power MOSFETs, allowing the channels to cool down.
The thermal sensor allows the converter to start a soft-start process and to regulate the output voltage again
after the junction temperature cools by 40ïC. The OTP is designed with a 40ïC hysteresis to lower the average
Junction Temperature (TJ) during continuous thermal overload conditions, increasing the lifetime of the device.
 
Enable/Shutdown
For each channel, driving EN to the ground places the channel in shutdown mode. When in shutdown, the inter-
nal power MOSFETs are turned off, all internal circuitry shuts down, and the quiescent supply current reduces to
1µA maximally.
 
Automoatic PFM/PWM mode Switch
The JTMA7179 is a fixed frequency PWM peak current modulation control step-down converter. At light loads,
the JTMA7179 will automatically enter in pulse frequency modulation operation to reduce the dominant switching
losses. In PFM operation, the inductor current may reach zero or reverse on each pulse. A zero current comparator
turns off the N-channel synchronous MOSFET, forcing DCM (Discontinuous Current Mode) operation at light
load. These controls get very low quiescent, help to main-tain high efficiency over the complete load range.

八,相关产品

Part_No	Package & Pins	Topology	Architecture	No. of PWM Outputs	Drive Lout (A)	Vin (V)		Fmax(Khz)	Vref (V)	R-Top (milohm)	R-Sync (milohm)	Iq (No load) (uA)
						min	max
jtma7083	TQFN5x6-28	Buck	CM	1	5	4.5	26	380	0.8	50	20	1000
jtma7085	SOP-8	Buck	CM	1	2	4.5	26	380	0.8	100		1000
jtma7089	SOP-8P	Buck	CM	1	4	4.5	26	380	0.8	80		1000
jtma7104	SOT-23-5	Buck	CM	1	1	2.7	6	1500	0.6	280	250	25
	TSOT-23-5
jtma7104A	SOT-23-5	Buck	CM	1	1	2.7	6	1500	0.6	280	250
jtma7142	SOP-8	Buck	CM	1	3	4.3	14	500	0.8	70	70	500
jtma7145	SOP-8P	Buck	CM	1	3	4.3	14	500	0.8	55	45	500
jtma7153B	TDFN3x3-10				3	2.6	5.5	2000	0.8	110	110	460
jtma7176	TDFN3x3-10	Buck	CM	2	1	2.7	6	1500	0.6	280	250	500
jtma7176A	TDFN3x3-10	Buck	CM	2	1	2.7	6	1500	0.6	280	250
jtma7178	TDFN2x2-6	Buck	CM	1	1	2.7	6	1500	0.6	280	250	25
jtma7178A	TDFN2x2-6	Buck	CM	1	1	2.7	6	1500	0.6	280	250
jtma7179	TDFN3x3-12	Buck	CM	2	1	2.7	6	1500	0.6	280	250	25
jtma7179A	TDFN3x3-12	Buck	CM	2	1	2.7	6	1500	0.6	280	250
jtma7290	TDFN2x2-8		CM	1	1	3.3	8	1500	0.6	280	250	25
jtma7300	SOP-8	Buck	CM	1	2	4.5	24	340	0.925	110	110	1900
jtma7301	SOP-8P	Buck	CM	1	3	4.5	24	340	0.925	110	110	1900
jtma7302	SOP-8	Buck	CM	1	2	4.5	24	340	0.92	130	130	1900
jtma7302B	SOP-8P	Buck	CM	1	2	4.5	24	340	0.92	130	130	1900
jtma7303	SOP-8P	Buck	CM	1	3	4.5	24	340	0.92	85	85	1900
jtma7304	SOP-8P	Buck	CM	1	4	4.5	24	340	0.8	85	85	1900
jtma7311	SOP-8P	Buck	CM	1	3	4.5	24	1300	0.925	110	110	1900
jtma7312	SOP-8	Buck	CM	1	2	4.5	24	340	0.925	110	110	1900
jtma7313	SOP-8P	Buck	CM	1	3	4.5	24	340	0.925	110	110	1900
jtma7314	TSOT-23-8	Buck	CM	1	2	4.5	24	500	0.8	150	70	500
jtma7322	SOP-8P	Buck	CM	1	2	2.5	6	1000	0.8	85	75	460
	TDFN3x3-10
jtma7323	SOP-8P	Buck	CM	1	3.2	2.5	6	1000	0.8	85	75	460
	TDFN3x3-10
jtma7324	SOP-8P	Buck	CM	1	4	2.5	6	500	0.8	85	75	460
	TDFN3x3-10
jtma7325	SOP-8P	Buck	CM	1	5	2.5	6	1000	0.6	65	55	460
jtma7334	SOP-8	Buck	CM	1	2	4.5	24	340	0.8	110	110	1900
jtma7335	SOP-8P	Buck	CM	1	3	4.5	24	340	0.8	110	110	1900
jtma7336	TDFN3x3-10	Buck	CM	1	2	4.5	24	340	0.8	110	110	1900
jtma7337	TDFN3x3-10	Buck	CM	1	3	4.5	24	340	0.8	110	110	1900
jtma8713	TQFN4x4-23	Buck	COT	1	6	2.7	28	100~1000	0.8	30	9	750
jtma8802	TQFN5x6-28	Buck	COT	1	8	3	25	500	0.75	12	12	400
jtma8804	TDFN3x3-10	Buck	CM	1	3	2.6	6	1000	0.6	65	55	460
jtma8805	TDFN3x3-10	Buck	CM	1	3	2.6	6	1000	0.6	75	55	460
jtma8807	TQFN3x3-16	Buck	COT	1	8	6	28	500	0.6	24	14	80
jtma8824	TSOT-23-6	Buck	CM	1	1	2.7	5.5	1500	0.6	280	250	25
jtma8835	TDFN3x3-10	Buck	CM	1	3	4.5	24	600	0.8	70	70	400
jtma7414	TSOT-23-8A	Buck	CM	1	2	4.5	24	500	0.788	150	70	1000
jtma7319	TSOT-23-8A	Buck	CM	1	2.5	4.5	24	500	0.807	140	60	1000
jtma8715	TQFN 4x4 23	Buck	COT	1	6	2.7	28	100~1000	0.8	30	12	700
jtma8716A	TQFN 5x5 30	Buck	COT	1	12	2.7	28	300~1000	0.8	14.6	7.8	750
jtma8715	TQFN 4x4 23	Buck	COT	1	6	2.7	28	100~1000	0.8	30	12	700
jtma8805B	TDFN 3x3 10	Buck	CM	1	3	2.6	6	1000	0.8	75	55	460
jtma8805A	TDFN 3x3 10	Buck	CM	1	3	2.6	6	1000	0.8	75	55	460