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SM8132A White LED Driver IC
OVERVIEW
The SM8132A is a charge pump DC/DC converter that switches between x1 and x1.5 automatically. The SM8132A switches between x1 and x1.5 according to detected LED drive current, so that the battery life can be prolonged to the fullest extent. Since the connected LED are all detected for the switching, the SM8132A can respond to the variation of LED forward voltage. 4-channel of LED drive current control circuit is built-in, the SM8132A can control 1 to 4 lights of white LED, which are connected in parallel. The LED drive current per channel is set up by external resistor. Besides, the input signal controlling of EN pin allows ON/OFF and dimming.
FEATURES
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Battery life extension by automatic charge pump switch between x1 and x1.5 according to the detection of the LED drive current Controlling 1 to 4 lights of white LED connected in parallel Set up LED drive current value by external resistor (5k:5mA/ch, 15k:15mA/ch, 20k:20mA/ch) 1-wire input controlling ON/OFF and brightness control by input signal controlling of EN pin Soft start circuit built-in Thermal shut down circuit built-in
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Supply voltage range * No-load current (IOUT = 0mA): 2.7 to 4.6V * Load current (IOUT = 80mA): 3.3 to 4.6V Maximum output voltage: 4.2V (typ) Maximum output current: 80mA (typ) Quiescent current * Not-switching (x1 mode): 0.3mA (typ) * Switching (x1.5 mode): 1.0mA (typ) Standby current (Power save mode): 0.01A (typ) Operating frequency (x1.5 mode): 750kHz (typ) LED drive current matching (RSET = 20k): 3% Package: 16-pin QFN WL-CSP (under development)
APPLICATIONS
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Cellular phone PDA Portable games Handy terminal Digital still camera Digital video camera LCD back light White LED driving
ORDERING INFORMATION
Device SM8132AB SM8132AW Package 16-pin QFN WL-CSP
NIPPON PRECISION CIRCUITS INC.--1
SM8132A
PACKAGE DIMENSIONS
(Unit: mm)
QFN-16
TOP VIEW 3.0 0.08 B A 3.0 0.08 0.3 0.1 3 = 1.5 0.05
BOTTOM VIEW 1.8
0.5
1.8 C 0.3 0.22 0.05
0.02 S A B 0.1 0.05 S 0.2 S
0.05 M S A B
0.2 0.05
0.05 S 0.5
WL-CSP (under development)
0.7 0.05
TBD
NIPPON PRECISION CIRCUITS INC.--2
SM8132A
PINOUT
(Top view)
QFN-16
GND ISET DIN3 NC
WL-CSP (under development)
DIN2 DIN1 C1P C1M PGND VOUT C2M C2P
EN DIN4 NC VIN
TBD
PIN DESCRIPTION
Number Name QFN-16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 WL-CSP - - - - - - - - - - - - - - - - PGND VOUT C2M C2P VIN NC DIN4 EN NC DIN3 ISET GND DIN2 DIN1 C1P C1M - O - - - - O Ip*1 - O I - O O - - Charge pump ground connection LED drive voltage output Charge pump capacitor connection 2M Charge pump capacitor connection 2P Voltage supply No connection LED drive current control output 4 (connect to ground when not used) Enable data input (High active) No connection LED drive current control output 3 (connect to ground when not used) LED drive current setting resistor connection Ground LED drive current control output 2 (connect to ground when not used) LED drive current control output 1 (connect to ground when not used) Charge pump capacitor connection 1P Charge pump capacitor connection 1M I/O Description
*1. Ip: Input with built-in pull-down resistor
NIPPON PRECISION CIRCUITS INC.--3
SM8132A
BLOCK DIAGRAM
C1M C1P C2M C2P
VIN
Charge pump 1 /1.5
VOUT
Mode control & Output voltage control & Protection Current control & Current detect
DIN1
DIN2
TSD
DIN3
DIN4 Control logic ISET
EN
GND
PGND
NIPPON PRECISION CIRCUITS INC.--4
SM8132A
SPECIFICATIONS
Absolute Maximum Ratings
