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100% Duty Cycle Low Dropout Operation
V
IN(min)
+ V
OUT(max)
) I
OUT(max)
ǒ
R
DS(on)MAX
) R
L
Ǔ
(7)
Enable
Undervoltage Lockout
Forced PWM Mode
bq25010
bq25011
bq25012
SLUS615B – DECEMBER 2004 – REVISED JULY 2007
The bq2501x offers a low input-to-output voltage difference while still maintaining operation with the use of the
100% duty cycle mode. In this mode the P-channel switch is constantly turned on. This is particularly useful in
battery-powered applications to achieve longest operation time by taking full advantage of the whole battery
voltage range. The minimum input voltage to maintain regulation depends on the load current and output voltage
and can be calculated as:
where
I
OUT(max)
= maximum output current plus indicator ripple current
R
DS(on)MAX
= maximum P-channel switch R
DS(on)
R
L
= DC resistance of the inductor
V
OUT(max)
= nominal output voltage plus maximum output voltage tolerance
Pulling the enable pin ( EN) low forces the DC-DC converter into shutdown mode, with a shutdown quiescent
current of typically 0.1 μ A. In this mode the P-channel switch and N-channel rectifier are turned off, the internal
resistor feedback divider is disconnected, and the converter enters shutdown mode. If an output voltage, which
could be an external voltage source or a super capacitor, is present during shut down, the reverse leakage
current is specified under electrical characteristics. For proper operation the EN pin must be terminated and
should not be left floating.
Pulling the EN pin high starts up the DC-DC converter with the soft-start as previously described.
The undervoltage lockout circuit prevents the converter from turning on the switch or rectifier MOSFET at low
input voltages or under undefined conditions.
The FPWM input pin allows the host system to override the power save mode by driving the FPWM pin high. In
this state, the DC-DC converter remains in the PWM mode of operation with continuous current conduction
regardless of the load conditions. Tying the FPWM pin low allows the device to enter power save mode
automatically as previously described.
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Product Folder Link(s): bq25010 bq25011 bq25012