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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
D 1-V Input Voltage Operation Start-up D D D D D D D
Ensured Under Full Load on Main Output With Operation Down to 0.4 V Input Voltage Range of 1 V to VOUT + 0.5 V 500-mW Output Power at Battery Voltages as Low as 0.8 V Secondary 9-V Supply From a Single Inductor Adjustable Output Power Limit Control Output Fully Disconnected in Shutdown Adaptive Current-Mode Control for Optimum Efficiency 8-A Shutdown Supply Current
VOUT VGD VIN SD
D OR N PACKAGE (TOP VIEW) 1 2 3 4 8 7 6 5
SW PGND SGND PLIM
UCC3941-ADJ ONLY (TOP VIEW)
VOUT VGD VIN SD
1 2 3 4
8 7 6 5
SW PGND FB PLIM
description
The UCC3941 family of low-input-voltage single-inductor boost-converters are optimized to operate from a single- or dual-alkaline cell, and step up to a 3.3-V, 5-V, or an adjustable output at 500 mW. The UCC3941 family also provides an auxiliary 9-V, 100-mW output, primarily for the gate drive supply, which can be used for applications requiring an auxiliary output such as a 5-V supply by linear regulating. The primary output starts up under full load at input voltages typically as low as 0.8 V, with a guaranteed maximum of 1 V, and operates down to 0.4 V once the converter is operating, maximizing battery utilization. Demanding applications such as pagers and personal digital assistants require high efficiency from several milliwatts to several hundred milliwatts, and the UCC3941 family accommodates these applications with > 80% typical efficiencies over the wide range of operation. The high-efficiency at low-output current is achieved by optimizing switching and conduction losses along with low-quiescent current. At higher output current the 0.25- charge switch, and the 0.4- synchronous rectifier, along with continuous-mode conduction, provide high efficiency. The wide input-voltage range on the UCC3941 family can accommodate other power sources such as NiCd and NiMH. Other features include maximum power control and shutdown control. The device is available in 8-pin SOIC (D) and 8-pin DIP (N).
AVAILABLE OPTIONS PACKAGED DEVICES SOIC (D) TA 3.3 -40_C to 85_C 0_C to 70_C UCC2941D-3 UCC3941D-3 5.0 UCC2941D-5 UCC3941D-5 VOUT (V) Adjustable 3.3 (1.3 V to 6 V) UCC2941D-ADJ UCC3941D-ADJ UCC2941N-3 UCC3941N-3 DIP (N) Adjustable (1.3 V to 6 V) UCC2941N-ADJ
5.0 UCC2941N-5 UCC3941N-5
UCC3941N-ADJ The SOIC (D) package is available left end taped and reeled. Add an R suffix to the device type (e.g., UCC2941DR-3) to order quantities of 2500 devices per reel.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright 2001, Texas Instruments Incorporated
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
functional block diagram
10 F + 0.8 V TO VOUT+0.5 V
22 H
VIN 3 8.5 V VGD 2 10 F STARTUP CIRCUITRY 8
SW
0.4 1 0.25
UCC3941-3 = 3.3 V UCC3941-5 = 5.0 V UCC3941-ADJ = 1.30 V TO 6 V VOUT
100 F
MODULATOR CONTROL CIRCUIT FOR UCC3941-ADJ ONLY
UDG-98147
S SYNCHRONOUS RECTIFICATION CIRCUITRY S ANTI-CROSS CONDUCTION STARTUP S MULTIPLEXING LOGIC S MAXIMUM INPUT POWER CONTROL S ADAPTIVE CURRENT CONTROL SD 4 UCC3941-ADJ OPEN = SD + 1.25 V 7 6 5
PLIM
{SGND/FB
PGND
For UCC3941-ADJ only: Pin 7 = SGND & PGND, Pin 6 = output sense feedback, FB
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
Terminal Functions
TERMINAL NO. NAME UCC2941-3 UCC2941-5 UCC3941-3 UCC3941-5 - UCC2941-ADJ UCC3941-ADJ 6 I/O DESCRIPTION
