High PFM Threshold

~1.016 × VOUT

Low1 PFM Threshold

~1.008 × VOUT

PFM Mode at Light Load

PWM Mode at

Moderateto-Heavy

Loads

Pfet on

until

Ipfm limit

reached

Nfet on

drains

inductor

current

until

I inductor = 0

High PFM

Voltage

Threshold

reached,

go into

sleep mode

Low PFM

Threshold,

turn on

PFET

Current load

increases,

draws VOUT

towards

Low2 PFM

Threshold

Low2 PFM Threshold,

switch back to PWM mode

Load current

increases

Low2 PFM Threshold

VOUT

13

LM3670

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SNVS250F – NOVEMBER 2004 – REVISED FEBRUARY 2016

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Device Functional Modes (continued)

Figure 16. Operation in PFM Mode and Transition to PWM Mode

7.4.3 Shutdown

Setting the EN input pin low (< 0.4 V) places the LM3670 in shutdown mode. During shutdown the PFET switch,

NFET switch, reference, control and bias circuitry of the LM3671 are turned off. Setting EN high (> 1.3 V)

enables normal operation. It is recommended to set EN pin low to turn off the LM3671 during system power up

and undervoltage conditions when the supply is less than 2.5 V. Do not leave the EN pin floating.