GND = 0V
Parameter VIN voltage range Input voltage range Output voltage range VOUT output current Power dissipation Junction temperature Storage temperature range *1. When mounted on a 4-layer PCB. Note. The device may suffer breakdown if any one of these parameter ratings is exceeded. Symbol VIN VEN VDIN1 to 4 VOUT IOUT PD TJMAX Tstg Rating -0.3 to 5.5 VGND - 0.3 to VIN + 0.3 VGND - 0.3 to VIN + 0.3 5.5 500 800 (Ta = 25C)*1 +125 -55 to +125 Unit V V V V mA mW C C
800 800 Power dissipation [mW] 640 600 480 400 320
200
0 25 35 45 55 65 75 85 Operating temperature [C]
Recommended Operating Conditions
GND = 0V
Rating Parameter Pin Symbol VIN0 VIN Input voltage range Ambient temperature range EN - VES Ta Conditions min Supply voltage range VIN x1.0 mode, IOUT = 0mA x1.5 mode, IOUT = 80mA Each logic-level pin 2.7 3.3 0 -30 typ 3.6 3.6 - - max 4.6 4.6 VIN +85 V V V C Unit
NIPPON PRECISION CIRCUITS INC.--5
SM8132A
Electrical Characteristics
VIN = 3.6V, GND = 0V, Ta = 25C unless otherwise noted.
Rating Parameter Standby current Quiescent current Output voltage Maximum output current Operating frequency Internal power-ON reset time*1 Soft start time LED drive pin leakage current LED drive current LED drive current matching LED drive pin voltage LED drive current setting resistance*1 Input signal frequency*1 Input pulse width*1 Pin VIN VIN VOUT VOUT C1M EN DIN1 to 4 DIN1 to 4 DIN1 to 4 DIN1 to 4 DIN1 to 4 ISET EN Symbol ISTB IDD1 IDD2 VOUT IOUT fOSC TPOR TSS Ileak1 to 4 ILED1 to 4 ILED VDIN1 to 4 RSET fENIN TENH TENL Hold time EN TCEH VIH VIL Input current *1. Design guaranteed value EN IIH IIL Condition min Power-save mode x1.0 mode, IOUT = 0mA x1.5 mode, IOUT = 0mA x1.5 mode, IOUT = 80mA x1.5 mode x1.5 mode switching frequency Time from when power is applied until internal circuits reset EN startup ILED rising edge Power-save mode, DIN pin = 4.2V x1.0 mode, RSET = 20k x1.0 mode, matching between channels with ILED maximum setting x1.0 mode, RSET = 20k RSET maximum value EN input pulse duty 50%, maximum signal input frequency Minimum EN pulse HIGH-level width Minimum EN pulse LOW-level width Time from when EN = LOW until LED drive circuit shutdown HIGH-level input voltage range LOW-level input voltage range Pull-down pin, EN pin = 3.6V EN pin = 0V - - - 4.0 80 650 - - - 19.0 -3.0 - - - 3.0 3.0 1.17 1.8 - - -1.0 typ 0.01 0.3 1.0 4.2 - 750 0.05 1.3 0.01 20.0 - 160 - - - - 1.37 - - 5.0 - max 1.00 1.0 3.0 4.4 - 850 1.00 5.0 1.00 21.0 +3.0 - 50 150 - - 1.63 - 0.6 10.0 - A mA mA V mA kHz ms ms A mA % mV k kHz s s ms V V A A Unit
EN
Input voltage
EN
NIPPON PRECISION CIRCUITS INC.--6
SM8132A
VOUT Efficiency
100
90 VOUT efficiency [%]
80
VF = 3.2V
70
VF = 3.4V VF = 3.6V
60
VF = 3.8V
50 3.2
3.4
3.6
3.8 4.0 VIN [V]
4.2
4.4
4.6
Efficiency of PIN vs. POUT (LED x 4pcs, ILED = 20mA, IOUT = 80mA)
100
90 VOUT efficiency [%]
80
VF = 3.2V
70
VF = 3.4V VF = 3.6V
60
VF = 3.8V
50 3.2
3.4
3.6
3.8 4.0 VIN [V]
4.2
4.4
4.6
Efficiency of PIN vs. POUT (LED x 3pcs, ILED = 15mA, IOUT = 45mA)
NIPPON PRECISION CIRCUITS INC.--7
SM8132A
FUNCTIONAL DESCRIPTION
LED Drive Current Setting
The SM8132A LED drive current setting is controlled by the combination of resistance connected to ISET and the EN input signals. (1) Setting LED Drive Current using RSET The maximum drive current per LED (when DATA = 1) is determined by the external resistance connected to ISET. For example, if ILED MAX = 15mA, from the graph below, a resistance "RSET" of 15k should be connected between ISET and GND. Note that while RSET can have a maximum resistance 50k, the total LED output current must not exceed the maximum output current of 80mA.