FB
I
Feedback control pin used in the UCC3941-ADJ version only. The internal reference for this comparator is 1.25V and external resistors provide the gain to the output voltage. Power ground of the IC. The inductor charging current flows through this pin. For the UCC3941-ADJ signal ground and power ground lines are tied to a common pin. Peak current limit Signal ground of the IC. For the UCC3941-ADJ signal ground and power ground lines are tied to a common pin Shutdown pin Inductor connection Gate drive supply Input voltage to supply the IC during startup. After the output is running the IC draws power from VOUT or VGD Main output voltage
PGND
7
7
-
PLIM SGND SD SW VGD VIN VOUT
5 6 4 8 2 3 1
5 - 4 8 2 3 1
I - I I O I O
detailed description
peak limit (PLIM) The PLIM pin is programmed to set the maximum input power for the converter. For example a 1-A current limit at 1 V would have a 333-mA limit at 3 V input keeping the input power constant at 1 W. The peak current at VIN = 1 V is programmed to 1.5 A (1.5 W) when this pin is grounded. The power limit is given by: PL + 11.8 n ) V IN R ) 6.7 PL 0.26 (1)
W
where RPL is equal to the external resistor from the PLIM pin to ground and n is the expected efficiency of the converter. The peak current limit is given by: I PK(A) + V IN 11.8 R PL n ) 6.7 ) 0.26 (2)
Constant power gives several advantages over constant current such as lower output ripple. shutdown (SD) When the SD pin is open, the built-in 7-A current source pulls up on the pin and programs the IC to go into shutdown mode. This pin requires an open circuit for shutdown and does not operate correctly when driven to a logic level high with TTL or CMOS logic. When this pin is connected to ground, (either directly or with a transistor) the IC is enabled and both output voltages regulate.
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
detailed description (continued)
needs a name (SW) The SW pin inductor is connected between this node and VIN. The VGD (gate drive supply) flyback diode is also connected to this pin. When servicing the 3.3-V supply, this pin goes low charging the inductor, then shut off, dumping the energy through the synchronous rectifier to the output. When servicing the VGD supply, the internal synchronous rectifier stays off, and the energy is diverted to VGD through the flyback diode. During discontinuous portions of the inductor current a MOSFET resistively connects VIN to SW damping excess circulating energy to eliminate undesired high frequency ringing. gate drive supply (VGD) The VGD pin is coarsely regulated around 9 V, and is primarily used for the gate drive supply for the power switches in the IC. This pin can be loaded with up to 10 mA as long as it does not present a load at voltages below 2 V. This ensures proper startup of the IC. The VGD supply can go as low as 7.5 V without interfering with the servicing of the 3.3-V output. Below 7.5 V, VGD has the highest priority, although in practice the voltage should not decay to that level if the output capacitor is sized properly. output voltage (VOUT) Main output voltage (3.3 V, 5 V, or adjustable) which has highest priority in the multiplexing scheme, as long as VGD is above the critical level of 7.5 V. Loads over 150 mA are achievable at an input voltage of 1-V. This output starts up with 1-V input at full load.
