SLM6305

Part: SLM6305

Type: Synchronous Step-Down Li-ion Battery Charger

Description: 4.6–26.0 V operating input, 2.5 A synchronous buck Li-ion charger with integrated switches, 550 kHz switching frequency, and ±1% 4.2 V float voltage accuracy.

Operating Conditions:

• Supply voltage: 4.6 to 26.0 V
• Operating temperature: -40 °C to 85 °C
• Switching frequency: 550 kHz (450 to 650 kHz)
• Preset float voltage: 4.2 V (4.158 to 4.242 V)

Absolute Maximum Ratings:

• Max supply voltage: 28 V (VIN: -0.3 V to 28 V)
• Max junction/storage temperature: 145 °C junction, -65 °C to 125 °C storage

Key Specs:

• Maximum programmable charge current: up to 2.5 A (IBAT = 0.0667 / RS)
• Float voltage accuracy: 4.2 V ±1% (4.158 V to 4.242 V)
• Efficiency: up to over 90%
• PMOSFET on-resistance: 100 mΩ
• NMOSFET on-resistance: 100 mΩ
• Standby supply current: 130 μA typ, 260 μA max (charge termination)
• Shutdown supply current: 20 μA typ, 40 μA max (NCE high)
• Trickle charge threshold voltage: 2.85 V typ (2.7 V min, 3.0 V max)
• Trickle charge current: 200 mA typ (RS = 33.3 mΩ)
• Automatic recharge threshold: ΔVRECHRG = 150 mV typ (100 to 250 mV)

Features:

• High input withstand voltage up to 28 V
• Fixed 550 kHz switching frequency
• Integrated power MOSFETs without external anti-reverse or freewheeling diodes
• Adapter-adaptive input voltage drop protection (VINSL = 4.55 V typ)
• NTC battery temperature monitoring
• Dual 28V-tolerant open-drain status outputs (NCHRG, NSTDBY)
• Automatic recharge and output short-circuit protection
• Soft-start function to limit inrush current

Applications:

• E-cigarettes
• Electric toys
• Electric tools
• MP3, MP4 players
• Digital cameras
• Electronic dictionaries
• GPS
• Portable devices, various chargers

Package:

• DFN3x3-10L

• Operating voltage up to 26.0V
• 550kHz fixed switching frequency
• Output efficiency up to over 90%
• Adjustable output current up to 2.5A
• Automatic input current identification, adapter adaptive
• No anti-reverse current diode required
• No external power MOS or freewheeling diode required
• 4.2V charging voltage with ±1% accuracy
• Dual-status charge indication outputs capable of withstanding 28V
• Shutdown current only 20μA
• 2.9V trickle charge
• Soft-start limits inrush current
• Battery temperature monitoring function
• Output short-circuit protection function
• Miniaturized DFN3x3-10L package

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• E-cigarettes
• Electric toys
• Electric tools
• MP3, MP4 players
• Digital cameras
• Electronic dictionaries
• GPS
• Portable devices, various chargers

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Figure 4. SLM6305 Pin Package Diagram

Pin	Name	Description
1	VIN	Input power supply terminal
2	VGC	Internal driver clamp terminal
3	NCHRG	Battery charging indication terminal
4	NSTDBY	Battery charge complete indication terminal
5	NCE	Enable control terminal
6	NTC	Battery temperature detection input terminal
7	BAT	Battery voltage detection terminal
8	VS	Battery current detection terminal
9	GND	Ground
10	LX	Switching terminal

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(Unless otherwise specified, VIN = 5V ±2%, NCE connected to GND, TA = 25 °C)

