MAX8625A Maxim Integrated Products, MAX8625A Datasheet - Page 10

• Manufacturer Part Number: MAX8625A
• Description: Step-Up/Down DC-DC Converter
• Manufacturer: Maxim Integrated Products

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shuttling current in and out of the output capacitor. If
SKIP is asserted high for forced-PWM mode, phase 4 is
not entered and current shuttling is allowed (and is
necessary to maintain the PWM operation frequency
when no load is present).
During medium and heavy loads when V
MOSFETs P1 and N2 turn on at the clock edge to ramp
up the inductor current. Phase 1 terminates when the
inductor current reaches the peak target current set by
the PWM comparator and N2 turns off. This is followed
by a slow-discharge phase (phase 2) instead of a
charge phase (since V
turns on. The slow-discharge phase terminates on a
clock edge. The converter now enters the fast-dis-
charge phase (phase 3). During phase 3, P1 turns off
High-Efficiency, Seamless Transition,
Step-Up/Down DC-DC Converter
Figure 2. State Diagram
10
______________________________________________________________________________________
FROM ANYWHERE)
(ASYNCHRONOUS
TIMEOUT
FAULT
Step-Up Operation (V
IN
is less than V
FAST DISCHARGE
SLOW CHARGE/
P1, P2 = OFF
N1, N2 = ON
N1, N2 = OFF
P1, N2 = OFF
DISCHARGE
P1, P2 = ON
P2, N1 = ON
OSC = ON
OSC = ON
PHASE 2
PHASE 3
ERROR
ON = 1
T2-3
OUT
IN
OSC = ON AND REF = ON IF UVLO OK
IN
) when P2
ON = 1, P1, P2 = OFF, N1, N2 = ON,
< V
< V
OUT
OUT,
T1-3
POWER-UP
(SKIP)
)
T1-2
T3-4
T3-1
and N1 turns on. At the end of the minimum time, both
P2 and N1 turn off and the cycle repeats.
If SKIP is asserted low, during light loads when inductor
current falls to zero in phase 3, the converter switches to
phase 4 (hold) to reduce power consumption and avoid
shuttling current in and out of the output. If SKIP is high
to assert forced-PWM mode, the converter never enters
phase 4 and allows negative inductor current.
When V
three phases for moderate to heavy loads. However,
the maximum time is now spent in phase 2 where
inductor current di/dt is almost zero, since it is propor-
tional to (V
IN
= V
IN
Step-Up/Down Transition-Zone Operation
FAST-CHARGE
P1, P2 = OFF
N1, N2 = ON
P2, N1 = OFF
P1, P2 = OFF
N1, N2 = ON
P1, N2 = ON
OSC = OFF
OSC = ON
- V
I
PHASE 1
PHASE 4
Q
ON = 0
OUT
HOLD
OFF
= 0μA
OUT
TRUN
T4-1
, the converter still goes through the
TPUP
). This eliminates transition glitches
REFOK = 0 OR
UVLO = 0
(ASYNCHRONOUS
FROM ANYWHERE)
ON = 0
(ASYNCHRONOUS
FROM
ANYWHERE)
(V
IN
= V
OUT
)