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)
Input voltage VIN, PLIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to 10 V Voltage range, VGD, SW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to 15 V Voltage range, SD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to VIN Output voltage range, VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to 10 V Operating virtual junction temperature range, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55_C to 150_C Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65_C to 150_C Lead temperature soldering 1,6 mm (1/16 inch) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . 300_C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CDM 1 kV
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. Currents are positive into, negative out of the specified terminal. DISSIPATION RATING TABLE PACKAGE D N TA 25_C POWER RATING 760 mW 980 mW DERATING FACTOR ABOVE TA = 25_C 6.1 mW/_C 7.9 mW/_C TA = 85_C POWER RATING 390 mW 510 mW
recommended operating conditions
MIN Input voltage Output voltage Output current 0.8 1.8 0 MAX 5.0 5.5 200 UNIT V V mA
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
electrical characteristics over recommended operating junction temperature range, for UCC3941, TA = 0_C to 70_C, for UCC2941, TA = -40_C to 85_C, VIN = 1.25 V, TA = TJ (unless otherwise noted) input voltage
PARAMETER TJ = 25_C, IOUT = 100 mA, Minumum startup voltage TEST CONDITIONS No external VGD load, See Note 1 MIN TYP 0.8 0.9 0.9 MAX 1.0 1.1 1.5 0.5 1 See note 2 SD = open 13 8 VOUT + 0.5 25 20 UNIT V V V V V A A
TJ = 0_C to 85_C, No external VGD load, IOUT = 100 mA, See Note 1 TJ = -40_C to 0_C, No external VGD load, IOUT = 100 mA, See Note 1
Minumum dropout voltage Input voltage range Quiescent supply current Shutdown supply current
IOUT = 0 mA, VGD = 6.3 V
No external VGD load,
output voltage
PARAMETER Quiescent supply current Shutdown supply current See note 2 SD = open 1 V < VIN < 3 V UCC3941-3 Regulation voltage UCC3941-5 Feedback voltage UCC3941-ADJ 1 V < VIN < 3 V, See Note 1 1 V < VIN < 5 V 1 V < VIN < 5 V, See Note 1 1 V < VIN < 3 V 0 mA < IOUT < 100 mA, 0 mA < IOUT < 150 mA, 3.18 3.17 4.85 4.8 1.212 TEST CONDITIONS MIN TYP 32 6 3.25 3.30 5.00 5.0 1.250 MAX 80 15 3.37 3.43 5.15 5.2 1.288 UNIT A A V V V V V
VGD output
PARAMETER Quiescent supply current Shutdown supply current See note 2 SD = open 1 V < VIN < 3 V Regulation voltage 1 V < VIN < 3 V, See Note 1 0 mA < IOUT < 10 mA, 7.5 7.4 TEST CONDITIONS MIN TYP 25 8 8.7 87 MAX 60 20 9.2 9.3 UNIT A A V V
NOTE 1: Performance from application circuit shown in Figures 3, 4, and 5. Ensured by design. Not 100% production tested. NOTE 2: For the UCC3941-3, VOUT = 3.47 V and VGD = 9.3 V. For the UCC3941-5, VOUT = 5.25 V, VGD = 9.3 V. For the UCC3941-ADJ, FB = 1.315 V, VGD = 9.3 V.
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
electrical characteristics over recommended operating junction temperature range, for UCC3941, TA = 0_C to 70_C, for UCC2941, TA = -40_C to 85_C, VIN = 1.25 V, TA = TJ (unless otherwise noted) (continued) inductor charging (L = 22 H)
PARAMETER Peak discontinuous current Peak continuous current Charge switch RDS(on) Current limit delay RPLIM = 6.2 , See Note 1 TEST CONDITIONS Over operating range See Note 1 0.5 MIN TYP 0.05 0.9 0.25 50 MAX 0.85 1.3 0.40 UNIT A A ns
N and D package, I = 200 mA
synchronous rectifier
PARAMETER UCC3941N-ADJ UCC3941D-ADJ Rectifier RDS(on) UCC3941N-3 UCC3941D-3 UCC3941N-5 UCC3941D-5 I = 200 mA, I = 200 mA I = 200 mA TEST CONDITIONS VOUT = 3.3 V MIN TYP 0.35 0.35 0.5 MAX 0.6 0.6 0.8 UNIT
shutdown
PARAMETER Shutdown bias current SD = 0 V TEST CONDITIONS MIN -10 TYP -7 MAX UNIT A
NOTE 1: Performance from application circuit shown in Figures 3, 4, and 5. Ensured by design. Not 100% production tested. NOTE 2: For the UCC3941-3, VOUT = 3.47 V and VGD = 9.3 V. For the UCC3941-5, VOUT = 5.25 V, VGD = 9.3 V. For the UCC3941-ADJ, FB = 1.315 V, VGD = 9.3 V.