50
ISET
ILED [mA]
40 30 20 10 0
RSET
GND
0
10
20
30
40
50
RSET [k]
LED drive current maximum setting using RSET
(2) Setting LED Drive Current using EN Input Signals The EN input ENABLE/DISABLE circuit, also simultaneously counts the number of input pulses using an internal counter and adjusts the LED drive current setting in response. The internal 4-bit counter provides 16step (DATA = 1 to 16) adjustment, where each step is 1/15th of the maximum current (ILED MAX) set by RSET. On the 16th pulse (DATA = 16), the LED drive current control circuit shuts down. On the 17th pulse (DATA = 1), the LED drive current is reset to the maximum current value. As the current is set to the maximum value on the first pulse, applications without pulse input can also be employed (by controlling brightness using RSET).
RSET=10k RSET=15k RSET=20k
EN
123
ILED [mA]
25 20 15 10 5 0 0 4 8 12 16
EN input pulse
GND
DATA set by EN input pulse
LED drive current setting variation using EN input pulse modulation Table. LED drive current setting and EN input pulse count
DATA 1 1 EN pulse count 17 33 49 ILED 2 2 18 34 50 3 3 19 35 51 4 4 20 36 5 5 21 37 6 6 22 38 7 7 23 39 8 8 24 40 9 9 25 41 10 10 26 42 11 11 27 43 12 12 28 44 13 13 29 45 14 14 30 46 15 15 31 47 16 16 32 48
15/15
14/15
13/15
12/15
11/15
10/15
9/15
8/15
7/15
6/15
5/15
4/15
3/15
2/15
1/15
0
NIPPON PRECISION CIRCUITS INC.--8
SM8132A EN input signal and LED drive current setting (startup) An internal startup signal goes HIGH on the first rising edge of EN, and LED drive current starts after the softstart time expires. The LED drive current control circuit sets the current by counting the input pulses on EN, hence the EN input voltage must be switched HIGH LOW HIGH the required number of data steps to reduce the current setting. When the desired setting is reached, the EN input voltage should be tied HIGH to maintain the setting. Note that the LED drive current does not flow when EN is LOW. The EN data input circuit operates during the soft-start time when no LED drive current flows, hence the current setting can be adjusted during the soft-start time and the LED drive circuit will then start at the desired current setting. However, setting the current using EN signal pulses is possible only when the power-ON reset ends after a rising edge on the VIN supply. Consequently, a delay of 1ms or greater should be allowed after VIN is applied before starting the EN input signals.
EN input signal
1
2
3
4
5
6
7
8
ILED 1 to 4
1
2
3
4
5
6
7
8
EN input signal and LED drive current setting
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The LED drive current is set by the number of EN input signal rising-edge. The LED drive current control circuit is disabled, and the LED drive current does not flow during EN input signal LOW interval or at startup until after the soft-start time expires.
