米6体育平台手机版

ZHCSHU0C March 2018 – October 2021 LM51501-Q1

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8.4.3.2 Emergency-Call Configuration (EC Configuration)

Figure 8-8 Typical Emergency Call Application

The EC configuration achieves high efficiency at light or medium load by alternating between the wake-up and the low I_Q standby modes. In EC configuration, the LM51501-Q1 limits the minimum duty cycle programmed by V_VOUT and V_VIN. The minimum duty cycle limit is calculated using Equation 12.

Equation 12.

Due to this minimum duty cycle limit, the boost converter sources more current than required when the load current is relatively small. As a result, the output voltage increases and eventually crosses the VOUT standby threshold which is typically 6% higher than the VOUT regulation target. The LM51501-Q1 then goes into the low I_Q standby mode. The LM51501-Q1 wakes up when VOUT drops below the VOUT wake-up threshold which is typically 3% higher than the VOUT regulation target. The device alternates between these two modes when the inequality in Equation 13 is true.

Equation 13.

Assuming V_LOAD = V_VOUT = V_VOUT-REG and V_SUPPLY = V_VIN, the skip cycle operation starts when the inequality in Equation 14 is true.

Equation 14.

In EC configuration, the LM51501-Q1 does not generate any pulse if V_COMP is less than the 0.3 V and the required minimum duty cycle limit is zero.

If the peak current limit is triggered before reaching the minimum duty cycle, the device terminates the LO driver output immediately.

If VOUT is greater than the VOUT status-off threshold (typically 12% higher than the VOUT regulation target), the LM51501-Q1 pulls the STATUS pin low.

In EC configuration, light-load efficiency is proportional with the inductor current ripple ratio.

Table 8-4 State of Each Pin in Wake-Up Mode

STATUS	SYNC	RT	COMP	EN	VOUT	PVCC/AVCC	LO	CS	VIN	VSET
Released	Enabled in SS configuration	Enabled	Enabled	Enabled	VOUT standby monitor is enabled. VOUT status-off monitor is enabled in EC configuration.	Enabled I_PVCC capability ≈ 75 mA	PWM	Enabled	I_Q ≈ 30 µA. VIN status-off monitor is enabled in SS configuration	Disabled

Table 8-5 Start-Stop vs Emergency-Call Configuration

CONFIGURATION	START-STOP	EMERGENCY-CALL
VOUT regulation options	6.0 V, 6.5 V, 9.5 V, 11.5 V
VSET resistor value [Ω]	29.4k, 19.1k, 9.53k, GND	90.9k, 71.5k, 54.9k, 41.2k
Clock Synchronization	Yes	No, SYNC should be grounded
VOUT wake-up threshold [V]	V_VOUT-REG × 1.03
VOUT standby threshold [V]	V_VOUT-REG × 1.24	V_VOUT-REG × 1.06
VOUT status-off threshold [V]	N/A	V_VOUT-REG × 1.12
VIN standby threshold [V]	V_VOUT-REG × 1.03 + 1.0 V	N/A
STATUS pin control (Open-drain with pullup resistor)	Released by VOUT wake-up Pulled down by VIN standby	Released by VOUT wake-up Pulled down by VOUT status-off
At heavy load when V_VIN « V_VOUT	Pulse width modulation (PWM)
At light or no load when V_VIN « V_VOUT	LO turns on at every cycle in wake-up configuration. Skip cycle operation by alternating between wake-up and standby configurations.
At light or no load when V_VIN « V_VOUT	Minimum on-time is limited	Minimum duty cycle is limited
When V_VIN ≈ V_VOUT or V_VIN ≥ V_VOUT	LO turns on at every cycle in wake-up configuration. On-time is limited by T_ON-MIN. VOUT goes out of regulation.	Duty cycle can drop to 0%. No pulses if V_COMP < 0.3 V and D_MIN ≤ 0%.
Maximum duty-cycle limit	Typically 87%