EP5357XUI Datasheet, PDF (11/19 Pages) Altera Corporation – 600mA PowerSoC Synchronous Buck Regulator With Integrated Inductor

EP5357LUI/EP5357HUI
exit LLM operation and begin normal PWM
operation. Figure 6 demonstrates V_OUT
behavior during transition into and out of LLM
operation.
V_MAX
V_NOM
V_MIN
LLM
Ripple
PWM
Ripple
V_OUT
Load
Step
I_OUT
Figure 6: V_OUT Behavior in LLM Operation
LLM Threshold Current vs. VOUT
250
200
150
VIN=5V (top curve)
100
VIN=4.2V
VIN=3.7V
50
VIN=3.3V (bottom curve)
0
0.8
1.1
1.4
1.7
2.0
2.3
2.6
2.9
3.2
VOUT (V)
Figure 8: Typical load current for LLM engage and
disengage versus V_OUT for selected input voltages
Table 1: Load current below which the device can be
certain to be in LLM operation. These values are
guaranteed by design
Device exits LLM,
tests load current
Figure 7: V_OUT Droop during Periodic LLM Exit
Many multi-mode DCDC converters suffer from
a condition that occurs when the load current
increases only slowly so that there is no load
transient driving V_OUT below the V_MIN threshold.
In this condition, the device would never exit
LLM operation. This could adversely affect
efficiency and cause unwanted ripple. To
prevent this from occurring, the EP5357xUI
periodically exits LLM mode into PWM mode
and measures the load current. If the load
current is above the LLM threshold current, the
device will remain in PWM mode. If the load
current is below the LLM threshold, the device
will re-enter LLM operation. There will be a
small droop in V_OUT at the point where the
device exits and re-enters LLM, as shown in
Figure 7.
VOUT
3.3
3.30
3.00
2.90
2.60
56
2.50
69
2.20
101
2.10
105
1.80
111
1.50
111
1.45
111
1.20
105
1.15
103
1.10
101
1.05
99
0.80
87
VIN
3.7
4.3
5.0
105
147
62
122
156
89
126
158
106
136
162
111
138
162
120
141
160
122
141
158
124
138
150
120
130
138
119
128
136
111
117
122
108
114
119
106
111
116
104
108
113
89
92
94
The load current at which the device will enter
LLM mode is a function of input and output
voltage. Figure 8 shows the typical value at
which the device will enter LLM operation. The
actual load current at which the device will
enter LLM operation can vary by +/-30%. Table
1 shows the minimum load current below which
the device is guaranteed to be in LLM
operating mode.
To ensure normal LLM operation, LLM mode
should be enabled/disabled with specific
sequencing. For applications with explicit LLM
pin control, enable LLM after VIN ramp up is
complete; disable LLM before VIN ramp
03409
11
October 11, 2013
www.altera.com/enpirion
Rev E