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION
A detailed block diagram of the UCC3941 is shown in Figure 1. Unique control circuitry provides high-efficiency power conversion for both light and heavy loads by transitioning between discontinuous and continuous conduction based on load conditions. Figure 2 depicts converter waveforms for the application circuit shown in Figure 3. A single 22-H inductor provides the energy pulses required for a highly efficient 3.3-V converter at up to 500 mW output power.
VIN 3 ANTI-RINGING SWITCH 1 VGD VGD 2 200 kHz STARTUP OSCILLATOR AND CONTROL VGD ZERO DETECT VGD + + + 5V FROM SD 1.7 S OFF TIME CONTROLLER VGD RECTIFIER CONTROL FROM SD VOUT ZERO DETECT VOUT SW 8
1.1 A 5 MAX PLIM 5 CURRENT LIMIT + 50 mV MAXIMUM VSAT SD SD 4 50 mV VIN VIN ON TIME CONTROLLER 11 SEC T ON = VIN R SD BOOST LATCH 6 + Q R SD + THERMAL SHUTDOWN VGD + * 3.3 V FOR UCC3941-3 5.0 V FOR UCC3941-5 1.25 V FOR UCC3941-ADJ ** 8.7 V FOR UCC3941-3 9.6 V FOR UCC3941-5/-ADJ *** 7.7 V FOR UCC3941-3 8.8 V FOR UCC3941-5/-ADJ *** 7 PGND ** VGD 6 SGND (UCC3941-3/-5 ONLY) * FB (UCC3941-ADJ ONLY) Q CLK D L1 Q
UDG-98146
NOTE: Switches are shown in the logic low state; external RPLIM = 6.2
Figure 1. 1-V Synchronous Boost
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION
UDG-96117
Figure 2. Inductor Current and Output Ripple Waveforms At time t1, the 3.3-V output drops below its lower threshold, and the inductor is charged with an on time determined by: t ON + 12 ms VIN (3)
For a 1.25-V input, and a 22-H inductor, the resulting peak current is approximately 500 mA. At time t2, the inductor begins to discharge with a minimum off time of 1.7 s. Under lightly loaded conditions, the amount of energy delivered in this single pulse satisfies the voltage-control loop, and the converter does not command any more energy pulses until the output again drops below the lower voltage threshold. At time t3, the VGD supply has dropped below its lower threshold, but the output voltage is still above its threshold point. This results in an energy pulse to the gate drive supply at t4. However, while the gate drive is being serviced, the output voltage has dropped below its lower threshold, so the state machine commands an energy pulse to the output as soon as the gate drive pulse is completed. Time t6, represents a transition between light and heavy load. A single energy pulse is not sufficient to force the output voltage above its upper threshold before the minimum off-time has expired, and a second charge cycle is commanded. Since the inductor current does not reach zero in this case, the peak current is greater than 0.5 A at the end of the next charge on time. This results in a ratcheting of the inductor current until either the output voltage is satisfied, or the converter reaches its programmed current limit. At time t7, the gate drive voltage has dropped below its threshold but the converter continues to service the output because it has highest priority, unless VGD drops below 7.5 V. Between t7 and t8, the converter reaches its peak current limit which is determined by RPL and VIN. Once the limit is reached, the converter operates in continuous mode with approximately 200 mA of ripple current. At time t8, the output voltage is satisfied, and the converter can service VGD, which occurs at t9.
