Product Specification
IXD3235/36/37
below the UVLO threshold for a very short time. The UVLO circuit does not cause a complete shutdown of the IC,
but causes pulse output to be suspended; therefore, the internal circuitry remains in operation.
PFM Switch Current
In PFM mode, the IC keeps the P-channel transistor on until inductor current reaches a specified level (IPFM).
P-channel transistor’s ON time is equal
tON = L×IPFM / (VIN - VOUT), µs,
where L is an inductance in µH, and IPFM is a current limit in A.
PFM Duty Limit
In PFM mode, P-channel ON time maximum (tPON_MAX) is set to 2DMAX, i.e. two periods of the switching frequency.
Therefore, under conditions, when the ON time increases (i.e. step-down ratio is small), it is possible that P-channel
transistor to be turned off, even when inductor current does not reach to IPFM. (See Figures 1 and 2 below)
Figure 1
CL High Speed Discharge
Figure 2
The IXD3235/36/37 B, C, D, E, F, and G series can quickly discharge the output capacitor (CL) to avoid application
malfunction, when CE pin set logic LOW to disable IC.
CL Discharge Time is proportional to the resistance (R) of the N-channel transistor located between the LX pin and
ground and the output CL capacitance as shown below.
tDSH = RCL x Ln (V OUT(E) / V), where
V - Output voltage after discharge
VOUT(E) - Output voltage
R = 300 Ω (Typical value）
Output Voltage Discharge Characteristics
PS034201-0515
PRELIMINARY
11
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