Symbol	Parameter	Conditions	Min	Typ	Max	Unit
VIN	Input Supply Voltage		4.6	5	26.0	V
VUV	VIN Undervoltage Lockout Threshold	VIN from high to low	3.8	3.95	4.1	V
VUVHYS	VIN Undervoltage Lockout Hysteresis			300		mV
IIN	Input Supply Current	Standby mode (charge termination)		130	260	μA
IIN	Input Supply Current	Shutdown mode (NCE connected to high)		20	40	μA
VFLOAT	Steady Output (Float) Voltage		4.158	4.2	4.242	V
IBAT	BAT Pin Current: (Current mode, test condition is VBAT = 3.8V)	RS = 33.3mΩ, current mode	1.8	2.0	2.2	A
IBAT	BAT Pin Current: (Current mode, test condition is VBAT = 3.8V)	Standby mode, VBAT = 4.2V		2.3	4.6	μA
IBAT	BAT Pin Current: (Current mode, test condition is VBAT = 3.8V)	Shutdown mode (VIN < VBAT or VIN < VUV)		2.6	5.2	μA
IBAT	BAT Pin Current: (Current mode, test condition is VBAT = 3.8V)	Shutdown mode (NCE connected to high)		0		μA
ITRIKL	Trickle Charge Current	VBAT < VTRIKL, RS = 33.3mΩ, current mode		200		mA
VTRIKL	Trickle Charge Threshold Voltage	VBAT rising	2.7	2.85	3.0	V
VTRHYS	Trickle Charge Hysteresis Voltage			100		mV
VBLV	Battery Terminal Short-Circuit Protection Threshold Voltage			2.2		V
VINSL	Input Voltage Drop Protection			4.55		V
VASD	VIN - VBAT Lockout Threshold Voltage	VIN from low to high	150	200	300	mV
		VIN from high to low	10	80	130	mV
ITERM	Charge Termination Current Threshold	RS = 33.3mΩ	100	200	300	mA
VNCHRG	NCHRG Pin Output Low Voltage	INCHRG = 5mA		0.5		V
VNSTDBY	NSTDBY Pin Output Low Level	INSTDBY = 5mA		0.5		V
VNCE_L	NCE Pin Low Level (Power On)				0.8	V
VNCE_H	NCE Pin High Level (Power Off)		2.5			V
INTC	NTC Pin Current		45	50	55	μA
VNTC_H	NTC Pin High-end Flip Voltage			1.35		V
VNTCH_HYS	NTC Pin High-end Flip Voltage Hysteresis			50		mV
VNTC_L	NTC Pin Low-end Flip Voltage			180		mV
VNTCL_HYS	NTC Pin Low-end Flip Voltage Hysteresis			40		mV
ΔVRECHRG	Recharge Battery Threshold Voltage		100	150	250	mV
FREQ	Oscillation Frequency		450	550	650	kHz
RPFET	PMOSFET 'ON' Resistance			100		mΩ
RNFET	NMOSFET 'ON' Resistance			100		mΩ
TLIM	Junction Temperature in Thermal Limit Mode			145		°C
tSS	Soft-start Time		300			us
tRECHRG	Recharge Comparator Filter Time	VBAT from high to low		1		ms
tTERM	Termination Comparator Filter Time	IBAT drops below ITERM		1		ms

• Input supply voltage (VIN): -0.3V~28V
• VGC: VIN-7V~VIN+0.3V
• NCHRG, NSTDBY: -0.3V~28V
• BAT: -0.3V~14V
• VS: -0.3V~14V
• LX: -0.3V~28V
• Others: -0.3V~7V
• BAT short-circuit duration: Continuous
• Maximum junction temperature: 145 °C
• Operating ambient temperature range: -40 °C ~85 °C
• Storage temperature range: -65 °C ~125 °C
• Soldering temperature (10 seconds): 260 °C

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The DFN3x3-10L package has small external dimensions. Due to thermal considerations for the chip, special attention must be paid to the PCB layout. This is crucial for maximizing the usable charging current. The thermal path used to dissipate the heat generated by the IC travels from the chip to the lead frame and reaches the PCB copper surface through the bottom heat sink. The copper foil of the PCB serves as the primary heat sink for the IC, and its area should be as wide as possible, extending outwards to a larger copper area to dissipate heat into the surrounding environment.

Placing vias on the PCB to internal or backside layers is also significantly effective in improving the overall thermal performance of the charger, see Figure 3. Place a 1.7*3.0mm square PAD at the SLM6305 location on the PCB as a heat sink, and place several 0.8mm diameter vias on the PAD as thermal vias. When soldering the chip, pour solder from the back of the PCB so that the heat sink on the bottom of the SLM6305 is effectively connected to the PCB heat sink, thereby ensuring efficient heat dissipation of the SLM6305. Efficient heat dissipation of the chip is a prerequisite for ensuring that the chip can maintain a large charging current for a long time.

Figure 5 PCB Layout

When designing the PCB layout, other heat sources on the circuit board unrelated to the charging IC should also be considered, because their own temperatures will affect the overall temperature rise and the maximum charging current.

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