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EP5357HUI Datasheet(PDF) 11 Page - Altera Corporation |
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EP5357HUI Datasheet(HTML) 11 Page - Altera Corporation |
11 / 19 page EP5357LUI/EP5357HUI exit LLM operation and begin normal PWM operation. Figure 6 demonstrates VOUT behavior during transition into and out of LLM operation. Figure 6: VOUT Behavior in LLM Operation Figure 7: VOUT 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 VOUT below the VMIN 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 VOUT at the point where the device exits and re-enters LLM, as shown in Figure 7. Figure 8: Typical load current for LLM engage and disengage versus VOUT 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 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 VOUT IOUT LLM Ripple PWM Ripple VMAX VNOM VMIN Load Step LLM Threshold Current vs. VOUT 0 50 100 150 200 250 0.8 1.1 1.4 1.7 2.0 2.3 2.6 2.9 3.2 VOUT (V) VIN=5V (top curve) VIN=4.2V VIN=3.7V VIN=3.3V (bottom curve) 3.3 3.7 4.3 5.0 3.30 105 147 3.00 62 122 156 2.90 89 126 158 2.60 56 106 136 162 2.50 69 111 138 162 2.20 101 120 141 160 2.10 105 122 141 158 1.80 111 124 138 150 1.50 111 120 130 138 1.45 111 119 128 136 1.20 105 111 117 122 1.15 103 108 114 119 1.10 101 106 111 116 1.05 99 104 108 113 0.80 87 89 92 94 VIN VOUT Device exits LLM, tests load current 11 www.altera.com/enpirion 03409 October 11, 2013 Rev E |
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