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION programming the power limit
The UCC3941 incorporates an adaptive power limit control that modifies the converter current limit as a function of input voltage. In order to program the function, the user simply determines the output power requirements and makes an initial converter efficiency estimate. The programming resistor is chosen by: R PL + P OUT 11.8 * 0.26 n n V BAT * 6.7 (4)
Where n is the initial efficiency estimate. For 500 mW of output power, with a 1.0 V input, and an efficiency estimate of 0.75: R PL + 11.8 0.5 * (0.26 0.75 0.75 1.0) * 6.7 + 22 W (5)
For decreasing values of RPL, the power limit increases. Therefore, to ensure that the converter can supply 500 mW of output power, a power limiting resistor of less than 22 must be chosen. P +V L BAT 11.8 ) (1.0 I+ L 22 ) 6.7 0.26) + 0.67 W
1 V TO 3.5 V +
(6)
10 F
MMSZ5240BT1 10 V
DT3316P-223 22 H
3 VIN 8.5 V 10 F 2 VGD UCC3941-3
8 SW 3.3 V AT 500 mW VOUT 1 10SN100M 100 F PLIM 5 R PL 6.2
4
SD SGND 6 7 WCR0805-6R207
OPEN = SD
PGND
UDG-98163
Figure 3. Dual Output Synchronous Boost, 3.3-V Version
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION programming the power limit (continued)
+ 1 V TO 5.5 V
10 F
MMSZ5240BT1 10 V
DT3316P-223 22 H
3 VIN 8.5 V 10 F 2 VGD
8 SW VOUT 1 10SN100M 100 F UCC3941-5 PLIM 5 RPL 6.2 WCR0805-6R207 5.0 V AT 500 mW
4
SD SGND 6 7
OPEN = SD
PGND
UDG-98159
Figure 4. Dual Output Synchronous Boost, 5-V Version
+ 1 V TO VOUT + 0.5 V
10 F
MMSZ5240BT1 10 V
DT3316P-223 22 H
3 VIN 8.5 V 10 F 2 VGD
8 SW VOUT 1 10SN100M 100 F VREF = 1.25 V R1 VOUT + 1.25 1 ) R1 AT 500 mA R2
UCC3941-ADJ FB PLIM 6 5
4 OPEN = SD
SD
(SGND) PGND
RPL 6.2 WCR0805-6R207 7
R2
UDG-98164
Figure 5. Dual Output Synchronous Boost, Adjustable Version
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION programming the power limit (continued)
This power limiting setting supports 0.5 W of output power. It should be noted that the power limit equation contains an approximation which results in slightly less actual input power than the equation predicts. This discrepancy results from the fact that the average current delivered to the load is less than the peak current set by the power limit function due to current ripple. However, if the ripple component of the current is kept low, the power limit equation can be used as an adequate estimate of input power. Furthermore, since an initial efficiency estimate was required, sufficient margin can be built into this estimate to ensure proper converter operation. The 6.2- external power limit resistor (shown in Figures 3, 4, and 5) results in approximately 700 mW of power capability with a 1.0-V input.
inductor selection
An inductor value of 22 H works well in most applications, but values between 10 H and 100 H are also acceptable. Lower-value inductors typically offer lower ESR and smaller physical size. Due to the nature of the bang-bang controllers, larger inductor values typically results in larger overall voltage ripple, because once the output voltage level is satisfied the converter goes discontinuous, resulting in the residual energy of inductor causing overshoot. It is recommended to keep the ESR of the inductor below 0.15 for 500-mW applications. A Coilcraft DT3316P-223 surface mount inductor is one choice since it has a current rating of 1.5 A and an ESR of 84 m. Other choices for surface mount inductors are shown in Table 1. Table 1. Inductor Suppliers
MANUFACTURER Coilcraft Coiltronics CONTACT INFORMATION Cary, Illinois Tel: (708) 639-2361 Fax: (708) 639-1469 Boca Raton, Florida Tel: (407) 241-7878 PART NUMBERS DT Series CTX Series
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION output capacitor selection
Once the inductor value is selected, the capacitor value determines the ripple of the converter. The worst case peak-to-peak ripple of a cycle is determined by two components, one is due to the charge storage characteristic, and the other is the ESR of the capacitor. The worst-case ripple occurs when the inductor is operating at maximum current and is expressed as follows: 2 DV + 2 where I CL V O L *V I )I C CL C ESR (7)
D ICL = the peak inductor current I CL + Power Limit V
IN
D D D D
V = output ripple VO = output voltage VI = input voltage CESR = ESR of the output capacitor
A Sanyo OS-CON series surface mount capacitor (10SN100M) is one recommendation. This part has an ESR rating of 90 W at 100 F. Other potential capacitor sources are shown in Table 2. Table 2. Capacitor Suppliers
MANUFACTURER Sanyo Video Components CONTACT INFORMATION San Diego, California Tel: (619) 661-6322 Fax: (619) 661-1055 Sanford, Maine Tel: (207) 282-5111 Fax: (207) 283-1941 Concord, New Hampshire Tel: (603) 224-1961 PART NUMBERS OS-CON Series
AVX
TPS Series
Sprague
695D Series
input capacitor selection
Since the UCC3941 family does not require a large decoupling capacitor on the input voltage to operate properly, a 10-F capacitor is sufficient for most applications. Optimum efficiency occurs when the capacitor value is large enough to decouple the source impedance. This usually occurs for capacitor values in excess of 100 F.
