LM43602 datasheet(21/44 Pages) TI2

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LM43602-Q1

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SNVSA83C – APRIL 2015 – REVISED OCTOBER 2017

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Device Functional Modes (continued)

In active mode, depending on the load current, the LM43602-Q1 is in one of four modes:

1. Continuous conduction mode (CCM) with fixed switching frequency when load current is above half of the

peak-to-peak inductor current ripple;

2. Discontinuous conduction mode (DCM) with fixed switching frequency when load current is lower than half of

the peak-to-peak inductor current ripple in CCM operation;

3. Pulse frequency modulation (PFM) when switching frequency is decreased at very light load;

4. Foldback mode when switching frequency is decreased to maintain output regulation at lower supply voltage

VIN.

7.4.4 CCM Mode

CCM operation is employed in the LM43602-Q1 when the load current is higher than half of the peak-to-peak

inductor current. In CCM operation, the frequency of operation is fixed unless the the minimum HS switch ON-

time (TON_MIN) or OFF-time (TOFF_MIN) is exceeded. Output voltage ripple is at a minimum in this mode and the

maximum output current of 2 A can be supplied by the LM43602-Q1.

7.4.5 Light Load Operation

When the load current is lower than half of the peak-to-peak inductor current in CCM, the LM43602-Q1 operates

in DCM, also known as diode emulation mode (DEM). In DCM operation, the LS FET is turned off when the

inductor current drops to 0 A to improve efficiency. Both switching losses and conduction losses are reduced in

DCM, comparing to forced PWM operation at light load.

At even lighter current loads, PFM is activated to maintain high efficiency operation. When the HS switch ON

time reduces to TON_MIN or peak inductor current reduces to its minimum IPEAK-MIN, the switching frequency

reduces to maintain proper regulation. Efficiency is greatly improved by reducing switching and gate drive losses.

Figure 35. VOUT = 5 V Fs = 500 kHz

Pulse Frequency Mode Operation

7.4.6 Self-Bias Mode

For highest efficiency of operation, TI recommends that the BIAS pin be connected directly to VOUT when VOUT ≥

3.3 V. In this self-bias mode of operation, the difference between the input and output voltages of the internal

LDO are reduced and, therefore, the total efficiency is improved. These efficiency gains are more evident during

light load operation. During this mode of operation, the LM43602-Q1 operates with a minimum quiescent current

of 27 µA (typical). Refer to VCC, UVLO, and BIAS for more details.

LM43602 Datasheet(PDF) 21 Page - Texas Instruments

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