EN input signal and LED drive current setting (disable interval) The LED drive current setting due to EN input is set by the 4-bit counter (16 steps). On the 17th pulse, the counter DATA = 1 and the current is reset to the maximum current value. When the counter DATA = 16, ILED = 0mA and the LED drive circuit shuts down.
EN input
11 12 13 14 15 16 17 18 19 20 21
ILED disable signal
ILED off
ILED 1 to 4
1 11 12 13 14 15 16
2
3
4
5
LED drive current setting disable interval When EN is held LOW for an extended interval, the internal enable signal "CE" goes LOW and the device enters power-save mode. In this mode, the EN input internal counter is reset and subsequent rising-edge pulses on EN restart the counter from DATA = 1.
NIPPON PRECISION CIRCUITS INC.--9
SM8132A
VOUT Output Circuit Mode Switching
The SM8132A switches between 3 output states: power-save mode (standby state), x1.0 mode (VIN through mode), and x1.5 mode (x1.5 charge pump boost). This automatically adjusts the VOUT output to match the drive LED characteristics and reduces the total power dissipation. Switching to and from x1.0 and x1.5 mode occurs automatically in an internal circuit, and cannot be controlled using an external input. Power-ON internal reset time The SM8132A switches from standby condition (power-save mode) to normal operating condition (x1.0/x1.5 mode) on the first rising edge of EN. Note that if the VIN supply voltage is applied when EN is HIGH, startup occurs after the internal power-ON reset time (approximately 50s) expires. At startup, operation commences in x1.5 mode for a fixed interval during the soft-start time in order to determine whether a LED is connected to each DIN pin.
VIN power source VIN
(1)
Power on reset output
POR time typ: 50s
(2)
Internal enable (CE)
Power save mode
Soft start time (3) 1.5 mode
Power-ON reset operation (1) VIN voltage rises when power is applied. (2) Power-ON reset (POR) circuit resets internal circuits approximately 50s after the power is applied. (3) If EN is HIGH when power is applied, the internal circuits start operating when the internal "CE" signal rising edge occurs after the power-ON reset time. If EN is LOW when power is applied, the "CE" rising edge occurs simultaneously with the first rising edge.
EN input signal
EN
Dimming pulses enable
(1)
LED current
Soft start time typ: 1.3ms
LED ON
(2)
Soft start time and LED current (1) If the EN signals are input after POR time is expired, the soft start time begin from the first EN input rising edge. The current setting can be adjusted during the soft-start time. (2) LED current starts flow immediately before the soft start time expires.
NIPPON PRECISION CIRCUITS INC.--10
SM8132A Switching to power-save mode The internal circuit operating mode switches from x1.0/x1.5 mode to power-save mode when EN goes LOW and do not switch HIGH for an interval of 1.63ms (max). This function turns the LEDs OFF and automatically transfers internal circuit control to power-save mode, suppressing current consumption.
EN
Internal enable (CE) Power save
1.0 or 1.5
CE hold time 1.63ms (max)
Power save
EN input signal and internal enable signal "CE"
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If the EN input signal is held for an interval greater than the "CE" hold time 1.63ms (max), the SM8132A switches to power-save mode. The internal circuits are reset on the "CE" falling edge, and the current setting must be re-established before restart.
Switching from x1.0 mode to x1.5 mode If the LEDs can be driven solely by the current determined by RSET and EN pulse input without boosting the VIN input voltage, the VOUT output operates in x1.0 mode. In other words, if sufficient current flows even with the LED forward-direction voltage drop "VF", then VOUT is less than 4.2V. Operation in the more efficient x1.0 mode reduces the total power dissipation and extends the battery drive time. And if low "VF" LEDs are used or the LED drive current setting is LOW, the operating time in x1.0 mode is also extended.