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION system shutdown
The UCC3941 is enabled by shorting the SD pin to ground either directly or through a transistor.The UCC3941 is shut down when the SD pin is floated (an internal current source pulls up on the SD pin). Since the SD pin is not TTL compatible, 0 V enables the part but 3 V or even 5 V does not properly shut down the device. The recommended circuit for a system requiring shutdown control is shown below. The enable line is driven from a microprocessor or system logic. If enable is low, the SD pin is floated since Q1 base voltage is too low to turn on. If enable is high, Q1 turns on and SD is grounded, enabling the UCC3941. A 1-M resistor to VGD allows Q1 to turn on if the enable pin is high impedance during startup. If shutdown control is not required for the application, SD should be grounded directly.
CAUTION: The UCC3941 should be allowed sufficient time to properly shutdown in a controlled manner. This is accomplished by ensuring that enable is held low at least 500 s before subsequently being brought high. Not adhering to the timings in Figure 7 can result in DEVICE FAILURE. SHUTDOWN INTERFACE CIRCUIT
10 8 6 VGD 2 4 2 1 M 20 k ENABLE 4 SD Enable Voltage - V 0 Ensure 500 s
PROPOGATION DELAY AND RISE TIME
VSD - Shutdown Voltage - V
~ ~
~ ~
6 4 2 0 0 500 t - Time - s 1000
Figure 6
Figure 7. SD Timings
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
APPLICATION INFORMATION SD interface circuit
reducing inrush current A switch mode boost converter requires VIN to be less than VOUT in order to control current in the inductor. Forward voltage is applied across the inductor during the tON time (increasing current) while reverse voltage is applied during the tOFF time (decreasing current). During startup, VOUT is less than VIN, resulting in inrush current until the output is charged. The UCC3941 has two outputs; VGD and VOUT. Inrush current in a two cell alkaline application is typically higher than with a single cell and should be minimized to reduce peak currents in the controller. The VGD inrush current can be minimized by reducing the value of the VGD capacitor. For example a 10-F capacitor may cause a 3-A inrush where a 1-F capacitor results in less than 1-A of inrush. Reducing the VOUT inrush current is more difficult since the output capacitance may need to be large to minimize output ripple. In a two cell application, a diode from VIN to VOUT (shown In Figure 8) precharges the VOUT capacitor and reduces inrush.
PRECHARGE DIODE
22 H + 2 CELL INPUT 220 F 10 V ZENER 2 1 F VGD 8 SW
3 VIN VOUT 1 100 F
UDG-00155
Figure 8. Optional Precharge Diode for VOUT for 2-Cell Input
avoiding inductor saturation
Inductor selection should take into account size, on resistance, and the current capabilities of the part. Inductor ratings include both saturation current and maximum operating current for the device. The RPLIM resistor and inductor should be selected to guarantee the inductor does not saturate during normal operation. A saturated inductor can cause excessive peak currents and i/t slopes which may result in part failure. Inrush and normal operating current should be viewed with a current probe and oscilloscope to ensure the inductor current is linear and controlled.