1.0 mode (high efficiency)
High VF LED
1.5 mode (low efficiency)
1.0 mode (high efficiency)
Low VF LED High VIN input
1.5 mode (low efficiency)
Low
VOUT mode switching time comparison due to drive LED "VF" variation If the VIN voltage falls or RSET increases such that the LED drive current is too low in x1.0 mode, then the LED drive circuit low-current detector operates, the VOUT output is automatically switched to x1.5 mode, and the charge pump boosts the output voltage. This occurs even if only one LED low-current condition is detected among the 4-channel LED drive circuits, thus it is recommended that LEDs have small "VF" variation to optimize the total efficiency.
NIPPON PRECISION CIRCUITS INC.--11
SM8132A
VIN input voltage
1.0
1.5 threshold
Low ILED detector
Low ILED detected
(1)
VOUT mode
(2) 1.0 mode 1.5 mode
VOUT output voltage
4.2V
(3)
VIN voltage drop and VOUT output voltage (1) When VIN falls, VOUT cannot overcome the LED "VF" rating, causing insufficient current flows and the ILED low-current signal becomes active. (2) When the ILED low-current condition is detected, the VOUT output circuit switches to x1.5 mode (charge pump mode). (3) Prior to switching to x1.5 mode, the VOUT voltage may be lower than 4.2V but sufficient current is supplied to the LED. If after startup, the LED connected to a DIN pin is switched, the LED connection detector circuit flags an error, and correct mode switching may not occur. If the DIN pin does not control the LED drive current, the low-current detector does not operate and the device cannot switch to x1.5 mode.
NIPPON PRECISION CIRCUITS INC.--12
SM8132A Switching from x1.5 mode to x1.0 mode VF increases immediately after the LED current starts to flow, and then decreases as the LED temperature increases due to the heating effect of the current flow. It can take about 10 seconds for the LED temperature to stabilize and for VF to reach equilibrium, and VF may fluctuate more than 200mV. The VF fluctuation is affected by the ambient temperature and LED current setting, and has a large affect on the automatic mode switching voltage tolerances. To counter the effects of VF fluctuation, the SM8132A outputs a mode reset signal once every 1.4 seconds which automatically switches the output mode to x1.0, and then a determination is made whether to make the x1.0 x1.5 mode switch.
1.4sec/cycle Mode reset
(1)
VOUT mode
(2)
1.5 mode 1.0 mode
Mode hold L: hold
min 80s max 200s
ILED detector ignore
(3)
VOUT output voltage
4.2V (4)
Low ILED detector
(5)
Switching from x1.5 to x1.0 mode due to the mode reset signal (1) Mode reset signal is output once every 1.4 seconds. (2) Switching from x1.5 to x1.0 mode due to the mode reset signal pulse. (3) The mode hold time of 200s (max) starts when output switches to x1.0 mode. During this interval, the mode is not switched even if an ILED undercurrent condition is detected. (4) If VIN is low, the VOUT voltage momentarily drops because the boost function stops as a result of switching to x1.0 mode. (5) The ILED undercurrent signal is ignored during the mode hold time, and the mode only switches in response to the detector output after the mode hold time expires.
NIPPON PRECISION CIRCUITS INC.--13
SM8132A For example, if the VIN voltage is low and the VOUT output voltage in x1.0 mode does not provide sufficient drive current, then the mode reset will cause a LED undercurrent condition. The LED undercurrent detector circuit will output an LED undercurrent signal immediately after the switch to x1.0 mode, but the output will stay in x1.0 mode and not return to x1.5 mode for the duration of the mode hold time. Consequently, the VOUT output is not boosted during the 85s (min) to 200s (max) mode hold time and the voltage drops and the LED brightness is reduced. However, the LEDs are OFF for a maximum of 200s only, and this is not discernible to the naked eye and thus is not a problem.
1.0
VIN input voltage
1.5 threshold
Mode reset (1.4sec/cycle) Mode hold (H: hold)
VOUT mode (H: 1.5, L: 1.0)
1.4sec
max 200S
VOUT output voltage Low ILED detector (H: low ILED)
4.2V
VOUT drop due to the mode reset single
NIPPON PRECISION CIRCUITS INC.--14
SM8132A
PERIPHERAL PARTS
About the External Capacitors
The best capacitors for use with the SM8132A are multi-layer ceramic capacitors. When selecting a multi-layer ceramic capacitor, only X5R and X7R dielectric types are strongly recommended, since the loss of capacitance in various conditions is less than other types such as Z5U and Y5V. The much loss of capacitance in various conditions may cause the output voltage unstable.
Table. The EIA three digit "TC" code
Lower temperature limit X = -55C Y = -30C Z = +10C High temperature limit 5 = +85C 6 = +105C 7 = +125C 8 = +150C Maximum allowable capacitance change from +25C (0V DC) F = 7.5% P = 10% R = 15% S = 22% T = +22%/-33% U = +22%/-56% V = +22%/-82% For example : X5R
About the Input Capacitor "C4"
The parts layout of PCB may merely cause the "VOUT" output voltage unstable. In this case, increasing the "C4" input capacitance value or adding another capacitor on the VIN input line is effective to solve the unstable output voltage.
About the LED Current Setting Resistor "RSET"
The LED drive current variation depends on the LED drive current setting resistor "RSET" variation. Therefore, a precise resistor is recommended for RSET. The ISET output current value is about 20A, so a 1/10 watt class resistor is acceptable as the RSET.
NIPPON PRECISION CIRCUITS INC.--15
SM8132A
TYPICAL APPLICATION CIRCUITS
C1 = 1F C1M C1P
C2 = 1F C2M C2P
2.8 to 4.3V C4 = 4.7F
VIN
Charge pump 1 /1.5
VOUT
C3 = 4.7F
20mA 4 DIN1 Mode control & Output voltage control & Protection Current control & Current detect
DIN2
TSD
DIN3
DIN4
EN
Control logic
ISET
RSET = 20k
GND
PGND
ILED MAX = 20mA circuit example
Note. If the driving LED is less than 4 pcs, unused DIN pins should be connect to GND.
NIPPON PRECISION CIRCUITS INC.--16
SM8132A
FOOTPRINT PATTERN
3.6 0.1 2.2 0.1 0.5 x 3 = 1.5 0.05
0.
32
0.5 x 3 = 1.5 0.05
3.6 0.1
2.2 0.1
0.25 0.05
NIPPON PRECISION CIRCUITS INC.--17
0.7 0.1
SM8132A
Please pay your attention to the following points at time of using the products shown in this document. The products shown in this document (hereinafter "Products") are not intended to be used for the apparatus that exerts harmful influence on human lives due to the defects, failure or malfunction of the Products. Customers are requested to obtain prior written agreement for such use from NIPPON PRECISION CIRCUITS INC. (hereinafter "NPC"). Customers shall be solely responsible for, and indemnify and hold NPC free and harmless from, any and all claims, damages, losses, expenses or lawsuits, due to such use without such agreement. NPC reserves the right to change the specifications of the Products in order to improve the characteristic or reliability thereof. NPC makes no claim or warranty that the contents described in this document dose not infringe any intellectual property right or other similar right owned by third parties. Therefore, NPC shall not be responsible for such problems, even if the use is in accordance with the descriptions provided in this document. Any descriptions including applications, circuits, and the parameters of the Products in this document are for reference to use the Products, and shall not be guaranteed free from defect, inapplicability to the design for the mass-production products without further testing or modification. Customers are requested not to export or re-export, directly or indirectly, the Products to any country or any entity not in compliance with or in violation of the national export administration laws, treaties, orders and regulations. Customers are requested appropriately take steps to obtain required permissions or approvals from appropriate government agencies. NIPPON PRECISION CIRCUITS INC. 15-6, Nihombashi-kabutocho, Chuo-ku, Tokyo 103-0026, Japan Telephone: +81-3-6667-6601 Facsimile: +81-3-6667-6611 http://www.npc.co.jp/ Email: sales@npc.co.jp
NC0411AE 2005.05
NIPPON PRECISION CIRCUITS INC.--18

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