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
TYPICAL CHARACTERISTICS
EFFICIENCY vs. OUTPUT CURRENT
100 VIN = 1.5 V VIN = 2 V 80 80 100
EFFICIENCY vs. OUTPUT CURRENT
Efficiency - %
Efficiency - %
60
VIN = 1.25 V
60 VIN = 3 V VIN = 2.5 V 40
40
VIN = 1 V
20 VOUT = 3.3 V 0 0.1 1 10 IOUT - Output Current - mA 100
20 VOUT = 3.3 V 0 0.1 1 10 IOUT - Output Current - mA 100
Figure 9
STARTUP CHARACTERISTICS
Figure 10
PSUEDO CONTINUOUS MODE OPERATION
RPL = 6 VIN = 1.25 V IOUT = 100 mA L = 22 H C = 100 F CVGD = 22 H
VOUT 1 V/div 3.3 V VOUT
VGD 5 V/div
VOUT RIPPLE 20 mV/div
IL 0.5 A/div
IL 0.2 A/div t0 t1 t2 t3 t4 2 ms/ div 20 s/div
Figure 11
Figure 12
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
startup characteristics timing sequence (for single output mode)
(see Figure 11)
D D D D D
t0 t1 t2 t3 t4
the 200-kHz srartup oscillator starts VGD rising VGD reaches sufficient voltage (5 V) to run in normal operating mode VGD reaches sufficient voltage (7.5 V) to start VOUT VOUT is serviced and starts up VOUT reaches sufficient voltage and VGD is serviced until it reaches 8.5 V
VGD LOAD = 10 mA VOUT LOAD = 50 mA VOUT AC COUPLED 50 mV/DIV
VGD AC COUPLED 100 mV/DIV
INDUCTOR CURRENT 200 mA/DIV t1 t2 t3 t4 t5
Figure 13.
startup characteristics timing sequence (for dual output mode)
(see Figure 13)
D t1 D t2 D t3 D t4 D t5
VOUT is serviced and inductor current goes continuous VGD is serviced with discontinuous operation and reaches its first threshold (7.5 V) VOUT requires servicing and because VGD has reached its minimum threshold of 7.5 V, VOUT takes priority VOUT is satisfied and VGD is serviced until the second threshold (8.7 V) is reached Both outputs are satisfied
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UCC2941-3, UCC2941-5, UCC2941-ADJ, UCC3941-3, UCC3941-5, UCC3941-ADJ 1 V SYNCHRONOUS BOOST CONVERTER
SLUS242B - JANUARY 1999 - REVISED JUNE 2001
TYPICAL CHARACTERISTICS
UCC3941-3 DROPOUT VOLTAGE vs. OUTPUT CURRENT
1.2 1.20 1.16 1.0 VIN - Dropout Voltage - V VIN - Startup Voltage - V 1.12 1.08 1.04 1.00 0.96 0.92 0.88 0.2 0.84 0 0 50 100 IOUT - Output Current - mA 150 0.80 0 50 100 IOUT - Output Current - mA 150
MINIMUM STARTUP VOLTAGE vs. OUTPUT CURRENT
0.8
0.6
0.4
Figure 14
UCC3941-ADJ (N and D PACKAGES) CURRENT LIMIT vs. PROGRAMMING RESISTANCE
2.1 1.9 1.7 IL - Current Limit - A 1.5 1.3 1.1 0.9 0.7 0.5 0.3 0 IL + 2 6 8 10 12 14 16 18 RP - Programming Resistance - 11.5 ) 0.26 P V BAT 4 20 VIN = 1 V 1.0 VIN = 1.25 V VIN = 1.5 V VIN = 1.75 V VIN = 2 V VIN = 3 V VIN - Startup Voltage - V 0.8 1.2
Figure 15
STARTUP VOLTAGE vs. TEMPERATURE
0.6
0.4
0.2
0 -40 -20 0 20 40 60 80 100 Temperature - _C
(Rp)
6.7 ) R
Figure 16
Figure 17
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